On land record of the Oligocene–Miocene transition. Climatic insights from a multiproxy study on a lacustrine system in the Ebro Basin (NE Iberia, SW Europe)

Abstract

The Oligocene–Miocene Transition is associated with climatic changes primarily related to Antarctic phenomena (Mi-1 glacial event), the effects of which are not well known on land. This work examines a continuous, well dated distal-alluvial and carbonate lacustrine and palustrine succession (23.56 to 22.1 Ma) in the Ebro Basin, through sedimentological analysis and carbonate δ¹³C and δ¹⁸O composition, to unveil climate-related variations and compare them with those in other terrestrial and marine Mi-1 records. Results indicate carbonate deposition in freshwater bodies having moderate-to-high plant-derived CO₂ supply and being affected by lake-level variations and evaporative processes (causing Mg carbonates precipitation in the Oligocene alluvial and saline mud flats), within a closed-lake environment. A significant decline in temperature and humidity centered around 23.16–23.14 Ma seems to correlate with Mi-1, but with earlier onset and earlier minimum temperature and humidity (minima ca 80–90 ka before) in the lake system. Low temperature and humidity are followed by oscillating but overall increasing humidity, varying Precipitation/Evaporation and slight warming until 23.1 Ma, coinciding with the development of mainly lacustrine and palustrine environments from ca 23.15 Ma onwards. Two falls in δ¹⁸O that concur with opposed δ¹³C trends, representing dissimilar climatic conditions, appear to match different long-term orbital configurations. The earlier response of the Ebro Basin-lake system to global changes, e.g. the Mi-1 event, is consistent with results from other continental records, and implies the sensitivity of lake systems to record initial stages of ongoing global changes, and the more lagging responses of marine systems to continental ¹²CO₂-input variations.