Paleoclimatic and paleoenvironmental framework of FLK North archaeological site, Olduvai Gorge, Tanzania

Ashley, Gail M.; Bunn, Henry T.; Delaney, J. S.; Barboni, Doris; Domı́nguez-Rodrigo, Manuel; Mabulla, Audax; Gurtov, Alia; Baluyot, Ronidell; Beverly, Emily J.; Baquedano, Enrique

doi:10.1016/j.quaint.2013.08.052

Cited by 21 publications

(12 citation statements)

References 40 publications

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“…This is, apparently, a common scenario along the EARS, as noted by Olago et al (2009) in the Central Kenya Rift, groundwater in the basins is derived from rainfall on the valley's upland flanks. A number of previous studies of paleoclimate and paleoenvironmental reconstructions at Olduvai have recognized former springs and wetlands associated with archaeological sites in Middle Bed I (Ashley et al 2010b), Upper Bed I (Ashley et al 2010a;Ashley et al 2014), and Lowermost Bed I (Liutkus and Ashley 2003;Ashley et al 2009;Deocampo and Tactikos 2010); but here we present a unifying conceptual model to explain the reoccurrence of fresh-water carbonates in this volcaniclastics-dominated arid basin.…”

Section: Climate and Hydrologymentioning

confidence: 89%

“…Megafauna-bone evidence from a nearby archaeological site, FLK North, suggests that animals found this water potable (Leakey 1971;Bunn et al 2010). Therefore, it is likely that hominids did as well, as supported by evidence of stone tools in the area around the seeps and springs Ashley et al 2014).…”

Section: Depositional Environmentsmentioning

confidence: 99%

“…d 18 O values range from 25.27% to 0.08%, with a mean of 23.11%, and d 13 C values range from 24.76% to 2.79% with a mean of 21.22%.Upper Bed IDepositional Characteristics.-This carbonate bed averages between 0.2 to 0.5 m thick, can be traced laterally for tens of meters, and locally forms a mound up to 1.4 m thick(Fig. 5B)(Ashley et al 2010a;Baluyot 2011;Ashley et al 2014). The outcrops are in close proximity to mapped faults.…”

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confidence: 99%

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Freshwater Limestone In An Arid Rift Basin: A Goldilocks Effect

Ashley¹,

Wet²,

Domı́nguez-Rodrigo³

et al. 2014

Journal of Sedimentary Research

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The Olduvai Basin (3u S), situated just west of the East African Rift System in northern Tanzania, contains a twomillion-year record of paleoclimate and paleoenvironmental change, as well as a rich archive of vertebrate paleontology (including hominins). Milankovitch precession cycles (, 20 kyr) regulate the mean annual precipitation (250-700 mm/yr), and the , 2500 mm/yr evapotranspiration results in a negative hydrologic balance. Despite persistent aridity, extensive deposits of freshwater limestone punctuate the stratigraphic record. Between 2 and 1 Ma, Lake Olduvai occupied the basin, and its sediments are a proxy for climate-driven cycles. Three limestones (1.84, 1.80, and 1.36 Ma in age), which formed within lakemargin floodplains adjacent to the lake, were studied to determine their depositional environment using field relations, sedimentary structures, fossils, petrography, and stable-isotope and major-element geochemistry. The three limestones are similar in that they contain peloidal micrite, siliciclastic detrital grains, and rhizoconcretions. Abundant faunal remains (gastropods, ostracods, Charaphytes, and fish) indicate that ponded water was relatively fresh and alkaline.Geochemical and stable-isotope data indicate two types of groundwater-sourced carbonate-producing waters: a deepersourced fluid that was enriched in iron and manganese due to extended water-rock interactions, and a shallower groundwater that traveled through alluvial-fan deposits. Regional faults tapped the deeper groundwater, producing carbonate at spring sites, while seeps associated with basinward changes in alluvial-fan slopes drew on shallower groundwater sources. Isotope compositions indicate that fault-related waters experienced some evaporation as water moved away from the spring sites while compositions of the seep-related carbonate remained relatively constant. Pedogenic alteration and meteoric calcite cementation affected the carbonate when the spring and seep sites dried out. Secondary strontium-rich dolomite precipitated within the limestones during burial under paleo-Lake Olduvai sediments and fluids during periods of lake expansion.Integrating these data within the geological context of regional paleoclimatic and local environmental change indicates that the freshwater carbonates formed periodically when the conditions were just right, i.e., a ''Goldilocks Effect.'' Carbonates near the basin center formed from groundwater flowing under a hydraulic head from faults or fractures during the falling limbs of Milankovitch cycles when the lake was in recession. Carbonates near the basin margin formed from an increased rate of groundwater seepage that occurred only on the rising limbs of cycles. In both contexts, the continuous flow of groundwater with surface evaporation and CO 2 degassing optimizes the conditions for limestone formation in this arid environment. These results help explain the formation of freshwater limestones in the rift basin, link the carbonates to specific portions of Milankovitch cycles, and document th...

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Section: Climate and Hydrologymentioning

confidence: 89%

Section: Depositional Environmentsmentioning

confidence: 99%

mentioning

confidence: 99%

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Freshwater Limestone In An Arid Rift Basin: A Goldilocks Effect

Ashley¹,

Wet²,

Domı́nguez-Rodrigo³

et al. 2014

Journal of Sedimentary Research

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“…The spring‐fed rivers of the Lake Victoria Basin add to the record of palaeoanthropological sites associated with tufa previously restricted to the Early and Middle Pleistocene (Wendorf, ; Haynes et al ., ; Nicoll et al ., ; Smith et al ., , ; Garcea & Giraudi, ; Barich & Garcea, ; Ashley et al ., , ,b,c, ; Johnson et al ., ; Johnson & McBrearty, ). The aquifers stored water during times of high rainfall, allowing for continual spring discharge which, in turn, allowed the landscape to host more diverse plant and animal communities (Cuthbert & Ashley, ).…”

Section: Discussionmentioning

confidence: 99%

“…These spring‐fed rivers could have functioned as a refugium for water‐dependent fauna (i.e. hominins) similar to the Turkana Basin (Quinn et al ., , ; Joordens et al ., , ), the Olduvai Basin (Ashley et al ., , ,b,c, ; Cuthbert & Ashley, ) or the Olorgesailie Basin (Lee et al ., ). Time‐equivalent palaeosol deposits from Nyamita (Tryon et al ., ) and microdebitage and surface‐collected artefacts from Obware suggest that early modern humans were utilizing this landscape during tufa deposition.…”

Section: Discussionmentioning

confidence: 99%

Recurrent spring‐fed rivers in a Middle to Late Pleistocene semi‐arid grassland: Implications for environments of early humans in the Lake Victoria Basin, Kenya

et al. 2015

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The effect of changing palaeoclimate and palaeoenvironment on human evolution during the Pleistocene is debated, but hampered by few East African records directly associated with archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age artefacts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on the mainland near Karungu, Kenya are provided from outcrop, thin sections, mineralogical, stable isotopic and U-series dating analyses. Tufa is identified in four sites: Nyamita (94Á0 AE 3Á3 and 111Á4 AE 4Á2 ka); Kisaaka, Aringo (455 AE 45 ka); and Obware. The age ranges of these tufa deposits demonstrate that spring-fed rivers were a recurrent, variably preserved feature on the Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy, ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal environments with d 13 C values of ca 10& indicative of C 3 plants and fossil Hippopotamus, all of which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo have a mixed C 3 /C 4 signature consistent with a semi-arid C 4 grassland surrounding these spring-fed rivers. The d 18 O values of tufa from Nyamita are on average ca 1& more negative than calcite precipitated from modern rainfall in the region, suggesting greater contribution of depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface-collected artefacts indicate that early modern humans were utilizing these spring-fed rivers. The presence of springÀfed rivers would have afforded animals a reliable water source, sustaining a diverse plant and animal community in an otherwise arid environment. 1611

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Widespread freshwater carbonate in the Olduvai Basin, a precursor to a major eruption in the East African Rift System

Ashley

Wet

Houser

et al. 2020

The Depositional Record

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Freshwater limestones are uncommon in the sedimentary record of the East African Rift System. Recent research in the Olduvai Basin, Tanzania has revealed an extensive carbonate unit ca 1.8 Ma in age that varies spatially in thickness, petrography, trace element and rare earth geochemistry, C and O isotope values and freshwater microfossils. Five distinct lithologies are recognized. Four reflect deposition in carbonate‐rich environments that occurred at the same time in a catena‐like pattern over a heterogeneous landscape: spring, wetland, freshwater lake/pond and saline playa lake. The fifth is carbonate nodular soil that formed by paedogenesis on areas of topographically higher terrane. The δ18O of the carbonate, as negative as −6.5‰, indicates that the groundwater is meteoritic derived. The origin of the carbonate comprising this thick, extensive, isochronostratigraphic deposit has not been determined, but it is believed that carbonatite volcanism may have supplied elevated levels of carbonate to the basin which then entered the groundwater system. The carbonate was deposited just prior to a major trachyte‐phonolite eruption of Mount Olmoti, and the deposition of a basin wide tuff, Tuff IF. The region is seismically active today and seismic events were likely associated with Olmoti volcanism. The widespread carbonate unit may have preceded the Olmoti eruption and formed from a recurring seismically induced increase in aquifer porosity and permeability. The carbonate‐enriched groundwater episodically discharged onto the land surface, interacting locally with both fresh and saline ponded water.

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Paleoclimatic and paleoenvironmental framework of FLK North archaeological site, Olduvai Gorge, Tanzania

Cited by 21 publications

References 40 publications

Freshwater Limestone In An Arid Rift Basin: A Goldilocks Effect

Freshwater Limestone In An Arid Rift Basin: A Goldilocks Effect

Recurrent spring‐fed rivers in a Middle to Late Pleistocene semi‐arid grassland: Implications for environments of early humans in the Lake Victoria Basin, Kenya

Widespread freshwater carbonate in the Olduvai Basin, a precursor to a major eruption in the East African Rift System

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