Drowning discontinuities and stratigraphic correlation in platform carbonates. The late Barremian-early Aptian record of southeast France

作者：Masse Jean Pierre^*; Fenerci Masse Mukerrem

来源：Cretaceous Research, 2011, 32(6): 659-684.

DOI：10.1016/j.cretres.2011.04.003

• Drowning discontinuities
• Carbonate platforms
• Barremian
• Bedoulian
• Stratigraphic correlations
• SE France

In Provence and Languedoc, four drowning events were identified in platform carbonates of late Barremian-Bedoulian age. Their recognition is based on sedimentological and stratigraphical evidence, and their timing, referred to ammonite zones or subzones, is as follows:
(1) Late Barremian, at the G. sartousiana-Imerites giraudi transition, or merely the lowermost part of the I. giraudi zone,
(2) Middle Bedoulian, at the Deshayesitesweissi-Deshayesites deshayesi transition,
(3) Mid late Bedoulian in correspondence with the "Roloboceras hambrovi subzone",
(4) Late Bedoulian at the Deshayesites grandis-Deshayesites furcata transition.
Corresponding events are also well expressed in basinal settings where they are marked by significant facies and faunal changes.
These four successive drowning events distinguish four successive steps in platform development and demise. Step 1 was coeval with the onset of the Bedoulian palaeogeography and started after drowning event (1) with a drastic reduction of shallow platform settings with rudists, usually replaced by Palorbitolina facies. The ensuing recovery of rudist facies and, following drowning event (2), subsequent step 2 marked the developmental phase of the platform system, whereas steps 3 and 4, each prefaced by a drowning event, were associated with its demise. Step 1 represents the major spreading phase of the Urgonian type facies spectrum including bioclastics, coral and rudist facies groups. In Provence, step 1 was characterized by a bipolar (N-S) progradation, and aggradation was coeval with a maximum of subsidence. The termination of step 1 was marked by the emergence of the antecedent platform margin. Step 2, which followed the disappearance of rudist facies and the extreme spatial reduction of both coral and bioclastic facies, started with the flooding of the antecedent platform and the development of Palorbitolina and cherty limestones. Shallow water bioclastics and/or coral facies recovered rapidly on top of the pre-existing emerged areas and developed locally as bioclastic shoals. Step 2 documents a regional reorganisation of subsidence patterns.
The infralittoral (high illuminated environments) "Urgonian facies" are therefore essentially present in the Lower Bedoulian, and circalittoral (relatively deep low illuminated environments) deposits dominate in the Upper Bedoulian. This pattern, typical for SE France and wide parts of the Helvetic shelf, departs from that of adjacent regions (e.g. SW France, Spain) where late Bedoulian platform carbonates have a significant record. The record thus shows that the demise of the Urgonian platform was a step-wise phenomenon which cannot be ascribed to a single event, i.e. the Goguel/Selli OAE1a main event.

• 出版日期2011-12