Microcodium-rich turbidites in hemipelagic sediments during the Paleocene–Eocene Thermal Maximum: Evidence for extreme precipitation events in a Mediterranean climate (Río Gor section, southern Spain)

An expanded record (~14 m)of the Paleocene–Eocene Thermal Maximum (PETM), a transient period of extreme global warming that occurred ~56 million years ago, has been found based on calcareous nannofossil and foraminifera stratigraphy in the deep marine Río Gor section, Subbetic Zone, SE Spain. During the early Palaeogene the Subbetic Zone was situated at a mid-palaeolatitude (~32° N), in the NW margin of the Tethyan Ocean. The most prominent features of the studied PETM interval are a significant increase in the proportion of palygorskite, a concurrent decrease in kaolinite and a high content in resedimented Microcodium remains, all of which imply arid/semiarid conditions, one of the distinctive features of the Mediterranean climate. The analysis of the event therefore provides new insights on the hydrological changes induced by the PETM in this climate. Microcodium remains mainly occur at Río Gor in ~450 thin-bedded turbidites, but also occurs redistributed by bioturbation throughout the entire PETM interval, and several centimetres below and above it. Microcodium has a very negative δ13C carbon isotope composition (from −8‰ to −20.7‰), and therefore distorts the global carbon isotopic signature of this thermal event at Río Gor. The increase in palygorskite indicates an intensification of aridity in the study area during the PETM. The Microcodium formed in or around roots of plants growing in subaerially exposed, uplifted massifs of Jurassic carbonates adjacent to the Río Gor area. The resedimentation in the deep sea as turbidites required major runoff episodes after heavy rainfalls. The concurrence of increased aridity and frequent episodes of precipitation extremes demonstrates that the PETM greatly enhanced the typical seasonal contrast of the Mediterranean climate in the Subbetic Zone.