Mediterranean Miocene Carbonates: Facies Models and Diagenesis: ABSTRACT

Abstract

Miocene carbonates can bridge the gap between Holocene and older carbonate sequences, thus enhancing understanding of depositional and diagenetic patterns. Miocene carbonates can bridge this gap because of their similarity to Holocene counterparts and the ease of using these carbonates to reconstruct tectonic, paleogeographic, and paleoclimatic settings. In the Mediterranean, the Miocene provides a superb set of exposures and a wide variety of facies models in different geologic settings. Mediterranean Miocene carbonates contain three major types of platform facies: coral reefs, macroforaminifer-rodolithic carbonates (rodalgal facies), and molluscan-bryozoan-foraminifer calcarenites (foramol facies). A combination of interrelated factors (e.g., water depth, temperature, and nutrients) control the distribution and lateral vertical transitions of these platform types. The rodalgal facies is widespread and occurs as a transition between the coral reef platform and the foramol platform. Modern carbonate sedimentation in the Mediterranean provides instructive analogies for many varieties of foramol and rodalgal facies. The most extensive porosity type is a combination of secondary intergranular and moldic porosity with chalky microporosity, locally in association with minor primary integranular porosity. This porosity is normally associated with dolomitization and is interpreted as having originated in intermediate burial environments. Miocene coral reefs were particularly abundant and well developed in the late Miocene, before and during the Messinian salinity crises and basinal evaporite deposition. These events implied drastic variations in sea level, water chemistry, and nutrients, and coincided with high sedimentation rates in coastal areas. To survive these adverse conditions, coral reefs grew very fast, with spacially successful colonial morphologies and intense carbonate cementation. Many coral reef sections present marked cyclicity with repeated intercalations of exceptionally well-developed stromatolitic carbonates. Present outcrops record details comparable to Quaternary reefs, as well as details of the facies geometry of the different reef complexes and their responses to Miocene sea level oscillations. End_of_Article - Last_Page 1440------------