21-5 Larger Benthic Foraminiferal Turnover during the Early Oligocene Glacial Maximum (EOGM) along the Western margin of Indian plate Baluchistan Basin (eastern Neo-Tethys, Pakistan)

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

Presenting Author:

Kamran Muhammad

Authors:

Muhammad, Kamran¹, Xi, Dangpeng², Frontalini, Fabrizio³, Papazzoni, Cesare Andrea⁴, Khameiss, Belkasim Kh.⁵, Fawad, Nadir⁶, Wan, Xiaoqiao⁷

(1) China Univ of Geosciences, Beijing, Beijing, China, China, (2) State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing, Beijing, Beijing, China, (3) Dipartimento di Scienze Pure e Applicate (DiSPeA), Universita degli Studi di Urbino “Carlo Bo”, Urbino, Italy, Urbino, Italy, (4) Dipartimento di Scienze Chimiche e Geologiche, Universit` a di Modena e Reggio Emilia, Italy, Modena, Italy, (5) Oklahoma Geological Survey, University of Oklahoma, Norman, OK, USA, (6) State Key Laboratory of Marine Geology, Tongji University, Shanghai, Shanghai, China, (7) State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing, Beijing, China,

Abstract:

The Early Oligocene Glacial Maximum event (EOGM, ~33.90 Ma) is widely recognized as one of the most intense cooling events of the Cenozoic, and significant changes in the atmosphere, biosphere, and hydrosphere took place across the Eocene/Oligocene (E/O) boundary. The EOGM is globally characterized by positive carbon and oxygen isotope excursion, which is associated with the expansion of Antarctic ice sheets, cooling, sea-level fall, and extinction in continental and marine settings. The shallow-marine Larger Benthic Foraminifera (LBF) are highly susceptible to even minor variations in the sea surface temperatures (SSTs), sea level, and nutrient influx. While deep-sea biotic changes have been well studied during this global cooling event, records on shallow-marine biotic changes remain limited. This study presents the first comprehensive record of the EOGM event from the shallow-marine Nisai Formation in the Baluchistan Basin. A prominent positive CIE of ~2.75‰ in the shallow-marine section is used to constrain the EOGM event accurately. At the onset of the positive CIE, the falling sea level and decreasing SSTs are associated with a significant turnover in LBF. This major LBF turnover at the SBZ 20/21 boundary is marked by the extinction of key Eocene LBF taxa, including Nummulites malatyaensis, Nummulites striatus, Orthophragminids sp., Nummulites incrassatus, Nummulites fabianii, Silvestriella tetraedra, Fabiania cassis, and Pellatispira madaraszi. These are followed by the proliferation of smaller-sized early Oligocene Nummulites vascus, Nummulites fichteli, Asterocyclina rotula haeringeensis, Sivasina egribucakensis, Operculina complanata, and Wilfordia sarawakensis. The sea-level fall and associated cooling of SST during the EOGM had a detrimental effect on Eocene LBFs, which were subsequently replaced by early Oligocene taxa. The significant LBF turnover observed at the SBZ 20/21 boundary is likely linked to climate-driven environmental changes, including increased nutrient input resulting from enhanced continental weathering. This weathering was triggered by sea-level fall and lowering of SSTs during the EOGM event. These environmental and biotic shifts can be attributed to the expansion of Antarctic glaciation, which was, in turn, driven by a decline in relative sea level and SSTs during the EOGM event.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6402

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