Carbonate horizons, paleosols, and lake flooding cycles: Beds I and II of Olduvai Gorge, Tanzania

Fine resolution of early hominin time, Beds I and II, Olduvai Gorge, Tanzania

“…The same cyclic character is further supported by d 13 C and d 18 O isotopic analysis (Bennett et al, 2012) of accretionary carbonate bodies within several paleosols of successive lake marginal parasequential couplets. Time series d 13 C and d 18 O isotope evolution paths show that the paleosols formed largely during the transgressive half of each lake cycle, with ultimate precipitation of strontianite and strontian dolomite derived directly from lacustrine groundwaters following lake inundation and prior to the eventual deposition of the next waxy clay unit.…”

“…During highstands in restricted sub-basins, these consisted almost entirely of the neoformed magnesian smectite end-member (stevensite) deposits, termed butter claystones. Lake withdrawal resulted in abandoned lake plains in which meteoric (fresh rainwater) conditions produced calcareous soils (Bennett et al, 2012) under the prevailing semi-arid conditions. Soil profiles were bioturbated by insect burrows, particularly termites, and root and rootlet systems, which could extend to form root mats.…”

Plio-Pleistocene synsedimentary fault compartments, foundation for the eastern Olduvai Basin paleoenvironmental mosaic, Tanzania

“…There, the FLK Fault controlled the position of the "permanent" part of the alkaline-saline lake edge on its western downthrown side (Hay, 1976). Across this divide permanent lake clays with turbidite layers to the west differentiate from marginal lake clays with calcareous, frequently rooted soil horizons (Bennett et al, 2012) to the east. Within the same stratigraphic interval, the Long K Fault differentiates lake marginal facies on the west from mudflow, shallow braided stream, and sheetflood dominated fan facies to the east.…”

“…Another contrast from downthrown to upthrown sides of faults, particularly recorded by the KK and FLK faults, is the architecture of calcareous paleosol profiles within lowermost Bed II (Bennett et al, 2012), reflecting the difference between waterlogged wetland settings and drier settings that also vary across a particular fault compartment. In addition, the upthrown side of the Long K Fault favored enhanced development of oxidized red clay paleosols in the JK to Long K area (Fig.…”

Olduvai Gorge and the Olduvai Landscape Paleoanthropology Project

“…It also required the development of finer stratigraphic control on landscape-scale paleoanthropological samples than availed by traditionally relied upon tephra-chronostratigraphic markers, between which longer-term, more substantial changes to landscape ecology can be expected. A battery of paleoenvironmental expertise was added to OLAPP beginning in 2000, including specialists in general and volcaniclastic facies analysis (e.g., Stollhofen and Stanistreet, 2012;Stanistreet, 2012) as well as macroplant fossil (e.g., Bamford, 2012) analysis, phytolith (e.g., Albert and Bamford, 2012) analysis, and stable isotope analysis of carbonates (Bennett et al, 2012). Finer stratigraphic control was achieved by determinations of cross-basinal geochemical correlations of tephra (e.g., McHenry, 2012) and the introduction of sequence stratigraphy to the lake-centered paleo-Olduvai Basin (e.g., Stanistreet, 2012).…”