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Volume 1, No. 3December 2003
INSIDE: PYRITE CONCRETIONS TURNED OUTSIDE-INPLUS: HAND LENS ARTICLE ON “THE KEY TO THE CONSERVATION”
PRESIDENT’S OBSERVATIONS - UPCOMING CONFERENCES DIRECTOR’S CHAIR - FIELD NOTES
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The Sedimentary Record
December 2003 | 3
The Sedimentary Record (ISSN 1543-8740) is published quarterly by theSociety for Sedimentary Geology with offices at 6128 East 38th Street,Suite 308,Tulsa, OK 74135-5814, USA.
Copyright 2003, Society for Sedimentary Geology, all rights reserved. Opinionspresented in this publication do not reflect official positions of the Society.
The Sedimentary Record is provided as part of membership dues to theSociety for Sedimentary Geology.
4 Turning Pyrite Concretions Outside-In:Role of Biofilms in Pyritization ofFossils
8 Field NotesView from a State Survey
9 The Hand Lens—a student forumSedimentary geology as key toconservation
10 Director’s ChairNon-Technical Session Activities at GSA
11 President’s ObservationsA Letter to Geology Students
CONTENTS EditorsLoren E. Babcock, Department of Geological Sciences, The Ohio State University, Columbus, Ohio 43210 <[email protected]>
Stephen A. Leslie, Department of Earth Science, University ofArkansas at Little Rock, Little Rock, Arkansas 72204<[email protected]>
Marilyn D. Wegweiser, Department of Biological andEnvironmental Sciences, Georgia College and State University,Milledgeville, Georgia 31061 <[email protected]>
SEPM Staff6128 East 38th Street, Suite #308,Tulsa, OK 74135-5814Phone (North America): 800-865-9765 Phone (International): 918-610-3361
Dr. Howard Harper, Executive Director<[email protected]>
Theresa Scott, Business Manager<[email protected]>
Kris A. Farnsworth, Publications Coordinator<[email protected]>
Judy Tarpley, Event and Conference Manager<[email protected]>
Michele Woods, Membership Services Associate<[email protected]>
Call for 2005SEPM AwardNominations
DO YOU KNOW OF SOMEONE WHODESERVES SPECIAL RECOGNITION?
Nominations are open for the following awards:• Twenhofel Medal – for excellence in overall sedimentary
geology• Pettijohn Medal – for excellence in sedimentology• Shepard Medal – for excellence in marine geology• Moore Medal – for excellence in paleontology• Wilson Medal – for outstanding work at the beginning
of a career in sedimentary geology• Honorary Membership – for outstanding service and
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Cover art: Cross-section of orthocone nautiloid showing pyrite crust onsoft parts lining the internal chambers and surrounding the siphuncle,associated with gas blowout structures; length of specimen approximately 5cm (see Borkow and Babcock, this issue).
INTRODUCTIONAmong the more intriguing aspects of the fos-silization process is preservation of soft tissues,chitinous coverings, or biomineralized struc-tures by pyrite. This type of preservation israther dogmatically referred to as replacementby pyrite in many geology textbooks. Studiesintegrating sedimentary geochemistry, diagen-esis, and taphonomic experimentation, howev-er, indicate that this notion of replacement isperhaps oversimplified because it fails toaccount for contrasts in the preservation ofdifferent types of organically produced struc-tures. Moreover, it fails to account for factorsinfluencing the formation of pyrite concre-tions as constrasted with the formation of thinpyrite crusts over organic structures.
Here, we present new information concern-ing the precipitation of sedimentary pyritemediated by organic decay. This and otherdeveloping information (e.g., Schieber, 2002)provide the basis for an hypothesis thataccounts for microbiological and geochemicalfactors leading to exceptional preservation ofnon-biomineralized tissues by means of pyrite.Also, preservation of biomineralized shells by
means of concretionary pyrite, without preser-vation of any associated non-biomineralizedparts, is discussed. In addition to factors previ-ously determined to play major roles in pyritepreciptation (e.g., burial of organics in lowoxygen environments, and ratio of sulfide ionsto dissolved reactive iron in sediment porewaters; e.g., Berner, 1970; Raiswell et al.,1988), pyrite precipitation seems to be strong-ly correlated with the development of micro-bial biofilms (Schieber, 2002). Such biofilmsappear to have two forms that result in differ-ent patterns of pyrite precipitation. Bacteria-dominated biofilms apparently result in coat-ing of tissues by thin pyrite crusts. Pyrite con-cretions (and sometimes pyrite rings) resultfrom microbial assemblages that grow halosaround decaying matter. Non-biomineralizedparts of organisms are preferentially preservedby thin pyrite crusts, and non-biomineralizedstructures appear to be preferentially preservedby pyrite concretions.
Characterizing how pyrite has preserved fos-sils contributes at least two noteworthyadvances: 1) a refined understanding of theconditions under which some exceptional
preservation of fossils has occurred (i.e., therather unusual preservation of non-biominer-alized tissues or so-called “soft parts;” e.g.,Bartels et al., 1998; Stanley and Stürmer,1987; Briggs et al., 1996; Grimes et al., 2002);and 2) a step toward more complete under-standing of the precipitation of concretions insedimentary strata. This work indicates thatconcretionary development is the result ofrapid formation of an organic matrix sur-rounding a decaying mass. The presence ofthis decaying mass created a chemicalmicroenvironment that induced precipitationof concretionary minerals. Crystal growthappears to have begun at multiple sites withinthe decaying mass, including the margin ofthe halo. The implication is that a pyrite con-cretion does not necessarily begin at the centerand grow outward.
METHODS, MATERIALS,AND GEOCHEMICAL MODELSDetailed study of sedimentary pyrite preserv-ing fossils was carried out principally on speci-mens from the Alden Pyrite Bed (LedyardShale Member, Ludlowville Formation,Hamilton Group; Middle Devonian) of west-ern New York (see Babcock and Speyer, 1987).The Alden Pyrite Bed, which ranges up toabout 1.5 m in thickness, is one of the bestdeveloped pyrite beds in the Hamilton Group(Dick, 1982), and yields fossils representing arange of shallow marine organisms and bodyparts. Pyritization of fossils ranges from thinsurficial coatings to round concretions that aretypically less than 2 cm in diameter.Specimens were studied macroscopically,through sectioning, and via image enhance-ment (see Schieber, 2003) of sectioned speci-mens. For comparative purposes, taphonomicexperiments were carried out on recently deador frozen arthropods (horseshoe crabs andcentipedes) in marine aquaria inoculated withmicroorganisms (see Babcock et al., 2000 andreferences therein). Finally, observational andempirical data were compared with geochemi-cal models for pyrite precipitation.
The interaction of sulfide and reactive ironin controlling pyrite precipitation can bedescribed using a double reservoir model(Helfferich and Katchalsky, 1970; Canfieldand Raiswell, 1991; Raiswell et al., 1993).This model for bacterially mediated pyritedeposition describes the interaction betweenvarying amounts of reactive iron and the sul-fide released through bacterial sulfate reduc-tion of organic structures having radii up to50 µm (Raiswell et al., 1993). According toCanfield and Raiswell (1991), two variables
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Turning PyriteConcretions Outside-In:Role of Biofilms inPyritization of FossilsPhilip S. Borkow and Loren E. Babcock; Department of Geological Sciences; The Ohio StateUniversity; Columbus, OH 43210; [email protected]; [email protected]
ABSTRACT: Studies integrating sedimentary geochemistry, diagenesis, and taphonomicexperimentation provide new understanding about the development of pyrite concre-tions around organisms and the exceptional preservation of some nonmineralized tis-sues by pyrite crusts.As now interpreted, at least three factors influence the preserva-tion of organisms by pyrite: 1) burial in a low oxygen environment or microenvironment;2) ratio of sulfide ions to dissolved reactive iron in sediment pore waters; and 3) pres-ence of reactive biofilms (microbial assemblages) associated with decaying organic mate-rial. Under low oxygen conditions, breakdown of organics allows for the release of sul-fide ions into sediment pore waters, where they combine with reactive iron ions to formiron sulfides.
Pyrite often preserves biomineralized structures (primarily shells) through concre-tionary overgrowths, whereas non-biomineralized tissues (such as internal soft parts) areusually preserved by thin pyrite crusts.The extent of pyrite precipitation and the type(s)of organically produced material(s) preserved by FeS2, seem to be related to the devel-opment of either reactive bacterial coatings that were in direct contact with decayingorganic tissues or microbial assemblages (including bacteria and probably fungi) thatformed halos around decaying organic tissues. Precipitation of pyrite to form a concre-tion apparently begins at multiple sites within a microbial halo, not just on the surface ofthe decaying mass.
control pyrite precipitation: 1) reactive ironcontent in the system; and 2) sulfide contentin the system. Reactive iron is the amount ofiron used in pyrite production as opposed toiron in the system as a whole (Raiswell et al.,1994). This iron may be introduced into a sys-tem through bacterially-catalyzed reduction ofiron oxides (e.g., hematite) or iron oxyhydrox-ides (e.g., goethite, ferrihydrite, and lepi-docrocite) by organic compounds (Jones et al.,1983; Lovely and Phillips, 1986a,b; Canfield,1989), and the partial oxidation of iron sulfideminerals (Lord, 1980; Giblin and Howarth,1984). Sulfide production, which influencesthe extent of pyrite precipitation around adecaying organism, is the result of bacterialdissimilation (Canfield and Raiswell, 1991).An increase in either of the reservoirs isexpected to shift the deposition of pyritetoward the other reservoir. In the case of adecaying organic mass, the sulfide reservoirbegins at the decaying organic mass andextends outward, whereas the reactive ironreservoir is in the surrounding sediment andassociated pore water (Canfield and Raiswell,1991). By using the flux of the two reservoirs,Canfield and Raiswell (1991) hypothesizedthat the three “types” of pyrite preservationoutlined by Allison (1988) can be accountedfor by: 1) precipitation of pyrite in the cellularpore spaces (permineralization); 2) precipita-tion of pyrite directly on the surfaces of thenon-biomineralized body parts without pre-serving internal structure (mineral crusts); and3) precipitation well outside of the boundary
of the organic material (mineral casts, molds,and concretions).
Here, the double reservoir model is emend-ed to include the role of microbionts in medi-ating pyrite precipitation (Schieber, 2002),especially for decaying masses beyond the sizeconstraints discussed by Raiswell et al. (1993).Biofilms help to explain the formation of bothpyrite crusts and pyrite concretions, but notnecessarily pyrite permineralization.
MODERN AND ANCIENTMICROBIOTAThe possibility of bacterial-fungal (or othermicrobial) interaction as a factor controllingpyritic macrostructure is supported based onresults of SEM analysis of the cohesive andstable balloonlike structures (referred to hereas microbial halos) that envelope decayingarthropods in laboratory experiments (Figs. 1,2). Three-dimensional microbial halos developaround decaying organisms whether they arefloating in water (Fig. 1), at the sediment sur-
face, or buried under sediment (Fig. 2). Scansof a microbial halo surrounding a decayingcentipede (Fig. 1) show an anastomosing net-work of strands representing hyphae of a com-plex fungal mycelium (Fig. 3). Interspersedamong the mycelia are small (0.5-2 ìm) coc-coid-shaped, gram-positive bacterial bodies(probably Staphylococcus or Streptococcus;Fig. 4).
Fungal mycelia that surround decayingorganic matter in aqueous environments act asstabilizing media and substrates for the growthof interdependent, coherent microbial com-munities referred to as consortia (Cullimore,2000). Modern microbial consortia canassume various forms, including crystallizedstructures such as nodules, crusts, rusticles,iron pans, stalactites, and stalagmites(Cullimore, 2000). An important product ofmicrobial consortia is the accumulation ofextraceullar polymeric substances (EPSs),commonly referred to as “slime” (Cullimore,2000). This slime acts as a three-dimensionalpathway for the transport of recalcitrant accu-mulates such as ferric iron and nutrients suchas nitrogen. Iron is a key component of EPSs
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Figure 1: Centipede (Scutigera) decaying in water and surrounded by transluscent bacterial-fungalhalo. Length of specimen approximately 3 cm
Figure 2 (top): Horseshoe crab (Limulus) decayingin sand and surrounded by dark bacterial-fungalhalo (arrow). Length of halo approximately 8 cm.
Figure 3 (middle): SEM image of network of fungalmycelia with interspersed bacterial cells extractedfrom halo surrounding specimen in Fig. 1. Length ofbar scale 100 µm.
Figure 4 (bottom): SEM image of bacterial cellswithin the microbial consortium illustrated in Fig. 3.Length of bar scale 10 µm.
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6 | December 2003
because some bacterial respiration mechanismsrely upon it. The presence of iron-bindingagents, called siderophores (Madigan et al.,1997), in some bacteria make the formation ofa consortium beneficial to those bacteria lack-ing in efficient iron-binding proteins. Theyallow iron to be transported throughoutmicrobial communities (Madigan et al.,1997), which is an important prerequisite forthe formation of FeS2.
We interpret microbial halos that surrounddecaying organic matter within sediment asprecursors of concretions. Darkened halosobserved to surround decaying horseshoecrabs (Fig. 2) consist of fungal hyphae thatsurround and ensconce grains of sediment.The halos are so cohesive that extracting sam-ples without disturbing the surrounding sedi-ment can be difficult. Under SEM and EDXanalysis, the dark halos appear to be largelybacterial in composition and not due to thepresence of iron monosulfide or manganesehydroxide.
SEM analyses of pyritized mollusks fromthe Alden Pyrite Bed reveal minute strandsand beadlike structures (Fig. 5) that closelyresemble microbionts observed in the halossurrounding organisms decaying in aqueouslaboratory experiments. The strands areinferred to be pyritized fungal hyphae(although the possibility that some may becyanobacterial strands cannot be ruled out atpresent), and the beadlike structures are inter-preted as coccoid bacteria. Similar structuresobserved previously from sedimentary rocks(e.g., Southam et al., 2001; Schieber, 2002;Grimes et al., 2002; Schieber and Arnott,2003) likewise have been associated with thedecay of animals or plants. Preservation ofbacterial cells, and by implication, also soft
internal tissues in pyrite tends to occur inrather sheltered areas (e.g., linings of thechambers of orthocone nautiloids; coverphoto). Pyritized areas have a honeycomb tex-ture that is different from the surroundingpyritic matrix. This texture is similar to thatobserved in carbonized Oligocene feathers andinterpreted as having a biofilm origin (Davisand Briggs, 1995).
BIOFILM RESPONSE PATTERNS IN PYRITIZEDFOSSILSThe composition of microbial consortiainvolved in the decay of organic tissues seemsto play a major role in the style of pyritizationof fossils. Bacteria-dominated consortia lead topyrite crusts and are preferentially associatedwith non-biomineralized tissues, whereasmicrobial consortia dominated by extensivenetworks of microbes (presumably fungalhyphae and bacteria) lead to pyrite concre-tions. Also, a relationship exists between thetypes of microbial consortia and the extent towhich integrity of the decaying organisms ismaintained within the resulting fossils: tissuespreserved by crusts seem to have been moresusceptible to development of blow-out struc-tures resulting from gas release during decay
than were structures preserved by network-supported microbial consortia.
Bacteria-dominated (fungi-depleted) sheetssurrounding decaying organic matter probablyresponded differently to gas release than didlarger, presumably mycelium-supported, micro-bial consortia. In order to study the differenteffects of biofilms influencing preservationstyle, images of cut and polished pyritized fos-sils were enhanced using Adobe Photoshop (seeSchieber, 2003). In examples where points ofrupture associated with gas release have beenstudied, pyritization was evidently associatedwith bacterial sheets lacking significant strandsor networks of microbes. Pressure associatedwith gas buildup in response to decay was notwell accommodated in the relatively non-elasticbacteria-dominated sheets. The more elastic,network-supported microbial halos were betterat accommodating gas pressure. As a result,rupture was more common in decaying organ-isms covered by bacteria-dominated sheets(cover photo). In specimens having more exten-sive microbial networks, biofilms were probablymore stable and able to distribute gas releasemore evenly over the circumference of the con-sortium. This may have been an important stepin the formation of a concretion (Fig. 6)around a decaying organic nucleus.
Figure 5: SEM image of pyrite crust over softparts associated with the siphuncle of an ortho-cone nautiloid showing probable fungal hyphae(strandlike structures) and bacteria (roundstructures); from the Alden Pyrite Bed (LedyardShale Member of Ludlowville Formation;Devonian) of western New York. Length of barscale 70 µm.
Figure 6: Cross-section of pyrite concretion formed around ammonoid shell; from the Alden Pyrite Bed(Ledyard Shale Member of Ludlowville Formation; Devonian) of western New York. Diameter of con-cretion approximately 2 cm.
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Under anaerobic conditions, halos com-posed of sulfate-reducing bacteria attached tofungal mycelia (or possibly cyanobacterialstrands) formed around decaying organic mat-ter, and the bacteria released pockets of sulfideinto slime. The pockets could extend into thesurrounding matrix. Bacteria deficient inmicrobial networks would, in contrast, formmats along organic surfaces. Sulfide producedat sites of bacterial colonization in network-stabilized EPSs would promote the depositionof pyrite throughout the consortia; thisexplains the precipitation of pyrite in concre-tions. By contrast, the lack of network-sup-ported consortia would restrict bacteria topositions close to decaying organisms, thuscausing pyrite precipitation close to nuclei ofdecay. In such cases, pyritization of bacterialsheets would occur through microbe entomb-ment (Schultze-Lam et al., 1996).
IMPLICATIONSThe implications of microbial consortia forinfluencing fossilization are far reaching. Inaddition to accounting for variation in the waysthat pyritization of fossils occurs, the biofilmconsortium hypothesis suggests a mechanismby which other types of concretions (e.g., car-bonate and silica) may form. Preservational dif-ferences within beds containing sedimentarypyrite seem to record variability in the compo-sition of microbial species involved in decay. Itis conceivable that there was also some environ-mental varibility in the composition of micro-bial communities, and that may help to explainsome differences in style of pyritization amongdifferent sedimentary strata.
ACKNOWLEDGMENTSThis work has benefited from the constructiveinput and support of numerous people. Inparticular, we thank S. Bhattiprolu for helpwith SEM and EDX analyses, C. Gardner forhelp with aqueous geochemical analyses, J.Palese and J. Altergott for loaning specimens,and J. and L. Crafferty for access to the col-lecting locality in New York. G.C. Baird, C.E.Brett, A.E. Carey, Y.-P. Chin, S. Lower, M.R.Saltzman, and J. Schieber provided helpfuldiscussion or other assistance. T.N. Taylor,S.A. Leslie, and A.L. Rode provided construc-tive review of this paper. This work was sup-ported in part by grants from the GeologicalSociety of America and the Friends of OrtonHall (The Ohio State University) to Borkow;and by grants from the National ScienceFoundation (EAR-0106883, EAR OPP-0229757) to Babcock.
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Alden Pyrite Bed, Ledyard Shale (Middle Devonian) of western NewYork: Journal of Paleontology, v. 61, p. 539-548.
BABCOCK, L.E., MERRIAM, D.F., and WEST, R.R., 2000,Paleolimulus, an early limuline (Xiphosurida) from Pennsylvanian-Permian Lagerstätten of Kansas and taphonomic comparison withLimulus: Lethaia, v. 33, p. 129-141.
BARTLES, C., BRASSEL, G., BRIGGS, D.E.G., 1998, The fossils of theHunsrück Slate, Cambridge University Press, Cambridge, 309 p.
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BRIGGS, D.EG., RAISWELL, R., BOTTRELLS, S.H., HATFIELD,D., and BARTLES, C., 1996, Controls on the pyritization of excep-tionally preserved fossils: an analysis of the Lower DevonianHunsrück Slate of Germany: American Journal of Science, v. 296, p.633-663.
CANFIELD, D.E., 1989, Reactive iron in marine sediments: Geochimicaet Cosmochimica Acta, v. 53, p. 619-632.
CANFIELD, D.E. and RAISWELL, R., 1991, Pyrite formation and fos-sil preservation, in Allison, P.A., and Briggs, D.E.G., eds.,Taphonomy: Releasing the Data Locked in the Fossil Record: PlenumPress, New York, p. 337-387.
COSTERTON, J.W., GEESEY, G.G., and CHENG, K.-J., 1978, Howbacteria stick: Scientific American, v. 238, p. 86-95.
CULLIMORE, D.R., 2000, Practical Atlas for Bacterial Identification,Lewis Publishers, New York, 209 p.
DAVIS, P.G., and BRIGGS, D.E.G., 1995, Fossilization of feathers:Geology, v. 23, p. 783-786.
DICK, V.B., 1982, Taphonomy and depositional environments ofMiddle Devonian (Hamilton Group) pyritic fossil beds in westernNew York: unpublished M.S. thesis, University of Rochester, NewYork, 118 p.
GIBLIN, A.E., and HOWARTH, R.W., 1984, Porewater evidence for adynamic sedimentary iron cycle: Limnology and Oceanography, v. 29,p. 47-63.
GRIMES, S.T., DAVIES, K.L., BUTLER, I.B., BROCK, F.,EDWARDS, D., RICKARD, D., BRIGGS, D.E.G., and PARKES,R.J., 2002, Fossil plants from the Eocene London Clay: the use ofpyrite textures to determine the mechanism of pyritization: Journal ofthe Geological Society, London, v. 159, p. 493-501.
HELLFERICH, F., and KATCHALSKY, A., 1970, A simple model ofinterdiffusion with precipitation: Journal of Physical Chemistry, v. 74,p. 308-314.
JONES, J.G., GARDNER, S., and SIMON, B.M., 1983, Bacterialreduction of ferric iron in a stratified eutrophic lake: Journal ofGeneral Microbiology, v. 192, p. 131-139.
LORD, C.J., III, 1980, The chemistry and cycling of iron, manganese,and sulfur in salt marsh sediments: unpublished Ph. D. dissertation,University of Delaware, Newark, 188 p.
LOVELY, D.R., and PHILLIPS, E.J., 1986a, Organic matter mineraliza-tion with reduction of ferric iron in anaerobic sediments: AppliedEnvironmental Microbiology, v. 51, p. 683-689.
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RAISWELL, R., ANDERSON, T.F., BERNER, R.A., BUCKLEY, F.,1988, Degree of pyritization of iron as a paleoenvironmental indica-tor of bottom-water oxygenation: Journal of Sedimentary Petrology, v.58, p. 812-819.
RAISWELL, R., WHALER, K., DEAN, S., COLEMAN, M.L., BRIG-GS, D.E.G., 1993, A simple three-dimensional model of diffusion-with-precipitation applied to localized pyrite formation in framboids,fossils and detrital iron minerals: Marine Geology, v. 113, p. 89-100.
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SCHIEBER, J., 2002, Sedimentary pyrite: a window into the microbialpast: Geology, v. 30, p. 531-534.
SCHIEBER, J., 2003, Simple gifts and buried treasures – implications offinding bioturbation and erosion surfaces in black shales: SedimentaryRecord, v. 1, no. 2, p. 4-8.
SCHIEBER, J., and ARNOTT, H.J., 2003, Nannobacteria as a by-prod-uct of enzyme driven tissue decay: Geology, v. 31, p. 717-720.
SHULTZE-LAM, S., FORTIN, D., DAVIS, B.S., and BEVERAGE, T.J.,1996, Mineralization of bacterial surfaces: Chemical Geology, v. 132,p. 171-181.
SOUTHAM, G., DONALD, R., RÖSTAD, A., and BROCK, C., 2001,Pyrite discs in coal: evidence for fossilized bacterial colonies: Geology,v. 29, p. 47-50.
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2004 ANNUAL BUSINESSMEETING/LUNCHEONTuesday,April 20, 2004The Fairmont Hotel, 11:30am-1:30pmTickets are $30 and can be purchased through the registration form for the convention.
This year’s SEPM luncheon speaker is Dr. John C. Van Wagoner, Senior ResearchAdvisor at ExxonMobil’s Upstream Research Company. Dr. Van Wagoner specializes instratigraphy and sedimentology. His principal areas of research have been in thedevelopment of sequence stratigraphy concepts, especially as applied to siliciclasticoutcrops and subsurface data sets; and facies architecture, especially in fluvial andshallow-marine strata.
The title of Dr. Van Wagoner’s talk is “Energy Dissipation: Origin of Structure andOrganization in Siliciclastic Sedimentary Systems.”
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8 | December 2003
My name is John Harper. I am Chief of Oil,Gas and Subsurface Services of thePennsylvania Geological Survey, and head ofthe Pittsburgh office. I hold a PhD inPaleontology and have a ProfessionalGeologist license (PG). My responsibilities,like those of my staff, are varied, but our pri-mary responsibility is to collect and dissemi-nate information about oil and gas and sub-surface geology in Pennsylvania to the oil andgas industry, geologic consultants, governmentofficials, academics, and the general public.We also provide information on a wide varietyof geologic topics for western Pennsylvania.We are, for all intents and purposes, THE geo-logical survey in western Pennsylvania.
Because 99% or more of westernPennsylvania’s bedrock above the crystallinebasement (16,000 feet beneath Pittsburgh) issedimentary (there are two known kimberlitedikes in the area), sedimentary geology plays avital part in our day-to-day efforts. All ofPennsylvania’s oil and gas reservoirs consist ofconglomerate, sandstone, siltstone, shale,
limestone, dolostone, and/or coal. Whatmakes them special are the characteristics ofthe rock that were imparted to the originalsediment and altered through diagenesis overthe past 250 to 500 million years. All of thesecharacteristics allowed the hydrocarbons to beemplaced, stored for hundreds of millions ofyears, and released during and after drilling.As such, the types of geologic studies weundertake typically involve interpreting depo-sitional environments, diagenetic processes,fluid migration pathways, current porosity andpermeability, and other physical, chemical,and engineering characteristics. Althoughsome of these characteristics can be deter-mined using geophysical logs and geochemicalanalyses, in the long run you need to study therock to get a good picture of what really hap-pened over geologic time. For example, we arecurrently engaged in a multi-state study of theUpper Ordovician Trenton and Black Rivercarbonates in the Appalachians. These rocks,which are normally limestones, recently havebeen shown to provide gas in great quantities
as a result of localized dolomitization.Hot fluids penetrated the limestone inthe geologic past along faults and other
fractures and turned the low porosity, low per-meability limestone to vuggy, porous dolo-stone. The hydrocarbons were emplaced atabout the same time. A small team of Surveygeologists is currently studying outcrops,cores, and drill cuttings both macroscopically(hand samples, outcrops) and microscopically(thin sections) to try to determine why someof the limestone was dolomitized and somewas not. In addition, the Survey is continuingits efforts to investigate landslides and land-slide potential, direct people to local fossil andmineral collecting sites, explore the geochem-istry of natural gases, trace the history of west-ern Pennsylvania drainage and landscapedevelopment, educate the public aboutgroundwater issues, map mineral resources,and many other sedimentary geology topics.In fact, the only non-sedimentary geologytopic anyone in this office has undertakenduring my tenure was collecting specimens ofone of the kimberlite dikes for study by gradu-ate students at Penn State University.
I am, and have always been, a sedimentarygeologist in one form or another, even when Iwas an invertebrate paleontologist. The studyof these rocks is very important. Not only dothey exist as matrix holding my beloved fossilsin place and protecting them from the ravagesof time, but they also contain much of thegeologic history of our planet. Much of ourwater, most of our oil and natural gas, andmany of our metallic and non-metallic miner-al deposits can be found in sedimentary rocks.Most sedimentary rocks, in fact, have beenused as a mineral resource at one time oranother - limestone for cement and blast fur-nace flux, dolostone for agricultural lime,shale and siltstone for fill, claystone for bricks,sandstone for sand in the making of glass andrefractories, to name a few uses. And all ofthem have been used for building materialsuch as aggregate and dimension stone. InPennsylvania, the use of sedimentary rocks forconstruction provides more capital to the statethan does oil, gas, and coal combined. Andsince there will always be a need for construc-tion material, energy minerals, groundwater,and other geologic resources, sedimentarygeology will remain an important topic ofstudy here and elsewhere.
John Harper; Pennsylvania Geological [email protected]
FIELD NOTES
SEPM Short Courses thatwill be given in conjunctionwith the AAPG/SEPMAnnual Meeting:• Siltstones, Mudstones and
Shales: Depositional Processesand Reservoir Characteristics
• Recognizing Continental TraceFossils in Outcrop and Core
• Sequence Stratigraphy forGraduate Students
SEPM Field Trips that willbe given in conjunctionwith the AAPG/SEPMAnnual Meeting:• Applied Sequence Stratigraphy:
Lessons learned from the Triassic Dockum Group, Palo Duro Canyon Area• Imaging and Visualization of Reservoir Analog Outcrops Field Trip andWorkshop• Fluvial-Deltaic-Submarine Fan Systems: Architecture & Reservoir Characteristics
For more information on leaders, dates and registration fees go towww.sepm.org
ALL SHORT COURSE AND FIELD TRIP REGISTRATIONS SHOULD BE MADE THROUGH THE AAPG PRE-REGISTRATION FORM OR ONLINE AT
www.aapg.org
View from a State Survey
The Sedimentary Record
December 2003 | 9
SEDIMENTARY GEOLOGYAS KEY TO CONSERVATION
Sedimentary rocks preserve the only record ofthe history of life, environment, climate, anddeposition through the history of the earth. Asour sole historical record, they offer great prom-ise for unlocking both the secrets of the pastand constraining the possibilities for the future.
This wealth of information has provided thebasis for much of our understanding of theevolution of the earth and its inhabitants overthe past 4.6 billion years. Deciphering thehistory locked in sedimentary rocks was a cru-cial step in the establishment of modern geol-ogy. Hutton (1788) espoused the use of mod-ern analogs to understand the processes thatformed the strata within the sedimentaryrecord, and Lyell (1830) based his entirePrinciples of Geology on uniformitarianism.Thus “the present is the key to the past”became perhaps the best known phrase ingeology. While this concept certainly alsoapplies to other aspects of geology, interpret-ing sedimentary units requires the use ofanalogs within modern depositional systems.The study of modern analogs to sedimentarydeposits progressed dramatically during the20th century including, for example, studiesof modern carbonate systems (e.g. Purdy,1963), turbidity currents (e.g. Kuenen, 1967),and modern marine traces (e.g. Seilacher,1967). Studies incorporating modern analogsto better characterize idealized sedimentarygeometries (e.g. Best et al., 2003), taphonomy(e.g. Duncan et al., 2003), and ichnofaunalassemblages (e.g. Hastiotis and Mitchell,1993) continue and are providing increasinglydetailed understanding of ancient depositionalsystems. Each additional study allows for fur-ther characterization of ancient environments,stratigraphic architecture, or biotic interac-tions. Continuing and expanding analyses ofmodern analogs is critical for developingincreasingly accurate estimates of ancient sedi-mentary environments for both scientific andeconomical purposes.
The increased precision and detailed workof recent studies also allows today’s sedimenta-ry geologists to take the inverse of Hutton’soft-repeated phrase and examine the past asthe key to the modern (or future). Much ofmodern biology and environmental sciencefocuses on identifying ways to mitigate thenegative changes being wrought by a variety ofcauses including global warming, habitatdestruction, increased coastal sedimentation,etc. Fortunately for historical geologists, most
(if not all) of these scenarios have already beenplayed out at some time in the geologic past.Their secrets are preserved in fossils, beddingplanes, and stacking patterns just waiting for adaring geoscientist to uncover.
The purpose of this forum is to present a stu-dent’s view on the field of sedimentary geologyand to inform both current students and profes-sionals of developments within the field. Iwould submit that the conservation arena is anarea where sedimentary geologists can makeboth significant and exciting contributions.Certainly a portion of the current sedimentaryliterature already falls within this area; in gener-al, however, this is an under developed realm inwhich we can have dramatic impact. This is anexciting area that graduate students (and profes-sionals alike) should consider seriously whenidentifying project ideas. Graduate studentscurrently building their base of expertise areparticularly well suited to adopting researchstrategies that combine several areas of sedimen-tary geology with pertinent modern problems.
The arena of conservation geology requiresan innovative research program. The ability tolink disparate fields of study, such as biology,geochemistry, and sedimentology, into a cohe-sive project is required for tackling these multi-faceted problems. Sedimentary geologists areperhaps uniquely qualified to undertake thistype of project since we have been engaging inthis type of comparative and integrativeresearch for years, albeit usually with somewhatdifferently stated objectives. The scope of con-servation questions that can be examined with-in a framework of sedimentary geology isalmost unbounded. Studies examining changesin sediment supply within individual riversheds can provide evidence of the impact ofhuman intervention in damming specific rivers,while core data from oceanic shelves can helpdetermine patterns of ancient oceanic circula-tion. Applying stratigraphic and paleontologicprinciples to these types of problems can helpto produce more informed policy decisions.
One example of this type of integrative,conservation-centered approach concerns therole of invasive species in mediation of massextinctions. Invasive species are species thatoriginally occupied restricted geographic rangesbut rapidly expanded their ranges following thebreakdown of barriers. The modern spread ofinvasive species, attributable primarily tohumans, is one of the primary causes of the cur-rent biodiversity crisis (Enserink, 1999). Speciesinvasions also occurred in the geologic past andcan be studied as analogs of modern events tocharacterize the long-term effects of species inva-
sions, which cannot be studied otherwise.Research focusing on changes in geographicrange associated with species invasions duringthe Late Devonian Frasnian-Famennian biodi-versity crisis has revealed a structural change inspeciation mode during this interval (Rode andLieberman, 2003). This type of informationcan be incorporated into predictive models forthe modern biodiversity crisis, but could not bediscerned from the modern biota alone.
Conservation approaches, however, neednot be limited to paleontologic questions.Differentiating historical and post-disturbance(development) rates of sedimentation and ero-sion can help determine sustainable coastalpolicy for costal regions including beaches andwetlands. Core data from peat bogs, ancientlakes, and continental shelves can aid in thereconstruction of paleoclimate and estimationof potential future warming trends.Distinguishing differences in stratal stackingpatterns in various paleoclimatic and tectonicregimes can aid in predicting areas of erosionand deposition within fluvial and shallowmarine systems. Assessing the timing and spa-tial scale of sedimentologic and paleoenviron-mental variations could provide constraints onthe areal extent required to preserve threat-ened ecosystems.
Understanding these types of conservationquestions and acquiring pertinent data to pre-dict long-term trends in the modern environ-ment will become increasingly important asglobal population continues to rise and natu-ral areas decrease. Geoscientists can play animportant role in promoting sustainable solu-tions to environmental problems by drawingon the rich historical data preserved within thesedimentary record.
Alycia L. Rode; Department of Geology,University of Kansas, Lawrence, KS, [email protected]
REFERENCES:BEST, J. L., ASHWORTH, P., BRISTOW, C. S., and RODEN, J., 2003.
Three dimensional sedimentary architecture of a large, mid-channelsand braid bar, Jamuna River, Bangladesh. Journal of SedimentaryResearch, v. 73, p. 516-530.
ENSERINK, M., 1999. Biological invaders sweep in. Science, v. 285, p.1834-1836.
HASIOTIS, S. T., and MITCHELL, C.E., 1993. A comparison of cray-fish burrow morphologies: Triassic and Holocene fossil, paleo- andneo-ichonological evidence, and the identification of their burrowingsignatures. Ichnos, v. 2, p. 291-314.
HUTTON, J., 1788. Theory of the Earth. Transactions of the RoyalSociety of Edinburgh, v. 1, p. 209-304.
LYELL, C., 1830. Principles of Geology, Volume 1. John Murray,London,
KUENEN, P. H., 1967. Emplacement of flysh-type sand beds.Sedimentology, v. 9, p. 203-243.
PURDY, E. G., 1963. Recent calcium carbonate facies of the GreatBahama Bank, II. Sedimentary facies. Journal of Geology, v. 71, p.472-497.
RODE, A. L., and LIEBERMAN, B. S., 2003. GIS and phylogenetics, acombined approach to understanding biogeographic changes in theLate Devonian. Geological Society of America Annual Meeting,2003, Abstracts with programs, v. 112, p. 157-8.
SEILACHER, A., 1967. Bathymetry of trace fossils. Marine Geology, v.5, p. 413-428.
The Hand Lens—a student forum
The Sedimentary Record
10 | December 2003
Having just returned from the GSA AnnualMeeting in Seattle, I thought I would sharewith you some very interesting things thatoccurred but cannot be found in theabstracts. The most significant of these, tome, is an effort to begin organizing the com-munity of sedimentary geologists. A first stepis to identify the current basic research ques-tions driving our field. In the first issue ofThe Sedimentary Record, I discussed predict-ing the future of Sedimentary Geology, nowthere is an effort to shape the future and eachof us should be part of it. The effort is timelybecause NSF is reorganizing the Geology and
Paleontology Program and is seeking inputfrom sedimentary geologists concerningresearch directions in the upper crustal inter-val. This presents an opportunity to revise theperception that Sedimentary Geology is an“old” or “applied” science. Another contribut-ing factor is the ever-increasing need for sedi-mentary geology specialists to work together,tackling some of the grand challenge prob-lems that cannot be addressed by smallgroups with limited funding.
About a dozen people had an informaldiscussion at GSA about how to begin a sus-tainable process of getting community input
on the future of our field. The consensus wasto have a series of workshops, starting withthe big picture and then dealing withhttp://serc.carleton.edu/earthworkshop02/.
A parallel effort in the sedimentary geolo-gy community will begin with the firstSedimentary Geology basic research forum inDallas, in April 2004 around the time of thenext AAPG/SEPM Annual Meeting. Theworkshop, co-sponsored by NSF, SEPM, andthe National Center for Earth-surfaceDynamics (NCED), is open to anyone inter-ested in shaping the future of sedimentarygeology. More information will be distrib-uted as details are set, but please mark yourcalendars for the day just before the Dallasmeeting, Friday, April 16.
Additionally, a small working group ofISES (Vladimir Davydov, Boise State;Rebecca Dorsey, University of Oregon; andTim Carr, Kansas Geological Survey) hasstarted an effort to understand the cyber-infrastructure (CI) needs of the stratigraphicand sedimentary geological community. Inaddition, a variety of data and tools arealready available to work on stratigraphicinformation, as well as some ongoing CIefforts in this direction. This working groupis planning an informal workshop at theSpring 2004 AAPG/SEPM meeting, so keepchecking the SEPM website for its schedule(probably Monday evening, April 19).
CHRONOS is another major push for-ward that benefits all areas of stratigraphyand earth history and is funded by NSF. Thiseffort was born out of combining severalindividual research efforts into a joint enter-prise. Again, NSF helped to develop the col-laboration with support for workshops,which helped focus the earth history com-munity. CHRONOS’s mission is to build anetwork of stratigraphic databases, tools andinformation, all centered on the goal of link-ing all of the data to geologic time. That iseasy to say but to get involved with thedetails that need to be done check out theCHRONOS website at www.chronos.org.
Two more examples of recent efforts with-in sedimentary geology can be found at:EarthTime — website — http://www-eaps.mit.edu/earthtime/ andNational Center for Earth-surfaceDynamics — website —http://www.nced.umn.edu/
Howard Harper; Executive Director, [email protected]
DIRECTOR’S CHAIR
Non-Technical SessionActivities at GSA
The Sedimentary Record
December 2003 | 11
First, let me apologize to the old timers in the field. This letter isdirected toward our younger colleagues who are still struggling to findtheir way through the gauntlet of higher education. To undergraduatestudents, hang in there. You have chosen an exciting field and, if youwork hard, you will never regret your decision. Sedimentology, sedi-mentary geochemistry and paleontology are the frameworks on whichEarth’s changing environments are slowly being revealed. We are thetrue time bandits; capable of walking up to an outcrop and recon-structing the environment in which rocks were deposited millions ofyears ago. This is what lured me to geology and I have never regrettedthat decision. But be careful in your academic journey, there are somepotential wrong turns.
Sedimentary geology, like every other field of Earth Science, isbecoming increasingly more quantitative. We are now faced with try-ing to understand such complex problems as how quickly mountainsare eroded and sediments are delivered to basins, the role of bacteriain sediment production and alteration, global climate change and itscauses, pathways of contaminated sediments through surface andgroundwater, and how strata record changing sea level, climate, andtectonic activity. As sedimentary geologists we are uniquely trained todetermine if changes that are occurring on Earth today are due tohuman influence or part of natural cycles. These endeavors requirestrong backgrounds in the allied sciences: mathematics, physics,chemistry and the biosciences. It is a shame that some schoolsstill do not require these supporting science courses as part ofthe Earth Science curriculum. Those students who followthat path will find their career options very limited. Indeed,the first major obstacle they will face will be that of gainingadmission to graduate school, a critical point in one’s career.
Undergraduates, you would be well advised to research theweb sites of grad schools while you are still sophomores orjuniors. Don’t wait until your senior year to begin makingthis important decision. Learn now about standards foradmission and research opportunities. If you have the oppor-tunity to attend a society meeting, visit the graduate schoolbooths. Choosing the right graduate school is one of themost important decisions you will make in your career.Choosing a specialization is another and you will need helpwith this one. Try to pick a graduate school where you willhave options.
Graduate students, you will find many mentors who areeager to help you through the next stages of your career.Don’t simply rely on your advisors to help you along the way.Become involved in professional societies and you will bedelighted to discover geologists from both academia andindustry who will share their experiences and knowledge withyou. We are talking about your career, don’t rely on advicefrom only a few to help guide you along your way.Professional societies provide vast opportunities for network-ing with senior colleagues. You will be welcomed into thesesocieties.
I recently returned from the Geological Society of Americameeting in Seattle. On Sunday there was a student breakfast,hosted by GSA and other societies, including SEPM, and
sponsored by ExxonMobil. I was delighted to discover that there wereno fewer than 500 students at the breakfast. I could not help butsmile as I watched my colleagues don aprons and began serving thestudents. What a magnificent idea, but what a change from when Iwas a student. My first GSA meeting was in New Orleans and I wasable to enter the icebreaker only after I found a nametag, whichturned out to be that of a rather famous sedimentologist, lying on thefloor. Back then students didn’t get much of a break in registrationfees, there were no student travel grants for meetings or student ses-sions, and there certainly was no student breakfast where one couldmeet and talk with leaders in the field. The profession has changed alot since I started. Students have many opportunities to becomeengaged in the profession at an early phase of their career.
Undergraduates, work hard. The road to success and happiness isnot an easy one to follow. Young sedimentary geologists who havemade it to graduate school, you are very lucky. You have chosen anexciting profession. Your senior colleagues do care about you and willencourage you to succeed. Take advantage of these opportunities. Youwill never regret your involvement. Join a society and becomeengaged with your profession.
John Anderson; President, [email protected]
PRESIDENT’S OBSERVATIONS
A Letter to Geology Students
www.geolsoc.org.uk/seismicgeomorphologywww.sepm.org
