The nature and possible origin of dolomite in Ar Rub’ Al Khali, the UAE

Abstract

Surface and near-surface sediments in southeastern part of the United Arab Emirates show extensive development of dolomite that is characterized by whitish, dense rocks, partially dissected by veinlets of gypsum and well-developed coarse calcite crystals. The dolomite reveals rather monotonous aphanocrystalline to very finely crystalline crystals (2–20 μm) composed of idiotopic or planar dolomite fabric. Densely packed dolomite aggregates of clotted texture are observed. Moreover, several horizons of peloidal textures are recognized. The fossil content includes freshwater molluscs, foraminifera and gastropods embedded in very fine dolomite crystals., whereas dolomite forming the skeletal grains is considerably coarser (about 40 μm). The most common carbonate porosity type is fossil moldic followed by vug and channel porosity. Interparticle and intraparticle porosity, that may suggest possible dissolution by later diagenetic fluids, are only locally significant. Vari-sized blocky sparry calcite crystals are frequently observed as pore-filling cement.