Resumen de A rare natural gypsum ooide (Gypsolites) in an evaporitic playa lake of late miocene (?) to pliocene age in central Anatlia, Turkey
Erdogan Tekin, Baki Varol, Turhan Ayyildiz
Gyposolites are found in the western part of Polatli town, Polatli-Sivrihisar basin, about 90 km from Ankara, Turkey. Gypsolites are observed in a transition zone between a siliciclastic marginal lake and an evaporitic inner lake. The ooide-bearing strata have a small to moderate thickness (10 to 50 cm), are laterally restricted, and partially exhibit a sandy appearance, including various amounts of volcanoclastic grain and mud pellets. They sometimes show micro-gradations, parallel or cross-laminations and rippled surfaces, in which macroscopically there are evidences of biogenic activity such as fossil tracks and burrows, but microbial activity is intensively present within the gypsum cortex, yielding micro-moldic porosity. Gypsolites fabrics suggest either (I) they occur under bacterial activity in local salines or short-lived ponds that occupied the low-energy part of the lake or (ii) weak currents or wind activity exert a significant influence on the gypsolites fabric. Some traces of microbial mats within the cortex and micro-gradations, parallel or cross-laminations indicate that the concomitance of bacterial activity and inorganic processes contributed to the construction of gypsum ooide structures in the Neogene evaporitic lake environment.
