GEOLOGY AND COASTAL PLAIN EVOLUTION OF TOWARATIT, SOUTH PORT-SUDAN, RED SEAy SUDAN

Abstract

ABSTRACT Towaratit coastal plain, Red Sea consist of three different environments: intertidal zone, hypersaline coastal lagoon and fringing reefs. Samples from each environment were obtained to textural, mineralogical and geochemical analysis. One borehole was drilled from supratidal zone for studying subsurface stratigraphy. The sabkha flat is composed of different types of facies (muddy sand, sandy mud and sand) as mixture of terrigenous and organic constituent. The sediments are generally, poor sorted, coarse skewed in range of -1.25 to 2.25 (I) in grain - size. The lagoonal sediments characterizes by medium poor sorted reefal sand whereas the reef flat consists of varying grain - size from fine to coarse due to the hydrodynamic conditions. The influence of the aeolain dust in the lagoon sediments and sabkha deposits is more than in the reef flat. This proved by the inverse relationship between aragonite and the high - Mg calcite and the variations in the Fe concentration in the three different environments. The carbonate minerals vary in the concentrations and the diagensis took place in the area. Dolomite is completely absent in the subsurface sediments as well as evaporations minerals which are replaced by carbonate. Mono and mixed calcite layers appear in different depths. Although, the total carbonate content (70 - 97%) and carbonate minerals (aragonite, high - Mg calcite) are higher in the concentration, but there is no clear relation with grain - size due to the variation in amount and types of biological communities which also affect in the concentration and distribution of carbonate minerals. The carbonate minerals are attrebuted to organic and non- organic materials. The nature of sediment and mineralogical results indicate that most sediments originated in the Pleistocene. Ca, Mg and Fe were detennined. Fe shows a significant variation with indication of influence of surrounding formation which supply the area by fine elastic terrigenous materials. The low Fe concentration and absence of quartz and feldspar in the reef flat indicated that the reef system protection by the lagoon. Five meters thickness of Pleistocene coralline limestone overlain by two meters of Holocene deposits inthe subsurface sequence give a good evidence of paleoclimate and sea level changes. Benthic foraminifera (Rotalina and Miliolina sp) are also used to identify the depths and the sea level fluctuation. From Pliocene to Recent the area is subjected to tectonic movement. The inner deeper part of the lagoon is result of uplift and eroded the exposed part by physical and chemical processes changing the geomorphology and causing an evolution of the area.