Authigenic clays in East Africa: Regional trends and paleolimnology at the Plio–Pleistocene boundary, Olduvai Gorge, Tanzania

Deocampo, Daniel M.

doi:10.1023/b:jopl.0000013353.86120.9b

Cited by 41 publications

(45 citation statements)

References 21 publications

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“…The presence of Mg-rich smectite is confirmed by chemical analysis of the total clay fraction. The d 0 6 0 values, which are similar to those reported elsewhere (Deocampo, 2004), indicate that no purely trioctahedral phase developed. The relatively high K values are in agreement with the presence of admixed and interstratified illite.…”

Section: Lake Margin Depositssupporting

confidence: 89%

“…The development of Mg-rich smectite in the study area is most pronounced in the upper part of Bed I, the interval for which this process is most extensively documented (Hover and Ashley, 2003;Deocampo et al, 2002;Deocampo, 2004). In higher strata, lower Mg values are compatible with lower salinities and alkalinities recorded by an interval with largely zeolite-free freshwater deposits (Mees et al, 2005).…”

Section: Lake Margin Depositsmentioning

confidence: 73%

“…The palaeoclimate was semi-arid at all times during the Bed I to IV stages, with indications for somewhat drier conditions from the upper part of Bed I onwards. Possible drier stages have been inferred for the upper part of Bed II (Hay, 1976), and an effect of climate change on palaeohydrology has been demonstrated for the basal part of Bed II (Deocampo, 2004).…”

Section: Settingmentioning

confidence: 96%

“…All other studies concentrate on a narrow stratigraphical interval that is most relevant for palaeoanthropological research, i.e. the top of Bed I and the base of Bed II (Hay and Kyser, 2001;Deocampo et al, 2002;Hover and Ashley, 2003;Deocampo, 2004). In this paper, we report clay mineral data for all main units, sampled in the southeastern part of the basin (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Palaeoenvironmental significance of the clay mineral composition of Olduvai basin deposits, northern Tanzania

Mees

Segers

Ranst

2007

Journal of African Earth Sciences

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Section: Lake Margin Depositssupporting

confidence: 89%

Section: Lake Margin Depositsmentioning

confidence: 73%

Section: Settingmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Palaeoenvironmental significance of the clay mineral composition of Olduvai basin deposits, northern Tanzania

Mees

Segers

Ranst

2007

Journal of African Earth Sciences

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“…This is not surprising considering Lake Kitagata brines have most likely been concentrated by evaporation to reach their high salinity, and bottom sediments contain calcite and magadiite. No Mg-bearing minerals, however, have yet been identified at Lake Kitagata, although detailed analysis of clay minerals may reveal the MgÁsilicate phase that readily forms in other saline alkaline lakes (Hay and Kyser 2001;Jones and Deocampo 2003;Hover and Ashley 2003;Deocampo 2004aDeocampo , 2005Deocampo et al 2009). Because Mg 2?…”

Section: Chemical Characteristics Of Modern Lake Kitagata Brinesmentioning

confidence: 99%

A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda

Lowenstein

Russell

2010

Aquat Geochem

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Lake Kitagata, Uganda, is a hypersaline crater lake with Na-SO 4 -Cl-HCO 3 -CO 3 chemistry, high pH and relatively small amounts of SiO 2 . EQL/EVP, a brine evaporation equilibrium model (Risacher and Clement 2001), was used to model the major ion chemistry of the evolving brine and the order and masses of chemically precipitated sediments. Chemical sediments in a 1.6-m-long sediment core from Lake Kitagata occur as primary chemical mud (calcite, magadiite [NaSi 7 O 13 (OH) 3 Á3H 2 O], burkeite [Na 6 (CO 3 )(SO 4 ) 2 ]) and as diagenetic intrasediment growths (mirabilite (Na 2 SO 4 Á10H 2 O)). Predicted mineral assemblages formed by evaporative concentration were compared with those observed in salt crusts along the shoreline and in the core from the lake center. Most simulations match closely with observed natural assemblages. The dominant inflow water, groundwater, plays a significant role in driving the chemical evolution of Lake Kitagata water and mineral precipitation sequences. Simulated evaporation of Lake Kitagata waters cannot, however, explain the large masses of magadiite found in cores and the formation of burkeite earlier in the evaporation sequence than predicted. The masses and timing of formation of magadiite and burkeite may be explained by past groundwater inflow with higher alkalinity and SiO 2 concentrations than exist today.

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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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Authigenic clays in East Africa: Regional trends and paleolimnology at the Plio–Pleistocene boundary, Olduvai Gorge, Tanzania

Cited by 41 publications

References 21 publications

Palaeoenvironmental significance of the clay mineral composition of Olduvai basin deposits, northern Tanzania

Palaeoenvironmental significance of the clay mineral composition of Olduvai basin deposits, northern Tanzania

A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda

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

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