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

Traditional applications of microfossils are central to many studies, while novel approaches (especially geochemistry) utilizing microfossils have expanded recently. This session highlights traditional and innovative microfossil applications in terrestrial and marine environments, including modern analogs.

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 303C

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

Paper number: 21-5
Program: Technical Sessions
Time: 9:10 AM – 9:25 AM

Authors

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 Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412323

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