ORDERED, STOICHIOMETRIC AND SUCROSIC DOLOMITIZATION - A RESULT OF PROLONGED EXPOSURE TO WARM SEA-WATER - PROTEROZOIC CHANDA LIMESTONE, ADILABAD, INDIA

Bounded gradationally between offshore and basinal shales, the marine Proterozoic Chanda Limestone Fm., India, records steady transgression of the sea in a rifting basin. Its basal 2 meters of pelloidal limesto ne is succeeded by a 200 meters-long sequence of thin-bedded lime-mud turbidites of slope and basinal origin, intervened only by veneers of wind-blown dust. The non-ferroan dolocrystals within these beds are su crosic, stoichiometric and well ordered. The limestones and dolostones bear marine carbon isotopic signatures. However, subsurface fluid exc hange modified the oxygen isotopic ratios. The dolostones were enriche d in (18)0. The source of the fluids responsible for (18)0 enrichment were those involved in dolomitization. These subsurface basinal brines circulated through the fault system and permeated the sediments along bedding planes. The oxygen isotopes bear the signature of paleotemper atures.