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Record of NW Mediterranean Geodynamics in Paleokarsts of Southern France

Eglantine Husson, Michel Seranne, Hubert Camus, Pierre Jean Combes, Renaud Couëffé, Mihaela Carmen Melinte-Dobrinescu, Marie José Fondecave-Wallez, and Bernard Peybernès

Paleokarsts are classically studied in term of reservoirs. They also constitute a record of base-level variation through time: they are formed during base-level drop and they trap internal sediment during base-level rise. Base-level movements are related to: 1) eustacy, 2) tectonics (subsidence and uplift) and 3) desiccation/flooding of endoreic basin. Dating and amplitude analysis of base-level variations in paleokarst therefore provide a record of geodynamics.

Mesozoic carbonate massifs are well exposed in southern France. They underwent successive karstification events in relation with the well-constrained regional geodynamics of this area. Mapping shorelines, correlative continental sediments and karst systems provide downstream-upstream profiles for each paleokarst event.

- Comparison of successive profiles allows to determine the amplitude of base-level changes and the amount of differential vertical movements across fault zones or flexure. In particular, Late Miocene uplift reached 400m amplitude in the hinterland, in the footwall of a major regional fault, while the hangingwall was uplifted by 250m.

- Occurrence of marine infill within paleokarst requires a base-level drop (karstification) followed by a rise (infill) of an amplitude at least equal to the vertical extend of the karst system. Early Paleocene forams and nannofossils found in karst infill indicate up to three base-level variations ≥ 350m amplitude. Matching well-dated base-level changes with eustatic curves discriminates the mechanisms of base-level variation. The measured amplitude of Early Paleocene events exceeds eustacy-driven base-level changes, and the rate of change exceeds that of tectonic movements: this points to desiccation/flooding cycles of a silled endorheic basins.

For the last 100My, we correlate upstream-downstream profile modifications due to base-level changes with the known geodynamics of Southern France. Such approach could constitute a tool to decipher geodynamics within the karst record of other (frontiers) areas.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013