11-4 The Tephrostratigraphy of Olduvai Gorge Coring Project 2023: Cores 4A, 5A, 6A

Session: Applications of Igneous Petrology, Geochemistry, and Geochronology to Understanding Earth and Other Planetary Systems (Posters)

Presenting Author:

Authors:

Abstract:

Olduvai Gorge lies west of the Ngorongoro Volcanic Highlands (NVH) along the East African Rift System (EARS). It preserves a history of tephra-rich Pliocene–Pleistocene stratigraphy which are key to understanding regional volcanism, sedimentation patterns, and hominin paleoecology. This study refines the tephrostratigraphy of the 2023 Olduvai Gorge Coring Project (OGCP23) through electron-microprobe (EMP) elemental analysis of feldspar, augite, hornblende, titanomagnetite, and volcanic glass from tuffs and other volcaniclastic deposits in cores 4A, 5A, and 6A. Mineral chemistry and borehole sedimentologic descriptions are integrated to (1) identify and correlate previously-described Bed I and II tuffs within cores 4A-6A, (2) establish a chronostratigraphic framework by comparing to published geochronological records, and (3) analyze petrogenetic links between tuffs, volcaniclastic sandstones, and their volcanic sources. Preliminary EMP results from cores 6A and 5A reveal compositional matches between multiple horizons and Bed I marker tuffs: several 6A intervals correlate with Tuff IE compositions, while a younger pumice-bearing unit records Tuff IF–like chemistry. A section of 5A ash and sandstone horizons overlap geochemically with Tuff ID and the Ng’eju Tuff, a correlation that could be improved with additional sampling. The 6A sequence between IE-equivalent and IF-pumice horizons lacks the expected interlaying Ng’eju Tuff, suggesting uneven deposition. These proposed correlations constrain these tephra-bearing intervals to ~1.79–1.81 Ma and support Olmoti as the principal source for upper Bed I tephra, while indicating different NVH inputs higher in the stratigraphic column. Ongoing work will expand EMP analyses, test priority core intervals collected from the Continental Scientific Drilling Facility, and confirm the mineral chemistry fingerprints of cores 4A-6A with published outcrop data from Beds I and II. The resulting framework will allow for more accurate subsurface correlations, improve volcanic source attributions, and will help correlate the detailed paleoecological record of these cores to the outcrops of sites that contain these tephra layers.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

doi: 10.1130/abs/2026SE-11636

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