DEPOSITIONAL AND DIAGENETIC INFLUENCES ON THE SPACING OF SUB-PARALLEL, BED-PERPENDICULAR JOINTS IN BEACH CARBONATES (GRANADA BASIN, SPAIN)

The present contribution focuses on the control exerted by both depositional setting and diagenetic evolution on the spacing of sub-parallel, bed-perpendicular joints in shallow-water, layered carbonate rocks. In particular, the study is conducted on bryozoan-dominated, skeletal carbonate grainstones and rudstones cropping out in the Granada Basin, southern Spain. The study carbonates, Tortonian in age, were deposited within different sectors of a beach-like environment. The several carbonate lithofacies recognized, after field and optical microscopy analyses, are related to specific biological (e.g. flourishment of bryozoan colonies) and sedimentary processes (fair weather versus storm wave action). The results of quantitative analyses, conducted on representative samples, allowed us to determine the mean values of grain size, grain sorting and grain shape. Taking into account the main diagenetic processes, cementation and dissolution, which affected the study carbonate rocks, we identify the principal controls on the resulting measured values of porosity and Uniaxial Compressive Strength. As a result, a key role was played by the mean grain size which, in turn, affected the diagenetic processes and the subsequent spacing of sub-parallel, bed-perpendicular joints. The depositional setting is identified therefore as the main control on grain size; in fact, the intrinsic environmental factors such as wave regime, water temperature and siliciclastic input influenced both the flourishment and growth form of the different biota and the sediment redistribution.