Architectural complexity of a carbonate transgressive systems tract induced by basement physiography



Three-dimensional exposure of the Plio-Pleistocene Calcarenite di Gravina Formation around Matera Horst, Italy, permits analysis of the architecture and internal complexities of carbonate sedimentary bodies around a palaeoisland. Spatial organization of the different lithosomes, along with their skeletal composition, sedimentary structures and bedding patterns, helps decipher the key factors that controlled platform architecture and distribution of heterogeneities: basement physiography, type and loci of carbonate production, bottom currents and changes in accommodation. Relative sea-level changes resulted from high-frequency glacioeustatic cycles that punctuated an overall tectonically induced transgression. Topographic relief, fragmentation of the limestone basement and wave energy controlled lithoclastic supply. Basement physiography and relative sea-level changes determined the area available for carbonate-producing biotas, and thus the amount and type of skeletal sediments. On the moderately dipping south-western margin, waves and associated currents re-distributed the lithoclasts derived from coastal abrasion. Bioclasts mostly derived from epiphytic seaweed production in the shoreface. Infralittoral prisms resulted from downdip transport (progradation) and longshore transport, which controlled along strike continuity of the prisms. Where basement continuity was interrupted at the margin of the palaeoisland, a lithoclastic fan was deposited from dumping sediments carried by shore-parallel currents. Fan-shaped skeletal bodies coalesced to form an apron on the steeper northern side of the palaeoisland, when a structural platform was flooded and epiphytic carbonates were shed. Red algae contribution depended on the available oligophotic area which, in turn, was controlled by high-frequency sea-level cycles, basement physiography and apron aggradation. The internal architecture of this apron resembles a low stand wedge but it accumulated during transgression. Deeper-water, contour-parallel currents formed a lithosome at the foot of the structural relief. Interpreted as drift deposits, it is composed of shallow-water benthonic skeletal components, planktonic foraminifera and some limeclasts.