EROSIONAL ALIASING OF BULK ORGANIC GEOCHEMICAL CLIMATE RECORDS IN A SALINE-ALKALINE PALEOLAKE, OLDUVAI GORGE, TANZANIA

Olduvai Gorge in northern Tanzania contains a fossiliferous, well-characterized Pleistocene sedimentary record, and provides the opportunity to study the relationship between changing climate, ecology, and hominin evolution. The Olduvai Gorge Coring Project (OGCP) collected three cores (1A, 2A, and 3A) from paleolake Olduvai in 2014 to achieve increased temporal resolution of local climate and ecological data, and investigate the influence and timing of regional climate and tectonics on local signals. Previous work at Olduvai shows excellent sediment preservation from 1.9-1.7 Ma, linking bulk organic carbon isotopes (δ¹³C_org, ‰) and percent total organic carbon (% TOC, wt. %) to orbitally paced variations in lake depth and regional hydroclimate dynamics. We present Pleistocene records of δ¹³C_org and % TOC from OGCP Cores 2A and 3A, representing sediments from the paleolake depocenter and lake margin, respectively. Core 2A and 3A δ¹³C_org and % TOC suggest three main periods of deposition as defined by shifts in variance and magnitude at 1.9 and 1.7 Ma. Within the 1.9-1.7 Ma interval, we compare % TOC and δ¹³C_org from both cores to sedimentary indicators of hiatus and erosion. Occurrences of hiatus and erosion are more frequent in the lake margin than in the lake depocenter, and appear to be associated with dry periods and dry-to-wet transitions. Core 3A bulk organic parameters record wetter mean climate and lower variability than coeval Core 2A sediments, suggesting a bias towards preservation of wetter periods in the lake margin compared to the deposition. Pleistocene climate reconstruction using Core 2A seems intuitive, however Core 2A comprises multiple depositional facies, as the lake depocenter has migrated eastward through time. Superficial interpretation of Core 2A δ¹³C_org suggests Olduvai Gorge became wetter through the Pleistocene, which does not agree with previous outcrop interpretations or other regional climate records. Future efforts to interpret sedimentary proxies of regional climate and tectonic activity must consider preservation biases inherent to different depositional environments.