High-frequency carbonate-siliciclastic cycles in the Miocene of the Lorca Basin (Western Mediterranean, SE Spain)

Abstract

The upper Miocene Parilla Formation, Lorca Basin, Spain, provides an example of stacked high-frequency cycles of mixed carbonates and siliciclastics. Cycles developed on a steep carbonate ramp bordering an alluvialfan system. Three cycle variants are distinguished: siliciclastic-dominated cycles at the proximal part of the ramp, mid-ramp mixed carbonate – siliciclastic cycles, and carbonate-dominated cycles on the more distal parts of the ramp. The vertical thickness of these stacked simple sequences ranges from 0.7 up to 8 m. High-frequency changes in relative sea level resulted in a dynamic interplay between terrigenous sediment supply and carbonate production rates. During falling stage and lowstands, the alluvial system migrated basinwards and coarse-grained siliciclastics were deposited, whereas rising sea level and highstands provided optimal conditions for the production and accumulation of biogenic carbonates. Coral colonies up to 4 m thick provide a minimum measure of the magnitude of sea-level change involved in the development of the cycles. In contrast to previously documented simple carbonate sequences, this hybrid system of carbonates and siliciclastics preserves a more complete record of cyclic sea-level change, where terrigenous sediment supply compensated for the reduction in carbonate production during periods of falling and low sea level.