Sedimentary Facies & Depositional Environment of Shendi Formation , AL- Musauwarat/ Umm Ali Area, Sudan.

Abstract

Shendi-Atbara Basin is an outerlier surrounded by Precambrian and Paleozoic crystalline rocks. South of Shendi, the basement is exposed at the Sabaloka inlier, and Butana plain at the east. The Shendi-Atbara Basin is now considered as an important target for hydrocarbon exploration in central Sudan. The study area is bounded by the longtitude 16°23'52.30"and 17° 15' 30.30'' & latitude 33018'51.9''and 33° 43" 33.85' , in eastern and western parts of River Nile State. Study area is dominated by Mesozoic sediments of continental origin from fluvial and lacustrine depositional environments which are widely spread in central Sudan. During the field work trip, fourteen vertical and three lateral sedimentary profiles have been examined and discussed. The studied profiles exhibit eleven lithofacies identified at the outcrop section which are matrix supported massive conglomerate (Gmm) facies, stratified conglomerate (Gt), trough cross-bedded sandstone facies (St), Shallow scour pebbly sandstone (Ss), planar cross-bedded sandstone facies (Sp), horizontally –bedded sandstone facies (Sh), ripple cross-bedded sandstone facies (Sr) , massive sandstone facies (Sm), massive mudstone (Fm), fine-laminated mudstone (Fl) and rootbed mudstone (Fr). The study aims to the interpretation of depositional environment using lithofacies analysis. On the basis of their sedimentological character theses f a c i e s are interpreted to be deposited in fluvial depositional environment , by multi braided river channels. Representative samples were subjected to various preparation methods to permit its investigation, both mechanically and microscopically. The laboratory methods include: grain size analysis, determination and calculation of statistic coefficient using Microsoft Office Excel software, drawing the sedimentary profiles using sed.log software , preparing maps using ArcGIS software for digital image processing, petrographic description, total organic carbon (TOC) analysis , heavy minerals analysis, palynological analysis & scanning electron microscope (SEM). The samples are very poor in term of TOC and hydrocarbon potential, they are barren in palynomorphs, the main cementing material is clay (Kaolinite & Chlorite) with low concentration, no significant concentration of heavy minerals is observed.