Abstract

The study area is located in Khartoum, Khartoum State, central Sudan. The research dealt with studying the ancient depositional environments, architecture, facies types, and sedimentary paleogeography of the Omdurman Formation (Upper-Cretaceous), northern part of the Khartoum Basin. Few studies were conducted in the study area, so this study will add more clarity to the Basin, fieldwork was conducted, geological observations were recorded, in addition to grain size analysis was done by using the sieve analysis technique. Lithofacies analysis indicates that the Omdurman Formation contains matrix-supported conglomerate (Gm), trough cross-bedded sandstone facies (St), plane cross-bedded sandstone facies (Sp), laminated silt facies (Fl), and massive mudstone facies (Fm).

The Omdurman Formation consists of two members, the first is the highest and is called the Al-Markhayyat Member (fining upward sequences) representing the deposits of braided rivers characterized by cohesive banks. In this member coarse facies are common and some fine facies appear such as the alluvial facies (Fl) and the massive mudstone facies (Fm). This facies was deposited by braided, slightly meandering rivers characterized by shallow channels. The second, which is the bottom, is called the Umbada Member, as this member shows fining upward facies sequences of vertically accumulated sediments of channels and islands.

The depositional model of the Omdurman Formation can be represented by a coarse-upward depositional cycle that appears to be controlled by internal and external factors. The change in the base level is closely linked to the gradual decrease and tectonic activity that finally led to the spread of an open or external drainage system during the period of deposition of the Markhiyat Member (lower part). The predominance of kaolinite and ironstones indicates that the Upper Cretaceous climate in the period was tropical with short terms of drought, supported by the prevalence of siliceous solidified wood, iron oxides, and a high percentage of clastic sediments. The sandy (CHs) and gravel (CHg) channel architecture was distinguished in the studied profiles.