NATURAL SODIUM SULFATE IN SHARI PLAYA, IRAQ: A CASE STUDY

Shari playa is a closed basin characterized by the development of seven sedimentary facies and five sedimentary subenvironments over the underlying clastic substrata facies. The sediments distribution and geometry indicate that the playa is a subsiding N-S oriented graben. The area show three sets of lineaments oriented NW-SE, NE-SW and N-S directions. A set of N-S step faults, partly affected by the other trends of lineaments, seems to control the subsidence and orientation of the graben. The age of the depression is suggested to be 6000-6500 years B.P. deduced from the palynological studies, assumed rates of precipitation and comparison with palaeoclimatic trends. Saline minerals found in the Shari Playa are: gypsum, glauberite, halite, thenardite and trace amounts of bassanite, natron, trona, huntite, d'ansite and hydrated magnesium brormide. They mainly occur in the facies that occupy the central part of the playa. The main saline minerals in the playa show spatial and vertical distribution reflecting the playa lake brine evolution and concentration following characteristic paths on the system CaSO4 - Na2SO4 ¿ NaCl - H2O.