The ICDP Deepdust project -Probing continental climate of the Late Paleozoic icehouse-greenhouse transition
Résumé
The tectonic, climatic, and biotic events of the Permian are amongst the most profound in Earth history. Global orogeny leading to Pangaean assembly culminated by early-middle Permian time, and included multiple orogenic belts in the equatorial Central Pangaean Mountains, from the Variscan-Hercynian system (east) to the Ancestral Rocky Mountains (west). Earth's penultimate global icehouse peaked in early Permian time, transitioning to full greenhouse conditions by late Permian time, archiving our only example of icehouse collapse while the Earth had an expansive terrestrial biosphere. The Late Paleozoic Icehouse was the longest and most intense glaciation of the Phanerozoic, with hypothesized low-moderate-elevation glaciation posited for both eastern and western tropical Pangaea during early Permian time. The atmosphere during this icehouse experienced the lowest CO2 and highest O2 levels of the Phanerozoic, but average CO2 levels were comparable to our present, rapidly warming climate. Fundamental shifts occurred in atmospheric circulation: a global megamonsoon developed and the tropics became anomalously arid with time. We have assembled expertise in sedimentary and planetary geology and paleoclimatology, climate modeling, structural geology, geochronology, paleobotany, geomicrobiology, and quantitative cyclostratigraphy. We will seek to elucidate paleoclimatic conditions and forcings through the Permian at temporal scales ranging from the sub-millennial to the Milankovitch and beyond by acquiring continuous core in continental lowlands known to harbor stratigraphically complete records dominated by loess and lacustrine strata, and adjacent upland-proximal sites hypothesized to have hosted glaciation. We have identified locales in the western U.S. and France as the 2 key coring sites globally to achieve our objectives, as these represent the western and eastern limits, respectively of the Pangaean tropics. Additionally, the Anadarko Basin (Oklahoma) and Paris Basin (France) archive arguably the most complete continental Permian sections at the paleoequator, and their adjacent paleo-uplands are the only sites globally for which Permian tropical glaciation has been hypothesized. We will also address the nature and character of the modern and fossil microbial biosphere and exhumation histories of source regions. The Deepdust project is still under development and follows the ICDP proposal submission process; our ICDP Workshop took place last March in Oklahoma (USA).