Abstract

Barremian-Aptian carbonate sediments in southern Provence belong to a drowning sequence within an intra-shelf basin and display organic-carbon-rich horizons corresponding to the demise of a rudists platform system and the onset of dysaerobic conditions. These horizons depart from the classical anoxic model accepted for most marine organic-carbon-rich deposits. They have a rich and diverse fauna documenting nutrient-rich waters with low oxygen content--an environment in which organic matter is preserved from both biological and chemical degradation. Sedimentological, geochemical and palaeoecological investigations suggest that the organic-carbon-rich carbonates reflect dysaerobic conditions favourable for organic matter preservation, the amount of dissolved oxygen being lower than the geochemical threshold for organic matter decay. These organic-carbon-rich sediments are the result of high sea surface productivity and sea bottom conditions favouring preservation. The kerogen is mainly amorphous sapropelic organic matter, essentially algal, with a high hydrogen index and is of marine origin, deposited during high sea-level.

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