Interaction of tectonics, eustasy, climate and carbonate production on the sedimentary evolution of an early/middle Jurassic extensional basin (Southern Provence Sub-basin, SE France)

This paper describes the evolution of an extensional basin in regard to the nature and sequence stratigraphic arrangement of its carbonate deposits. The purpose of this study is to evaluate the respective effects of tectonism, eustasy, climate and oceanography on a carbonate sedimentary record. The case study is the early to mid-Jurassic age carbonate succession of the Southern Provence Sub-basin (SE France), located within the southern part of the extensional Western European Tethyan Margin. This work is based on sedimentologic, biostratigraphic (using ammonites and brachiopods) and sequence stratigraphic analysis of the carbonate facies of the Cherty Reddish Limestone Formation (late Sinemurian to earliest Bajocian). These strata were deposited in shoreface to lower offshore depositional environments. The succession of the various environments together with the recognition of key stratigraphic surfaces allow us to define four second-order depositional sequences; of late Sinemurian to earliest Pliensbachian, early Pliensbachian to late Pliensbachian, earliest Toarcian to middle Aalenian and late Aalenian to early Bathonian ages. The architecture of the depositional sequences (thickness and facies variations within the systems tracts, wedge-shaped geometries) reflects a strong tectonic control. The sub-basin was structured by extensional faults (oriented approximately 070-090/250-270). Sea-level variations, fluctuations in carbonate production and preservation, and environmental changes were also significant controlling factors of the carbonate deposition. The interplay of the tectonic control with the other factors resulted in five main phases in the sedimentary evolution of the sub-basin: (1) dominant tectonic control during the initial rifting stage (late Sinemurian to early Pliensbachian); (2) increasing extensional tectonics (mid-Pliensbachian); (3) global climato-eustatic sea-level fall (latest Pliensbachian) and global climato-eustatic sea-level rise plus hypoxia/anoxia (early Toarcian); (4) relative sea-level fall linked to tectonic uplift related to the 'Mid-Cimmerian phase' (mid-Aalenian) and (5) oceanographic events (upwelling) and reduction in carbonate production (hypoxia/anoxia) plus tectonic downwarping (late Aalenian/earliest Bajocian).