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Keywords:

  • Carbonate;
  • France;
  • heterozoan;
  • incised valley;
  • limestone;
  • Miocene;
  • tidal;
  • warm temperate

Abstract

The Saumane-Venasque compound palaeovalley succession accumulated in a strongly tide-influenced embayment or estuary. Warm-temperate normal marine to brackish conditions led to deposition of extensive cross-bedded biofragmental calcarenites. Echinoids, bryozoans, coralline algae, barnacles and benthic foraminifera were produced in seagrass meadows, on rocky substrates colonized by macroalgae and within subaqueous dune fields. There are two sequences, S1 and S2, the first of which contains three high-frequency sequences (S1a, S1b and S1c). Sequence 1 is largely confined to the palaeovalley with its upper part covering interfluves. Each of these has a similar upward succession of deposits that includes: (i) a basal erosional surface that is bored and glauconitized; (ii) a discontinuous lagoonal lime mudstone or wackestone; (iii) a thin conglomerate generated by tidal ravinement; (iv) a transgressive systems tract series of cross-bedded calcarenites; (v) a maximum flooding interval of argillaceous, muddy quartzose, open-marine limestones; and (vi) a thin highstand systems tract of fine-grained calcarenite. Tidal currents during stages S1a, S1b and S1c were accentuated by the constricted valley topography, whereas basin-scale factors enhanced tidal currents during the deposition of S2. The upper part of the succession in all but S1c has been removed by later erosion. There is an overall upward temporal change with quartz, barnacles, encrusting corallines and epifaunal echinoids decreasing but bryozoans, articulated corallines and infaunal echinoids increasing. This trend is interpreted to be the result of changing oceanographic conditions as the valley was filled, bathymetric relief was reduced, rocky substrates were replaced as carbonate factories by seagrass meadows and subaqueous dunes, and the setting became progressively less confined and more open marine. These limestones are characteristic of a suite of similar cool-water calcareous sand bodies in environments with little siliciclastic or fresh water input during times of high-amplitude sea-level change wherein complex inboard antecedent topography was flooded by a rising ocean.