ABSTRACT

Three generations of sparry calcite, defined by variations in fabric and their reaction with artificial stains, occupy primary and secondary voids in the Corallian Beds of southern England. They appeared in the order; non-ferroan calcite, fibrous ferroan calcite, granular ferroan calcite. Non-ferroan calcite has a restricted distribution and is suggested to he the result of exposure of the unconsolidated carbonate sediments to the subaerial environment. The ferroan calcites are widespread; they were precipitated after the sediments had become sufficiently buried to isolate them from the subaerial and submarine environments. Some of the calcite was produced from calcium carbonate released by dissolution of skeletal aragonite and some from grain contact solution, but other sources must lso have been involved. Similar diagenetic sequences are present elsewhere in the Jurassic of southern England.