|
Shari Playa, which is the only source of natural sodium sulphate in Iraq, is a longitudinal closed basin located about 150 Km to the north of Baghdad, Central Iraq. The Playa receives its sediments from major ephemeral streams originated from Hemrin Mountain, which surrounds the playa from the northeast and east, forming a seasonal lake. Seasonal flooding of the ephemeral streams into Shari playa, followed by periods of evaporation and desiccation resulted in the development of many sedimentary facies. They were developed in a set of interrelated subenvironments controlled by hydro1ogica1, biological, chemical and sedimentological processes.
Five, roughly concentrically arranged subenvironments are recognized including from the center outwards, glauberite mudflat, gypsum mudflat, sandflat, ephemeral stream floodplain -alluvial fan and dune field subenvironments. The glauberite mudflat sudenvironment occupies the central area of the playa and is characterized by the development of salt crust facies on the surface underlain successively by black mud facies, glauberite - rich bluish green - gray mud facies, gypsum - rich dark gray mud facies and clastic substrata facies. The gypsum mudflat subenvironment surrounds the glauberite mudflat subenvironment and like wise is characterized by the development of thin salt crust underlain by gypsum - rich dark gray mud facies and clastic substrata facies. The sandflat subenvironment is mainly dominated by fine sand - silt - clayey silt facies, which roughly surrounds the central area of the playa. The ephemeral stream floodplain - alluvial fan subenvironment is dominated by sand - silt facies and occurs on the northern, eastern and western sides of the playa at the mouths of incoming ephemeral streams. The dune field subenvironment is comprised of aeolian sand facies that lie on the margins of the playa.. Those on the western side are gypsified and seem to be older whereas those on the northeastern, eastern and southeastern sides are active. The sediments distribution and geometry indicate that the Playa is a subsiding N-S oriented graben.
|
