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

Abstract. The Middle Eocene Climatic Optimum (MECO) is a global warming event mainly described in the marine domain but less in the terrestrial domain. This study presents a comprehensive geochemical record of the MECO from the Escanilla Formation, a fluvial sedimentary succession in the southern Pyrenees, Spain, based on a suite of sampled paleosols, fluvial stromatolites and pedogenic nodules. Our multiproxy approach involves using carbon and oxygen stable isotope compositions to identify the regional preservation of the MECO, calculate chemical weathering intensity and identify the clay mineralogy of paleosols, as well as to estimate mean annual precipitation using temperature estimates based on clumped isotope compositions of carbonates. Results indicate that the Middle Eocene interval in the south central Pyrenees was characterized by low weathering rates under warm and arid climatic conditions. This is further supported by the presence of smectite, palygorskite, illite, and chlorite, which suggest seasonal rainfall but under generally dry conditions resulting in weak chemical weathering. Importantly, an isotopic excursion indicates a regional, terrestrial impact of the MECO, highlighting that fluvial sedimentary successions even in active foreland basins can represent particularly interesting terrestrial archives of past changes in global climate.