Stratigraphic architecture of a saline lake system: From lake depocentre (Alès Basin) to margins (Saint‐Chaptes and Issirac basins), Eocene–Oligocene transition, south‐east France

Abstract

ABSTRACTChanges in sedimentary profiles and stratigraphic architecture over time in lake basins are shown to be relevant markers of climate changes in terrestrial palaeoenvironments. The stratigraphic architecture of the Priabonian (late Eocene)–early Rupelian (early Oligocene) Alès–Saint‐Chaptes–Issirac saline lake system has been reconstructed from the sedimentological, biostratigraphic and magnetostratigraphic analysis of outcrops and well cores. As a function of the inflow–evaporation balance, three distinct depositional models have been proposed for the Priabonian Alès–Saint‐Chaptes–Issirac lake system which is characterized by both fault‐controlled and low‐angle ramp‐like margins: (i) freshwater to oligohaline lake; (ii) oligohaline to mesohaline closed‐lake; and (iii) hypersaline, evaporitic closed‐lake. Two major stages of lake spreading (possibly middle Priabonian and late Priabonian–early Rupelian) separated by two stages of significant lake closure represented by evaporite succession in the Alès Basin depocentre (middle to late Priabonian) have been evidenced. Regional tectonics and climate induced changes in inflow–evaporation balance of the lake and controlled the development of transgressive–regressive cycles with calcium‐sulphate sedimentation during regression in the lake depocentre (Alès Basin) and during early transgression in lake margins (Saint‐Chaptes and Issirac basins). The correlation between the palaeohydrological cycles inferred for the Alès–Saint‐Chaptes–Issirac lake system and the regional climate changes of Priabonian stage, prior to the Eocene–Oligocene transition, strongly suggests that climate significantly impacted the nature of lacustrine depositional models and the depositional architecture of Palaeogene, syn‐rift, saline lake basins from Western Europe.