Lithofacies analysis and depositional model of the Late Quaternary sediments of southeast Atbara River, East– Central Sudan

Abstract

The Quaternary sediments of the lower reaches of Atbara River in southeast Atbara town, East- Central Sudan have been investigated. The aim is to study the palaeo-environmental and palaeo-climatic changes that took place in the area during Late Quaternary time, using evidence from sediments and fossils association. Three vertical sedimentary profiles were measured and five sedimentary depressions have been studied. Five lithofacies have been recognized: massive sandstone (Sm), planar cross-bedded sandstone (Sp), horizontal bedded sandstone (Sh), massive siltstone lithofacies (Fsl) and paleosol (P). The identified lithofacies exhibit extensive bioturbation representative of typical sand ridge, shoreline, near shoreline and lake shrinkage deposits of Atbara Palaeolake during Late Pleistocene to Early Holocene; being totally dry by the end of middle Holocene. Grain size analysis, binocular microscopic analysis and bulk XRD mineralogical analysis have been carried out. Grain size analysis results showed a fluvio-lacustrine setting for the Atbara sediments. Binocular microscopic study and bulk XRD mineralogical analysis signify considerable amounts of kaolinites and k-feldspars which reflect warm and humid climate. A shift to semi-arid and arid climate by mid Holocene is supported by the widespread deposition of calcretes and carbonate concretions in the upper part of most of the studied depressions. The presence of opal clasts within the studied sandy sediments suggests that the source area could be the Ethiopian highland. Two hundred specimens of Late Quaternary molluscs and mammals remains have been collected and studied. The molluscs are dominated by Corbicula spp. and Anadonta grandis, which are excellent colonizers of Late Quaternary freshwater lakes. Faunal remains such as bones, jaws and teeth of subfamily Bovinae, task of hippopotamus and turtles suggest the occurrence of grassland savannah, which contained a major lake..