Biostratigraphy and determination of the K/Pg boundary in the upper Cretaceous sediments in northeast Kazerun, Fars zone (Zagros)

Document Type : علمی -پژوهشی

Author

Department of Mining, Imam Khomeini International University, Qazvin, Iran

Abstract

IntroductionOne of the most extensive Cretaceous and Paleogene deposits in Zagros are the marine sediments of the Gurpi Formation, they were first identified in the Zagros based on stratigraphy and paleontology. One of the most important researches that can be done given this formation in Zagros, is determining the exact boundaries, by calcareous nannofossil assemblages. At the Anar anticline section, the Gurpi Formation with 163 m thickness was selected which mainly consists of shale, silty shale and plagic limestone.Material and MethodsIn this study, 58 samples from Gurpi Formation have been examined. Samples were prepared following a standard smear slide method (Bown and Young 1998). All slides were studied under polarized light microscope at ×1000 magnification. Calcareous nannofossil nomenclature follows the taxonomic schemes of Perch-Nielsen (1985).Results and discussionCalcareous nannofossils recorded in the Mesozoic and Cenozoic strata are believed to be an appropriate means for biostratigraphic studies. The nannofossil zonation used in the present study is based on the Nannoplankton zonation of Sissingh (1977), Burnett (1998) and Martini (1971), respectively. As a result of this study, 39 species belonging to 21 genera of calcareous nannofossils were detected. Eight bio events were recorded and based on these bio-events, the Ceratolithoides aculeus Zone (CC20) - Nephrolithus frequens Zone (CC26) were recognized based on Sissingh (1977). Subsequently, Markalius inversus zone (NP1) was identified at the top of the Gurpi Formation.- Bio zones of the Cretaceous Seven bio zones of the zonation of Sissingh (1977) and Burnett (1998) were recognized in the Cretaceous:Ceratolithoides aculeus Zone / UC15bTP­The first nannofossil unit recorded in this study is the CC20 zone. This bio zone is recorded from the FO C. aculeus to the FO of Quadrum sissinghii. The age of this zone is late early Campanian.Quadrum sissinghii Zone/ UC15cTPThe second nannofossil unit recorded in the Gurpi Formation is the CC21 zone. This bio zone is recorded from the FO Quadrum sissinghii to the FO of Quadrum trifidum. The age of this zone is early/late Campanian.Quadrum trifidus Zone/ UC15dTP, UC15eTPThe next nannofossil unit recorded in this study is the CC22 zone. This bio zone is recorded from the FO of Quadrum trifidum to the LO of Reinhardtites anthophorus. The age of this zone is late Campanian.  Tranolithus orionatus Zone/ UC15eTP, UC16TP, UC17TP­The next nannofossil unit recorded in this study is the CC23 zone. This bio zone is recorded from the LO of Reinhardtites anthophorus to the LO of Tranolithus  phacelosus. The age of this zone is late late Campanian/early Maastrichtian.Reinhardtites levis Zone/ UC18TP The next nannofossil unit recorded in this study is the CC24 zone. This bio zone is recorded from the LO of Tranolithus phacelosus to the LO of Reinhardtites levis. The age of this zone is early Maastrichtian.Arkhangelskiella cymbiformis Zone/ UC19TP, UC20aTP, UC20bTPThe next biozone recorded is the CC25 zone. This bio zone is recorded from the LO of Reinhardtites levis to the FO of Micula murus. The age of this zone is early late Maastrichtian.Nephrolithus frequens Zone / UC20c, dTPThe next biozone recorded is the CC26 zone. This bio zone is recorded from the FO of Micula murus to the FO of Biantholithus sparsus. The age of this zone is late late Maastrichtian.-Bio zone of the Paleocene One bio zone of the zonation of Martini (1971) recognized at the top of Gurpi Formation:Markalius inversus ZoneThe last nannofossil unit recorded at the top of Gurpi Formation is the NP1 zone. This bio zone is recorded from the extinction of the Cretaceous flora to the FO of Cruciplacolithus tenuis. The age of this zone is Danian.ConclusionIn this study Cretaceous-Paleocene sediments have been investigated at the Gurpi Formation at Anar anticline section in northeast of Kazerun. The Gurpi Formation mainly consists of shale, silty shale and pelagic limestone. The detailed study based on calcareous nannofossils, enables the subdivision of the studied deposits into 8 bio zones. As a result of this study and based on the identified bio zones, the age of the Gurpi Formation is middle Campanian to early Danian, and K/Pg boundary is continuous at the studied interval.

Keywords

References

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