Integrated Sedimentologic/Magnetic Records of Late Paleozoic Climate, Western Pangea

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9805130SoreghanThe history of late Paleozoic climate is of great interest. Polar glaciation characterized Pennsylvanian time, and continental assembly apparently initiated megamonsoonal conditions by Permian time. These events are likely recorded by significant climatic trends and/or fluctuations, but the evidence for and character of these climate changes remain poorly constrained. The objective of the proposed research is to (1) confirm the feasibility of obtaining paleoclimatic data from upper Paleozoic loessite using an integrated sedimentologic/rock-magnetic approach, and (2) apply these techniques to elucidating low-latitude paleoclimate of western Pangea. Recent studies of Quaternary-Pliocene loess sequences in many regions have demonstrated the utility of rock-magnetic analyses for paleoclimate studies. These studies indicate pedogenic production of ultra-fine and fine-grained magnetic material during relatively warm, wet (interglacial) periods. Magnetic proxies signal climatically and temporally dependent soil formation even where sedimentologic evidence for pedogenesis is equivocal. Our preliminary analyses establish that susceptibility enhancement linked to pedogenically formed magnetic material is preserved in very ancient loessite. We propose to extend these analyses by collecting detailed sedimentologic and rock magnetic data from upper Paleozoic (Pennsylvanian-Permian) loessite sections exposed in Colorado and Utah. In the lab, we will perform rock-magnetic analyses (e.g., normalized ferrimagnetic susceptibility, frequency-dependent susceptibility, anhysteretic remanent magnetization, low-temperature remanence) to access the origin of magnetic susceptibility variations, and integrate these data with sedimentologic/paleopedologic and diagenetic data to evaluate the paleoclimatic signal. Ultimately, we hope to link these data to an improved age resolution in order to assess short-and long-term climatic trends across the middle Pennsylvanian-early Permian interval both within and between the target sections. To our knowledge, our effort represents the first attempt to apply rock-magnetic techniques for paleoclimatic analyses in pre-Cenozoic (Plio-Pleistocene) loessite; we believe that demonstration of the applicability of an integrated sedimentologic/rock-magnetic approach to upper Paleozoic loessite will represent a significant (1) technical advance for paleoclimatic studies in very ancient strata, and (2) contribution toward our comprehension of the low-latitude paleoclimate of late Paleozoic western Pangea.