气候变化领域集成服务门户(CCPortal): Changing depocentre environments of Palaeolake Olduvai and carbonates as marker horizons for hiatuses and lake-level extremes

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DOI	10.1016/j.palaeo.2020.110032
	Changing depocentre environments of Palaeolake Olduvai and carbonates as marker horizons for hiatuses and lake-level extremes
	Stanistreet I.G.; Doyle C.; Hughes T.; Rushworth E.D.; Stollhofen H.; Toth N.; Schick K.; Njau J.K.
发表日期	2020
ISSN	0031-0182
卷号	560
英文摘要	Primary carbonate and marl layers and limestone nodular horizons were intersected in OGCP Boreholes 1A, 2A, 3A, 3B, drilled into the depocentre of Palaeolake Olduvai. The various carbonate types were analysed, employing petrographic (including cathodo-luminescence), stable isotope, and sequence stratigraphic techniques, and recorded important information concerning lake evolution. Primary carbonate and marl layers are preserved at the top of lake deepening cycles (lake-parasequences), marking maximum flooding, followed by lake withdrawal, and then fluvial erosion, leading to the next depositional cycle. Presence of pelagites and a meromict lake favouring anoxic conditions, show it to be not a playa lake, but a deeper fault-bound lake, akin to present day Lake Eyasi. Carbonate and marl layers were exclusively deposited when claystone facies show a geochemical magnesium anomaly associated with a phase of basaltic volcanism affecting the basin, marked by mafic tuffs and basaltic lava flows. Calcium was partitioned into evaporites, such as gypsum/anhydrite, together with the nodular horizons and carbonate soil profiles in the sequence. The resulting high Mg2+/Ca2+ ratio in the lake waters promoted dolomite deposition and replacement, and the formation of aragonite. The nodular horizons yield rainfall isotope values and mark times when the lake was empty and the lake-bed fell under meteoric conditions, precipitating limestone nodules just below the sediment surface under pedogenic vadose, groundwater interface, and groundwater phreatic conditions. The nodular limestone horizons sit below erosional/hiatal surfaces and show vadose micritic and fibrous types to phreatic sparry and other accretionary type textures. Enterolithic to chickenwire textured nodules indicate the pseudomorphing of anhydrite nodules that form beneath salt marshes. Thus, the two carbonate types, primary layers and nodular horizons, provided depth gauges, respectively for the extremes of lake expansion and emptying/drying out. In the case of nodular horizons, the maturity of the carbonate profile gives an indication of the magnitude of the hiatal time gap represented, ~ 1 kyr to 2 kyr for a single horizon to ~ 3 kyr to 9 kyr for more mature soil profiles. Emptying/drying out episodes of Palaeolake Olduvai were not uncommon, and often short-lived. A spectrum of hiatal disconformities in the Olduvai Basin vary from multimillennial hiatuses to mega-disconformities of ~ 40 kyr and ~ 75 kyr. © 2020
英文关键词	Dolmicrite layer; Enterolithic nodule; Magnesium anomaly; Micrite limestone; Soil profile; δ13C and δ18O graph
语种	英语
scopus关键词	anhydrite; claystone; dolomite; facies; magnesium; Olduvai event; precipitation intensity; soil profile; volcanism
来源期刊	Palaeogeography, Palaeoclimatology, Palaeoecology
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/150318
作者单位	Dept. Earth, Ocean and Ecological Sciences, University of Liverpool, Brownlow Street, Liverpool, L69 3GP, United Kingdom; The Stone Age Institute, Bloomington, IN 47407-5097, United States; School of Earth and Environmental Sciences, University of Manchester, United Kingdom; GeoZentrum Nordbayern, Friedrich-Alexander-University (FAU) Erlangen-Nürnberg, Schloßgarten 5, Erlangen, 91054, Germany; Department of Earth and Atmospheric Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405-1405, United States
推荐引用方式 GB/T 7714	Stanistreet I.G.,Doyle C.,Hughes T.,et al. Changing depocentre environments of Palaeolake Olduvai and carbonates as marker horizons for hiatuses and lake-level extremes[J],2020,560.
APA	Stanistreet I.G..,Doyle C..,Hughes T..,Rushworth E.D..,Stollhofen H..,...&Njau J.K..(2020).Changing depocentre environments of Palaeolake Olduvai and carbonates as marker horizons for hiatuses and lake-level extremes.Palaeogeography, Palaeoclimatology, Palaeoecology,560.
MLA	Stanistreet I.G.,et al."Changing depocentre environments of Palaeolake Olduvai and carbonates as marker horizons for hiatuses and lake-level extremes".Palaeogeography, Palaeoclimatology, Palaeoecology 560(2020).