Diagenesis of Reef Limestones: ABSTRACT

Abstract

The main original reef constituents are a skeletal carbonate framework, syngenetic carbonate detritus, and pore space. Diagenesis alters these materials by various processes involving addition, removal, and reconstitution of materials. End_Page 1766------------------------------ Additive processes include the mechanical deposition of secondarily infiltered detritus; the precipitation of calcite in fibrous or bladed, turbid cavity linings; and precipitation of calcite in coarse, clear mosaics. Subtractive processes involve removal of aragonite in solution and, during dolomitization, similar leaching of low-magnesium calcite. Reconstitution includes (1) recrystallization or aragonite to calcite, and (2) reorganization of the unstable, high-magnesium calcite. This reorganization can go in two directions: to stable, low-magnesium calcite by the of excess magnesium (which is probably generally removed in solution); or to dolomite, by similar purging of excess calcium. In either process, attendant recrystallization leads to loss of microstructure and the obscuring of surface boundaries; if both framework and matrix are affected, they may blend into a homogeneous rock fabric which bears little resemblance to the original sediment. The various diagenetic steps are illustrated by examples from the Permian Capitan reef, from the Triassic reefs of the Alps, and from the Cenozoic of Florida. End_of_Article - Last_Page 1767------------