MICROTAPHOFACIES OF A WARM-TEMPERATE CARBONATE RAMP (UPPERMOST TORTONIAN LOWERMOST MESSINIAN, SOUTHERN SPAIN)

The combined analysis of the sedimentary structures, internal depositi onal geometries, and microfacies of uppermost Tortonian/lowermost Mess inian shallow-marine carbonates (Agua Amarga Basin, southern Spain) ha s aided in unraveling the geological record of a highly dynamic ramp e nvironment. The biogenic BRYOMOL association with large benthic forami nifers inhabited a warm, temperate climate (17-20 degrees C). Sediment distribution was governed by physical parameters, and redistribution and mixing of particles blurred original biogenic zonations. Thus, alt hough the carbonate factory can be localized on the mid ramp based upo n sedimentary structures and depositional textures, sediment compositi on is quite uniform over the depositional profile, and only qualitativ e paleontological evidence exists for the original presence of seagras s patches (benthic foraminifers, biomuration fabrics in bryozoans). Or iginally aragonitic biota (i.e., molluscs), quantitatively important i n all Cenozoic shallow-marine environments, were dissolved during or s oon after deposition and left no significant trace in the fossil recor d. Consequently, the diagenetic potential of the sediments was low and the deposits remained essentially unlithified for a long period. Duri ng lowstands and transgressions, particles were partly reworked from p reviously deposited material. Sediment compositions within these units are increasingly biased toward concentrations of mechanically more re sistant carbonate grains as a function of many deposition and exhumati on cycles. In line with taphonomic experiments, nodular (celleporiform ) bryozoans disappear before robust and delicate branching bryozoans. Resistant grains include echinoderm ossicles, bivalve shell materials (calcitic), foraminifers, balanids, and non-carbonate particles. The q uantitative proportions of these grains have been used to define micro taphofacies (new term). Particle and, therefore, sequence dynamics of temperate carbonate-ramp systems resemble these in siliciclastic Envir onments, and challenge the classic concept of (tropical) carbonate seq uence stratigraphy. Careful microfacies analysis of temperate skeletal carbonate depositional systems and depositional sequences provides an important additional tool in further understanding the architecture o f bioclastic carbonate bodies in the subsurface.