40
APPENDIX II: SHIPBOARD SCIENTIFIC PROCEDURES 451
APPENDIX II: SHIPBOARD SCIENTIFIC PROCEDURES
451
APPENDIX II - SHIPBOARD SCIENTIFIC PROCEDURES
CONTENTS
Introduction
Glomar Challenger and Her Capabilities
Ship Operations
Procedure for Handling Cores
Time Stratigraphic Framework
Well Logging
Scientific Records
INTRODUCTION
The original Core Description Manual, which is usedaboard the drilling vessel Glomar Challenger in carryingout the programs of the Deep Sea Drilling Project is anextensive and detailed work representing the cummu-lative efforts of many individuals, notably those of theJOIDES Advisory Panel on Sedimentary Petrology andthe JOIDES Advisory Panel on Paleontology and Bio-stratigraphy. The JOIDES Advisory Panels on WellLogging, Interstitial Water, Heat Flow, Paleomagnetism,Igneous and Metamorphic Petrology, and InformationHandling have also contributed to the original com-pilation. Working with these groups have been manyother individuals.
The Core Description Manual performs a threefoldpurpose: that of briefly informing participants in theProject about the facilities available to them; that ofdefining the laboratory procedures to be followed inorder to achieve a measure of uniformity in core de-scription and investigation; and, thirdly, as a source ofreference material, particularly for the paleontologists.
The purpose of the present presentation is to place inthe public domain a short account of the facilities ofthe drilling vessel, Glomar Challenger, the operationscarried out at sea, and the procedures followed in theshipboard laboratory for describing the core materialsrecovered. Experience has shown us that the details oflaboratory procedures vary from cruise leg to cruiseleg, as experience is gained and techniques are refined.There would appear then to be little value to the generalreader in spelling out in detail techniques followed fora particular procedure. However, it is clearly important
to the understanding of the Initial Reports that thereader should have a general knowledge of the proce-dures followed on board ship, the basis for thevarious methods used and, where necessary, the limita-tions or inadequacy of these methods. The followingcontribution has been prepared with this in mind.
A large part of the reference material which appears inthe biostratigraphic section of the Core DescriptionManual is unpublished material supplied through thegenerosity of many recognized authorities on thevarious fossil groups. It is therefore not possible for usto present this information in detail here. The paleon-tological content of this summary is, therefore, limitedto a statement of the time-stratigraphic frameworkdrawn up by the JOIDES Advisory Panel of Paleonto-logy and Biostratigraphy and within which the ship-board paleontologists have worked when preparingtheir descriptions.
THE GLOMAR CHALLENGERAND HER CAPABILITIES
The vessel used in the Deep Sea Drilling Project,Glomar Challenger, is a specially designed drillingvessel having a length of 400 feet, beam of 65 feet,and draft of 20 feet. She is a completely self-sustainingunit carrying sufficient fuel, water and stores to enableher to remain working at sea for 90 days without re-plenishing. On site, she is capable of handling drillstring lengths of up to 22,500 feet (6860 meters),her performance generally being limited to a maximumwater depth of 20,000 feet (6096 meters) and a maxi-minimum penetration into the sea bed of 2500 (762 me-ters). The drilling propulsion and positioning equipment
452
are diesel-electric powered, and the twin screws giveher a cruising speed between sites in excess of 12knots. Special features of her design particularly valu-able for deep-sea drilling include a dynamic positioningequipment with a computerized control system, a tankstabilizing system, and satellite navigation equipment.
Dynamic Positioning
Glomar Challenger is the largest commercial vesselafloat to be equipped with dynamic positioning. Thepositioning system employs four tunnel thrusters, twoin the bow and two aft, each of which is capable ofproducing 17,000 pounds of thrust. The tunnel thrust-ers are mounted transversely and, operated in conjunc-tion with the ship's main screws, they enable her tomove in any direction. While on site, four hydrophonesare extended below the hull. They continually receivesignals transmitted from a sonar beacon implanted onthe ocean floor. The signals are fed into a computer,which on the basis of the delay times of the arrivingsignals calculates the position of the ship relative to thebeacon. The computer automatically controls thethrusters and main propulsion unit to maintain theship's heading and location over the hole. The dynamicpositioning system has both computerized and manualcontrols. Experience so far, has shown that undernormal operating conditions it is easily possible tomaintain the ship within 80 feet (24 meters) of thedesired location for periods as long as six days.
Stabilizing System
The gryoscopically controlled tank stabilizing systemis located amidships. This system substantially reducesthe vessel's motion. Experience has shown that vesselroll or pitch is not a problem, provided the roll orpitch does not exceed 5 degrees half amplitude and ifthe period of the roll or pitch is not short. To date,the vessel motion has not been the determining factorin drilling being curtailed due to weather conditions.
Satellite Navigation System
The satellite navigation system is an ITT Model 4007AB;this is one of the first commercially available navigationinstruments to offer all weather world-wide operation.It provides the ship with access to the precise naviga-tional information which is continuously transmittedfrom the satellites of the U.S. Navy Navigation Satel-lite System (NNSS).
This system consists of four satellites in polar orbit,tracking stations, injection stations and a computingcenter. The tracking network tracks every pass of everysatellite and measures the doppler shift very precisely.These data are transmitted to the computing centerwhere they are used as the basis for computation ofpredicted satellite orbital information. The orbital in-formation is transmitted to the satellite by the injection
stations and is normally updated several times eachday. The NNS System is operated by the NavyAstronautics group headquartered at Point Mugu,California. The system's satellites continuously re-transmit the orbital information back to the ship onultra stable carrier frequencies. The user remains com-pletely passive and merely receives the transmittedsignals. The Model 4007AB collects the orbital infor-mation, measures the doppler shift and makes this dataavailable to be fed directly into a PDP 8S computerfor position-fix computation. This system enablesGlomar Challenger to fix her geographical positionwith accuracies better than one tenth of a nauticalmile anywhere in the world, day or night, regardlessof local weather conditions.
Drilling Equipment
Situated amidships is the 142 foot, Global Marine de-signed derrick, which has a hook load capacity of1,000,000 pounds. Immediately forward of the derrick,is the automatic pipe racker, which can carry 23,000feet (7010 meters) of drill pipe, with below-deckspace for additional storage.
Office and Laboratory Facilities
In general, all living spaces and office and laboratoryfacilities are air conditioned and acoustically insulated.In addition to laboratory facilities, a library lounge,office space, drafting room, and electronics laboratoryare available. Laboratory facilities are housed in a sep-arate structure installed on the floor of the casingrack. The upper laboratory is at the same level as therig floor and has access to the rig floor via a catwalk.This laboratory is designed for core receiving andgeneral processing. It, therefore, contains equipmentfor X-radiography, GRAPE (Gamma-Ray AttenuationPorosity Evaluator), natural gamma, and sonic velocitymeasurements, and for splitting and describing coresections. On the bottom level of the laboratory struc-ture, the paleontology and chemistry laboratories aresituated with their appropriate equipment for handlingmicropaleontological samples and interstitial waterchemistry. Running from the upper laboratory downthrough the laboratory structure into the core-storagearea is an electrically driven dumbwaiter with access toboth laboratories and to the storage area. This is usedfor the transportation of cores and supplies. Situatedat an intermediate level are a photographic laboratory,a dark room, and a small laboratory for the preparationof thin sections. Eight refrigerated storage vans main-tained at a temperature of about 3°C. are provided inthe cargo hold of the ship for core storage. Cores areaccumulated in these storage vans and then are off-loaded at convenient ports for shipment to the shorerepositories on the East and West Coasts of the U.S.A.The vans are also used for temporary storage of sam-ples while on board the vessel.
453
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BRIDGE DECK (ELECTR. LAB)SUPERSTRUCTURE DECK (CAPTAIN, DRILLING SUPERINTENDENT)BOAT DECK (SCIENTIST QUARTERS, COMPUTER ROOM)POOP DECK (CREW QUARTERS, MESSHALL, GALLEY)MAIN DECK (CREW QUARTERS, SHOPS, STORES)PILOT HOUSEELECTRONICS LAB, RADIO ROOMCORE LABPHOTO LAB, DARKROOM, THIN SECTION LABMICROSCOPY LAB, CHEMISTRY LABCORE VAN STORAGEDERRICKDRAWWORKS SHELTERAUTOMATIC PIPE RACKERTHRUSTERS (2 FWD; 2 AFT)POSITION SENSING HYDROPHONES (TOTAL OF 4)
15
Figure 1. Glomer Challenger.
SHIP OPERATIONS
Underway Surveys
When cruising between drilling sites, oceanographicdata are collected by a magnetometer and an air gun.A bottom profile is also taken with a precision depthrecorder. The magnetometer utilized is a proton pre-cession Varian 4970, the magnetic field values beingpresented in gammas on a direct readout of total field,accurate to within plus or minus one gamma. No attemptis made to process magnetometer data on board, al-though gross positive and negative magnetic anomaliesmay be identified. The seismic reflection profiler systemuses a Bolt air gun with a modified Gifft oscillatingblade recorder coupled to a hydrophone array forreceiving.
Site Surveys
The proposed drilling sites have been selected byJOIDES Advisory Panels on the basis of informationalready available. The sites are then surveyed in detailby another, less expensive, vessel. Site surveys in theAtlantic Ocean have been conducted by the researchvessel Vema, of Lamont-Doherty Geological Observa-tory and in the Pacific by the R/V Argo, of ScrippsInstitution of Oceanography. On arrival at the selecteddrilling site, a limited survey, specified by the shipboardscientists, is conducted to locate the optimum drillinglocation. These surveys are limited and directed specif-ically towards locating the best site. Immediately afterthe actual site is selected, a sonar beacon is loweredover the side and dropped to the bottom. The ship isthen maintained on the selected station by the com-puter control system. Drilling operations can thencommence.
Coring Equipment
Equipment from two major coring companies is usedto give maximum flexibility in coring; tungsten car-bide, diamond and milled cutter core bits are used. Avariety of inner tube assemblies are available. Theseinclude non-rotating, rotating, and punch-type assem-blies. The inner core barrel is lined with a plastic tubeto assist in core handling and storage. The nominalsizes of the core cutting and bottom hole assemblyare: hole diameter 9-1/4 inches; core diameter 2-1/2inches; outer tube OD 8-1/4 inches; drill collar OD8-1/4 inches; bumper sub OD 8-1/4 inches with a fivefoot stroke; and, drill pipe 5 inches OD, 19.5 poundsper foot grade.
Drilling and Coring
A power sub is used as the primary rotating systemsince the drill pipe can then be rotated at any height inthe derrick, while the conventional kelly limits thedrill pipe rotation to the length of the kelly above therotary table. Standard wire line coring techniques areused. Coring is accomplished by dropping empty plastic
lined metal barrels through the drill string and after thecore is cut recovering them with a half-inch sandline. Two sand line reels are situated on the derrickfloor for this purpose. After recovery, the filled plasticliners are extracted from the core barrels and the corematerial is handed over to the scientific party for pro-cessing.
PROCEDURE FOR HANDLING CORES
The general procedure for handling cores is outlined inFigure 2, which is a simplified diagram showing theflow of core materials through the laboratories. Thefollowing notes are intended to amplify some of theprocedures. Some of the processes which are not yetin general use are discussed here in more detail.
1. Core Cutting
Cores are received from the drill rig in clear 30 foot(9.1 meters) plastic liners, which are inscribed withlongitudinal lines for orientation reference. Immediatelyafter the core is received it is clearly labeled and sam-pled at the top and bottom before preliminary paleon-tological age determinations are made. These imme-diately provide useful information to guide futurecoring. The core is then cut into 150 centimeterlengths (sections) for processing. Each section is clearlylabeled to show leg, site, core and section.
2. Core Section Weight - Bulk Density
The purpose of this procedure is to make a roughestimate of bulk density and core quality. The un-opened 150 centimeter section of core is placed on ascale and weighed to the nearest 10 grams. The tareweight of an empty 150 centimeter core liner withplastic closures is then subtracted from the weight ofthe core section. For the purposes of this observationthe assumption is made that the plastic liner and closureshave a constant weight from one sample to another. Thefollowing simple calculation is then made to obtainan estimate of bulk density:Core section bulk density =(total core section weight)—(weight of liner & closures)
(volume of plastic liner)Whenever the core section length is other than 150centimeters an appropriate correction is made in thecomputation.
3. Core Radiography
In order to check core quality and to study minor struc-tures and compositional differences, the core sectionsare X-rayed using a Faxitron X-ray machine. The un-opened core sections are run through the Faxitronmachine in a standard orientation and the X-radiographsare recorded on MP381 film, which is later processedin accordance with the manufacturers instructions.
456
CORE RECEIVED
TOP AND CATCHERSAMPLES
CORE CUT ANDLABELED
CORE SECTION WEIGHTCORE X-RAYNATURAL GAMMAGAMMA RAY ATTENUATION •_SONIC VELOCITY ^ _ _THERMAL CONDUCTIVITY(SEQUENCE DEPENDING ONAVAILABILITY OF EQUIP-MENT)
CORE SPLIT
ARCHIVE WORKINGINTERSTITIALWATER SAMPLES
PHOTOGRAPH (9 PENETROMETER (11
VISUAL DESCRIPTION (12J
SAMPLING BY GEOLOGISTSAND PALEONTOLOGISTS
SHORE LABORATORYSAMPLES
CORE STORAGE
SMEAR SLIDES
SAMPLE STORAGE
PALEONTOLOGICALSAMPLES 1
i SHIPBOARDLABORATORY
Figure 2. Block diagram of procedure for handling core materials.Numbers refer to paragraphs in the appropriate section of the text.
457
4. Natural Gamma Radiation Scanner(H. B. Evans & J. A. Lucia)
Natural Gamma Radiation Measurements
Natural gamma radiation measurements provide a basicmeans of identifying lithology and lithologic variations,either in cores or in boreholes. The minerals giving riseto the gamma radiation include gamma-ray emittingisotopes of the uranium series, the thorium series,potassium minerals or phosphates. Diagnostic isotopesinclude U 2 3 5 , Ra2 2 6 , Pb 2 1 2 , Pb 2 1 4 , K40 , T l 2 0 8 ,Bi214 and Ra30. Potassium contributes about halfthe total natural gamma-ray count in consolidatedsedimentary rocks. The remainder can be attributed touranium and thorium isotopes. Thus potassium-richrocks are easily detected by gamma-ray measurements,exceptions occurring where the depositional environ-ment has favored excessive accumulation of otherradioactive minerals. Commonly, for example, thecount rates obtained in fine-grained sediments are muchhigher than those in sandstones and carbonates tend tobe particularly low in gamma-ray emitting isotopes.
In the equipment used on board ship only the totalcount rate is recorded; although, there is much to begained from multichannel recording, where the totalgamma-ray spectrum or the count rate contribution ofindividual isotopes can be recorded.
Applications to Deep Sea Sediments
A continuous, natural gamma-ray scan of deep seasediments, in liners, obtained during the Deep SeaDrilling Project operations is desirable for a numberof reasons. Continuous coring is carried out only on alimited basis; and, even where attempts are made toobtain continuous cores, in practice only partial re-covery is possible. More often, intermittent coring anddrilling are carried out since coring is expensive andtime consuming. Therefore, the intermittent core seg-ments which are obtained must be related to theirproper vertical sequence or position in the geologicsection drilled or cored. The most effective way, per-haps the only way, to affect this relationship betweenthe core recovered and the geologic interval from whichit was obtained is to scan the core segment with gamma-ray detectors, record the total count rate and/or gamma-ray spectra, and correlate these curves to a correspond-ing in-hole logging curve recorded over the total lengthof the hole. The logs, therefore, whether total countor spectra recording devices, are necessary to fill thegaps between core data and to place the core at itsproper stratigraphic position. Because logging is con-siderably less expensive than coring, it is a reasonablesubstitute when some core is initially available to forma basis for log-lithology interpretation.
The natural gamma-ray scanner permits the marinegeologist to extend meager information concerning
geologic and mineralogic characteristics of the core,recovered over the complete length of the geologicinterval drilled, by making use of the relationship be-tween the gamma-ray scan curve and the gamma-raylog. Features which may be obtained in this mannerinclude lithology identification, stratigraphic proper-ties such as bed definition, bedding sequences, andfacies changes, plus information related to depositionalprocesses where isotope identification is carried out.
Until now information concerning continuous, naturalgamma-ray scans of relatively large sediment samples orcore segments was extremely limited. Measurementssuggest that, despite the relatively low counting ratesencountered in gamma-ray measurements on deep seasediments, sufficient differences exist between the sam-ples low in radioactive minerals and those high inradioactive minerals to make scanning of cores fortotal gamma-ray count rate feasible, without intro-ducing excessive counting times.
Some work has been done with discontinuous, colli-mated, pulse height analysis and spectra recordingsystems in identifying isotopes and lithology variationsin deep sea sediment cores (Hori and Folsom, 1958)and with gamma-ray spectrometry in analyzing crushedmineral samples for uranium, thorium, and radium(Bunker and Bush, 1966). Gamma-ray spectroscopyhas been used by the Marathon Oil Company (DenverResearch Center), and probably by others, in definingstratigraphic intervals for correlation, which are dif-ficult to detect by other methods.
Radioactivity measurements in red clays have beenmore revealing than resistivity measurements. Oceanbottom sediment radiation levels of potassium anduranium are relatively high; hence, the gamma-radiationof these sediments has proven to be a reliable lithologyindicator, particularly when combined with in-hole,gamma-ray measurements.
Because of the increased sensitivity required to obtaingood gamma-ray energy (spectra) definition, it isnecessary to count a small core interval over a longperiod of time, advance the core, and repeat themeasurement until the total core segment has beenscanned on a step-by-step basis. Although the informa-tion obtained by this technique is preferable to totalcount rate measurements, the counting times aresignificantly increased. Hence, there would be a pro-portionate delay in handling core aboard ship. Becauseof the advantages inherent in this technique, it is hopedthat gamma-ray spectroscopy and spectra analyses willbe carried out on all core samples obtained during thedeep sea drilling operations, even if it is necessary tomake preliminary measurements aboard ship and con-duct detailed analyses in the laboratory. While this de-lay is a disadvantage, the data obtained through core
458
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Figure 3. Gamma Core Scanning System
459
scan-log correlation may be one of the most powerfultools the marine geologist has available in interpretingthe total geologic section.
Scan System
The natural gamma-ray scan system which is used bythe Deep Sea Drilling Project is based on a design pro-vided by the Marathon Oil Company (Denver ResearchCenter). This is a multipurpose system consisting of:a) four shielded 3" x 3" scintillation detectors located90 degrees apart in a plane normal to the direction oftravel of the sample to be scanned; b) an incrementaltime-step sample transport mechanism; c) two dual-ininput, single channel analyzers to accumulate totalcount rate; d) a multichannel analyzer to accumulategamma-ray spectra from each of the four detectors;e) a timing unit to regulate both core transport activa-tion and counting times; f) a digital to analog converterto supply the analog signal with the total count rate tog) two strip chart recorders. One recorder charts thecount rate on a 1:1 correspondence with the core sothat the recorded curve can be compared directly withthe cored sample. The other recorder is scaled to theratio of 5 centimeters of chart to 10 meters of core sothe recorded curve can be compared directly withgamma-ray well logs. A printed tabulation of totalcount rate is also supplied. The core is advanced inincrements adjustable from 1 inch to 6 inches percount interval, and counting times can be varied, butin general a 3 inch increment and a count time of2-1/2 minutes per increment are used. Figure 3 is ablock diagram of the total count rate system.
REFERENCES
Bunker, C. M. and Bush, C. A., 1966. Uranium, thoriumand radium analyses by gamma ray spectroscopy.lh Geological Survey Research, U.S. Geol. Surv.Profess. Paper 550-B. p. B176.
Hori, S. and Folsom, T. R., 1958. (Unpubl. M. S.Aug. 7) Nondestructive Analysis of Geologic Coresfor Potassium, Radium and Thorium by GammaRay Spectrometer. (Scripps Inst. Oceanography).
samples, encased sediments or other materials from 1 to4-1/2 inches in diameter or thickness. The basis for thisdevice is the equation for gamma-ray attenuation in anideal slab absorber which is shown below:
T -1 -
PB = \ Inµ•
or 0)
(2)
Here I is the intensity of the gamma-ray beam whichpenetrates the absorber with no loss of energy,
I is the source intensity,
o ß is the bulk density in gm/cm3,
µ is the mass absorption coefficient in cm2/gm, and
d is the thickness or diameter of the sample incentimeters.
In porous materials:
where p is the matrix or grain density,O
pc is the density of the fluid filling the pores, and
Φ is the porosity (or liquid content in completelysaturated samples) of the material.
Combining these two expressions in bulk density (2)and (3) results in an equation in which the general un-known parameters are the grain density, the absorptioncoefficient, and the fluid density. The equation forporosity or liquid content is:
5. Gamma-Ray Attenuation Density Scanner1
(Hilton B. Evans and C. H. Cotterell)
Design, Development, and Evaluation
Summary
The Gamma-Ray Attenuation Density Scanner is de-signed to provide a continuous calculated porosity orliquid content from bulk density measurements in core
This system is frequently referred to by its trade name,GRAPE, an acronym for Gamma-Ray Attenuation PorosityEvaluator.
Pα-Pf(4)
Both the initial and the transmitted gamma-ray inten-sity (or count rate) can be measured.
For most geologic materials which are of interest, theabsorption coefficient is constant (about 0.1 cm2/gm).The grain density and fluid density are variables whichmust be provided to evaluate equation (4) for porosityor liquid content. A reasonable value of grain densitycan be assigned to the common sedimentary rock types
460
(after visual examination of the sample) and a suffi-ciently accurate estimate of the fluid density is usuallypossible, since samples directly from a well are usually80 to 100 per cent fluid saturated and laboratory orcore storage samples are nearly dry (0 to 30 per cent).
Encased samples, particularly unconsolidated sea bot-tom sediments, may be partially gas saturated. However,the initial porosity or liquid content record can becorrected when the liquid contents have been deter-mined by heating; furthermore, the samples can bererun after drying to obtain the corrected curve usingmeasured grain and fluid densities.
Bulk density is measured continuously by this device atvarious sample drive rates. Only the values for graindensity and fluid density are supplied by the operatorto make the porosity or liquid content calculation.
The measured sample density, computed porosity (orliquid content), and the measured sample diameter arerecorded on a strip chart. Two recorders are used: oneyields a chart scale which correlates directly to thesample, permitting a comparison of chart anomalies andsample characteristics; the second strip chart, recordsthese data at the same depth scale used in recording theresponses of the in-hole logging devices (5 centimetersof chart =10 meters of hole logged) permitting a directcomparison between core scan data and log response.
Introduction
The objective which initiated the development of thisgamma-ray attenuation device was to find more accu-rate and detailed knowledge of the porosity, density,and variations of density and porosity in sedimentaryrocks. Because continuous density and porosity meas-urements along the length of the core was devised.Therefore, the principal technical advantage of thismethod is that variations in density and porosity en-countered by a moving, pencil-sized gamma-ray beamare recorded continuously. Conventional core analysismethods yield only an average porosity for a given corepiece or plug. Conventional measurements of densityand porosity of unconsolidated sediments are not suffi-ciently accurate or detailed for quantitative application.Other advantages of the GRAPE system are accuracy,rapidity and, therefore, economy, very little samplepreparation (limited to removal of mud or cuttings fromthe core surfaces), and the nondestructive nature ofthe measurement.
rapid, simple methods for evaluating core porosity anddensity are available.
Basically, the gamma ray attenuation device consists ofa variable speed drive system to move geologic mate-rial between a shielded gamma-ray source and a shieldedscintillation detector, an optical caliper to measure thesample thickness, and an analog computer to calculatedensity and porosity (or water content) from themeasured parameters. The complete system is shownin Figure 4. The individual components are identified.
Theoretical Considerations
The theoretical basis for this density-porosity deviceis a simple, idealized gamma-ray attenuation experi-ment. The source is a beam of parallel, monoenergeticgamma rays of intensity IQ. The source gamma raysare incident on one face of a uniform slab absorberwhich has a thickness (d), a bulk density (pB), and amass attenuation coefficient (µ). Some of the gammarays penetrate the absorber without energy loss. Allother incident gamma rays are absorbed or scatteredout of the direct beam. Either type of interaction re-sults in a change of energy and/or a change in directionof travel of these gamma rays.
The intensity of the gamma-ray beam is altered withinthe slab absorber by one of three major attenuationprocesses. These processes are photoelectric absorption,Compton scattering and pair production (Evans, 1965).The process which is most effective in removing gammarays from the incident beam depends upon the energyof the incident gamma rays. Compton collision orattenuation results when part or all of the incidentgamma-ray energy is transferred to a free orbital elec-tron of the absorbing material. When only part of thegamma-ray energy is lost, the direction of travel of thegamma-ray is changed. That is, scattering occurs. Formost absorbers, the Compton process is the predomi-nant means of gamma attenuation in the energy range0.2 to about 4 MeV. Compton attenuation, therefore, isdirectly related to the number of electrons in thegamma-ray beam, and the number of source gammarays which penetrate a given thickness of absorberdepends upon the electron density of the absorber. Ineffect, the gamma-ray density device measures thenumber of electrons between the source and thedetector.
These core-derived porosities and bulk densities are use-ful in studying sediment deposition and diagenesis,evaluating physical properties of encased samples, andin estimating values of acoustic velocity and averagedensity used in logging and geophysical exploration.Studies of this type, however, are not practical unless
If the intensity of the parallel beam of gamma rayswhich passes through the opposite face of the absorberwith essentially no energy loss, as measured at a detec-tor, is I, then
I = I^B<1 ( 1 )
461
or
P B - 1 m (2)
The intensity of the gamma rays at the detector de-pends upon the geometry of the gamma-ray beam, onthe energy of the source gamma rays, on the sourceintensity (IQ), and on the thickness (d), density (pB),and attenuation properties (µ) of the absorber material(Evans, 1965).
Further, the Compton mass attenuation coefficientdepends on the gamma-ray energy and the nature of theabsorber.
The proper choice of gamma-ray energy insures that themass attenuation coefficient of different materials areall about the same. The mass attenuation coefficientsof aluminum, water, air, and a variety of minerals androcks of different mineral composition do not differgreatly for gamma-ray energies between 0.2 and 3.0MeV (Evans, 1965).
For a particular gamma-ray energy, in this energy range,the values of the attenuation coefficients of commonmaterials are all about the same which reflects thenear constancy of Z/A1 in these materials. For elementshaving atomic numbers between 6 and 20, Z/A =0.487 ± 0.013, so that the attenuation coefficient (µ)is nearly constant for compounds of carbon, oxygen,sodium, aluminum, magnesium, calcium and silicon.Using a B a 1 3 3 source, for example, the measuredattenuation coefficients of many geologic materials isapproximately 0.1 cm2/gm.
Therefore, use of a constant for the attenuation coeffi-cient of geologic materials is justified providing theenergy of the source gamma ray is within the specifiedenergy interval. Sources which satisfy this requirementfrom a practical standpoint include Ba 1 3 3 (0.3 to 0.36
s 1 3 7 (0.662MeV), and Co 6 0 (1.17 to 1.33MeV).
In some geologic materials, it is necessary to makecorrections for variations in µ. That is, if the measuredintensity I is related to the electron density throughCompton scattering, bulk density measurements usingthis attenuation technique will not be accurate unlessthe ratio of electron density to bulk density:
is a constant. Corrections must be provided when theelectron factor θ varies significantly (±3 per cent orgreater).
Ratio of the number of electrons per atom to the atomicweight of the absorber.
A convenient unit for θ is the number of electrons percubic angstrom per unit density. This ratio is 0.303 formany common rocks and minerals, such as calcite,quartz, dolomite, and some clays which are composedof elements having atomic numbers in the 6 to 20 rangewhere Z/A is approximately constant. Electron factorssmaller than 0.303 occur in compounds containingheavy elements such as iron, barium and lead. Values ofθ greater than 0.303 frequently occur in compoundsrich in hydrogen such as water, petroleum and plastics.Calculated electron factors for minerals or liquidscommon in sedimentary rocks are reported in Table 1(Harms and Choquette, 1965).
The number of electrons per unit volume for a numberof minerals and liquids common in sedimentary rocksis shown in this table. The minerals are listed in threemajor groups, the silicates, the carbonates, and a mis-cellaneous group which includes some sulfates, sulfides,chlorides and a phosphate. A fourth group includesliquids that might commonly be encountered in thepore spaces of sedimentary rocks: water, a brine, and avariety of hydrocarbons.
The second column of Table 1 lists the electron densityor number of electrons per cubic angstrom for eachcompound. Each compound scatters gamma rays inproportion to its electron density, thereby reducing theintensity of the collimated gamma-ray beam receivedby the detector. Among the minerals most common insediments—those which are underlined in Table 1—silicates contain 0.758 to 0.802 electrons per cubicangstrom, carbonates 0.820 to 0.853, and other crys-talline compounds 0.624 for halite to 0.905 for anhy-drite. Less common minerals have a much greater rangein number of electrons per unit volume, as shown inTable 1. These values for the number of electrons percubic angstrom were derived from the composition anddimensions of unit calls for the minerals. The numberof electrons per cubic angstrom for water, a brine, andsome paraffinic and aromatic hydrocarbons rangesfrom 0.25 to 0.40. Values for these liquids were com-puted from specific gravity and composition.
Because it is generally more convenient to think ofcompounds in terms of their density rather than thenumber of electrons per unit volume, the third columnof Table 1 lists densities in grams per cubic centimeter,a figure numerically equivalent to specific gravity.Column 4 of Table 1 lists the ratio of the number ofelectrons per cubic angstrom to density, and number(the electron factor) that indicates the degree of corre-spondence between number of electrons and density.The value of this ratio for many minerals approaches0.303. The near constancy of this ratio reflects thepreponderance of elements with atomic numbers of 6to 20 within these compounds.
462
TABLE 1Densities of Common Minerals and Liquids
See text for discussion. The minerals mostcommon in sedimentary rocks are in italics.The corrected gamma-ray density is calcu-lated by dividing electrons/Å3 by 0.303.
Corrected
r-i-1
SIL
ICA
TI
Lig
ht
<uOO<n
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Compound
HalloysiteAl2Si2O4(OH)4 2H2O
Mon tomrilloniteAl2Si4010(OH)2
(Na-1 layer H2O)
Chlorite (average)(Mg,Al)5(Si,Al)4O10(OH)8
OrthoclaseKAISLC•
0 0
AlbiteNaAlSLC
•3 0
AnorthiteCaAl2Si208
KaoliniteAl2Si205(0H)4
MontmorilloniteAl2Si4010(OH)2
(collapsed)
Quartz (low)SiO2
MuscoviteKAl2(AlSi3)O10(OH)2
DiopsideCaMg(SiO3)2
Hypersthene(Mg,Fe)SiO3
TermoliteCa2H2Mg5(Si03)8
AnthophylliteMg?H2(Si03)8
Electrons/A
0.637
0.717
0.769
0.758
0.772
0.820
0.793
0.790
0.802
0.846
0.987
1.035
0.917
0.880
(g/cnV)
2.1 (?)
2.5 (?)
2.75
2.57
2.62
2.76
2.65
2.6 (?)
2.65
2.76
3.25
3.45
3.00
2.85
L>ensity
0.303
0.286
0.279
0.295
0.295
0.297
0.300
0.304
0.303
0.307
0.304
0.300
0.306
0.309
Density
2.10
2.37
2.54
2.50
2.55
2.70
2.62
2.61
2.65
2.79
3.25
3.42
3.03
2.90
463
TABLE l-Continued
Corrected, 3 Density Electrons/A Gamma-Ray
CΛ<L>
Car
bon
aal
su
s M
iner
Mis
cella
neo
Compound
CalciteCaCO3
DolomiteCaMg(CO3)2
SideriteFeCO3
AragoniteCaCO3
BariteBaSO4
AnhydriteCaSO4
GypsumCaSO4 2H2O
HaliteNaCl
SylviteKCl
PyriteFeS2
GalenaPbS
ApatiteCa 1 0(Cl,F) 2(PO 4) 6
Electrons/A
0.820
0.853
1.185
0.891
1.208
0.905
0.634
0.624
0.578
1.236
1.870
0.960
(g/cmd)
2.71
2.82
3.88
2.93
4.5
2.98
2.32
2.16
1.99
5.02
7.5
3.17
Density
0.302
0.303
0.305
0.304
0.268
0.303
0.273
0.288
0.290
0.246
0.249
0.303
Density
2.71
2.82
3.91
2.93
3.98
2.98
2.09
2.06
1.91
4.08
6.17
3.17
464
TABLE 1-Continued
CompoundO 3 Density
Electrons/A (g/cm3)
O 3 CorrectedElectrons/A Gamma-Ray
Density Density
Liq
uid
s
WaterH 2O
BrineH2O + NaCl(100,000 ppmNaCl)
n-DecaneC 1 0 H 2 2
n-HexadecaneC , 6 H 3 4
Benzene
TolueneC Λ C H 3
NaphthaleneC , o H
8
AnthraceneC6H4(CH)2 C 6 H 4
0.334
0.354
0.254
0.269
0.285
0.284
0.367
0.398
0.9982*
1.071*
0.730*
0.775*
0.879*
0.866*
1.145*
1.250*
0.334
0.331
0.348
0.347
0.325
0.329
0.320
0.318
1.10
1.17
0.84
0.89
0.94
0.94
1.21
1.31
*20°C
465
The ratio of electrons per unit volume to density departssignificantly from 0.303 in several instances. Smallerratios are found in compounds containing heavier ele-ments (barite, pyrite and galena) and in hydratedminerals (halloysite, expanded montmorillonite andgypsum). These lower ratios indicate fewer electronsper unit volume as compared to density, either becauseof the presence of heavy atoms where atomic weightsexceed atomic numbers by a ratio larger than 2, orbecause of the water molecules which expand thelattice. Ratios larger than 0.303 are found for liquidswhich contain high proportions of hydrogen. Hydrogenaffects the ratio in this fashion because the atomic num-ber and the atomic weight are very nearly equal.
A relative density, correct in terms of electrons perunit volume, can be calculated from the data on Table 1.This corrected density is calculated simply by dividingthe number of electrons per cubic angstrom by 0.303,and places all compounds on a scale relative to quartzand some other common silicates and carbonates. Thiscorrected density is shown in column 5 of Table 1. Ineffect, all compounds are given a constant Comptonattenuation coefficient of 0.100 cm2/gm by thisapproach, eliminating the attenuation coefficient as avariable in computing porosity (Evans, 1965). Theseare the densities used in the porosity computer.
The concept of "density phases" emerges from a con-sideration of Table 1. A "density phase" is definedhere as all compounds having the same number of elec-trons per unit volume. All compounds having this samecharacteristic number of electrons per unit volumewould cause identical intensity reduction by Comptonscattering of a collimated gamma-ray beam. Thus, eachsuch compound would cause identical effects in thegamma-ray porosity device. Compounds making up asingle density phase have identical corrected densities.
Many common silicates could be considered for practi-cal purposes as one density phase of 2.65, as shown byTable 1. For example, quartz, feldspar with a composi-tion intermediate between albite and anorthite, kaoli-nite, and collapsed montmorillonite all have correcteddensities of between 2.6 and 2.65. The potassium andsodium feldspars (orthoclase and albite), along withchlorite, have somewhat lower densities of 2.50 to 2.55.Hydrated clays, such as halloysite and expanded mont-morillonite, have much lower densities. The pyroxenesand amphiboles of both orthorhombic and monocliniccrystal systems are much heavier and their densitiescommonly exceed 3.00. Each of these groups of com-pounds could be considered a density phase.
Of the common carbonate minerals, none is sufficientlysimilar in corrected density to be considered identical.The sulfate, sulfide, and chloride minerals of Table 1each constitute a density phase, with the exception ofgypsum and halite which are together a density phase.
Porous rocks contain two or more density phases. Thedensity phases common in sedimentary rocks are: (1)average silicates—quartz, plagioclase feldspars of inter-mediate composition, most micas, and unhydrated clays;(2) light silicates—potassium and sodium feldspars suchas orthoclase and albite, some micas, and slightly hy-drated clays, (3) calcite, (4) dolomite, (5) anhydrite,(6) gypsum and halite, (7) gas-filled pores—air or gaseoushydrocarbons; and (8) liquid-filled pores—water or oil.
Analog Calculations
The actual attenuation system which approximates theideal absorber is shown in Figure 5. The energy of thesource gamma rays is fixed within certain limits. Thegamma-ray beam is shielded and collimated to make itapproximately parallel; and, a cylindrical or slabbedcore sample replaces the uniform absorber. A Ba 1 3 3
source of 5 to 10 millicuries is generally used as a"monoenergetic" gamma-ray beam. A shielded, colli-mated scintillation detector is used to insure that thetransmitted gamma rays are parallel and monoenergetic.Both the source and the detector collimation slits are1/4 inch diameter cylindrical ports approximately 1-1/2inches long. Figure 5 shows the relative position of thesource and detector shields, the calipers, the drivecarriage, and the liner or core holder.
If the absorber is porous, the bulk density (p B ) is relat-ed to the matrix density (PQ), the density of the fluidin the pore space (p F ), and the amount of pore spaceor porosity (0) by the expression:
(3)
Combining equations (2) and (3) gives
7In = P G ( 1 • Φ) + 0 P F
PG-PT
or
(4)
Since IQ, I, µ and d are easily measured and Pç and p F
of common geologic materials are not difficult to esti-mate with sufficient accuracy for this purpose, theporosity (or liquid content) of the material can be read-ily evaluated from equation (4).
It is convenient to use a small analog computer to makethe porosity calculations at the same time the gamma-ray intensity and the sample thickness are measured.Standard diameter cylinders are used to calibrate thecaliper. The sample thickness (d) from the caliper and
466
the countrate I from the detector are fed into the com-puter. The source intensity I Q is nulled and values forp G , p F , and µ are set on the appropriate potentiometer.
In evaluating equation (4) the most convenient compu-tational procedure is to consider µ a constant, 0.100cm2 /gm, and use corrected grain densities for any sam-ple components having electron factors in the range0.294 >0>O.312.
The corrected grain densities are calculated from thefollowing relationship:
f>GC=T (5)
where θ is the electron factor of the "abnormal" com-ponent, θ is the normal electron factor 0.303, andPç L is the measured grain density of the componentwhich required correction. The corrected densities arelisted in Table 1.
Bulk density is directly measured by the GRAPE devicethrough the determination of the scattering caused bythe rock sample. This bulk density measurement corre-sponds to an evaluation of the number of electrons perunit volume and can be converted to an apparent densi-ty. If values for grain density and fluid density areassumed in equation (2) or (3), porosity can be calcu-lated. If a rock contains two density phases, for examplequartz and air-filled pores, the selection of grain densityand fluid density is straightforward and a porosity canbe directly calculated.
The assumptions made to solve equations (2) or (3) aresomewhat more complex if three or more density phasesare present in the rock sample. If, for example, therock is a calcite-cemented quartz sandstone with air-filled pores, a grain density between quartz and calciteproportional to the relative abundances of the twominerals must be assumed before equations (2) or (3)can be solved. Similarly a quartz sandstone with poressaturated with both gas as a liquid requires the assump-tion that the fluid density is intermediate betweenthose of the gas and the liquid, and is dependent uponthe relative saturation.
Complexities in the mineralogy or the saturation haveeffects on the accuracy of density and porosity deter-minations. It is our experience that most sedimentaryrock systems are sufficiently simple to allow quite accu-rate porosity determinations by the gamma-ray tech-nique—after a brief examination of the rock samples bya geologist.
In summary, the gamma-ray attenuation device is appli-cable to geologic materials. Factors that make the appli-cation of this technique practical are the preponderance
of Compton scattering for gamma rays with the energyused, the close relationship of number of electrons perunit volume to density for most minerals common insedimentary rocks, and the general accuracy with whicha geologist or engineer can judge both grain and fluiddensities in common sedimentary rocks.
The measured bulk density and sample thickness aswell as the computed porosity or liquid content arerecorded on a strip chart. Standard cores or emptyliners are used to calibrate the detector-computer sys-tem. Because the core sample and the recorder chartare driven at the same speed, a direct comparison of therecorded parameters and the actual sample character-istics can be made (Evans, 1965; Harms and Choquette,1965). In addition, a second strip chart records theseparameters on a scale of 5 centimeters of chart to 10meters of core. This scale is identical to the one used inrecording well logs; therefore, a direct comparison ofcore parameters and well logs is possible.
When space is left between samples on the carriage bar,a small section on the ends of each sample is lost to thedensity-porosity computer because the response of thesystem is not immediate. The length of these sectionsdepends on the time constant of the ratemeter, the drivespeed and the condition of the ends of the sample butsections longer than 1/2 inch at either end are unusual.Difficulties due to response time characteristics can beavoided by leaving no space between samples, when thesamples are small.
System Characteristics
Specifically, the GRAPE system was constructed forrapid porosity evaluation of cores in storage as well ascore samples cut during exploration and developmentdrilling, however, the device is quite versatile. Core sam-ples 1 to 4-1/2 inches in diameter, conventional coreplugs, slabbed core, encased, unconsolidated sediments,and other materials can be analyzed at drive speeds upto about 6 inches per minute. At this speed, some 200feet of core can be analyzed in about 6 hours. Thecarriage handles 5-foot lengths of core or liner.
The 1/4-inch diameter collimating slits produce agamma-ray beam which varies in size with the sourceutilized to the detector spacing (which, in turn, dependson the sample thickness), but the average beam diame-ter at the center of the spacing is slightly less than1 /2 inch. Inhomogeneities such as layers, inclusions, vugsand other minor features with dimensions which are notsmall compared with the beam diameter have a majorinfluence on the calculated porosity. The sample can berotated to change the beam path and rerun to alter theeffect of vugs or nodules. The relation of the stripchart to the path of the beam penetrating the sample isthen necessary for future reference.
467
The device is designed for use in either the field or thelaboratory by one operator. The same operator canassemble or disassemble the device without assistance.Because the device is readily portable, it provides aninexpensive and rapid method of evaluating old or newcore for porosity and density. This information is ofimmediate interest to the log analyst, the geologist, thegeophysicist and the engineer in both exploration andreservoir evaluation.
The total error of the system, including statistical vari-ations in source strength and electronic drift, is less than±1 per cent porosity at the 20-per cent porosity level.Errors due to poor choices of matrix density or fluidsaturation for a particular sample are discussed else-where (Harms and Choquette, 1965).
Applications of the Attenuation Method
The gamma-ray technique yields a value for bulk densi-ty which may be applied to some geophysical problems.For example, a knowledge of bulk density or porosityand lithology allows the estimation of acoustic wavevelocities. Values of bulk density can therefore beuseful for interpreting effects seen on acoustic and den-sity logs. Detailed knowledge of acoustic wave veloci-ties can, of course, be applied to many general seismicproblems.
Bulk density values readily obtained by the gamma-raytechnique can also be useful in the interpretation ofgravity data, and in determining the physical propertiesof encased geologic materials.
The proportions of two density phases within a rocksample can be analyzed if there is a reasonable contrastin grain density between the two phases and if the rockis non-porous. Several examples of this application ofthe gamma-ray technique can be pointed out.
It is possible to determine the proportion of kerogenin oil shales. Oil shale is non-porous, contains littlewater, and commonly is layered in a manner reflectingthe per cent of kerogen. The kerogen has a density ofabout 1.10 and the rock matrix has a density that aver-ages about 2.70. Since in an oil-shale core the corre-sponding trace records the per cent of kerogen, thekerogen layering is clearly recorded on the gamma-raytrace. Average values of the per cent of kerogen reportedfor an interval correspond reasonably well to the amountof oil recorded from the same interval (Evans, 1965;Harms and Choquette, 1965).
Variations of the gamma-ray trace recorded for a rocksample can be used simply to locate changes within thesample and to guide sampling procedure. In applicationsaimed at the determination of porosity, bulk densityor compositions, assumptions concerning the graindensity and fluid density are made that are based on
observation or experience. In cases where observationor experience can be used to only a limited degree as aguide to analysis, the variations in the gamma-ray tracecan be employed to select material for more compre-hensive or complicated types of analyses. Such a guidecan be very important in optimizing the amount of in-formation derived from these additional analyses.
An example may serve to illustrate this point. The coresare taken from a potential reservoir interval. Someknowledge of the porosity distribution within thisreservoir is desired, but it is known that the mineralogyof the rock is complex and many density phases arerepresented. The core is run through the gamma-raydevice using intelligent guesses for grain and fluid den-sities. The trace recorded for this core may show rela-tively little or a great deal of variation. It is commonpractice in the industry to take samples at one-footintervals for porosity, density, permeability, and satu-rated determinations. When such a sampling program iscompared to the gamma-ray trace, the sampling may befound to be entirely inadequate or much too complete,depending on the degree of heterogeneity expressed bythe trace. The implications are obvious: in the onecase, an inadequate representation of porosity andporosity variations is obtained; and, in the other case,the additional analyses represent an unwarranted ex-pense. Obviously, the same reasoning applies to encased,unconsolidated sediments obtained in deep sea coring.
The basic assumption made in the use of the gamma-ray device as a sampling guide is that related rockmaterials made up of numerous density phases will notappear homogeneous to the device unless they areindeed alike. Although exceptions to this assumptioncan be found, such cases are extremely uncommon.
Samples are sometimes encased in metal or plastic con-tainers and cannot be analyzed in conventional ways.Cores of modern sediments are commonly taken inaluminum or plastic tubing, and cores of unconsolidatedor fractured reservoirs are taken in rubber sleeves, sothat direct observation of the core material in an un-disturbed state is impossible. Most of our experiencehas been with cores of Recent carbonate sedimentsencased in aluminum tubing and cores cut in rubbersleeves. The traces clearly locate areas of bubbles andliquid distribution (or content) porosity or composi-tional changes which can guide sampling. Such a tracepreserves an important permanent record of the condi-tion of the core material before it is disturbed by sampl-ing or removal from confinement.
The GRAPE device can be adapted to determine densityor locate density contrasts in pressure bombs or tubessubjected to elevated pressures and temperatures. Forexample, the existence of a fluid interface and the posi-tion of the interface in a pressure bomb can be
468
determined. Such information is valuable in establishingphase relationships. The bulk density or porosity ofjacketed rock samples can be measured while the sam-ple is subjected to elevated pressure. This informationis useful for determining properties of rocks undervarious states of stress.
Conclusions
A rapid, accurate, and continuous method for measur-ing porosity or bulk density of cores from bore holeshas been developed. The method is based on gamma-ray scattering. The principle technical advantage of thisporosity measuring method is that variations in porosityencountered by a moving, pencil-sized gamma-ray beamare recorded continuously.
Excellent agreement exists between porosities anddensities of common sedimentary rocks obtained bythis method and other conventional methods. Thisagreement reflects two factors. First, Compton scatter-ing, the collision of gamma rays with electrons withinthe measured material, is essential for the productionof the energy of gamma-rays emitted by the sourceused in this device. Second, the number of electronsper unit volume is closely related to density for mostminerals commonly found in sedimentary rocks. There-fore, the amount of Compton scattering can be used toaccurately measure the bulk density of the rock sam-ple penetrated by the gamma-ray beam.
Porous rocks contain two or more "density phases". Adensity phase is defined as one or more non-porousminerals or fluids having a characteristic number ofelectrons per unit volume. If a rock contains two densityphases and the density of each phase is known, thevolumetric proportions of each phase can be directlydetermined. If a rock contains three or more densityphases, the determination of the proportions of eachphase is more complicated, but it can be achieved ifaccurate average densities are assigned to the grains andto the fluids. This can commonly be done with enoughprecision to yield accurate porosities or fluid contents.
Porosity variations within sedimentary rocks reflect thefactors controlling the development of porosity. Porosi-ty variations are commonly -more extreme and lesspredictable where controlled by cementation, solutionor fracturing.
The GRAPE device can be applied to a variety ofproblems. These include saturation determination ofcomponents or front identification of recovery floodfluids in observation wells, in engineering geophysicsproblems, and, in the mining industry, as a means ofmeasuring the ore content of drill core or rock sampleson the surface or in hole. The principle application is tothe determination of density and porosity and theirvariations within sedimentary rocks. However, the
results can also be applied to geophysical problemswhere values for bulk density are useful. The gamma-ray device can be used to analyze the composition ofrocks under certain conditions. Traces derived from thegamma-ray device can be used simply as guides to sam-pling for further analyses. Samples encased in metal orplastic under normal or elevated pressures and tempera-tures can be analyzed without disturbing sample condi-tions. Directional properties of rocks can, in some situ-ations, also be detected. The most important applica-tions at present are to measuring the average porosityand porosity and density variations of sedimentaryrocks and to developing guides for sampling.
Acknowledgemen ts
Attention should be drawn to significant contributionsto this work by C. H. Cotterell, who was responsiblefor development and testing of the device as an opera-ting system, by I. D. Johnson, who designed the opticalcalipers and most of the basic electronic circuits of theratemeter and drive system, and by J. E. Beitel, whoassisted in the design, development, and testing, andalso established operating procedures for the GRAPEsystem. Cotterell and Beitel also carried out the experi-mental porosity and absorption coefficient determina-tions. J. C. Harms and P. W. Choquette selected mostof the minerals and rock samples for use in porosity,grain density and absorption coefficient measurements,and C. L. Sutula assisted in computing the electrondensity. Finally, the Marathon Oil Company should beacknowledged for granting permission to publish thissection.
REFERENCESBeitel, J. E., Cotterell, C. H. and Evans, H. B., 1965.
"Gamma-Ray Attenuation Porosity Evaluator Op-eration and Service Manual." Internal Report No.65-6. Marathon Oil Company, Jan. 1, 1965.
Devar-Kinetics Division of Consolidated Electrody-namics. "18-301A Recorder Instruction Manual."No date.
Devar-Kinetics Division of Consolidated Electrody-namics. 1963. "Porosity Computer Component Man-ual." 1963.
Evans, H. B., 1965. "GRAPE-A Device for ContinuousDetermination of Material Density and Porosity."Transactions, Sixth Annual SPWLA Logging Sym-posium. 2, B1-B25, Dallas, Texas, May 4-7, 1965.
Evans, H. B., Harms, J. C. and Choquette, P. W., 1965."A Device for Continuous Determination of CorePorosity." Technical Report No. 65-8U, MarathonOil Company, March, 1965.
Harms, J. C. and Choquette, P. W., 1965. "GeologicEvaluation of a Gamma-Ray Porosity Device."Transactions, Sixth Annual SPWLA Logging Sym-posium, 7, C1-C37, Dallas, Texas, May 4-7, 1965.
469
Figure 4. The Complete GRAPE System (Single Recorder)Showing: A. Power Supply Case, B. Computer Case,
C. Strip Chart Recorder, D. Optical Caliper,E. Core Sample, F. Source Shield (TheDetector Shield is Directly Behind TheSource Shield and Hidden by it), G. MainFrame, H. Core Carriage, . Direction ofCore Travel, J. Vertical Centering Spacers.
470
Figure 5. Frame and Carriage AssemblyA) Optical Caliper B) Source ShieldC) Detector Shield D) Core SampleE) Carriage Bar F) Carriage BedG) Main Frame
471
General Information
Frame Section
The frame section is the measurement portion of thegamma-ray attenuation device. It consists of the sourceshield, detector shield, moving carriage and calipers(see Figure 5). The source shield contains the gamma-ray source capsule (either a Ba133 or Cs137 source of1 to 10 millicurie is used). This shield is a lead spherewith an outer shell of steel for support. The sourceshield has a removable front with a 1/4 inch diameterhole for collimating the gamma-ray beam. The back ofthis shield is removed when the source is placed in theshield or removed from the shield.
The detector shield contains the crystal which is 1-1/2inch diameter by 2 inches long, and a 2-inch photo-multiplier tube (see Figure 5).
The carriage for the core consists of a bar for support-ing the core and a bed which moves down a track be-tween the source and detector (see Figure 5). Thedrive mechanism is controlled by a speed selectorswitch with positions 0.5 through 3.5 inches/minute.This varies the rate of travel of the carriage throughthe gamma-ray beam.
The optical caliper is in two sections. One section islocated on top of the source shield, and the other islocated on top of the detector shield (see Figure 5).Reflecting tape is located below these caliper sections.The principal of operation of these units is as follows:A light beam from a light source is reflected by thetape back to a photodiode in the caliper. The photo-diode, senses the light and moves forward until the sideof the core blocks the reflected light. The sensing por-tion then holds in a position that allows only part ofthe light to be reflected. If the core diameter getslarger, the light is cut off and the caliper retracts untilpart of the light is again reflected. This system enablesthe calipers to follow both sides of the core. Becauseboth of the trackers are connected electrically, adifferential output voltage is applied to the computerand to the recorder. This voltage is calibrated to givethe core diameter.
Power Supply and Controls
The power supply section contains the direct currentpower supplies for the stepper motors, the motordriver circuits, the caliper servomotors, the caliperlamps, and the photomultiplier tube. This case has thespeed controls as well as the power supply switches.
Analog Computer
The analog computer case contains a special purposecomputer designed to evaluate equation (3) in thefirst section of the Introduction. The computer operateson all of the input variables from the different sections
of the GRAPE device and uses them to evaluate theequation. The outputs from the computer and thecaliper are recorded on strip chart recorders.
The computer case also contains the caliper servoam-plifiers, the scintillation detector ratemeter and loga-rithmic amplifier, and the recorder calibration voltagenetwork.
Recorders
The output from the computer is recorded on thepaper strip charts of two 3-pen recorders. The threevariables recorded are: 1) core diameter - red pen scaled0-5 inches, 2) bulk density - green pen scaled 0-2.5gm/cc or 1.0-3.5 gm/cc, 3) computed porosity - bluepen scaled 0-50 per cent with possibility of scalingfrom 0-100 per cent.
The chart drive of one recorder is driven by a steppermotor at the same rate the core samples move past thesource and the detector. This recorder gives a one toone correlation between the strip chart record and thecore. The second recorder is driven at a 200:1 reduc-tion, yielding a chart curve that is comparable to a logrecorded at 5 centimeters of chart per 10 meters ofhole.
6. Sonic Velocity Measurements
General Considerations and Equipment
The objective of the sonic velocity measurements is tomake continuous sound speed measurements along thecore lengths in order to provide the basic informationnecessary for understanding the acoustic propertiesof the ocean bottom and their relationships to sedi-mentary properties and processes. The measurementsare generally made at three places along each 150-cen-timeter core section using a pulse system capable ofmaking sound speed measurements through a coreliner with minimum disturbance to the sediment sam-ple. The velocity profile for each core section is meas-ured four hours after the core has been recovered. Thisallows this core to come to the ambient laboratorytemperature. The measurements through the core linerare accomplished by using a specially designed trans-ducer configuration that is coupled directly to the coreliner. The transducer head is moved along the coreliner to repeat the measurements at any desired inter-val. The transducer head is illustrated in Figure 7.
The pulse method involves measuring the travel timeof a transmitted wave over a known path length. Thetechnique employed for the sediment sound speedmeasurements differs from direct measurements oftravel time in that sound speed is determined by com-paring the travel time through the core sample to thetravel time through a reference sample having a knownsound speed. Distilled water is used as the reference
472
OUTPUT
PULSE AMPLIFIER
(UNDERWATER SYSTEMS, INC.)
IIV PUT
TRANSDUCER HEAD
(UNDERWATER SYSTEMS, INC. MODEL 102 B)
INPUT OUTPUT
PULSE GENERATOR
(GENERAL RADIO MODEL 1217C)
+OUTPUT -OUTPUT
r
INPUT
OSCILLOSCOPE
(TEKTRONIX 561)
EXTERNAL TRIGGER IN.
Figure 6. Block Diagram of Sediment Velodmeter.
TRANSDUCER HEAD WITHCORE LINER TRANSDUCER HEAD
Figure 7. Photos of transducer heads.
sample. The advantage of the comparison method isthat it eliminates the need for absolute measurementsof transit time.
The sediment velocimeter system is illustrated in ablock diagram in Figure 7. Barium titanate transducersare excited to emit ultrasonic pulses in the compressionalmode. A General Radio 1217C pulse generator, followedby an Underwater System, Inc. pulse amplifier, is usedto excite the transmitting crystals at their naturalresonant frequency of approximately 400 kHz. A 250volt pulse of about 0.5 microsecond duration is usedto obtain the sonic ring. The transmitted pulse is alsoused to trigger the sweep of a dual trace Tektronix561 oscilloscope-with a 3A72 and a 3B3 plug-in unit-which is used to display the received signals.
Sound Speed Measurements Across theDiameter of the Core
The sediment sound speed across the diameter of thecore (through the core liner) is determined by meas-uring the difference between the transmission timethrough the core sample and the transmission timethrough the reference distilled water sample. Beforestarting the sediment sound speed measurements, aseries of tests are conducted to insure that the systemis functioning properly. After completing the check-out procedure the first step in the actual measurementis to insert the reference sample into the transducerhead. Both the reference and sediment sample linersshould be kept moist when inserted into the trans-ducer head to insure maximum coupling between thecore liner and the transducers and to prevent damageto the membrane enclosing the transducer crystals.Either a soapy water solution or glycerine is used asthe lubricant. The reference sample is contained ina core liner identical to the liners used for the coresections. The crystals in the transducer head arereciprocal, and either one can be used as the trans-mitter. The pulse repetition rate is adjusted so thatreverberation from the preceding pulse has fully decayedprior to the next pulse.
After the reference sample is in the transducer headand the acoustic signals are transmitted, the delay timecontrol, delay time multiplier, and sweep rate on theoscilloscope are adjusted so that one of the receivedpulses is conveniently expanded, in order that the de-sired portion of the wave train is displayed at thevertical center line of the oscilloscope. Generally, thethird cycle of the wave train is used for the measure-ment. After the peak of the third cycle is aligned at thecenter of the oscilloscope face, the delay time and delaytime multiplier settings are recorded in the data logbook.
The reference sample is then removed from the trans-ducer head and replaced by the core section. The
oscilloscope sweep rate and delay time multipliershould not be changed. The signal transmitted throughthe core sample is then aligned using the delay timecontrol, so that the third cycle of the received wavetrain is at the center line of the oscilloscope. The delaytime control setting is then recorded in the data log.It is important that the same portion of the referenceand core sample wave train be used for making thetravel time difference determination.
After completing the series of sediment sound speedmeasurements along the core section, the referencesample time measurement is repeated. The referencetime measurement may be repeated more often if de-sired; however, this is not necessary unless the tem-perature in the laboratory is fluctuating rapidly duringthe course of the measurements. It is important thatthe temperature of the reference sample and the coresample be measured at the time the measurements aremade. A thermometer is sealed in the reference sample,while the temperature of the core sample is determinedby inserting a thermistor probe or small thermometerin the ends of the core section. The temperaturemeasurement is essential, since both the reference andcore sample velocities are a function of temperature.
The core liner surrounding the reference sample com-pensates for the contribution of the liner surroundingthe core sample and the transmitter-receiver pathlength is fixed, so that the only difference between thetwo samples is in the sound speeds corresponding to thedistilled water and sediment. The difference in traveltimes between the water and sediment is determinedfrom the delay time settings and the difference thenis used to compute sediment sound speed as follows:
w Cw ew s S es
where:Cs = sediment sound speed,Cw = sound speed of reference sample (distilled
water),Tw = transit time through reference sample, in-
cluding core liner, and electronic delay,Ts = transit time through sediment sample, core
liner, and electronic delay,d = inside diameter of core liner,Tew = electronic delay time for reference sample,
andTAO = electronic delay time for sediment sample.
SinceT = Tes, sediment sound speed is determined by
^"rë "w
475
Measurement Accuracy
The overall estimated accuracy for the measurementmade across the diameter of the core depends on:(1) the accuracy to which Cw is known; (2) theaccuracy in measuring (T - Ts); (3) the accuracy inmeasuring the diameter of the core liner; (4) theoscilloscope incremental time delay error; and, (5) thedifference in electronic delays associated with thereference and core sample measurements.
The estimated total error is determined by taking thesquare root of the sum of the squares of the individualerrors. While it is difficult to assess the individualerrors, the following factors should be considered:(1) Cw is known from Wilson's tables and is subject toto error in determining the reference temperature andpossible contamination of the distilled water; (2) thetravel time difference (T - T ) can be measured witha maximum error of 0.02 microseconds; (3) the insidediameter of the core liner can be measured to 0.001inch, although some error may result from possiblevariations in the thickness of the core liner; (4) thereis a maximum oscilloscope incremental time delayerror of 0.4 per cent, and, (5) the electronic delaysfor both the reference and sediment samples are equal.Considering these factors, the overall estimated accu-racy is about 0.5 per cent.
7. Thermal Conductivity
Thermal conductivity measurements are made on onesection of each core using a probe device. The proce-dures followed are essentially the same as those de-scribed by Van Herzen and Maxwell (1959).
Reference
Von Herzen, R. P. and Maxwell, A. E., 1959. Meas-urements of thermal conductivity of deep seasediments by a needle probe methods. /. Geophys.Res. 64, 1557.
8. Core Splitting
A whole 150 centimeter core section is placed in thecore cutting jig so that the core can be split longitudi-nally along an inscribed mark separating the identifiedsides of the core. A partial cut is made through bothsides of the core liner with a circular saw mounted onthe jig. Care is taken to avoid cutting through theplastic into the sediment since this might contaminatethe sediment with a variety of plastic and other mater-ials which are stuck to the cutting blade. After cuttingpartially through the plastic liner, a modified tilecutter is used to cut through the remaining thicknessof plastic. This avoids cutting deeply into the core.After the core liner has been cut completely through ondiametrically opposed longitudinal lines a coping sawfitted with a stainless steel piano wire blade is usedto cut entirely through the sediment by drawing the
piano wire through the longitudinal cuts as if cuttingcheese. After cutting through the unconsolidated sedi-ment with the piano wire cutter, the two half sectionsare separated and, if necessary, the cut surface of thecore is cleaned by scraping the sediment with a spat-ula. The sections are then designated working andarchive halves, respectively. In order to protect themwhen they are not being processed, the core halvesare stored in protective plastic tubing, D-shape incross-section.
9. Core Photography
The photographic equipment in use aboard GlomarChallenger was especially designed to take picturesof core samples. The equipment consists of:
(1) A ten-foot rubber belt conveyor and two 150-centimeter length core trays to transport thecore samples into picture-taking position belowthe cameras.
(2) Two cameras, one containing black and whitefilm and one containing color film, set to con-tinuously record 25-centimeter lengths of coresample.
(3) An electronic flash strobe unit to supply thenecessary light.
(4) A dual relay and timer circuit to control thesequence of pictures taken.
The procedure then is to photograph a split half-sectionof core which is clearly identified with all the necessarynumbers. The core is always positioned so that thecamera travels from the top to bottom of the core sec-tion in fixed increments.
Aligned with the core sample is a 150-centimeter scalemarked in centimeters with heavy markings each 25centimeters. The scale is photographed along with thecore section. The core camera tray is painted with an18 per cent gray scale. A Kodak color scale is photo-graphed along side each core section so that color re-production can always be related to a standard, therebymaking it possible for any color processing laboratoryto produce the correct printed color temperature.Panatomic X and 5251 Kodak color negative film arethe two films used. These are processed in the mannerspecified by the manufacturer, the black and whitefilm being processed on board ship, using a Houstonmodel BW-3510 film processor.
10. Procedure for Shipboard Sampling and Analysis ofInterstitial Water in the Cores
The purpose of this operation is to preserve sedimentand pore water samples for onshore laboratory studiesof components of interstitial waters, and to make ship-board analyses of the more perishable components.
In a few cases prior to cutting the core it is drilled withan auger and any gases released are collected with a 20 ccvacutainer. About 200 milliliters of gas are collected
476
with a plastic syringe at the exit to the drill; this syr-inge is first quickly washed with some of the gas. Thissample is injected into a 10-foot gas chromatographycolumn.
Later, after splitting, three samples are taken fromthe core center for each 20 meters of sediment pene-trated. A 2.5-centimeter diameter plastic syringe withthe end cut off, and sharpened, or one of the plasticsamplers provided, is driven 5 centimeters into the sedi-ment. If the sediment is hard or brittle, an equivalentsection is removed with a hammer and knife. One sam-ple is immediately placed in a wide-mouthed bottle withPolyseal screw cap. Excess space in the bottle is filledwith Saran Wrap enveloping moistened laboratorytissue (to maintain constant water vapor pressure inthe bottle). The bottle is stored cool (not frozen) in acontainer in a refrigerated core van.
The second and third samples are extruded into thebarrel of a specially designed passivated stainless steelsqueezer (Manheim, 1966) which is placed in a hy-draulic press and squeezed under 2,000 to 10,000pounds pressure. During squeezing the pore waterpasses into a plastic syringe forcing the plunger beforeit, essentially prohibiting evaporation. The syringe isthen capped with a millipore filtering attachment; 12to 15 milliliters of fluid will often, but not always, beobtained.
About 0.6 milliliters of fluid is expressed through thesyringe needle with half of this amount going into eachof two evacuated glass stopcocks which have an en-larged center hold. These stopcocks are designed fora direct attachment to extraction lines for H/D andO18/Ox 6 analyses. In view of the later limited quantitythe interstitial-water samples, it is extremely importantto follow the correct sampling and storage proceduresin order to avoid alteration of the original isotope con-tent through evaporation, exchange or contamination.
An additional drop or two of fluid is expressed forsalinity determination with a Goldberg hand refracto-meter, about 0.3 milliliters for gas analysis, and 1.2milliliters for Eh, pH, S=, and Ca++ analysis with theU.C.L.A. electrochemical unit.
An additional 5 to 6 milliliters are fuse sealed in poly-ethylene tubing for later laboratory analysis of sodium,potassium, calcium, magnesium, strontium, chlorine,sulfate and iron, silicon, barium, boron, etc. in the >1 mg/1 range. The remainder of the fluid is frozen in apolyethylene bottle with a nitrogen gas phase.
A fourth small sample from the core center is taken ona series of at least 4 cores from each of 4 or 5 holesfor various carbon dioxide analyses. The objective is totake at least 20 of these samples per leg, such as sevenfrom each of 3 or 4 holes top to bottom, or four from
each of 5 holes. Five milliliters of fluid squeezed fromthis sample is injected directly into a double glassstopcock for measurement of pCO2 and total CO2
(carbon dioxide) ashore. The sample is to be acidifiedwith phosphoric acid, or one that does not containsulphur. Subsequent to the carbon dioxide analysis,the water will be used to determine sulphur isotoperatios on the sulphates. Five milliliters of solution arealso to be apportioned for carbon-isotope studies. Onlyrarely will the single sediment sample for the carbondioxide studies provide the 10 milliliters required forthe two aliquots (5 milliliters for total CO2 - pCO2
and 5 milliliters, for C-isotope). When more solution isrequired to achieve a total of 10 milliliters, theamount needed would be taken from the aliquot of thesolution for major element analysis that is ordinarilyfrozen (that stored in the polyethylene bottle with anitrogen atmosphere only). The removal of some ofthe latter solution must be done prior to freezing, andthe two portions (that from the polyethylene bottleand that from squeezing the sample whose effluent isfor carbon-dioxide analysis) must be mixed before thetwo 5-milliliter samples are apportioned.
Dense samples are squeezed in a similar manner withsomewhat higher pressures and longer squeezing periods.If the volume of squeezed water is less than 2 cc, it maybe necessary to duplicate the second sample, or reducethe scope of the analysis. If a sample has porosity butit is too lithified to be squeezed, such as, a metamorphicrock, it is preserved in a wide-mouthed bottle forfuture leaching to determine the chlorine content andpossible other major constituents.
On each leg, four large samples are taken, one in each of4 holes preferably at depths below 100 meters. Ideally,the samples should be fine grained and the least con-taminated with drilling fluid. They should be largeenough to yield a total of 100 to 125 cc of fluid onsqueezing (probably 800 to 1000 grams) successiveportions.
11. Penetrometer Measurements
This test is made to give a relative measure of indura-tion of unlithified sediment. Its purpose is to supple-ment the core description made aboard ship, and itshould not be considered a true measure of sedimentstrength. The instrument used here is the AP-210penetrometer (Soil Test, Inc.) which consists of a testrod into which a standard needle can be mounted andwhich can be released under known loads by a clutchmechanism. Penetration of the needle into a sedimentsample can be read on a four-inch diameter dial. Theequipment comes with weights for penetration loadsof 50 and 100 grams. The test follows the "Standardmethod of test for penetration of bituminous mater-ials" (American Society for Testing and MaterialsDesignation D-5-65).
477
SLIGHT \ MODERATE ' GREAT
Plate 2. Degrees of mottling.
In measuring the induration of a core of uniform sedi-ment, tests are made at 3 points on each core section(the same as those where sonic velocity measurementsare made). However, if a variety of lithologies arepresent then the spacing of the tests is varied to givea better representation of these different lithologies.
12. Visual Core Descriptions
As soon as possible after splitting, a visual descriptionof the split core is made. This is probably one of themore important records made aboard ship. Photo-graphs certainly duplicate some aspects of this de-scription, but the on-the-spot observations of trainedgeologists are invaluable. If the description is delayed,the colors of the core materials may change and, aftermany of the cruise legs, core materials do not reachthe shore laboratories in time to be described beforepreparation of the initial report.
A free form of description is commonly followedwhich allows the geologists to make whatever observa-tions they feel are most significant. However, particularattention is paid to such features as color, internalstructures, and disturbances due to drilling, texture andcomposition of the core material. Color determinationsare made as far as possible on the freshly split, wetcore by comparison with the GSA rock and soil colorcharts under uniform lighting conditions by usingdaylight fluorescent illumination. Munsell Color Chartsare also available.
Visual description of the minor structures is to someextent supplemented by the X-radiographs, and partic-ular attention is paid to such things as: the nature ofthe bedding, disturbance of the core due to drilling,the presence or absence of mottling, etc. The degreeof mottling (from slight, moderate, to great) is assignedaccording to the standards given in Plate 2.
When describing, in general terms, the texture of thecore material, the Wentworth scale is commonly used.Any textural classification is, of course, superseded orsupplemented by the results of the on-shore labora-tory work on grain size analysis. In general, sedimentsare classified by texture according to the classificationscheme devised by Shepard (1954).
The major components of the sediment composition, tothe extent that these can be recognized with the nakedeye, are described in general terms. These descriptionsare supplemented by smear slide studies and later, on-shore studies of the coarse fraction composition andthe overall X-ray mineralogy of the sediments. In gen-eral, the scientists have attempted to follow thecompositional classification for marine sediments pro-posed by Olausson (1960).
13. Sampling
After a visual description of the cores has been made,they are sampled before being sent to the refrigeratedcore vans for storage. Because the cores, traveling inrefrigerated storage on the Glomar Challenger, areonly off-loaded at American ports, there is an extensiveshipboard sampling program. On board ship, the sam-ples are stored under refrigeration until the end of eachcruise leg, when they are flown back to the mainlandfor further study in shore-based laboratories. Thesestudies are then incorporated into the initial reportsof the Project.
In dealing with soft sediments, larger samples are takenby means of a tube or syringe that can be packaged ina labeled vial with the sample. Smaller samples aretaken with a scoop or knife. Every precaution is takento avoid possible contamination. Hard sediments aresampled by breaking off pieces with a scoop, knife,spatula or hammer and they are packaged and labeled inthe same manner as soft sediments. Igneous or meta-morphic rocks are not sampled on board beyond a fewsmall pieces which are taken for the preparation of thinsections.
The results of the visual core description and smearslide examination determine whether or not samplesfor particular purposes are taken and, to some extent,these results effect the size of those samples. Similarly,the spacing of samples is governed by the variabilityof lithological types cored. In long sections of uniformsediment, however, every attempt is made to obtaina reasonably representative and uniform coverage ofsamples.
The following table gives a list of the main types ofsamples, together with the purposes for which theyare taken, and the approximate size of the samples.This list does not include the interstitial water sam-ples or any samples, which may be taken for thinsectioning.
Type and Purpose Sample Size
Grain size and coarse fractionWater content and carbon
carbonate
X-ray mineralogy
Shipboard foraminiferalstudies
Shore-lab foraminiferalstudies
Shipboard radiolarianstudies
10 cc
2 cc
10 cc
2-10 cc, depending onthe abundance offoraminifera
2-10 cc, depending onthe abundance offoraminifera
1-10 cc, depending onthe abundance ofRadiolaria
479
Shore-lab radiolarian studies
Nannoplankton studies -Shipboard
Nannoplankton studies -USGS, La Jolla
Nannoplankton studies -Miami
1-10 cc, depending onthe abundance ofRadiolaria
1 cc
2cc
2cc
The grain size and coarse fraction samples are used forpaleomagnetic studies prior to grain size analysis. Forthis reason, they are taken in oriented sample tubes,which are scribed in such a way that the vertical andhorizontal axis within the core can be readily deter-mined.
Samples taken for smear slide preparations are not re-corded since the volume of material taken is trivial.
TIME STRATIGRAPHIC FRAMEWORK
Because a large number of paleontologists with differ-
ent views are participating in the work leading to the
initial core descriptions, the JOIDES Advisory Panel on
Paleontology and Biostratigraphy recommended a sche-
me of period/system, epoch/series, age/stage classifica-
tions for uniform application in this work. It is pro-
bable that no worker will be happy with all of the
details of this scheme—indeed, there was not unanimity
among the members of the panel that formulated it.
But it has been necessary to apply such a scheme uni-
formly in order that the contributions of diverse
authors can be integrated into a coherent whole.
TIME STRATIGRAPHIC FRAMEWORK
CE
NO
ZO
IC
QU
AT
ER
NA
RY
TE
RT
IA
RY
PLE
IST
OC
EN
E-
RE
CE
NT
PLIO
CE
NE
MIO
CE
NE
Upp
erL
ower
Upp
er
Stage
Calabrian
//
/Astian '
//
//
//
// Piacenzian
//
Zanclian (A)*
Messinian
Bibliographic reference to the concept of the stratotype beingapplied for the purposes of this manual.
Gignoux, M., 1910. Compt. Rend. Acad. Sci. Paris. 150, 841.Gignoux,M., 1913. Ann. Univ. Lyon. 36.Gignoux, M., 1948.Intern.Geol. Congr. 18th (Report published 1950).Gignoux, M., 1952. Congr. Geol. Intern. Compt. Rend. 19th (Report
published 1954).Gignoux, M., 1954. Congr. Geol. Intern. Compt. Rend. 19th p. 249.Selli, R., 1962. Quaternaria. 6, 391.
Astian:de Rouville, P. G., 1853. Description geologique des environs de
Montpellier. Boehm (Montpellier), 185.
Piacenzian:Mayer-Eymar, C, 1858. Verhandl Schweig. Naturforsch. Ges. 17-19
Aug. 1857.Pareto, L., 1865.Bull. Soc. Geol. France. (2), 22, 209.Gignoux, M., 1915. Bull. Soc. Geol. France. (4), 14, 338.Gignoux, M., 1924. Boll. Soc. Geol. ltd. 42, 368.di Napoli-Alliata, 1954. Congr. Geol. Intern. Compt. Rend. 19th.
p. 229-234.
Seguenza, G., 1868. Bull Soc. Geol. France. (2) 25,465.Baldacci, L., 1886. Mem. Descrit. Carta Geol. ltd. 1,1.Ogniben, L., 1954. Mem. 1st Geol. Mineral. Univ. Padova. 18.Wezel, F. C , 1964. Riv. ltd. Pal. Strat. 70, 307.
Mayer-Eymar, C, 1867. Catologue systématique et descriptif desterrains tertiariris qui se trouvent au musée federal de Zurich.(Zurich) 2, 13.
^Capital letters in parentheses refer to "Notes on concepts of stages and other boundaries".
480
u1—1
oNOzw
>:<H
wH
W
zwo5;i =S
ww00
0
UJZPJu0tü
0)PH
P
J2
3
Tortonian (B)
Langhian (C)
Burdigalian
Aquitanian
Bormidian
Chattian
Rupelian
Lattorfian
in<u
P
„'*Priabonian ^
Mayer-Eymar, C, 1858. Verhandl Schweiz. Naüirforsch. Ges. 17-19Aug., 1857.
Gino, G. F. etal, 1953.Riv. Ital Paleont. Mem. 6. 7.Giannoti, A., 1953. Riv. Ital. Pal. Strat. Mem. VI, 168.Cita, M. B. etal, 1965.Riv. Ital. Pal. Strat. 71, 217.
Pareto, L., 1865. Bull. Soc. Geol. France. (2) 22, 229.Cita, M. B. and Silva, I. P., 1960. Intern. Geol Congr. 21st, Copen-
hagen, 1960, Rep. Session, Norden. 22, 39.Cita, M. B. and Elter, G., 1960. Accad. Nazi dei Lincei. Ser. 8 (5),
29, 360.
>»oo *ö <ÜO ^ K <ü
S 00 ^ &a
S S a. c
3 £ <*
<U s* cd Q _,«•G 5i tt) i i °^tβ ^ M r t OS
si, cj rr g T3 s >
S 0 S δ
2 ob 2 0O> δ G
Burdigalian :Depei et, C, 1892. Compt. Rend. Soc. Geol
France. (11), 145.Deperet, C, 1893. Bull Soc. Geol France. (3)
21,263.Dollfus, 1909. Bull Serv. Carte Geol France.
(124) 19, 380.Drooger, C. et al, 1955. Koninkl Ned. Akad.
Wetenschap. Verslag Gewone Vergader.AfdelNat. Ser. 1 (2)21,1.
Aquitanian:Mayer-Eymar, C, 1858. Verhandl. Schweiz. Nat-
urforsch. Ges. 17-19 Aug., 1857, p. 188.Tournouer, R., 1862. Bull Soc. Geol. France.
Ser. 2, 19, 1035.Drooger, C. W. et al, 1955. Koninkl Ned. Akad.
Wetenschap. Verslag Gewone Vergader. AfdelNat.
Szots, E., 1965. Bull. Soc. Geol France. (7) 7,743.
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Lorenz, L., 1964. Bull. Soc. Geol. France. Ser. 7, 6, 192.
Fuchs,T., 1894. Jahresber. Ungar. Geol. Anstalt. 10, 172.Gorges, J., 1952. Abhandl Hess. Landesametes Bodenforsch. 4, 1.Hinsch, W., 1958. Lexique Strat. Intern. I 5hl.Anderson, H. J., 1961. Meyniana. 10, 118.Hubach,H., 1957. Ber. Naturhist. Ges. Hannover. 103.
Dumont, A., 1849. Bull. Acad. Roy. Med. Belg. (1) 16, 370.Batjes, A., 1958. Inst. Roy. Sci. Nat. Belg. Bull. Mem. 143.
Mayer-Eymar, C, 1893. Bull. Soc. Geol France. (3) 21, 8.Munier-Chalmas, E. and de Lapparent, A., 1893. Bull. Soc. Geol.
France. 21,478.vonKoenen, A., 1893-1894. Abhandl. Geol Spec. Preussen. 10, 1005.Krutzsch, W., and Lotsch, D., 1957. Geologic 6, 476.Krutzsch, W. and Lotsch, D., 1958. Ber. Deut. Geol. Ges. 3, 99.
Priabonian:Munier-Chalmas, E. P. and de Lapparent, A., 1893. Bull. Soc. Geol.
481
Bartonian
Priabonian
wZw
oT 3
oNozwu
£
a
s
Bartonian
(F)
Lutetian
Ypresian
France. (3)21,471.Roveda, V., 1961. Riv. Ital. Pal. Strat. 67, 153.Fabiani, R., 1915. Mem. 1st Geol. Mineral Univ. Padova. 3, 1.
Bartonian:Mayer-Eymar, C, 1858. Verhandl. Schweiz. Naturforsch. Ges. 178.Prestwich, J., 1847. Quart. J. Geol. Soc, London. 3, 354.Prestwich, J., 1857. Quart. J. Geol. Soc, London. 13, 108.Curry, D., 1958. Lexique Strat. Intern. I 3a 12.
de Lapparent, A., 1883. Traite de Geologie. 1st Ed., p. 989.Blondeau, A. and Curry, D., 1964. Bull. Soc. Geol. France. (7) 5, 275.Blondeau, A. etal, 1966. Bull. Soc. Geol. France. (7) 7, 200.Blondeau, A., 1964. Mem. Bur. Rech. Geol. Min. No. 28. 21.
Dumont, A., 1849. Bull. Acad. Roy. Med. Belg. (1) 16, 368.Kaasschieter, J.P.H., 1961. Inst. Roy. Sci. Nat. Belg. Bull. Mem. 147.
wzwuow
Thanetian
Montian
Renevier, E., 1873. Tableau des terraines sedimentaires (in 4°) et untexte explicatif. Lausanne (G. bridel).
Renevier, E., 1897. Chronogr. Geol.Prestwich, J., 1852. Quart. J. Geol. Soc, London. 8, 235.Barr, F. T. and Berggren, W.. A., 1965. Stockholm Contrib. Geol.
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Dewalque, G., 1868. Prodrome d'une description geologique de laBelgique. p. 185.
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20, 108.Rutot, A. and von den Broeck, E., 1886. Ann. Soc. Geol. Belg. 13,94.Rutot, A. and von den Broeck, E., 1887. Bull. Soc Geol. France.
(3) 15, 157.Marliere, R., 1955. Ann. Soc. Geol. Belg. 78, 297.Berggren, W. A., 1964. Stockholm Contrib. Geol. (5) 11, 135.
\ Tertiary
\
\
\\
Cretaceous \
Danian
Tertiary:de Grossovure, A., 1897. Bull. Soc Geol. France. Ser. 3, 25, 57.Loeblich, A. R., Jr. and Tappan, H., 1957. U. S. Nat. Museum Bull.
215, 173.Troelsen, J., 1957. U. S. Nat. Museum Bull. 125.Berggren, W. A., 1962. Stockholm Contrib. Geol. (2) 9, 103.Berggren, W. A., 1964. Stockholm Contrib. Geol. (5) 11, 103.
Cretaceous:Eames, F. E. (in press), 1968. J. Geol. Soc. India.Desor, E., 1841. Bull. Soc Geol. France. Ser. 2,4, 179.Brotzen, F., 1959. Sveriges Geol. Underokn Arsbok, Ser. C. (571),
81pp.Rasmussen, H. W., 1965. Mededel. Geol. Sticht. N.S., (17), 33.
(Supplemented by M. Meijer, loc cit., pp. 21-25).
δN
oenW
inOOtüU<
Ë s Maestrichtian
Dumont, A., 1849.Bull. Acad. Roy. Sci. Lettres, Beaux-Arts,Belgique,351.
Hofker, J., 1966. Paleontographica. Supplement-Band 10, Atlas ofForaminifera, 5.
Jeletzsky, J., X951. Beih. Geol. Jahrb. (1), 1.
482
Campanian (G)
Santonian S.S.(H)
LowerSantonian —
Coniacian (I)
0
Turonian
N
CΛ
o
o
Cenomanian
Coquand, H., 1857. Bull. Soc. Geol. France. 749.Van Hinte, J., 1965. Koninkl. Ned. Akad. Wetenschap. Proc. Ser. B.
(1)68,14.Marie, P., 1941. Mem. Museum Nat. Hist. Nat. (Paris). 12, 1.
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Schijsfma, E., 1946. Medeskl. Geol. Sticht. Ser. C-V (7), 1.
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by author) 256 pp.Marks, P., 1967. Koninkl. Ned. Akad. Wetenschap., Proc, Ser. B.
(3) 7, 264.
Albian
Aptian
f
Barremian
Hauterivian
Valanginian
Collignon, 1965. Rapport sur L'Etage Albian. In Colloque sur leCre'tace'Inferieur, Lyon. Mem. Bur. Rech. Geol. Min. (34) (Lyon),313.
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Fabre-Taxy, Moullade, M. and Thomel, G., 1965. A-Les stratotypesde l'Aptien. In Colloque sur le Crétace' Inferieur, Lyon. Mem.Bur. Rech. Geol. Min. (34), 173.
Casey, R., 1961. The stratigraphical paleontology of the Lower Green-sand. Paleontology. 3, 487.
Busnardo, R. 1965. Le stratotype de Barremien. In Colloque sur leCre'tace'Inferiéur, Lyon. Mem. Bur. Rech. Geol Min. (34) (Lyon),101.
Debelmas, J. and Thieuloy, J., 1965. E'tage Hauterivian. In Colloquesur le Crétace' Inferiélir, Lyon. Mem. Bur. Rech. Geol. Min. (34),85.
Barbier, R. and Thieuloy, J., 1965. E'tage Valanginien. In Colloquesur le Cre'tace' Inferieur, Lyon. Mem. Bur. Rech. Geol. Min. (34),79.
483
Berriasian
Tithonian
Kimmeridgian
Oxfordian
Busnardo, R., Hegaret, G. L. and Magne, J., 1965. Le stratotype duBerriasien. In Colloque sur le Crétace' Inferieur, Lyon.Mem. Bur.Rech. Geol. Min. (34) (Lyon), 5.
Enay, R., 1964. L'etage Tithonique. In Colloq. du Jurassique (Luxem-bourg, 1962). Compt. Rend. Mem., Luxembourg. 355.
Ziegler, B., 1964. Das Untere Kimeridgien in Europa. In Colloque duJurassic (Luxembourg, 1962). Compt. Rend. Mem., Luxembourg.345.
Callomon, J. H., 1964. Notes on the Callovian and Oxfordian Stages.In Colloque du Jurassique (Luxembourg, 1962). Compt. Rend.Mem., Luxembourg. 269.
Enay, R. etal. (in press). Les Faunes Oxfordiennes d'Europe Meridion-ale. Essai de Zonation. In Colloque International du Jurassique(Luxembourg, 1967).
Callovian
uoNO
m
o
on<
Bathonian
Bajocian
Callomon, J. H., 1964. Notes on the Callovian and Oxfordian Stages.In Colloque du Jurassique (Luxembourg, 1962). Compt. Rend.Mem., Luxembourg. 269.
Cox, L. R. 1964. The type Bathonian. In Colloque du Jurassique(Luxembourg, 1962). Compt. Rend. Mem., Luxembourg. 265.
Torrens, H. S. (in press). Standard zones of the Bathonian. In ColloqueInternational de Jurassique (Luxembourg, 1967).
Elmi, S., 1964. Precisions stratigraphieques sur la Bathonien supérieurdu nord de 1'Ardeche. In Colloque du Jurassique (Luxembourg,1962). Compt. Rend. Mem., Luxembourg. 535.
Elmi, S., Enay, R. and Mangold, C, 1964. La stratigraphie et lesvariations de faciès du Bajocien de lTle Cremieu (Jura meridionaltabularie). In Colloque du Jurassique (Luxembourg, 1962). Compt.Rend. Mem., Luxembourg. 539.
Aalenian
PS
IToarcian
Pleinsbachian
Sinemurian
Hettangian
Enay, R. and Elmi, S., 1964. Precision sur la stratigraphie de 1'Aale'niendansle Bugey occidental. In Colloque du Jurassique (Luxembourg,1962). Compt. Rend. Mem., Luxembourg. 559.
Maubeuge, P. L., 1963. La position stratigraphique du gisementFerrifèreLorrain(LepreblemedeFAalenian).J?H//. Tech. ChambreSyndicate Min. Fer France. (72).
Elmi, S. et al. (in press). L'etage Toarcien. Zones et Sous-Zonesd'Ammonites. In Colloque International de Jurassique (Luxem-bourg, 1967).
Howarth, M. K., 1964. Whilbian and Yeovilian Substages. In Col-loque du Jurassique (Luxembourg, 1962). Compt. Rend. Mem.,Luxembourg, 189.
Geyer, O. F., 1964. Die typuslokalitat des Pliensbachian in Wurt-temberg (Sudwer deutchland). In Colloque du Jurassique (Luxem-bourg, 1962). Compt. Rend. Mem., Luxembourg. 161.
Maubeuge, P. L., 1964. Quelques remarques a propos de 1'Hettangiendu Sinemurien et du Lotharingien. In Colloque du Jurassique(Luxembourg, 1962). Compt. Rend. Mem., Luxembourg. 127.
Elmi, S. et al. (in press). Les Subdivisions biostratigraphiques de1'Hettangien en France. In Colloque International du Jurassique(Luxembourg, 1967).
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NOTES ON CONCEPTS OF STAGE-AND OTHER BOUNDARIES
(A) Zanclian is used in preference to Tabianian becausethe former has been shown to contain a better andmore diverse marine fauna which can be used inregional stratigraphic correlation.
(B) Tortonian is placed in the Upper Miocene because:1) This was its original placement;2) Although subsequently placed in Middle Mio-
cene, it has now been returned to its originalposition because the Langhian has been movedup from the top of the Lower Miocene into theMiddle Miocene. The type Tortonian is subse-quent to beds called "Elveziano" or "Tortonianof Vienna basin", from which many species ofMollusca, especially, have been described astypical of the Middle Miocene. These "Viennabeds" are within the same stratigraphic intervalas the beds of the Langhian (=Serravallian ofVervloet, 1966).
(C) The Langhian is restricted, for the purposes ofthis Manual, to the beds included in the CessoleFormation, and excludes the older horizons in-cluded in the Langhian by Cita and Elter.
This essentially follows the usage of Pareto (1865),who directly referred only to the section north ofCessole, which commences with the Cessole For-mation. This is in accordance with the results ofthe work carried out by Drooger and colleagues,who recommended that the first evolutionaryappearance of the genus Orbulina occurs fromthe base of the Middle Miocene, which is a fewmeters above the base of the exposed CessoleFormation at Cessole.
This is supported by the fact that the base of theFrench stage Sallomacian (which falls within theLanghian Stage) has always been regarded by theFrench as the commencement of the Middle Mio-cene. (The name "Sallomacina" has two years'priority over the term "Vindobonian".) The bedsincluded in the Langhian and Sallomacian Stagesare also equivalent to the Badenian Stage of Reissand Gvirtzman, which covers beds included in theVindobonian from which virtually all the typicalMiddle Miocene molluscs were obtained.
(D) The Girondian Stage (Vigneaux et al, 1954) iscoextensive with the Aquitanian and Burdigalian,and forms a stratigraphic unit well defined interms of larger Foraminifera and Mollusca.
(E) Regarding the position of the Oligocene-Mioceneboundary, for the purposes of this Manual, thepanel has accepted (by majority opinion) the baseof the stratotype Aquitanian to represent the base
of theNeogene (Oligocene-Miocene boundary), asrecommended by the Comite du Nebge'ne Mediter-raneen in 1959 (published 1960), 1961 (published1964), 1964 (published 1966) and 1967 (in press),but not yet formally approved by the IUGS.
There is a radical dichotomy of opinion represent-ed among the panel members, and the two view-points are explained below, labelled 1 and 2.
1. It has been recommended that the base of thestratotype Aquitanian should be taken as thebase of the Miocene (and, therefore, the baseof the Neogene). The following points apply:(1) When originally proposed, the Bormidian
was regarded as Miocene, and one of thelatest publications (Lorenz, 1964), alsoregarded it as Miocene.
(2) The Bormidian is highly conglomeraticand rests directly upon the Triassic; nor-mally it would not be considered suitablefor a stratotype for a standard stage.There has been no indication whether anyof the fossils recorded are derived or not(the pebbles of phyllites, schists, etc.obviously are derived). Some fossils werebelieved later to be Oligocene, but somehave been found elsewhere only in bedsof Miocene age. To the east of the areathe Bormidian is cut out, and the over-lying Aquitanian rests directly on num-mulitic Oligocene (not present to thewest) so that there is an unconformityat the base of the Bormidian—the Trias-sic underlying it in one area, and num-mulitic Oligocene underlying it in an-other area.
(3) The European stage names on the Terti-iary Chart prepared by this panel wereall based upon marine megafossil faunassuch as Mollusca, Echinoidea, larger Fo-raminifera, etc. (except for the Paleo-cene, which originally was based uponplant evidence). The evidence of plank-ton foraminifera, however important anasset it may be in the refinement ofzonation within and correlation of thesestages, did not enter into the primarydefinitions. It seems quite wrong arbi-trarily to select one level of planktonicforaminiferal zonation to define theMiocene-Oligocene boundary; it remainsbut one part of a much larger field forsynthesis. In any case, terms such as"Miocene" and "Oligocene" are time-stratigraphic units, and cannot be strato-typified. Consequently, the evidence ofmegafossils should be considered whenattempting to find a suitable position
485
for the Miocene-Oligocene boundary.(4) In the Marnes Blanches de Bernachon,
which immediately and conformably un-derlie the stratotype Aquitanian, thereare 7 species of Gastropoda, 9 species ofbivalvia, and 20 species and 1 subspeciesof Ostracoda, all of which occurred inthe overlying Miocene faunas, but havenot been found anywhere else in bedsregarded as being of Oligocene age. Therewere a few Ostracoda having known longranges, but not a single mollusc or os-tracod previously known only from theOligocene or from Oligocene and olderbeds. This fauna is to be regarded asNeogene and Miocene. In the same bedsare found Miogypsina at a more advancedstage of evolution than those of theEochattian of Bunde. These beds restunconformably upon nummulitic Mid-dle Oligocene.
(5) In the Nordic Province of NorthwesternEurope, the fauna of the VierlanderStage, although originally regarded asAquitanian, was later regarded by Kaut-sky (1925) as being of Burdigalian oreven younger age. Consequently, in thisNordic province, there are no basal Mio-cene megafossil faunas at all available forcomparison with the megafossil faunas ofthe stratotypes of the Chattian, Eochat-tian and Neochattian. Furthermore, it isevident that the top ends of the ranges ofthe megafossils in the stratotype Chattianare completely unknown since some ofthem may well (and probably do) rangeup into the basal Miocene age. If the basalMiocene age of much of the Eochattian-Neochattian succession were not realized,such extensions of ranges would nevernever come to light.
(6) With regard to the Eochattian-Neochat-tian succession it is perhaps significantthat: (a) there are several commonmolluscan species in the Neochattian ofwhich there is no sign in the Eochattian,and (b) there are three levels in theEochattian at which derived Liassic am-monites occur.
(7) The fauna of the Escornebe'ou beds aspublished by Butt (1966) was regardedby him (and Drooger) as late Oligocene("Chattian"). Not only does this materialcontain derived material from at leasttwo older levels, and not only do thebeds in the area rest unconformably onthe Cretaceous, but the faunas includegood Globigerinoides which correlatethe material with material within the
type Aquitanian at the oldest. Thismaterial is therefore younger than theNeochattian.
(8) Conclusions: The terms "Miocene" and"Oligocene" are time-stratigraphic unitsand cannot be stratotypified. Miocenefaunas occur beneath the stratotypeAquitanian, and at Escornebe'ou (wherethey were called Oligocene). Much of theEochattian-Neochattian succession canreasonably be regarded as basal Miocene.Useful levels of changes in planktonicforaminiferal faunas are certainly to beused to refine the time-limits withinsuch successions of megafossil faunasoccur, but any single one of these aloneshould not be taken to define a boundarysuch as "Miocene-Oligocene" withoutsynthesizing the planktonic foraminiferalfaunal evidence with that of the mega-fossils. Any attempt to take the "Mio-cene-Oligocene" boundary at the in-coming of Globigerinoides (i.e., base ofstratotype Aquitanian—would result ina large number of molluscan, echinoid,larger foraminiferal, etc. faunas havingtheir ranges extended a very short dis-tance down into the "Oligocene" (sic),which at level there is not only a verynoticeable faunal change in many groupsof fossils (justifiably taken as the Neo-gene-Paleogene boundary) but very of-ten evidence of unconformity in theAlpine-Himalayan region (used in a broadsense). It seems to be highly undesirableto have a major faunal change occurringa short distance below one of relativelyminor significance, and to use the latterrather than the former as a "Miocene-Oligocene" boundary.
2. The stratigraphic extent of the Bormidiancan be shown in terms of planktonic fora-miniferal zones to include much of the in-terval ascribed to the Eochattian and Neo-chattian of Northern Germany. The upper-most part of the Bormidian is approximatelyat the same level as the middle part of theNeochattian, and both are prior to the Globi-gerinoides datum which can be recognized atthe base of the stratotype Aquitanian. ThisGlobigerinoides datum, as expressed in thestratotype Aquitanian, was recommended in1959 and reaffirmed in 1963 and 1967, by theNeogene Commission on Mediterranean Neo-gene as the horizon to be taken to mark thebase of the Miocene. The base of the Bormi-dian falls within the upper part of the Eochat-tian succession, while the lower part of Eochat-tian succession has been correlated, Hubach
486
(1957), and Anderson (1961) with the typeKassel Sands representing the type Chattian.Therefore, there is a prima facie case for re-garding the Bormidian as post-Chattian, butpre-Aquitanian. German workers have long re-garded the successions seen at Kassel, Dobergand Astrup as being a single major lithologicalunit, and have considered them as Oligocene.However, where Beyrich (1854 and 1858) didnot discuss the present exposure at Astrup,he did discuss the beds at Doberg which in-clude both Eochattian and Neochattian. There-fore, in Beyrich's terminology, the term "Oli-gocene" should be applied, not only to theKassel Sands, but also to the succession atDoberg.Miogypsina septentrionalis occursfromnear the exposed base of the succession atDoberg (Bed Number 10 of Hubach). Thishorizon is referable to Zone P. 19 of Blow,and also was correlated by Hubach and Ander-son to be within the interval of the type Kas-sel Sands. Furthermore, the latest horizon re-cognized within the Boom Clay of Belgium(type Rupelian) is also within Zone P. 19. Thus,in agreement with the work of Batjes (1958),there is a reasonable case for considering theChattian as part equivalent, at least, of thelater parts of the Rupelian. The range ofMiogypsina ss. must include a part of theOligocene, and, therefore, cannot be used todecide Neogene or Paleogene affinities.
(F) The Biarritzian Stage has been shown to be partlyupper Lutetian and partly lower Auversian. Curry(1967) has suggested that the term "Auversian"covers a recognizable and useful sequence, althoughit is not quite as extensive stratigraphically assuggested by its usage by some previous Frenchworkers. Since the terms Biarritzian and Auversianare provincial in nature they are not used in thismanual.
(G) Van Hinte (1965) erected a neostratotype for theCampanian which contains planktonic foramini-feral faunas in the lower part and orbitoides in thehigher part. The Campanian planktonic foramini-feral faunas are, from analysis of Van Hinte'sfigured forms (by Pessagno and Blow), an as-semblage which is long-ranging in the broad con-cept of Campanian, but is not likely to be thatwhich occurs in immediately pre-Maestrichtianhorizons. There is no justification for acceptingVan Hinte's supposition that G. calcarata bearingbeds (his Unit G), immediately overlie the neo-stratotype G of Van Hinte. In support of this,Blow (unpublished) has observed a single brokenspecimen of G. calcarata presumably from thesame Unit G from which Van Hinte recorded hisplanktonic 'faunas. In view of the fact that the
occurrence of G. calcarata is sporadic and thefauna from the neostratotype is very much re-stricted in diversity and in number of species, itappears that Van Hinte's Unit G is in part, atleast, representative of the G. calcarata zone.However, there is an interval between the top ofUnit G and the first horizon of occurrence ofundoubted orbitoides (e.g. Orbitoides media)which have been accepted by many authors ascharacteristic of Maestrichtian.
It should be noted that many small "Orbitoides"occur in the interval between the first occurrenceof O. media and the top of the planktonic for-aminiferal fauna of Bed G. These forms (e.g.Schlumbergeria) have been accepted as Campanianforms by many authors; therefore, at least thelower half of Van Hinte's Unit F must be con-sidered as Campanian, whereas the upper half ofUnit F and the younger horizons should be as-cribed to Maestrichtian. Because of this, thismanual shows G. calcarata disappearing just priorto the Campanian-Maestrichtian boundary andG. ventricosa disappearing at or very near theCampanian-Maestrichtian boundary.
(H) Santonian s.s. is that part of the Santonian repre-sented by the stratotype.
(I) Beneath the exposed beds of the stratotype San-tonian is an interval, part of which is undoubtedlyConiacian as represented in its "stratotype", butbetween the two there are both beds and faunaswhich have not been unambiguously differ-entiated.
(J) The Vraconian of certain Continental authors ishere arbitrarily included as low Cenomanian.
REFERENCES
Anderson, H. J., 1961. Meyniana. 10, 118.Batjes, D. A. J., 1958. Foraminifera of the Oligocene of
Belgium. Inst. Roy. Sci. Nat. Belg. Bull. Mem. 143.Beyrich, E., 1854. Uber die Stellung der Hessischen
Tertiàrbildung. Ber. Verhandl. Preussen Akad. Wiss.Ber. 640.
- 1858. Uber die Abgrenzung der OligocànenTertiàrzeit.Monatsber, kgl. Preussen Akad. Wiss. Ber.54.
Butt, A. A., 1966. Late Oligocene Foraminifera fromEscornebeou, S. W. France. Utrecht (Schotanus &Jens).
Cita, M. B. and Elter, G., 1960. La posizione strati-grafica delle marne a Pteropodi delle Langhe dellaCollina di Torino ed il significato cronologico delLanghiano. Accad. Nazi, dei Lincei. Ser. 8 (5), 29,360.
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Curry, D., 1961. Correlations within the Anglo-Paris-Belgian Palaeogene Basin. Proc. Geologists' Assoc.
Eames, F. E., (in press) 1968. On Cretaceous-Tertiaryboundary. /. Geol. Soc. India.
Hubach, H., 1957. Das Oberoligocàn des Doberges beiBundein Westf.iter. Naturhist. Ges. Hannover. 103, 1.
Kautsky, 1925. Abhandl. Geol. Landesamst. Ber. N. F.,97, 1.
Lorenz, L., 1964.5M//. SOC. Geol. France. Ser. 7, 6, 192.
Rasmussen, H. W., 1965. Mededel. Geol. Stricht. N. S.,(17), 33.
Reiss, Z. and Gvirtzman, G., 1966. Borelis from Israel.Eclog. Geol. Helv. (1), 5*, 437.
Van Hinte, J. E., 1965. The type Campanian and itsplanktonic Foraminifera. Koninkl. Ned. Akad. Wet-enschap. Proc, Ser. B. (1), 68, 8.
Vervloet, C. C, 1966. Stratigraphical and Micropaleon-tological Data on the Tertiary of Southern Piedmont(Northern Italy). (Thesis) University Utrecht. Utrecht(Schotanus & Jens).
Vigneaux, M., Magne, A., Veillon, M. and Moyes, J.,1954. Compt. Rend. Acad. Set Paris. 239, 818.
WELL LOGGING
The term "logging" is generally used to cover the ac-quisition of petrophysical information sensed by prox-imal devices lowered in the drilled holes. There areseveral reasons for making in-hole measurements ofphysical properties. First, such measurements providedata which may permit an inference of the lithologyof intervals where no cores are recovered and it mayrelate these intervals to seismic profiles. Second,measurements of the physical properties on cores andin the hole may make it possible to tie core samplesrecovered to their proper position within the strato-graphic section; and, third, some physical measure-ments, such as heat flow, have validity only whenmade on rocks in situ.
The importance of the fact that information aboutthe earth beneath the oceans can be derived not onlyfrom the examination and study of core samples ob-tained by drilling, but also by measuring some of thephysical properties of these rocks in situ was wellunderstood by those who planned the Deep SeaDrilling Project, although logging in deep water andpelagic sediments had not yet been accomplished andthe conditions of the holes were not, at that time,predictable.
Of the logging tools in existence, only the character-istics of those in current use aboard the GlomarChallenger will be discussed. These include the gamma-ray, neutron, gamma-density, acoustic and caliper,and electrical survey tools.
The gamma ray tool records the natural radioactivityof the rocks penetrated. This tool consists of an eightinch scintilliation counter with an electronic cartridgepowered from the surface. The cartridge suppliesvoltage to the counter to shape and amplify the pulsesand transmit them to the surface. At the surface, thepulse rate is converted into voltage and the voltage isrecorded continuously as the sonde is pulled up thehole. A time constant for averaging counts is chosen,which is a compromise between the desire to minimizestatistical fluctuations and the desire for high strati-graphic resolution.
Tools in current use are calibrated in test pits. OneAPI unit equals 1/200th of the difference between theresponse of the tool operated under fixed conditionsin a pit with known standard radioactivity and in a pitthat is not radioactive. Formerly, tools were calibratedin radium equivalents per ton. One microgram ofradium equivalent per metric ton equals about 11.7API units. The following concentrations of radio-active minerals give about the same response as onemicrogram of radium per ton:
2.8 ppm Uranium3.5 ppm Thorium2000. ppm Potassium.
The neutron tool now being used aboard the GlomarChallenger consists of an Americumberyllium sourceof fast neutrons placed about 15 inches from a detec-tor, sensitive to both high energy captured gammarays and thermal neutrons. As the emitted neutronspass through the rock, they collide with other nucleilosing momentum until they reach the thermal veloc-ity of the atomic nuclei of the surrounding material.When so slowed, they may be absorbed by surround-ing nuclei and this absorption results in the emissionof gamma rays which can be detected by the counter.
The number of gamma rays emitted is related to thenumber of neutrons absorbed, but only those emittednear the counter are detected and recorded. Hydrogen,having a mass almost equal to the neutrons, is mosteffective in slowing down the neutrons.
For practical purposes, the neutron tool can be con-sidered to respond to the hydrogen content of therock. In the presence of relatively large amounts ofhydrogen, most of the neutrons will be slowed andcaptured in the immediate vicinity of the neutronsource.
If the rock is relatively free of hydrogen, the neutronshave a greater chance of reaching the rock near thedetector where either the captured gamma rays result-ing from their absorption or the neutrons themselvescan be counted by the detector. Therefore, a highcounting rate indicates that relatively few of the
488
neutrons were impeded in their transmission and, thus,the hydrogen content of the rock is low. Conversely,a low counting rate implies a high hydrogen content.
The response of the neutron tool depends not only onthe characteristics of the rock penetrated but on thedesign of the tool (including its diameter, the nature ofthe source, and the distance between the source andthe detector), on the diameter of the hole and on thenature of the fluid in the hole.
The neutron tools used are calibrated in test pits ofknown lithology, porosity, and fluid content. Empiri-cally derived departure curves are available for theinterpretation of records produced by the tools. Ingeneral, it can be considered that the neutron logs ob-tained here respond as follows, when properly corrected:
1680 API units ~ 2 per cent water content1000 API units ~ 19 per cent water content640 API units ~ 40 per cent water content370 API units ~ 100 per cent water content
The gamma-gamma tool: In the case of the gamma-gamma tool, the rock is bombarded by gamma raysemitted from a caesium source in the sonde. Thegamma rays suffer Compton scattering and the scatteredradiation is measured by a detector in the sonde. TheCompton scattering is a function of the electrondensity. For most sedimentary rocks, the electrondensity is almost exactly a function of the bulk densityof the rock. The tool is normally operated pressedagainst the borehole wall in order to suppress bore-hole effects. The tool on the Glomar Challenger doesnot have this capability, hence, there are large andunknown effects on the measurements made withthis instrument, making the log impossible to inter-pret quantitatively without caliper data and calibration.
The acoustic tool measures the time required for thetransmission of a compressional wave over a shortinterval of rock, and this time is measured continuouslyas the sonde is pulled up the borehole. The tool usedaboard the Glomar Challenger consists of a soundgenerator separated from two receivers by low veloc-ity material. Because the travel time is a least time,and the velocity of sound in the rock is higher thanthat either in the sonde or in the borehole, it is theenergy that has traversed the rock that is recorded. Thetravel path of the sound must traverse the fluid in theborehole to reach the rock from the source and toreach the receiver; but, when two receivers are used,the difference in the travel time can be considered toreflect essentially travel time in the rock between thetwo receivers only. The travel time is measured in micro-seconds per foot.
The caliper tool measures the diameter of the borehole.As the tool is pulled up the hole a collapsable set of
arms is expanded to wipe against the walls of thehole. The amount of the expansion is transmitted tothe surface where it is recorded in inches.
The electrical survey tool measures both the spontane-ous potential and resistivity.
The spontaneous potential log responds to minute cur-rents that flow in the borehole both as a result of dis-similarities between the borehole fluid and the inter-stitial fluid in the rocks and as a result of differencesin the electrical quality of the sediments—these differ-ences being related to lithologic differences. It is re-corded in millivolts.
The resistivity tools constitute a conventional resisti-vity measuring electrode arrangement. A known poten-tial is applied to a source electrode and the potentialdifference between other electrodes suspended at knownfixed distances from it is recorded in ohm-meters. Thepotential difference is a function of the resistivity ofthe formation separating the electrodes. The resistivitylog in the sedimentary materials expected should re-spond primarily to the amount and distribution ofinterstitial fluid in the rocks and its total salinity. Re-sistivity logs are extremely sensitive to differences incementation.
The winch used for logging on Glomar Challenger isthe one designed and built for the Mohole Project. Itis powered with a 580 horsepowered diesel engine.The winch drum carries 24,500 feet of 5/32 inchdiameter, seven-conductor, double armored loggingcable. The logging procedures which are followed arein accordance with the operating instructions put out bythe companies furnishing the logging equipment.
SCIENTIFIC RECORDS
All information gathered in the course of the DrillingProject is filed at the Drilling Project Headquarters atScripps Institution of Oceanography and that pertainingto the Atlantic is filed, in addition, at Lamont-DohertyGeological Observatory.
Observations are recorded on a set of appropriate datasheets, which have been designed in the anticipationthat ultimately it will be possible to process much ofthis data by computer. All records are duplicated, andthe copies are stored in separate places. The only rec-ords which cannot be easily duplicated are the analogrecords. These are digitized as soon as possible so thatthere will be a means of reproducing the curves, shouldthe originals be destroyed.
The Initial Reports of the Deep Sea Drilling Projectare basically intended to be a compilation of the in-formation gathered on shipboard and in laboratories
489
on shore which will enable scientists to select sam-ples for further study in their own research projects.It is not intended that the Initial Reports should ex-haust the data from the point of view of the researchscientist, in fact, scientists involved in their compila-tion are free to publish whatever interpretive ideasthey wish.
In addition to the information appearing in the InitialReports, at the repositories there are copies of the
color photographs, X-radiographs, the originals of theanalog records and well logs, original observations onsmear slides and thin sections, site survey information(including topographic magnetic and seismic data), andvarious other observations and measurements whichdo not in every case find their way into the initialcore reports. These are available, following publicationof the Initial Report, for inspection by any qualifiedperson and it is hoped that, ultimately, arrangementscan be made to supply copies of these data to interestedpersons at cost.
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