TITLE:
Field, Mega- and Microscopic Description of the Volcaniclastic Red Beds and the Associated Scoriaceous Basalt of Wadi Al Roaian, Ablah Area, Assir Terrain
AUTHORS:
Abdullah R. Sonbul
KEYWORDS:
Scoriaceous Basalts, Arabian Shield Rocks, W. Al Roaian, Ablah Area, Volcaniclastic Red Beds
JOURNAL NAME:
Open Journal of Geology,
Vol.6 No.7,
July
28,
2016
ABSTRACT: The study area is located in the entrance of Wadi Girshah in Ablah area, Assir terrain, southwestern Saudi Arabia. The present study aims
to shed light on the field, mega- and microscopic description of the
volcaniclastic red beds and the associated scoriaceous basalts of Wadi Al
Roaian. It is based mainly up on the field works augmented by petrographic
description. The present study revealed that, the succession of the upper part
of Girshah Formation comprises three main horizons: 1) lower unit of epidotized
and silicified basaltic and andesitic tuffs; 2) middle unit of volcaniclastic
red beds-scoriaceous basalts of successive cycles (each of these cycles begins
by reddish tuffaceous mudstone and sandstone and is terminated by the
calcite-bearing scoriaceous basalt). This unit indicated the deposition in
lacustrine environments and the red iron oxyhydroxides minerals were formed
either by the direct hematitization of the deposited tuffs or by the diagenetic
hematitization of the green clays formed instead of the precursor tuffaceous
materials; 3) upper scoriaceous basalt unit composed from hematitized and
calcitized basalt. The unit was formed by basic volcanic eruptions in subaerial
condition which was predominated by the formation of calcium carbonate lakes
associated with the progressive and subsequent calcitization of the
Ca-plagioclase minerals of the basalt and the associated glassy tuffaceous
material. The scoriaceous basalts of Wadi Al Roaian area represent subaerial
basic volcanic eruption in continental situation and are associated with
subsequent events of mineral alteration and formation of secondary minerals i.e. calcite, hematite and goethite.