Sunday, February 21, 2016

Cooling in an Early Devonian Greenhouse Climate? From a VERY hot Lochkovian to a hot & Humid Pragian

Warming or cooling in the pragian? Sedimentary record and petrophysical logs across the lochkovian-pragian boundary in the Spanish Central Pyrenees


Slavik et al


High-resolution petrophysical correlation methods were applied, for the first time, to mid-Paleozoic rocks of the Pyrenees. The methods included magnetic susceptibility measurements (MS), gamma-ray spectrometry (GRS), and alignment of MS logs using the dynamic time warping (DTW) algorithm. Conodont biostratigraphy provided the basic framework necessary for work with the GRS and MS logs. In spite of differences in the sediment patterns and accumulation/erosion rates, the logs from two selected sections in the Spanish Central Pyrenees show a striking symmetry that correlates well with the previously published logs from the Barrandian area in the Czech Republic. The high similarity between the petrophysical records from paleogeographically related but distant areas has the potential to contribute to the current discussions about the eustatic and climatic changes that took place in the overall greenhouse settings, where evidence for any polar ice sheets is still absent. In addition to the extant evidence of a major Lochkovian-Pragian offlap, combined with sea level lowering known from the North America, evidence about a major sea level fall and drastic reconstruction of the climatic system in the Pragian is now expanding over significant parts of the peri-Gondwanan belt. The data from Spain provide many new details about this change, including the phenomenon of a stratigraphically condensed upper Lochkovian, a dramatically different type of sedimentation in the Pragian, and a GRS-Th-and-MS anomalous stratigraphic interval in the middle Pragian. The multifaceted evidence allows us to determine the essential parts of the Pragian as a still “hot and humid” period, even with the strong differences from the possibly “extremely hot” Lochkovian.

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