New insights on the age of the post-Urgonian manly cover of the Apt region (Vaucluse, SE France) and its implications on the demise of the North Provence carbonate platform
Résumé
Our contribution presents an integrated litho-, bio- and chemostratigraphic study of the best-preserved outcrops of the post-Urgonian manly cover (A(l) unit) of the North Provence carbonate platform. The study of the rich ammonite fauna from the Apt-Gargas area (SE Vaucluse) confirms that the Al unit is older than previously assumed and dated to the upper (but non-uppermost) part of the lower Aptian Deshayesites forbesi Zone of the Mediterranean standard zonation. This interval is assigned to the lower part of the Roloboceras hambrovi Subzone as defined in the present contribution which is time equivalent to the spreading of the OAE 1a. Microfossil occurrences previously documented in the Al unit are consistent with our ammonite-age calibration. Unfortunately, the curves of the carbon and oxygen stable isotopes exhibit a correlative signal probably caused by an early diagenetic overprint which questions the previous use of the C-isotope signal for precise chronostratigraphic correlation with respect to the OAE la excursion. The top of the Al unit is marked by a burrowed firmground locally infilled and capped by glauconite-rich sandy marls which grade into the blue-grey muddy marls of the overlying A(2) unit. The hiatus associated to this discontinuity is equivalent to the culmination of the OAE la, including the uppermost D. forbesi Zone (= upper R. hambrovi Subzone as herein defined) and the lower D. deshayesi Zone. The revised calibration of the post-Urgonian marl implies that the ammonite-age calibration of the North Provence carbonate platform should be revised and questions the timing and driving mechanisms of its stepwise demise. (C) 2017 Elsevier B.V. All rights reserved.