|
|||||
|
|
Lake Shala: Water chemistry,mineralogy and geochemistry of sediments in an Ethiopian Rift lake |
|
| Authors: | Dr Albrecht Baumann Doz Dr Ulrich Förstner Dr Rudolf Rohde |
| Institution: | 1. Institut für Geologie und Pal?ontologie der Technischen Universit?t, Pockelsstr. 4, D-3300, Braunschweig 2. Laboratorium für Sedimentforschung, Mineralogisch-Petrographisches Institut der Universit?t, Berliner Str. 19, D-6900, Heidelberg 1 3. Preussag AG., Werk Berkh?pen, D-3150, Peine |
| Abstract: | Lake Shala, the deepest lake in the internal Galla lakes basin of the Ethiopian Rift, fills a depression in Pleistocene volcanic rocks. Its sodium-bicarbonate (-chloride) water (salinity 16 g/l) is remarkably low in earth alkalines and sulphate. Stratification is indicated by different ion concentrations in the surface and bottom waters and by a thermocline in a water depth of 50–70 m. Hot soda springs emerging on the shores of Lakes Shala and Langano are believed to be derived from a hot saline underground reservoir recharged by meteoric waters. The ion composition of the hot spring waters is uniform and matches that in the Galla Lakes except for total salinities. Anomalous heavy metal concentrations are lacking in lake and hot spring waters. Sediments of Lake Shala belong to an extremely fine-grained group of deposits. They are poorly sorted and the lateral distribution of the grain sizes does not follow the normal scheme for aquatic depositional environments. A belt, 50–100 m below lake level containing the finest-grained sediments, separates the shallow periphery of the lake bottom from the deep center, both characterized by coarser-grained deposits. The sediments consist of a large portion of glassy components. A poorly cristallized smectite is most abundant in the clay mineral group. The components of the sand fraction are quartz, feldspar, glass particles and occasionally calcite. Nickel, cobalt and lead are depleted in the Lake Shala sediments compared with the averages of shales. Iron, manganese and zinc are relatively high. Silver, cadmium and some of the rare earth elements are enriched by factors of > 5. |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ | |