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Paleosol carbonates from trenches excavated as part of a landscape-scale project in Bed I of Olduvai Gorge, Tanzania, were analyzed for stable carbon and oxygen isotopic composition. The similar to 60,000-year interval (similar to 1.845-1.785 Ma) above Tuff 113 records evidence for lake and fluvial sequences, volcanic eruptions, eolian and pedogenic processes, and the development of a fluvial plain in the western margin of the basin. Significant temporal variation in the carbonate delta O-18 values records variation of local precipitation and supports the shifts in climatic conditions interpreted from the lithologic record. During this period, carbonate delta C-13 values varied between depositional facies indicating that the paleolandscape supported a local biomass of about 40-60% C-4 plants within a mosaic of grassy woodlands and wooded grasslands. The lithologic and stable isotope record in this small lake basin indicates the area was much wetter, with more woody C-3 plants, during this interval than is the semi-arid area today. The record also reflects the variation in climatic conditions (wet/dry) documented by other global climate proxies for this time. (C) 2007 Elsevier Ltd. All rights reserved.