A DEPOSITIONAL MODEL AND PALEOECOLOGICAL RECONSTRUCTION OF THE LOWER TORTONIAN DISTALLY STEEPENED RAMP OF MENORCA (BALEARIC ISLANDS, SPAIN)

Abstract

In carbonate depositional environments, sediment is mostly produced by different groups of organisms. Ecological parameters, thus, play a major role controlling carbonate production. In the present work, carbonate-producing biota, especially foraminifers, are studied to construct a depositional model and paleoecological interpretation of the lower Tortonian distally steepened ramp of Menorca (Balearic Islands, Spain). This carbonate platform corresponds to a highstand systems track prograding and aggrading over a Paleozoic, Mesozoic, and, locally, lower Tertiary basement. Outcrops are excellently exposed in the southern part of the island. Five facies associations are observed, which, in downdip direction, correspond to inner ramp, middle ramp, ramp slope, toe of the slope, and outer ramp. Samples have been studied using point counting of 102 thin sections. Six foraminiferal assemblages have been distinguished. Eight microfacies are identified (IR.1, IR.2, MR, URS, LRS, TS.1, TS.2, and OR), based on the abundance and ecological significance of the foraminifers (large benthic foraminifers, epiphytics, low-oxygen indicators, and planktonics) and other carbonate-producing organisms (echinoids, mollusks, barnacles, bryozoans, serpulids, coral genus Porites, and green and red algae). Seagrass meadows in the inner ramp correspond to the euphotic carbonate factory, whereas red algae and large benthic foraminifers dominate the oligophotic carbonate factory in the middle ramp and upper ramp slope. Microfacies composition verified intense sediment-transport processes from inner and middle ramp down to lower ramp slope, toe of the slope, and outer ramp. Finally, microfacies analysis also indicates that carbonate-production took place in warm-water conditions, in oligotrophic-to-mesotrophic waters.