Biostratigraphy and paleoecology of the Qom Formation, Iran 555
ABSTRACT
A study of large benthic foraminifera from the 147 m-thick Qom Formation in the Chenar area (northwestern Kashan) is reported. One hundred and twelve thin sections were prepared and the distribution of benthic foraminifera was analyzed to reconstruct paleoenvironmental conditions. Study of these sections led to the identification of 28 genera and 38 species. On the basis of the recognized foraminifera, the section is comparable to Lepidocyclina- Operculina- Ditrupa Assemblage zone, and the age of the Qom Formation in the studied section is assigned to the Oligocene.
Evidence of sea level changes is observed from bottom to top of the studied section. On the basis of large benthic foraminifera assemblages and microfacies features, three major depositional environments (inner shelf, middle shelf and outer shelf) were defined. The inner shelf facies is characterized by wackstone-packstone, dominated by miliolid and small perforate foraminifera. The middle shelf facies is represented by packstone-grainstone with diverse assemblage of large perforate benthic foraminifera. Outer shelf facies is dominated by large perforate benthic foraminifera as well as planktic foraminifera. The distribution of the Oligocene large benthic foraminifera in the studied area indicates that shallow marine carbonate sediments of the Qom Formation were deposited in a photic zone of tropical to sub-tropical environments. Finally, the correlation between the study area and some other sections of Central Iran indicates that sedimentation of the Qom Formation is continued from Late Rupelian to Chattian in northwest and Late Rupelian to Aquitanian in southeast direction.
Key words: biostratigraphy, benthic foraminifera, Qom Formation, Oligocene. Aquitanian, Iran.
RESUMEN
Se reporta el estudio de foraminferos bentnicos grandes de la Formacin Qom, con 147 m de espesor, en el area de Chenar (noroeste de Kashan). Ciento doce secciones delgadas fueron preparadas y la distribucin de foraminferos bentnicos fue analizada para reconstruir las condiciones paleoamebietales. El estudio de esas secciones llev a la identificacin de 28 gneros y 38 especies. Con base en los foraminferos identificados, la seccin es atribuible a la zona de Lepidocyclina- Operculina- Ditrupa y la edad de la Formacin Qom en la seccin estudiada es asignable al Oligoceno.
Evidencias de cambios del nivel del mar pueden ser observados desde la base y hacia a cima de la seccin estudiada. Con base en los ensambles de foraminferos bentnicos grandes y en las caractersticas de las microfacies, tres ambientes de depsito fueron definidos (plataforma interna, media y externa). Las facies de plataforma interna se caracterizan por wackstone-packstone, dominada por mililidos y
BiostratigraphyandpaleoecologyoftheQomFormationinChenararea(northwesternKashan),Iran
Elham Behforouzi* and Amrollah Safari
Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran, 81746-73441.* [email protected]
Revista Mexicana de Ciencias Geolgicas, v. 28, nm. 3, 2011, p. 555-565
Behforouzi,E.,Safari,A.,2011,BiostratigraphyandPaleoecologyoftheQomFormationinChenararea(northwesternKashan),Iran:RevistaMexicanadeCienciasGeolgicas,v.28,nm.3,p.555-565.
Behforouzi and Safari556
pequeos foraminferos perforados. La plataforma media est representada por packstone-grainstone, con diversos ensambles de foraminferos bentnicos grandes perforados. Las facies de plataforma externa estn dominadas por foraminferos bentnicos perforados grandes, as como por foraminferos planctnicos. La distribucin de los foraminferos bentnicos grandes del Oligoceno indica que los sedimentos marinos carbonatados someros de la Formacin Qom fueron depositados en la zona ftica de un ambiente tropical a sub-tropical. Finalmente, la correlacin entre el rea estudiada y otras secciones de Irn Central indica que la sedimentacin de la Formacin Qom fue continua en direccin noroeste desde el Rupeliano Tardo al Chattiano, y lo fue en direccin sureste del Rupeliano Tardo al Aquitaniano.
Palabras clave: bioestratigrafa, foraminferos bentnicos, Formacin Qom, Oligoceno, Aquitaniano, Irn..
INTRODUCTION
Inthisstudy,theforaminiferaassemblageinthestrati-graphicsectionlocatedatChenarvillage,50kmnorthwestofKashan,isdescribed.ThestudyareaexposesCenozoicsedimentsandis locatedat510902Elongitudeand340537Nlatitude(Figure1).
Duetothehighevolutionrate,abundance,widespreaddistributionandabruptextinctionofspecies,benthicforaminiferaareconsideredanimportanttoolforthestudyofthebiostratigraphyandevolutionofgeneraandspecies,relativedepthorpaleoenvironmentalreconstruction(Vaziri-Moghaddamet al.,2010).Consideringthedistributionofforaminiferaandanalyzingsomefactors likelight,temperature,nutrientsupply,substrate,hydrodynamicenergy, depth,water locomotion and symbiosis, thepaleoenvironmentcouldbereconstructed.TherearesomesimilaritiesbetweenthebenthicforaminiferaassemblagesofQomFormationandAsmariFormationandduetolackofaformalproposedbiozonationintheQomFormation,thebiozonationofferedbyWynd(1965)andLaursenet al.(2009)fortheAsmariFormationwereusedinthisinvestigation.
Geological investigationof theQomFormationinCentralIranstartedwiththeworkofTietze(1875).SubsequentworkerssuchasStahl(1911),Riben(1935),FuronandMarie(1939),Furon(1941),FurrerandSoder(1955),Gansser(1955),Dozy(1944,1955),Abaieet al.(1964)andBozorgnia(1966)reportedonthemarinesedimentsoftheQomFormation.AfewforaminiferalspecieswereillustratedbyFuronandMarie(1939),Furon(1941),FurrerandSoder(1955),Abaieet al.(1964)andBozorgnia(1966).Rahimzade(1994)collectedthenamesofmostresearchers,partofwhoseworkcoveredtheQomFormation.
FurrerandSoder(1955)dividedtheQomFormationintosixmembers;Abaieet al.(1964)increasedthenum-berofmembers to ten.Abaieet al. (1964)notedthat twomembers,c-1andc-3,werethemainobjectivesinexplorationwells,duetofracturedevelopmentenhancingporosity/permeabilityandhydrocarbonshows.Bozorgnia(1966)proposedandintroductiontenmembersfortheQomFormationanddistinguishedseverallocalbasinsofdeposi-
tioninCentralIran,onthebasisofitslithologicalcharacters.Rahaghi(1973,1976,and1980)suggestedOligo-MioceneagefortheQomFormation.OkhraviandAmini(1998)reconstructedpalaeoenvironmentofthef-memberoftheQomFormationbasedonmicrofaciesanalysis.Basedonechinodermsandmicrofosils,KhaksarandMaghfouri-Moghaddam(2007)proposedMiddletoLateOligoceneagefortheQomFormation.Aalaeobiogeographicrecon-structionoftheQomFormationwasproposedbyReuteret al.,2007.
METHODS AND STUDY AREA
FieldworkwasconcentratedonanoutcropoftheQomFormation,located10kmtothenorthofChenarvillage.A
CaspianSea
Persian Golf
Kashan
N44
38
24
Aran-Bidgol
Kashan
Isfahan
GhamsarBarzak
Niasar
JoshaghanChenarJoshagh Ravand
N
345'
51 9'
10 kmStudy area
I R A N
Oman Sea
64
Figure1.LocationmapofthestudiedareaincentralIran.
Biostratigraphy and paleoecology of the Qom Formation, Iran 557
itscoevalcounterpartintheZagrosbasininsouthwestIran(AsmariFormation)(Stcklin1952;Bozorgnia1966and Kashfi 1988). Therefore, biozonations established for theQomFormationinthisworkarelargelybasedonthebiozonationsofWynd(1965)andLaursenet al.(2009),whichwasusedfortheAsmariFormationthatcomprisesanOligocenetoEarlyMiocenecarbonatesequence(Table1).
Frombasetotopatwoforaminiferaassemblageswererecognizedinthestudiedsection(Figure3):
Assemblage1: Ischaracterizedby thepresenceofLepidocyclinasp., Eulepidinasp., Eulepidinadila-tata, Eulepidinaelephantina,Nephrolepidinacf. mar-ginata,Nephrolepidina cf. tournoueri,Nephrolepidinasp.,Operculina complanata, Operculina sp.,Sphaerogypsina globulusa, Haplophragmium slingri, Planorbulinasp.,Neorotalia viennoti, Neorotalia sp.,Valvulinid sp.,Amphistegina sp.,Amphistegina lessonii, Elphidium sp.,Bigenerina sp.,Textulariasp., Discorbis sp.,Quinqueloculinasp., Triluculina trigouenula, Globorotalia cf. nana, Globorotalia siakensis (Figures4and5).Thisassemblage
147mthicksectionwasmeasuredindetail,andatotalof112 specimens were sampled during the detailed field inves-tigation.Samplesweretakenfromthecarbonateandmarlylayersalmosteverymeteraccordingtofaciesvariation.Thinsectionswereprovidedforharderlitologieswhilstsofterli-tologiesweredisaggregatedandtheforaminiferapickedandanalyzed.Disaggregatedsampleswerewetsievedthrougha 151 m. Thin sections were studied under the microscope fortheanalysisofbenthicforaminifera.Taxonomicclas-sification was based on Loeblich and Tappan (1988), Adams andBourgeois(1967)andAdams(1969).
GEOLOGICAL SETTING
Onthebasisofthesedimentarysequence,magmatism,metamorphism, structural setting and intensity ofdeformation,Iranianplateauhasbeensubdividedintoeightcontinentalfragments,including,Zagros,Sanandaj-Sirjan,Urumieh-Doktar,CentralIran,Alborz,Kopeh-Dagh,LutandMakran(Heydariet al.,2003).ThestudyareaislocatedintheCentralIranbasin(Figure2).
DuringtheEarlyPaleogene,theTethyanseawaywasawideoceanthatconnectedthetwomajoroceanicrealms,the Atlantic and the Pacific (Schustr and Wielandt, 1999). The subduction and final collision of the African-Arabian platearoundEocene-OligoceneboundarywasaccompaniedbythevanishingoftheTethyanseaway,thedisconnectionof the Atlantic and the Pacific Ocean and the birth of the IndianOceanandtheMediterranean.Asaconsequence,Central-IranianpaleogeographychangeddramaticallybythedevelopmentofavolcanicarcwhichseparatedaforearcfromabackarcbasinduringEocenetimes.MarinesedimentationoftheQomFormationbeganduringtheOligoceneandcontinuedtotheendoftheEarlyMioceneintheEsfahan-SirjanforearcandintheQombackarcbasin(SchustrandWielandt,1999).
BIOSTRATIGRAPHY OF FORAMINIFERA
LargerbenthicforaminiferaarewidelydistributedintheTertiarycarbonateplatformoftheQomFormation.Theydevelopedcomplicatedinternalstructureswhichcanbe identified when they are randomly thin sectioned. These organismscanprovidecompleteanddetailedevidenceforbiostratigraphicanalysisoftheshelflimestonebecauseof rapid diversification, abrupt extinction and abundance (Beavingtone-PennyandRacey,2004).
The sedimentary deposits of the study areayieldedabundantlargerbenthicforaminifera,therefore,biostratigraphiczonationisbasedontheseorganisms.Sofar,aformalbiostratigraphicframeworkhasnotyetbeenestablishedfortheQomFormation.However,basedonforaminiferalsimilaritiesageneralagreementexiststocorrelatetheQomFormation(CentalIranBasin)with
Zagros Province
Sanandaj-Sirjan Province
Urumieh-Dokhtar Province
Central Iran Province
Makran Province
Alborz Province
Lut ProvinceKopeh DaghProvince
Suture
Fault
Study area50 60
Persian Gulf
Pakistan
30
Afghanistan 35
Turkmenistan60
Caspiansea
50
Turkey
35
Iraq
30
Figure2.SubdivisionsoftheZagrosorogenicbelt(adoptedfromHeydariet al.,2003),andzonationinAsmariFormation(Laursenet al.,2009andWynd,1965).
Behforouzi and Safari558
correspondstotheLepidocyclina-Operculina-Ditrupa assemblagezone.AssemblagezoneofWynd(1965)andLaursenet al.(2009)appliedfortheAsmariFormation.ThisassemblageisattributedtotheOligoceneandiscorrelatedwiththelowerpartoftheAsmariFormation.
Assemblage2:Lepidocyclina-Operculina-Ditrupa assemblagezone.Theassemblagehasthisassociatedfauna:Planorbulinasp.,Eulepidina dilatata,Haplophragmium slingri,Rotalia viennoti,andalgae.ThiszonerangesfromtheRupelianintotheChattian(Laursenet al.,2009).
PALEOECOLOGY
Inthissection,anattempttoinvestigatefactorsthatinfluence the benthic foraminifera distribution in the Qom Formationispresented.Inthisregards,environmentalagentssuchasnutrientsupply,light,temperature,waterlocomotion,substrate,salinity,hydrodynamicenergy,depth and symbiosis are very significant. In terms of the paleoecology,paleoecologicalconstraintsporposedbyHallokandGlenn(1986)includethreefamiliesobservedinstudiedsection(Nummulitidea,AmphisteginideaandPeneroplidea).
Nutrient supply
Largebenthicforaminiferaarehighlyadaptedtostable, oligotrophic and nutrient-deficient conditions, but theycannotrespondcompetitivelywhennutrientresourcesbecomeabundant(Hallock,1985).Inorganic,biolimitingnutrientsentershallow-watercommunitiesprincipallybyturnoverorupwellingofdeeperwaters,byrun-offfromland
orbyadvectionfromareasofupwellingorrunoff(HallockandSchlager,1986).
Largesymbiont-bearingbenthicforaminiferaarecompatible to nutrient deficiency conditions and in such situation,thealgalsymbiontusesorganicwastesubstancesofthehostandCO2originatedfromhostrespirationforphotosynthesis(Beavingtone-PenneyandRacey,2004).Andso,theproducedsubstancessuppliesnutrientforthehost.
In the studied section, semi-restricted lagoon environmentsinferredbythepresenceofperforateandimperforateforaminiferaindicatemesotrophictoeutrophoticconditionsandshallowtodeepmarineenvironmentspointtomesotrophic tooligotrophicconditions.ShowthatLepidocyclinaharbouredendosymbionticalgaetoprovidesufficient light for the photosynthesis of the symbionts (Chaproniere,1975).NumerouschambersoftwentytestsofNephrolepidinacf.tournouer indicatedinsample(B16)(Figure6).
Light
TheabundanceofrobustandthicktestsofOperculinain the study area reflects increasing light intensity (Figure 7).Lightintensityandhydrodynamicforcecontroltestmorphologythroughsymbioticinteractions.Inshallow,well-lit waters the calcification rate in foraminiferal test isenhancedbyphotosyntheticsymbionts,inordertopre-ventphotoinhibitionofsymbioticalgaewithinthetestortestdamageinturbulentwater(Beavingtone-PenneyandRacey,2004).
Larger foraminifera are sensitive to changesinenvironmentalfactors includinglight intensityandhydrodynamicforcealongdepthgradientswhichare
Epoch Stage Biozonation of Laursen .et al(2009)
Biozonation of Wynd (1965)
Burdigalian Borelis melo curdica -Borelis melo melo Borelis melo curdicaAssemblage zone(zone 61)
Assemblage zone (zone 59)
Miocene
AquitanianMiogypsina-Elphidium sp. 14Peneroplis farsenensis Archaias
operculinoformisAssemblage zone
(zone 58)
Nummulitesintermedius-Nummulites vascusAssemblage zone
(zone 57)
ChattianArchaias hensoni-Miogypsinoidescomplanatus
Nummulites vascus-Nummulites fichteli
Lepidocyclina-Operculina-Ditrupa
Oligocene Rupelian
Globigerina-Turborotalia cerroazulensisHantkenia
Lepidocyclina-Operculina-DitrupaAssemblage zone (zone 56)
Globigerina .sppAssemblage zone (zone 55)
Table1.ZonationinAsmariFormation(Laursenet al.,2009andWynd,1965).
Biostratigraphy and paleoecology of the Qom Formation, Iran 559
Lithology
B1B4
B8
B15
B23
B26B28B30B32
B35
B41
B46
B50
B53
B57B63B65
B68
B72
B78
B83
B87
B90B94
B98
B102B107B110
B6
B11
Sampleno.
Stage
Formation
Qom
Rupelian-Chattian
B20
10
20
30
40
50
60
70
80
90
100
110
120
130
140
Thicknes(m)
Series
Oligocene
Eoce
ne
Volcanic
Quinq
uelocu
linasp.
miliolids
Amph
istegina
.sp
Ope
rculina
.sp
Textullaria
.sp
Bige
rina
.sp
Elph
idium
.sp
Lepido
cyclina
.sp
Trilu
culin
atrigou
enula
Nep
hrolep
idina
.sp
V alvulinidsp.
Globo
rotalia
siak
ensis
Globo
r otalia
nana
cf.
Hap
loph
ragm
ium
slinge
nDisco
rbissp
.
Pene
roplis
evolutus
Spha
erog
ypsina
sp.
Plan
orbu
linasp.
Neo
rotalia
vien
noti
Pyrgosp
.
Ditr
upasp
.Heteros
tegina
.sp
Neph
rolepidina
.margina
tacf
Eulepidina
sp.
Nep
hrolep
idina
tour
noue
ricf.
Ope
r culinaco
mplan
ata
Eulepidina
dilatata
Recent alluvium
Sandy limestone
Thick bedded limestone
Marly limestone
Medium bedded limestone
Gravely limestone
Thin bedded limestone
Volcanic
Figure3.LitostratigraphiccolumnandverticaldistributionofsomebenthicforaminifersinChenararea,northwestKashan.
Behforouzi and Safari560
Figure4.a)Neorotalia viennoti,subaxialsection(sampleNo.B72),b) Neorotalia viennoti,equatorial section(sampleNo.B102),c) Planorbulinasp.,subaxialsection(sampleNo.B98),d) Elphidium sp.,subaxialsection(sampleNo.B76),e) Sphaerogypsina sp.,axial section(sampleNo.B68),f) Ditrupasp.(sampleNo.B73),g) Haplophragmiumsp.,subaxialsection(sampleNo.B63),h)Amphistegina sp.,subaxialsection(sampleNo.B34).
Biostratigraphy and paleoecology of the Qom Formation, Iran 561
mirroredbychangesintestshapeandsizeofsymbiont-bearingforaminifera(Beavingtone-PenneyandRacey,2004).Theshallowdwellingmicroperforatedhyalineforaminiferaproducesmall,robustandovatetestsandincrease calcification rate which brings about a thick wall structuretopreventphotoinhibitionoftheendosymbiontwithinthetestinhighlyilluminatedshallowwaters,ortestdamagesinmobilesubstrates,whilehyalineforaminiferafromgreaterdepthsshifts to larger, thinnerandmoretransparenttesttothriveinstronglyreducedlightintensity(Beavingtone-PenneyandRacey,2004).Onthebasisofthedependenceofcarbonateproductiontolightpenetration,
20 m 20 m
50 m
500 m 20 m
1 mm
20 m
d)
a)
c)b)
e)
f)g)
Figure6.Lepidocyclinatest.Smallporesandlateral chamberlets,whichresultedfromalgalsymbiosisreplacement(sampleB16).
Figure5.a)Eulepidina cf.dilatata,axialsection(sampleNo.B80),b) Nephrolepidina cf.marginata,axialsection(sampleNo.B38),c)Nephrolepidinacf.tournoueri,axialsection(sampleNo.B65),d)Operculina sp.,axialsection(sampleNo.B55),e)Operculina sp.,equatorialsection(sampleNo.B70),f)Globorotalia siakensis, axialsection(sampleNo.B97),g) Globorotalia cf.nana, subaxialsection(sampleNo.B86).
Behforouzi and Safari562
threedifferentgroupsofbenthicorganismscouldbeconsidered.
RedalgaeandsomehyalinebenthicforaminiferasuchasHeterostegina,OperculinaandLepidocyclina identified intheQomFormationsamplesareindicatorsofdysphoticzones.Bassiet al.(2007)dividedthephoticzoneintoup-per and lower parts; in this classification, Neorotalialiveintheupperpartoftheupperphoticzone,andHeterostegina,OperculinaandLepidocyclinaaredominantinthelowerpartoftheupperphoticzone,whilstinthelowerphoticzoneLepidocyclinaisdeveloped.
Light-independentbiotaincludesbryozoans,mol-lusks,crinoids,brachiopodsandspongesthatarewidespreadinstudiedsection(sampleB12).Organismsthatcomposethe light-dependent biota identified include green algae, reef-buildercoralsandmiliolidsconstitutingindicatorsofphoticzone.
Severallargeforaminifersthathostalgalsymbiontspresentamoreevolvedskeletalstructurethanthosewithoutsymbiont.ThisprocessisalsoseeninLepidocyclina(Figure4).Largebenthicforaminifershostunicellulareukaryoticalgalsymbiontsthataredependentonlightandnutrientandarethereforerestrictedtoeuphoticzone(Romeroet al.,2002).Symbiont-bearinglargeforaminiferaarerestrictedtowarmwateroftropicalrealmswherewatertemperatureishigherthan1418Cinthecoldestmonthsoftheyear(Renema,2006).
Figure7.a)Operculinawiththicktest,whichisindicatorofshallowdepthandincreasinglightintensity(sampleB12);b)Operculinawiththintestfromhighdeepanddecreasinglightintensity(sampleB16).
Figure8.a)Amphistegina(sampleB12)withthicktestandsmallsizewhichisanindicatorofincreasinghydrodynamicregime;b)Amphistegina(sampleB17)withthintestandlargesizeindicatedecreasinghydrody-namicregime.
Water motion
This factor influences the test shape (diameter/thick-nessratio).Generally,lightintensityandwatermotionpromotestheformationofsecondarylayersinforaminif-eraltests.Onthecontrary,whenthelightintensityandthehydrodynamicsareweakthegrowthratedecreases.Inthestudiedarea,Amphistegina fromlagoonenvironmentwithhighenergyandintenselightarethickerthanthoseofdeeperenvironmentswithlowerenergy(Beavingtone-PenneyandRacey,2004)(Figure8).
Substrate nature
Substratenaturealsodependsonwaterturbulence.Foraminiferawhichliveonacoarsegrainsubstratehavethickertestsandarefusiform.Amphistegina alsopreferhardsubstrateswithhighenergy(Figure8),whileOperculinaliveonsoftandmuddysubstratesandhavethinshells(Figure8).
Salinity
Highsalinityplaysapreventativeroleingrowthandevolutionoflargeforaminifera,butmediumdegreeofsalin-ityisnotsoeffective.Insemi-restrictedlagoonenvironment,
Biostratigraphy and paleoecology of the Qom Formation, Iran 563
a) b)
c) d)
20 m
20 m
100 m
50 m
Figure9.a)Perforateforaminiferainassociationwithimperforateforaminifera(sampleB9toB12);b)Perforateforaminifera(sampleB13toB17);c)echinoid;d)bryozoans.
becauseoftheconnectionwithopenmarineenvironmentsandlowpercentofsalinity,perforateandimperforatefora-miniferscanbeobservedtogether(Figure9a),whereas,consideringnormalsalinityinshallowpartsofopenmarineofthestudiedsection,onlyperforateforaminifershavebeenfound(Figure9b).Thepresenceofstenohalineorganisms(echinoidandbryozoan)isanindicatorofmarinenormalsalinity(Figure9c,9d).
Hydrodynamic energy and depth
The occurrence of benthic organisms reflects their compatibilityinhighorlowenergyenvironments(Flugel,2004).Forinstance,inshallowenvironmentswithinthephoticzone,withincreasingwatermotion,benthicfor-eminifersshapechanges.Itmeansthathighenergycausesthetesttobethick(increasingincarbonateproduction)anddecreasesitsgrowthrateandeventuallyreducestheirtestsize(Beavingtone-PenneyandRacey,2004).Haynes(1965)statedthattheshapeoflargeforaminiferachangesunder the influence of hydrodynamic conditions and its symbioticrelationshipwithalgae.Theauthorexpressedthatspecieswithfreelife(non-epizoan)andsphericalspeciesare indicators of reef environment cleaned by flows, while
fragilethintestswithmaximumsurface/volumeratiocouldbefoundincalmenvironmentswithlowlight.Generally,foraminifersincompatibilitywithhighenergy,createslamellarandthicktestslikeAmphistegina.TheelongatedOperculinawiththintestfoundinthisworkisanindicatorofdeepenvironments(Beavingtone-PenneyandRacey,2004).Inthisresearch,acomparisonisshownbetweenthickAmphisteginawithlamellartestsinhighenergylagoonenvironmentandelongatedAmphisteginathatisindicatoroflowenergyenvironment(Figures10and11).
(1) (2) (3) (4) (5)
A. Lobifera A. Lessonii A. Papillosa
Increasing water energyand light intensity
Figure10.ChangeintheshapeandsizeofAmphistegina testduetochangeinlightintensityandhydrodynamicenergy(Beavingtone-PenneyandRacey,2004).
Behforouzi and Safari564
CONCLUSION
Onthebasisoftheforaminiferarecognizedinthestudiedsection,theQomFormationiscomparabletotheLepidocyclina-Operculina-Ditrupa AssemblageZone.TheageoftheQomFormationinthestudiedsectionisOligocene.
Thecarbonaterocksofthestudyareacontainaphoto-zoanassociationcomposedpredominantlyoflargebenthicforaminiferaandcorallineredalgaeinassociationwithcorals,heterotrophs.Thisphotozoanassemblageindicatesoligotrophicconditions.Moreover,theabundanceandas-sociationoflargebenthicforaminiferawithcorallineredalgaearereferredtoasforalgalfaciesdevelopedinshal-low,warmwaterenvironmentsofthephoticzonewhereoligotrophicconditionwasprevalent.
Basedonthepaleoecologyandlithology,threedistinctdepositionalsettingcanberecognized:innershelf,middleshelfandoutershelf.
Innershelffaciescontainabundantimperforatetestsofforaminifera.Middleshelffaciesarecharacterizedbyabundantlargeperforateforaminifertests.Towardthebasin,plankticforaminiferaandlargeforaminiferswithperforatetestsoccurcontemporaneously.Basin(outershelf)faciesismarkedbyhighplankticforaminiferacontentsembeddedinwackstone.
ACKNOWLEDGMENTS
Inparticular,wewouldliketoexpressourmostsinceregratitudetoProf.Dr.FranciscoVegaforhishelpfuladviceandguidance.Theauthorswishtothankthereviewersfortheirhelpfulandconstructivecomments.WealsothankDr.HosseinVaziri-Moghaddam,Dr.AliBahrami,Dr.AkbarGhazi-FardandDr.MohammadAliMakki-Zadeforhissup-portandthoughtfulcomments.Wealsowouldliketothankthe University of Isfahan for providing financial support. AlsowethanktheRevistaMexicanadeCienciasGeolgicasreviewersfortheirconstructivecomments.
REFERENCES
Abaie,I.,Ansari,H.J.,Badakhshan,A.,Jaafari,A.,1964,Historyanddevelopment of the Alborz and Sarajeh fields of Central Iran: BulletinofIranianPetroleumInstitute15,561-574.
Adams,T.D.,1969,TheAsmariFormationofLurestanandKhuzestanProviences: National Iranian Oil Company Report 1151,unpublished.
Adams,T.D.,Bourgeois,F.,1967,Asmaribiostratigraphy:IranianOilOperatingCompanies,GeologicalandExplorationDivision,Report1074.
Bassi,D.,Hottinger,L.Nebelsick,H.,2007,LargerForaminiferafromtheUpperOligoceneof theVenetianarea,northeast Italy:Palaeontology,5(4),845-868.
Beavingtone-Penney, S.J., Racey,A., 2004, Ecology of extantnummulitidsandotherlargerbenthicforaminifera.applicationsinPaleoenvironmentalanalysis:EarthScienceReview,67(3-4),219-265.
Bozorgnia,F.,1966,QomFormationstratigraphyoftheCentralbasinofIrananditsintercontinentalposition:Bull.IranPet.Inst.,24,69-76.
Chaproniere,G.C.H.,1975,PaleoecologyofOligocene-MiocenelargerForaminiferida:Australia:Alcheringa,1,37-58.
Dozy,J.J.,1944,Commentsongeologicalreportno.1byThiebaud(ontheQum-Saveharea):GeologicalReport308.
Dozy,J.J.,1955,ASketchofpastCretaceousvolcanisminCentralIran:Leidsche,GeologischeMededeelingen20,48-57.
Flugel.E.,2004,MicrofaciesofCarbonateRocks,Analysis,InterpretationandApplication:Berlin,Springer-Verlag,Berlin,976pp.
Furon,R.,1941,GeologieduplateauIranien(Perse-Afghanistan-Beloutchistan):MmoiresduMusumNationaldHistoireNaturelle,NouvelleSerie,Paris7(2),177-414.
Furon,R.,Marie,P.,1939,SurlamicrofaunedesmarnesaquitaniennesLepidocyclinesdeQoum(inPersian):CompteRenduSommairedesSancesdelaSocitGologiquedeFrance,79-80.
Furrer,M.A.,Soder,P.A.,1955.TheOligoMiocenemarineformationintheQomregion(CentralIran):Proceedingsofthe4thWorldPetroleumCongress,Rome,SectionI/A/5,267-277.
Gansser,A.,1955.Newaspectsof thegeology inCentral Iran, inProceedingsof the4thWorldPetroleumCongress,Rome,SectionI/A/5,279-300.
Hallock,P.,1985,Whyarelargerforaminiferalarge?:Paleobiology11,p.195-208.
Hallock, P., Glenn, E.C., 1986, Larger foraminifera: a tool forpaleoenvironmentalanalysisofCenozoicdepositionalfacies:Palaios,1(1),55-64.
Hallock,P.,Schlager,W.,1986,Nutrientexcessandthedemiseofcoralreefsandcarbonateplatforms:Palaios1,389-398.
Haynes,J.R.,1965,Symbiosiswallstructureandhabitateinforaminifera:
Figure11. ChangesinshapeandsizeofLepidocyclinatests thatresults,fromrighttoleft,fromdecreasingdepth,andincreasinglightintensityandhydrodynamicenergy(samplesB37,B39,B41).
Biostratigraphy and paleoecology of the Qom Formation, Iran 565
SpecialPublication-CushmanFoundationforForaminiferal:Research,16,40-43.
Heydari,E.,Hassanzadeh,J.,Wade,W.J.,Ghazi,A.M.,2003,PermianTriassicboundaryintervalintheAbadehsectionofIranwithimplications for mass extinction, Part 1-Sedimentology:Paleogeography,Paleoclimatology,Paleoecology,193(3),405-423.
Kashfi, M.S., 1988, Evidence for non-collision geology in the Middle East: JournalofPetroleumGeology11(4),443-460.
Khaksar,K.,Maghfouri-Moghadam,I.,2007,PaleontologicalstudyoftheechinodermsintheQomFormation(CentralIran):IslamicAzadUniversity,EarthSci.Res.11(1),57-79.
Laursen,G.V.,Monibi,S.,Allan,T.L.,Pickard,N.A.,Hosseiney,A.,Vincent,B.,Hamon,Y.,Van-Buchem,F.S.P.,Moallemi,A.,Druillion,G.,2009,TheAsmariFormationrevisited:changedstratigraphicallocationandnewbiozonation:Shiraz,FirstInternationalPetroleumConference&Exhibition,EuropeanAssociationofGeoscientistsandEngineers.
Loeblich,A.R.,Tappan,J.H.,1988,ForaminiferalGeneraandtheirClassification. Van Nostrand Reinhold. 2 vols. pls. 847. New York,869p.
Okhravi,R.,Amini,A.,1998,Anexampleofmixedcarbonate-pyroclasticsedimentation(Miocene,CentralBasinIran):SedimentaryGeology,118,37-57.
Rahaghi,A.,1973,tudedequelquesgrandsforaminifresdelaFormationdeQum(IranCentral):RevuedeMicropaleontologie,16,2338.
Rahaghi,A.,1976,ContributionaltudedequelquesgrandsforaminifresdelIran:SocitNationalIraniennedesPtrolesLaboratoiredeMicropalontologie,Publication6,1-79.
Rahaghi,A.,1980,TertiaryfaunalAssemblageofQumKashan,SabzewarandJahrumarea:NationalIranianOilCompany,GeologicalLaboratories,Publication8.
Rahimzade,F.,1994,TreatiseontheGeologyofIran:Oligocene-Miocene,Pliocene(inPersian):MinistryofMinesandMetals,GeologicalSurveyofIran,12.
Renema,W.,2006,Largebenthicforaminiferafromthedeepphoticzoneofamixedsiliciclastic-carbonateshelfofEastKalimantan:Indonesia,MarineMicropaleontology,58,73-82.
Reuter,M.,Pillar,W.E.,Harzhauser,M.,Mandic,O.,Berning,B.,Rogl,F.,Kroh,A.,Aubry,M.P.,Wielandt,U.,Hamedani,A.,2007,TheOligo-MioceneQomFormation(Iran):evidenceforandearlyBurdigalianrestrictionofTethyanSeawayandclouserofitsIraniangetways:InternationalJournalofEarthSciences,98,627-650.
Riben,H.,1935.ContributionalagologiedelAzerbeidjanPersan:BulletindelaSocitNeuchateloisedesSciencesNaturelles,59(1934),20-144.
Romero,J.,Caus,E.,Rossel,J.,2002,AModelforthePalaeoenvironmentaldistributionoflargerforaminiferabasedonLateMiddelEocenedepositsonthemargineofthesouthPyreneanBasine(SESpain):Palaeogeography,Palaeoeclimatology,Palaeoecology,179,43-56.
Schustr,F.,Wielandt,U.,1999,OligoceneandEarlyMiocenecoralfaunasfromIran:palaeoecologyandpalaeobiogeography:InternationalJournalofEarthSciences,88,571-581.
Stahl,A.F.,1911,Persien, inHandbuchderRegionalenGeologie:Heidelberg(Winter),Hft.8,5(6),46pp.
Stocklin,J.,1952,StratigraphicalinvestigationintheQom-Arak-GulpaiganDelidjanarea:NationalIranianOfOilCompany,Report95.
Tietze, E., 1875, Ein Ausflug nach dem Siahkuh (Schwarzer Berg) in Persien.MitteilungenderGeographischenGeographischenGesellschaftWien18(8),257-267.
VaziriMoghaddam,H.,Kimiagari,M.,Taheri,A.,2010,PrinciplesofForaminifera:Isfahan,Isfahan,366p.
Wynd,J.,1965,BiofaciesofIranianoilconsortiumagreementarea:IranianOilOffshoreCompany,Report1082,unpublished.
Manuscriptreceived:December18,2010Correctedmanuscriptreceived:June16,2011Manuscriptaccepted:June26,2011
