6 Integrating 20 Years of Scientific Drilling in the East African-Syrian Rift: A Session In Honor of Andrew Cohen, Part I

Continental drilling extending from the East African Rift into western Asia has yielded transformative discoveries, altering our understanding of paleoenvironments, paleoclimatology, paleoecology, and paleoanthropology. This session, in honor of Andrew Cohen, will celebrate these successes and define new directions.

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 214A

The Olduvai Gorge Coring Project: Eleven Years of Multi-Proxy Research to Constrain Hominin Paleoenvironments

Paper number: 6-10
Program: Technical Sessions
Time: 10:40 AM – 10:55 AM

Authors

Abstract

In 2014, The Olduvai Gorge Coring Project (OGCP) recovered four cores from three borehole sites in the Pleistocene rift shoulder Olduvai basin in Tanzania. The continued study of these amazing cores over the last eleven years has fundamentally changed our understanding of the Olduvai basin and the environments it once provided to our hominin ancestors.

Borehole sites targeted primarily lacustrine lithologies (based on previous outcrop study and extrapolation) to maximize the recovery of paleoenvironmental and paleoclimatic proxies. In total, 612 meters of core (94% recovery) were recovered, with the longest core (Core 2A) reaching a depth of 245 meters. This was remarkable, considering that before drilling the base of the Olduvai basin was assumed to be at 110 meters depth based on its contact with Precambrian basement outcrop in the western basin. This deep record, with ~150 meters never before explored, revealed a much more continuous record of lacustrine sedimentation than predicted based on outcrop exposures. In addition, Core 3A, recovered to the north of Olduvai Gorge in an area with little to no outcrop exposure, revealed an unexpectedly thick and continuous lacustrine record, often with deeper water facies than Core 2A (which lay closer to the previously estimated depocenter). Paleolake Olduvai was thus more extensive, more continuous, and longer lasting than previously understood. The lacustrine intervals that preceded the previously defined Olduvai Beds (those newly discovered are now termed the Naibor Soit Formation) also displayed fresher water characteristics than the notably saline-alkaline deposits above. The cores also provide a more continuous record of the eruptive histories of Olmoti and Ngorongoro volcanoes, including tephra, ignimbrite, and debris flow intervals.

40Ar/39Ar and paleomagnetic dating and tephrostratigraphy provide links between the cores and outcrops of paleoanthropological interest and a chronologic framework for the cores. Detailed sedimentology, isotopes, phytoliths, mineralogy, and biogeochemistry of the recovered cores constrains the paleoclimate and paleoenvironment of the Olduvai basin. Combined, these show a paleolake that expanded and contracted due to both longer-scale changes to basin geometry and shorter-term climatic fluctuations. Interdisciplinary work on these cores continues, and we eagerly anticipate the results of future coring.

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

doi: 10.1130/abs/2025AM-414874

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