Reef slope geometries and facies distribution: controlling factors (Messinian, SE Spain)

Abstract

Sea-level fluctuations and changes in sediment grain size are widely thought to be the main factors controlling carbonate platform slope geometries. Two successive clinoform bodies from the Upper Miocene Cariatiz carbonate platform (SE Spain) were selected to analyze geometry and facies distribution in relation to sea-level oscillations. Facies occurring in these clinoform bodies are from top to bottom reef-framework, reef-framework debris, Halimeda breccia, Halimeda rudstone, and bioclastic packstone, as well as siltstone and marl. Slope geometry and facies, composition, and distribution, are significantly different in each clinoform body. These differences are the result of the interaction of several factors such as coral growth, in situ slope carbonate production, rockfalls and sediment gravity flows, hemipelagic rain, reworking of reef-slope facies and siliciclastic input. Changes in accommodation were related to sea-level fluctuations and controlled the relative impact of these factors. A sea-level fall took place in the time between deposition of the selected clinoform bodies and changed the hydrographical conditions of the basin. These changes influenced the presence of Halimeda and the grain-size distribution, and consequently the slope geometries. Reef-slope geometry is not exclusively controlled by changes in grain size. The stabilization by organic binding is proposed to be a significant factor controlling the slope deposition.