Sedimentary signatures of the Paleocene-Eocene Thermal Maximum (PETM) in the South-Pyrenees and Laboratory experiments

Chen, Chen; Castelltort, Sébastien

Deciphering sedimentary signatures has prominent implication for paleogeographic reconstruction and interpreting the sedimentary record of Earth history: what can sediments and rocks tell us about the past? The Paleocene-Eocene Thermal Maximum (PETM) is an extreme global warming event that occurred about 56 million years ago. Global temperatures are estimated to have increased by 5-8°, and it has been proposed to be a geologic analogue for anthropogenic climate change. In the southern Spanish Pyrenees, based on outcrops and borehole information from the Tremp-Graus Basin, it is shown that a sea-level fall of at least 20 m occurred less than 75 kyr prior to the PETM. In the central part of the Tremp-Graus basin, the Paleocene to early Eocene record is shown by the Esplugafreda section. A paleo-incised valley carved into Esplugafreda formation and is interpreted as the unconformity boundary produced in response to the pre-PETM sea level fall. The valley filled by channel-like conglomeratic sandbodies at the bottom and finer reddish floodplain deposit in the rest of the section. The incised valley is capped by the Claret Conglomerate — an extensive sheet-like unit which ranges in thickness between 1m and 4m of and is generally interpreted as the river response to a dramatic climate change at the PETM because of its occurrence at or close to the PETM signal recorded in the stable isotope composition of paleosoil nodules (Pujalte et al. 2014). The conglomerate unit ends abruptly and is overlaid by fine-grained yellowish soil which is mainly made up of silty mudstones with abundant small size carbonate nodules suggesting another shift in the hydrological cycle after the PETM. Sea level kept rising after the PETM and all of the section was inundated by the ocean in terms of Ilerdian of marine limestone on the top of the section. Many studies (Schmitz &Pujalte 2003, 2007; Pujalte et al, 2014) suggested that grain size changes significantly across the based essentially on the observation of the coarse-grained Claret Conglomerate. We tested this assumption by performing a thorough field analysis of grain size within conglomerates in the formations below, at, and above the Claret conglomerate. Our results show that there is no significant grain size variation across the PETM. To test our hypothesis, we performed several experiments of incised valley filling during a single base-level rise in the Saint Antony Falls Laboratory (SAFL, University of Minnesota). We systematically changed water discharge, sediment flux and the rate of base level rise rate to document the resulting effect on the stratigraphic signature preserved in the valley fill and compare it with the sedimentary record of the Esplugafreda section.

Sedimentary signatures of the Paleocene-Eocene Thermal Maximum (PETM) in the South-Pyrenees and Laboratory experiments

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