Las microfacies carbonatadas neógenas en un sector occidental de la depresión del Bajo Guadalquivir

Abstract

It sets up limestone microfacies (microfacies A to G) in the neogene calcarenitic materials of Carmona, Alcalá de Guadaira and Arcos de la Frontera-Bornos, localizated in the occidental sector of the Guadalquivir Basin. Their analysis allow to define the implantation of a mixed shelf environment, a carbonate ramp in a open marine ambient, during Upper Miocene-Lower Pliocene, in such sectors. The composition of these limestones represents the «Foramol» lithofacies. More closely, «molechfor» (Carmona-Alcalá de Guadaira) and «bryomol» (Arcos de la Frontera-Bornos). Minimum and medium temperature were < 15 and < 180 ºC. Salinity varied between 30-40 ‰ (marine normal salinity). It diferenciates the standard microfacies types SMF 9 and SMF 11 and the facies zone FZ 2 and FZ 6 that respond to shallow waters with open circulation in (or below) wave base and winnowed shelf edges with constant wave action in (or above) wave base, in the Carmona area platform. Ambient energy varied between intermitent (microfacies A) and moderated (microfacies B-C). In Alcalá de Guadaira and Arcos de la Frontera-Bornos sectors have been stablished SMF 11, SMF 12 (Shelf edges) and FZ 6. These microfacies are deposited in moderated (microfacies D,E,F) and strongly agitated water (microfacies G). Two shallow subtidal zones with lower boundary at about 30 m (microfacies B-e and F-G) have been delimitated. Limestones are temperate-polar carbonates. Exactly, the carbonate platform is «cold temperate ».