Comment on egusphere-2022-891

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The early Cenozoic marine sedimentary record is punctuated by several brief episodes (&lt; 200&thinsp;kyr) of abrupt global warming, called hyperthermals, that have disturbed ocean life and water physicochemistry. Moreover, recent studies of fluvial-deltaic systems, for instance at the Palaeocene-Eocene Thermal Maximum, revealed that these hyperthermals also impacted the hydrologic cycle, triggering an increase in erosion and sediment transport at the Earth&rsquo;s surface. Contrary to the early Cenozoic hyperthermals, the Middle Eocene Climatic Optimum (MECO), lasting from 40.5 to 40.0&thinsp;Ma, constitutes an event of gradual warming that left a highly variable carbon isotopic signature and for which little data exist about its impact on Earth surface systems. In the South-Pyrenean Foreland Basin (SPFB), an episode of prominent deltaic progradation (Belsu&eacute;-Atar&eacute;s and Escanilla formations) in the middle Bartonian has been usually associated with increased Pyrenean tectonic activity, but recent magnetostratigraphic data suggest a possible coincidence between the progradation and the MECO warming period. To test this hypothesis, we measured the stable isotope composition of carbonates and organic matter of 257 samples in two sections of SPFB fluvial-deltaic successions covering the different phases of the MECO and already dated with magnetostratigraphy. We find a negative shift in 𝛿 ¹⁸O_carb and an unclear signal in 𝛿¹³C_carb around the transition from magnetic Chron C18r to Chron C17r (middle Bartonian). These results allow, by correlation with reference sections in the Atlantic and Tethys, to identify the MECO and document its coincident relationship with the Belsu&eacute;-Atar&egrave;s fluvial-deltaic progradation. Despite its long duration and a more gradual temperature rise, the MECO in the South Pyrenean Foreland Basin may have led, like lower Cenozoic hyperthermals, to an increase in erosion and sediment transport that is manifested in the sedimentary record. The new data support the hypothesis of a more important hydrological response to the MECO than previously thought in mid latitude environments, including those around the Tethys.