Fluvio-deltaic record of increased sediment transport during the Middle Eocene Climatic Optimum (MECO), Southern Pyrenees, Spain

Abstract

Abstract. The early Cenozoic marine sedimentary record is punctuated by several brief episodes (<200 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's surface. Contrary to the early Cenozoic hyperthermals, the Middle Eocene Climatic Optimum (MECO), lasting from 40.5 to 40.0 Ma, constitutes an event of gradual warming that left a highly variable carbon isotope 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 (Belsué–Atarés 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 (δ13Ccarb and δ18Ocarb) and organic matter (δ13Corg) 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 δ18Ocarb and an unclear signal in δ13Ccarb 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, the MECO to be identified and its coincident relationship with the Belsué–Atarès fluvial–deltaic progradation to be documented. 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.

Middle Eocene Climatic Optimum (MECO) and its imprint in the continental Escanilla Formation, Spain

“…In summary, stable isotope data from the Escanilla Fm at Olson is compatible with climate perturbations through excursions similar to the isotope excursions in the marine records, even though there are differences in the 255 magnitude of excursions. These excursions have also been identified downstream in the time-equivalent marine sediments in the Jaca Basin, Spain [Peris Cabré et al, 2023]. This indicates the preservation of MECO climate perturbation signals in the source-to-sink Escanilla sediment routing system.…”

An eosimiid primate of South Asian affinities in the Paleogene of Western Amazonia and the origin of New World monkeys

“…The hyperthermal conditions of the late middle Eocene climatic optimum [MECO; ∼40.5 Ma ( 55 , 56 )] resulted in particularly intense meteorological episodes in tropical/equatorial regions, most certainly associated with intense flooding events (e.g., refs. 57 – 59 ). These particular paleoenvironmental conditions may have enhanced riverbank break-ups more frequently, increasing the likelihood that some elements of riparian biological communities may have been carried away on natural rafts.…”