High-frequency cycles in Upper-Miocene ramp-temperate carbonates (Sorbas Basin, SE Spain)

Abstract

Uppermost-Tortonian temperate carbonates occur at the southern margin of the Sorbas Basin (Almeria, SE Spain). These carbonates, included in the Azagador Member, formed in a gentle, shallow-water ramp. Six facies cycles in ramp deposits comprise alternating bivalve-shell concentrations and coralline algal beds. The basic cycle reflects the landward advance, as relative sea level rose, of coralline algal deposits, which were the facies of the outer ramp, over bivalve biostromes, which grew in the shallower areas of the mid-ramp. Biostromes were mainly built by oysters and locally by Isognomon. In many cases, however, the removal of smaller shells by storms left only thin, discontinuous patches of large bivalves as residual remains of the oyster biostromes. Some original cycles might be missing due to complete removal of bivalve shells from the biostromes. The six cycles recognised, therefore, should be considered as the minimum number of original cycles in the Azagador carbonates. The available age constraints suggest these cycles were forced by orbital precession or some higher-frequency process. Lithological cycles forced by precession are characteristic of the basinal deposits laterally equivalent to the Azagador carbonates.