Séminaire de Sébastien CASTELLTORT, UNIGE, Genève

Supply-forced deltaic regression during early Eocene hyperthermals, Roda de Isabena, Spain

Séminaire de Sébastien CASTELLTORT, 2018


The sequence stratigraphic architecture of the Roda formation shows several episodes of deltaic progradation followed by carbonate accumulation that have been classically ascribed to sea-level changes or hinterland tectonic pulses. However, the Early Eocene was punctuated by important climate variations and carbon cycle perturbations (hyperthermals) that are also plausible candidates for forcing deltaic movements during this time interval. We here document the links between these prominent early Eocene climatic signals and the stratigraphic evolution of the Roda formation in order to explore landscape response to hyperthermals. We generated carbon and oxygen stable isotope proles, which show that Deltaic progradation is systematically correlated with hyperthermals, while carbonate deposition systematically occurs at the end of hyperthermals or in between. Based on analogy with similar observations in New Zealand these results suggest that deltaic progradation of the Roda formation could be related to increased sediment transport and continental weathering due to enhanced hydrology during hyperthermals. Conversely, carbonate deposition could result from simple unavailability of sediment after hyperthermal “clearing events”. If this is correct, unlike classical sequence stratigraphic models, our results imply that deltaic progradation is primarily driven by climate-controlled sediment supply in a background of rising and high sea-level, while carbonate deposition represents maximum ooding because of a lack of available clastic material in generally lower sea-level stands. These ndings also highlight the dominant role of climate on landscape evolution and stratigraphic records even in an active foreland basin.