The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence strat...The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.展开更多
In this study, to identify and analyze facies of depositional environment and depositional model of Qom Formation, stratigraphic Saran Section (southwest of Semnan) was selected. Qom Formation in Saran section include...In this study, to identify and analyze facies of depositional environment and depositional model of Qom Formation, stratigraphic Saran Section (southwest of Semnan) was selected. Qom Formation in Saran section includes about 380 meters of conglomerate at the base, chalk, limestone, marl, and shale. Petrographic studies with facies analysis have led to the identification of 12 microfacies, these microfacies have been deposited in four facies groups including tidal flat, lagoon, barrier and open marine. Study of horizontal and vertical facies changes and their comparison with recent and ancient environments reveals that Qom Formation in this section relates to shallow marine environment and its facies were deposited in a shelf carbonate platform and are comparable with contemporary shelf platforms such as Florida and old shelf platforms such as Mozduran. The most important diagenetic processes affecting the studied section include micritization, bioturbation, cementation, dissolution, neomorphism, fracturing, mechanical and chemical compaction, hematitization and dolomitization. These processes have formed in marine, meteoric and burial diagenetic environments.展开更多
Deposits of the Qom Formation (Oligocene-Miocene) in Rameh section are located in northeastern Garmsar and contain dominantly 420 m Limestone, pebble-rich to sandy Limestone and marl Limestone. This formation is uncon...Deposits of the Qom Formation (Oligocene-Miocene) in Rameh section are located in northeastern Garmsar and contain dominantly 420 m Limestone, pebble-rich to sandy Limestone and marl Limestone. This formation is unconformably overlaid and underlaid with siliciclastic deposits of Upper Red Formation and Lower Red Formation. Field observations, along with laboratory investigations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the studied formation. Open marine facies association consists of bioclast mudstone, bioclast wackestone, bioclast packstone and bioclast roadstone;shoal facies association consists of ooid grainstone, bioclast grainstone and coral boundstone;lagoon facies association is composed of dolomitic mudstone, intraclast bioclast wackestone and bioclast packstone;and tidal flat facies association is sandy dolomudstone and stromatolite boundstone. The qom formation rocks in Rameh section are deposited in a rimmed shelf carbonate ramp. This formation undergoes various diagenetic processes including dissolution, porosity, cementation, micritization, compaction and dolomitization.展开更多
Postmiogypsinella intermedia Sirel and Gedik,2011 is reported for the first time from the shallow-marine limestones of the upper Chattian Qom Formation,Central Iran.This miogypsinid species has so far only been record...Postmiogypsinella intermedia Sirel and Gedik,2011 is reported for the first time from the shallow-marine limestones of the upper Chattian Qom Formation,Central Iran.This miogypsinid species has so far only been recorded from the upper Oligocene of Malatya(type locality)and Sivas(Central Anatolia)in eastern Turkey and from the upper Oligocene of the Prebetic Domain,SE Spain.The new record from Central Iran,paleobiogeographically located at the Eurasian margin of the Tethyan Seaway between the Western and Eastern Tethys realms,indicates that the paleogeographic distribution of this species has to be extended eastwards as far as Central Iran.This observation is not unexpected,since miogypsinid foraminifers with eccentric embryonic-nepionic apparatus(e.g.,Miogypsinella,Miogypsinoides,Miogypsina)are usually widely distributed.The accompanying larger benthic foraminifera,including Miogypsinoides complanatus(Schlumberger),Miogypsinoides formosensis Yabe and Hanzawa,Spiroclypeus margaritatus(Schlumberger),Operculina complanata(Defrance),and Risananeiza pustulosa Boukhary et al.,indicate the late Chattian age(corresponding to SBZ 23 Biozone).Postmiogypsinella intermedia is indicative of a shallow-marine middle ramp environment with oligotrophic conditions and inhabited the relatively deeper part of the photic zone.展开更多
The shallow marine carbonates of the upper Oligocene Qom Formation yielded several occurrences of the foraminiferan genus Neoplanorbulinella Matsumaru. Neoplanorbulinella saipanensis Matsumaru has so far been recorded...The shallow marine carbonates of the upper Oligocene Qom Formation yielded several occurrences of the foraminiferan genus Neoplanorbulinella Matsumaru. Neoplanorbulinella saipanensis Matsumaru has so far been recorded from the late Eocene-early Miocene of Japan and late Oligocene of NE Italy whereas N. malatyaensis Gedik is only reported from the Oligocene from its type locality in the Malatya Basin, eastern Turkey. The new records reported here from the Qom Formation indicate that both species occur in the Dobaradar section, ca. 10 km south of the city of Qom in North-Central Iran. The palaeogeographic distribution of these two species therefore has to be extended as far as the palaeolongitude of current Central Iran.The accompanying larger benthic foraminifers, including Miogypsinoides complanatus(Schlumberger),M. formosensis Yabe and Hanzawa, Spiroclypeus margaritatus(Schlumberger), Operculina complanata(Defrance), and Risananeiza pustulosa Boukhary et al., indicate the upper Chattian SBZ 23 Zone. The coexistence of the N. saipanensis and N. malatyaensis points to suitable palaeobiogeographic conditions of Central Iran to host Western and Eastern Tethyan taxa.展开更多
文摘The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.
文摘In this study, to identify and analyze facies of depositional environment and depositional model of Qom Formation, stratigraphic Saran Section (southwest of Semnan) was selected. Qom Formation in Saran section includes about 380 meters of conglomerate at the base, chalk, limestone, marl, and shale. Petrographic studies with facies analysis have led to the identification of 12 microfacies, these microfacies have been deposited in four facies groups including tidal flat, lagoon, barrier and open marine. Study of horizontal and vertical facies changes and their comparison with recent and ancient environments reveals that Qom Formation in this section relates to shallow marine environment and its facies were deposited in a shelf carbonate platform and are comparable with contemporary shelf platforms such as Florida and old shelf platforms such as Mozduran. The most important diagenetic processes affecting the studied section include micritization, bioturbation, cementation, dissolution, neomorphism, fracturing, mechanical and chemical compaction, hematitization and dolomitization. These processes have formed in marine, meteoric and burial diagenetic environments.
文摘Deposits of the Qom Formation (Oligocene-Miocene) in Rameh section are located in northeastern Garmsar and contain dominantly 420 m Limestone, pebble-rich to sandy Limestone and marl Limestone. This formation is unconformably overlaid and underlaid with siliciclastic deposits of Upper Red Formation and Lower Red Formation. Field observations, along with laboratory investigations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the studied formation. Open marine facies association consists of bioclast mudstone, bioclast wackestone, bioclast packstone and bioclast roadstone;shoal facies association consists of ooid grainstone, bioclast grainstone and coral boundstone;lagoon facies association is composed of dolomitic mudstone, intraclast bioclast wackestone and bioclast packstone;and tidal flat facies association is sandy dolomudstone and stromatolite boundstone. The qom formation rocks in Rameh section are deposited in a rimmed shelf carbonate ramp. This formation undergoes various diagenetic processes including dissolution, porosity, cementation, micritization, compaction and dolomitization.
基金supported financially by National Iranian Oil Company Exploration Directorate。
文摘Postmiogypsinella intermedia Sirel and Gedik,2011 is reported for the first time from the shallow-marine limestones of the upper Chattian Qom Formation,Central Iran.This miogypsinid species has so far only been recorded from the upper Oligocene of Malatya(type locality)and Sivas(Central Anatolia)in eastern Turkey and from the upper Oligocene of the Prebetic Domain,SE Spain.The new record from Central Iran,paleobiogeographically located at the Eurasian margin of the Tethyan Seaway between the Western and Eastern Tethys realms,indicates that the paleogeographic distribution of this species has to be extended eastwards as far as Central Iran.This observation is not unexpected,since miogypsinid foraminifers with eccentric embryonic-nepionic apparatus(e.g.,Miogypsinella,Miogypsinoides,Miogypsina)are usually widely distributed.The accompanying larger benthic foraminifera,including Miogypsinoides complanatus(Schlumberger),Miogypsinoides formosensis Yabe and Hanzawa,Spiroclypeus margaritatus(Schlumberger),Operculina complanata(Defrance),and Risananeiza pustulosa Boukhary et al.,indicate the late Chattian age(corresponding to SBZ 23 Biozone).Postmiogypsinella intermedia is indicative of a shallow-marine middle ramp environment with oligotrophic conditions and inhabited the relatively deeper part of the photic zone.
基金funded by Damghan University (Grant No. 653/19)。
文摘The shallow marine carbonates of the upper Oligocene Qom Formation yielded several occurrences of the foraminiferan genus Neoplanorbulinella Matsumaru. Neoplanorbulinella saipanensis Matsumaru has so far been recorded from the late Eocene-early Miocene of Japan and late Oligocene of NE Italy whereas N. malatyaensis Gedik is only reported from the Oligocene from its type locality in the Malatya Basin, eastern Turkey. The new records reported here from the Qom Formation indicate that both species occur in the Dobaradar section, ca. 10 km south of the city of Qom in North-Central Iran. The palaeogeographic distribution of these two species therefore has to be extended as far as the palaeolongitude of current Central Iran.The accompanying larger benthic foraminifers, including Miogypsinoides complanatus(Schlumberger),M. formosensis Yabe and Hanzawa, Spiroclypeus margaritatus(Schlumberger), Operculina complanata(Defrance), and Risananeiza pustulosa Boukhary et al., indicate the upper Chattian SBZ 23 Zone. The coexistence of the N. saipanensis and N. malatyaensis points to suitable palaeobiogeographic conditions of Central Iran to host Western and Eastern Tethyan taxa.
