Plio-Pleistocene facies environments from the KBS Member, Koobi Fora Formation: implications for climate controls on the development of lake-margin hominin habitats in the northeast Turkana Basin (northwest Kenya) Christopher J. Lepre a, * , Rhonda L. Quinn a,c , Josephine C.A. Joordens b , Carl C. Swisher III c , Craig S. Feibel a,c a Department of Anthropology, Rutgers The State University of New Jersey, New Brunswick, NJ 08901-1414, USA b Department of Paleoclimatology and Geomorphology, Vrije Universiteit Amsterdam, De Boelelaan 1085 1081 HV, Amsterdam, The Netherlands c Department of Geological Sciences, Rutgers The State University of New Jersey, Piscataway, NJ 08854, USA Received 4 November 2005; accepted 22 January 2007 Abstract Climate change is hypothesized as a cause of major events of Plio-Pleistocene East African hominin evolution, but the vertically discontin- uous and laterally confined nature of the relevant geological records has led to difficulties with assessing probable links between the two. High- resolution sedimentary sequences from lacustrine settings can provide comprehensive data of environmental changes and detailed correlations with well-established orbital and marine records of climate. Hominin-bearing deposits from Koobi Fora Ridge localities in the northeast Turkana Basin of Kenya are an archive of Plio-Pleistocene lake-margin sedimentation though significant developmental junctures of northern African climates, East African environments, and hominin evolution. This study examines alluvial channel and floodplain, nearshore lacustrine, and off- shore lacustrine facies environments for the approximately 136-m-thick KBS Member (Koobi Fora Formation) exposed at the Koobi Fora Ridge. Aspects of the facies environments record information on the changing hydrosedimentary dynamics of the lake margin and give insights into potential climatic controls. Seasonal/yearly climate changes are represented by the varve-like laminations in offshore mudstones and the slick- ensides, dish-shaped fractures, and other paleosol features overprinted on floodplain strata. Vertical shifts between facies environments, however, are interpreted to indicate lake-level fluctuations deriving from longer-term, dry-wet periods in monsoonal rainfall. Recurrence periods for the inferred lake-level changes range from about 10,000 to 50,000 years, and several are consistent with the average estimated timescales of orbital precession (w20,000 years) and obliquity (w40,000 years). KBS Member facies environments from the Koobi Fora Ridge document the development of lake-margin hominin habitats in the northeast Turkana Basin. Environmental changes in these habitats may be a result of monsoonal rainfall variations that derive from orbital insolation and/or glacial forcing. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Depositional environments; Lacustrine sedimentation; Hominin evolution; East Africa Introduction Analyses of benthic d 18 O records from marine cores place the onset of Northern Hemisphere Glaciation at w2.7 Ma (Shackleton et al., 1984; Lisiecki and Raymo, 2005). The consequences of increased climate variability and aridity across northern low-latitude Africa are evident in marine dust-flux (deMenocal et al., 1993; deMenocal, 1995) and pal- ynological (Dupont and Leroy, 1995) sequences. These increases are roughly contemporary with significant periods of grassland ascension in East Africa, as suggested by terrestrial evidence from mammal fossil assemblages (Vrba, 1999; Bobe and Behrensmeyer, 2004; Ferna ´ndez and Vrba, 2006), isotopic * Corresponding author. E-mail address: clepre@rci.rutgers.edu (C.J. Lepre). 0047-2484/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jhevol.2007.01.015 ARTICLE IN PRESS Please cite this article in press as: Christopher J. Lepre et al., Plio-Pleistocene facies environments from the KBS Member, Koobi Fora Formation: implications for climate controls on the development of lake-margin hominin habitats in the northeast Turkana Basin (northwest Kenya), J Hum Evol (2007), doi:10.1016/ j.jhevol.2007.01.015 Journal of Human Evolution xx (2007) 1e11 + MODEL