T297 Lakes of the World through Time and Space II

Wednesday, 25 September 2019
1:30 PM - 5:30 PM
Room 222BC, North Building

CORE-DERIVED ZEOLITES RECORD CHANGING ENVIRONMENTAL CONDITIONS IN PLEISTOCENE PALEOLAKE OLDUVAI, TANZANIA

Paper number: T297-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

Olduvai Gorge, Tanzania, has yielded a famous record of Pleistocene hominin evolution in the form of stone tools and fossils, along with a well-preserved record of paleoenvironmental indicators that help provide context for changes in hominin behavior. In 2014, the Olduvai Gorge Coring Project (OGCP) recovered 612 m of core from three sites targeting different parts of the Olduvai paleolake. These cores provide a record of a lake that was longer lasting and less ephemeral than anticipated based on outcrop exposures. Samples were collected from Cores 1A, 2A, and 3A at 32-cm intervals throughout the cores (where fine sediments were recovered) for a variety of paleoenvironmental proxies. One sample split of each was powdered and analyzed by X-Ray Diffraction (XRD) to determine the bulk mineralogy. Changes in mineral assemblage reveal changes in sediment source and changes in water conditions.

The paleolake sediments of Olduvai Bed I and Lower Bed II are carbonate and clay rich. Intervals rich in zeolites and/or authigenic K-feldspar alternate with “fresher” intervals with little or none of these phases. The lowest part of the Bed I paleolake (below the Bed I basalts, preserved only in Core 3A) is particularly fresh, containing no zeolite. Below this lacustrine interval lies a thick fan deposit of volcaniclastic material from Ngorongoro volcano, below which lies another lacustrine interval (not known from outcrop, and preserved only in Core 3A). Carbonates and authigenic K-feldspar are almost absent from this section, and zeolites are dominated by chabazite and erionite (rather than phillipsite and analcime), indicating greater Ca2+ and silica activity. The final lacustrine interval, below a 2nd fan of Ngorongoro volcaniclastics, is also poor in carbonates, but contains phillipsite (near the top), analcime (near the base), and clinoptilolite (throughout).

Fresher intervals (characterized by an expanded lake, with little authigenic K-feldspar and zeolite) could have provided better aquatic resources and indicate times of overall more water availability, which would have benefited hominins and more humid-adapted fauna in the Olduvai basin. The quick alternation of fresher and more saline-alkaline conditions documented by paleolake mineral assemblages for Beds I and II shows a dynamically changing landscape.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-339127

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