Diagenetic fabrics in some British Dinantian limestones

Abstract

Abstract Diagenetic fabrics (textures and structures) have been examined in thin sections of Dinantian limestones mainly from the Avon Gorge, North Wales and Yorkshire. Six processes are shown to have been responsible for the change from unconsolidated sediment to limestone. These are: (1) granular cementation and drusy growth, (2) rim cementation (secondary enlargement), (3) pressure solution, (4) grain growth sensu stricto , (5) mechanical deposition in cavities of post‐depositional age, and (6) post‐depositional formation of cavities by erosion and solution in a carbonate mud. Grain growth, a process well known to metallurgists, acts in monomineralic fabrics of low porosity in the solid state. The intergranular boundaries wander so that some grains enlarge while others shrink and disappear, so bringing about a general increase in coarseness. In all the limestones the mosaic between the mechanically deposited particles (skeletal debris, pellets, ooliths) is one of three types. These are granular cement, rim‐cemented detrital crystals, and a mosaic caused by grain growth.