MODELING POST-DEPOSITIONAL ACCUMULATION OF 10BE IN SANDSTONES FROM THE HOMININ SITES AND PALEOLAKES DRILLING PROJECT (HSPDP) CORES FOR IN SITU COSMOGENIC RADIONUCLIDE PALEOEROSION RATE ANALYSES

Sandstones from drill cores collected in Ethiopia and Kenya by the Hominin Sites and Paleolakes Drilling Project (HSPDP) present a novel opportunity to reconstruct paleoerosion rates utilizing in situ cosmogenic radionuclides (CRNs). Concentrations of CRNs such as ¹⁰Be indicate the amount of time a material has been exposed to cosmic radiation at or near the earth’s surface. CRNs are produced in the watershed while the material is actively being eroded and transported, and decay at a fixed rate over time upon burial and shielding from further CRN accumulation. We collected 20 total samples from the Baringo Basin/Tugen Hills, Chew Bahir, Northern Awash and West Turkana drill cores for paleoerosion rate analyses to investigate global climate variation, regional orography, local faulting and fluvial network reorganization within the watersheds of the drill sites. In addition, there is a unique opportunity to tie the inferred paleoerosion rates to the rich paleoenvironmental proxies determined by the HSPDP. However, an important consideration when calculating paleoerosion rates is the amount of ¹⁰Be accumulated after sediments have been deposited. Material will only be shielded from significant nuclide accumulation when buried by ~3–5 m of additional sediment. The simplest scenario assumes no significant post-depositional ¹⁰Be accumulation, but sediment burial histories are likely more complex and varied. We model the potential range of post-depositional ¹⁰Be accumulation in the HSPDP sandstone samples to examine its importance when calculating paleoerosion rates. We utilize sedimentation rates derived from age models of the cores to assess post-depositional nuclide accumulation. Because the drill cores are predominantly lacustrine, we also identify sandstone units overlain by lacustrine sediments and model post-depositional ¹⁰Be accumulation for sediment shielding under a water column. Given that the cores range in age from <500 ka to >3 Ma, we finally consider the amount of ¹⁰Be lost to radioactive decay and its impact on post-depositional ¹⁰Be accumulation.