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

摘要

An expanded record (similar to 14 m) of the Paleocene-Eocene Thermal Maximum (PETM), a transient period of extreme global warming that occurred similar to 56 million years ago, has been found based on calcareous nannofossil and foraminifera stratigraphy in the deep marine Rio Gor section, Subbetic Zone, SE Spain. During the early Palaeogene the Subbetic Zone was situated at a mid-palaeolatitude (similar to 32 degrees 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 Rio Gor in similar to 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 delta C-13 carbon isotope composition (from - 8 parts per thousand to - 20.7 parts per thousand), and therefore distorts the global carbon isotopic signature of this thermal event at Rio 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 Rio 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.