Calcareous Nannofossils as an Evidence of Paleocene-Eocene Thermal Maximum Event in Zagros Sedimentary Basin

Document Type : Original Articles


1 Ph.D. Student in Stratigraphy and Paleontology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran

2 Assistant Professor, Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran

3 National Iranian Southern Oil-Field Company (NISOC), Ahwaz


Paleocene-Eocene Thermal Maximum (PETM) is a short-term climatic event that occurred about 56 million years ago, crucially affecting the global biological ecosystems, especially calcareous nannoplankton. Analysis of the fossilized remains of calcareous nannoplanktons in the sedimentary successions deposited during the said interval of time in Zagros Sedimentary Basin points to the presence of a rich nannofloral assemblage consisting of 112 species belonging to 31 genera. The observed distribution and calculated abundances of calcareous nannofossils confirm occurrence of PETM event in the area under investigation. The findings which point towards sudden release of carbon to the ocean-atmosphere system, indicate a decrease in pH of oceanic waters leading to shallowing of Carbonate Compensation Depth (CCD) and dissolution of limestones. This is reflected in the diversity and abundance of nannofloral assemblages due to the availability of carbon dioxide and increased rate of calcification process. The phenomenon also brought about a reduction in the oxygen content of atmosphere and global warming. Slower rate of carbon release during PETM as compared to that of present day, points to the possibility of a more catastrophic acidification of today’s oceans. Moreover,expected release of about 2000 pg carbon during the next 200 years (based on current trends) will result in a 2000-4000 pg increase of additional carbon in the oceanic sediments which is much in excess of what happened during PETM, thus accelerating therate of current global warming.


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