SEDIMENTOLOGICAL AND MINERALOGICAL STUDIES ON THE NEOGENE CLASTICS OF THE WADI ABU GHUSUN--WADI LAHMI AREA, RED SEA, EGYPT

Abstract

The area between Wadi Abu Ghusun and wadi Urn Ghazal exposes an almost complete section of the Oligocene (?) and Neogene sediments. Outcrops of Oligocene siliciclastics (Abu Ghusun Formation) and Lower Miocene (Ranga Formation) as well as the Middle Miocene carbonates (Urn Mahara carbonates) and evaporites (Abu Dabbab) are confined to the north and exhibited by a narrow belt extending to the east of the Precambrian rocks. The rest of the area is extensively covered by Upper Miocene-Pliocene siliciclastic sediments of the Marsa Alam Formation and the Plio-Pleistocene coarse siliciclastics of the Samadai Formation. This latter area represents one of the few areas along the Red Sea coastal plain where huge amounts of siliciclastic sequences fill a wide and elongate topographic depression. The carbonate beds are very rare in this area.

The Abu Dabbab (Evaporites) Formation, which separates Early Neogene continental and mar1.ne sequences from Late Neogene mixed siliciclastic -carbonate sequences in other parts of the Red sea, is missing in the area between Wadi Qulan (15 Km south of Abu Ghusun Port) and Wadi Urn Ghazal (45 Km south of Abu Ghusun). This leads to

some difficulties 1.n discriminating the various siliciclastic sequences in the particular area. In order to solve this problem, in addition to study the paleoclimatic conditions that prevailed during the late Paleogene and Neogene, detailed lithological, textural and

mineralogical studies comprising heavy mineral analysis,

clay

minerals and quartz grain-surface features were carried out on the

dominantly siliciclastic formations of the area.

Twelve columnar sections representing the different formations were measured and described in some detail. About 50 samples from the hard sandstones were collected for microscopical study. Also, about 97 representative friable sandy samples were subjected to mechanical analysis. The sandy fractions; 250-125 p, 125-63 p were separated in order to identify the heavy and light minerals contents. Quartz grains of 39 representative samples were studied under scanning electron microscope (SEM) to show the main characteristic surface features. The clayey fraction (< 2 p) of 25 representative shaly