Orbital rhythms, monsoons, and playa lake response, Olduvai Basin, equatorial East Africa (ca. 1.85–1.74 Ma)

Research Article| December 01, 2007 Orbital rhythms, monsoons, and playa lake response, Olduvai Basin, equatorial East Africa (ca. 1.85–1.74 Ma) Gail M. Ashley Gail M. Ashley 1Geological Sciences, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854-8066, USA Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (12): 1091–1094. https://doi.org/10.1130/G24163A.1 Article history received: 09 Jun 2007 rev-recd: 11 Jul 2007 accepted: 16 Jul 2007 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gail M. Ashley; Orbital rhythms, monsoons, and playa lake response, Olduvai Basin, equatorial East Africa (ca. 1.85–1.74 Ma). Geology 2007;; 35 (12): 1091–1094. doi: https://doi.org/10.1130/G24163A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The lithostratigraphy at the Pliocene-Pleistocene boundary exposed in Olduvai Gorge, East Africa, was used to determine the duration and cause of climate variations (wet-dry periods). The area has rich paleontological and archaeological records, and the time interval is a critical period in human evolution. Five episodes of lake expansion and contraction can be interpreted from a stratigraphic interval (defined by tuffs) between ca. 1.85 and 1.74 Ma, suggesting precession-controlled cyclicity. The geochronometry of the sequence was determined using the paleomagnetic record (top of subchron CN2, 1.785 Ma), the ages of two tuffs (Tuff IB and Tuff IF), and sedimentation rates. Insolation (W/m2) variations calculated as a function of eccentricity and precession predict five cycles of varying insolation (±10%) between 2.0 and 1.5 Ma. Rainfall would have increased by one-third between dry and wet portions of each ∼21,000 k.y. cycle. This study represents the first dated terrestrial record at the Pliocene-Pleistocene boundary with sufficient resolution to link lake cycles (a climate proxy) to astronomic forcing. The wet-dry climate pendulum may have been a factor in the natural selection processes of hominin evolution and the first wave of hominin migrations out of Africa (1.8 Ma). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.