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

• Published in: Acta geologica hispanica 2006-01, Vol.4 (3), p.343-354
• Main Authors: Thrana, Camila, Talbot, Michael R.
• Format: Article
• Language: English
• Subjects: Carbonates; Cyclical sedimentation; level change; Miocene; Mixed carbonates; Mixed carbonates-siliciclastics; Sea; Sea level; Sea level rise; Sea-level change; siliciclastics; Spain
• ISSN: 1695-6133; 0567-7505; 1696-5728
• DOI: 10.1344/105.000000348

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.