Deposition and Diagenesis of the Miocene Saumane-Venasque Limestones, southeastern France
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The Burdigalian Saumane-Venasque carbonate succession is located in the Rhodano-Provençal basin of southeastern France. These carbonates accumulated in a paleovalley that was flooded by marine waters. This marine embayment was filled by carbonates composed of twelve different facies. These sediments form two thick third-order sequences (S1 & S2) and several, thinner higher-order sequences (S1a, S1b, S1c). S1a is composed of quartzose grainstones with barnacles, echinoids, and bivalves derived from a rocky substrate paleocommunity in a high-energy, open-marine environment during the early phases of sea level rise. Compound dunes of S1a and S1b are composed of bryozoans and echinoids that are mixed with bioclasts from seagrass facies. Pervasive cross-bedded grainstones grade upward into low-energy mudstones and packstones of the S1 highstand. Bryozoan thickets populated sequence 2 during the second sea level cycle. Seven different phases of cement, including cloudy epitaxial, fibrous, isopachous columnar, isopachous equant, clear epitaxial, blocky, and pendant types, can be distinguished in these limestones. Marine hardgrounds are present throughout the area as steep, stepped margins in tidal channels. Marine cements are interpreted to have precipitated in the upper portion of subaqueous dunes with their location controlled by sedimentation rate and tidal pumping. Zoned epitaxial cements are interpreted to record shifts in the paleo-water table related to fluctuations in sea level throughout the Miocene in the Rhodano-Provençal basin. Shallow burial pressure dissolution features are present throughout the deposit. They are interpreted to result from extended exposure to fresh water, which produced grains that were particularly susceptible to compaction. The Saumane-Venasque temperate carbonates are different in that they were lithified without significant burial diagenesis, a situation that resulted from multiple sources of cement from marine and meteoric waters.