Abstract: Miocene Carbonate Platforms in Southern Italy: The Effect of Global Changes on Carbonate Depositional Facies

Maria Mutti, Daniel Bernoulli

Miocene carbonates are widespread worldwide and form important reservoirs in several regions. However, depositional models developed from modern carbonate systems often are insufficient to predict their depositional systems and facies associations. The Miocene was a time characterized by intense global changes. Miocene carbonates outcropping in Southern Italy provide a case history to understand their effects over carbonate deposition and the links among different processes occurring at a global scale.

Along the Maiella platform margin, Lower and Middle Miocene carbonates were deposited on a low angle ramp. The large scale packaging of the sediments reflects a second order eustatic cycle and contains three depositional sequences. Each of these is wedge shaped in cross-section and consists of a lower shallow-water unit sharply overlain by an upper hemipelagic wackestones-packstone unit. The drowning surfaces are marked by the occurrence of phosphatic hardgrounds. Similar facies packaging occurs in age equivalent strata throughout the Southern Apennines. Integration of stratigraphic data with ^dgr¹³C-isotope profiles indicate that the major drowning events are synchronous throughout the area.

Benthic associations include bryozoa, large foraminifera, echinoderms, and red algae (foramol association) and reflect deposition in temperate waters and/or in a high-productivity settings. High contents of silica and phosphorus in the strata suggest meso- to eutrophic conditions.

Drowning in the late Langhian immediately precedes the onset of the Monterey ^dgr¹³C excursion and the onset of glaciation with the related changes in oceanic circulation. Overlying hemipelagic sediments are commonly organic-rich, reflecting globally increased organic carbon burial.

The relatively low growth potential of foramol systems makes them very sensitive to environmental changes and probably plays a major role in the failure of these platforms to keep up with sea-level. Our data suggest that the integration of changing environmental parameters in carbonate depositional models would result in better prediction of Miocene depositional systems and their facies associations in subsurface settings.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France