Holocene Gypsum Types and Formative Processes in Tidal Flat Settings, Carnarvon Basin, Western Australia: ABSTRACT

Abstract

Study of gypsum presently forming in terrigenous and carbonate tidal flats along the semiarid coastline of Western Australia indicates that gypsum crystal habits, textures, structures, and fabrics developed on or within host sediments can be correlated with the physical, chemical, and hydrologic conditions of formation. By treating the study of gypsum from a sedimentologic approach, a classification of gypsum types is developed which allows comparative analysis and appears to be applicable to the interpretation of ancient evaporitic sequences. Gypsum precipitated on a substrate from a free-standing body of water crystallizes in a habit dominated by the prism (110) and displays variations in texture, fabric, and structure that are related to the maintenance or progressive change in environmental conditions within the brine body. The action of physical and organic agencies is important in the genesis of the fabrics and structures displayed and in their destruction to form clastic gypseous sediments. Gypsum precipitated within a host sediment crystallizes in a habit dominated by the hemi pyramid (111) and displays textures, fabrics, and structures that are related to host sediment properties, brine chemistry, ground-water hydrology, and the mechanisms for maintenance of such environmental conditions. Gypsum emplacement acts to disrupt and modify sedimentary features within the host and to form new textures, fabrics, and structures which are related to, and overpoint, their precursors. End_of_Article - Last_Page 556------------