MICROSPAR DEVELOPMENT DURING EARLY MARINE BURIAL DIAGENESIS - A COMPARISON OF PLIOCENE CARBONATES FROM THE BAHAMAS WITH SILURIAN LIMESTONESFROM GOTLAND (SWEDEN)

Comparison of ultrastructures in Pliocene periplatform carbonates from the Bahamas with Silurian limestones from Gotland (Sweden) reveals th at despite the differences in primary sediment composition and age, th ey reflect a similar mechanism of lithification. In both sequences cal cite microspar was formed as a primary cement at an early stage of mar ine burial diagenesis. Neither significant compression nor meteoric in fluence are necessary for the formation of calcite microspar. A model is proposed for the process of microsparitic cementation of fine-grain ed aragonite needle muds comprising four stages: (1) unconsolidated, a ragonite-dominated carbonate mud; (2) precipitation of microspar that engulfs aragonite needles; (3) dissolution of aragonite, resulting in pitted surfaces of the microspar crystals; and (4) slight recrystalliz ation. Our results contradict the widespread opinion that microspar ne cessarily is a product of secondary recrystallization of a previously lithified micrite.