Monday, December 07, 2015

Climate Variability during the Carnian Pluvial Phase (Carnian Triassic Wet Phase)

Climate variability during the Carnian Pluvial Phase — A quantitative palynological study of the Carnian sedimentary succession at Lunz am See, Northern Calcareous Alps, Austria


Mueller et al


The Middle and Upper Triassic prevailing dry climate was interrupted by a global phase of increased humidity during the Early Carnian, the Carnian Pluvial Phase (CPP). It started at the Julian 1–2 boundary and lasted approximately until the latest Julian or early Tuvalian. In the Tethys this is reflected by a change from limestone deposits to, first, organic rich mudstones and then to siliciclastics. The CPP occurred along the northern rim of the Tethys and is reported from many locations within and surrounding Europe. In this study samples from Lunz am See in Austria were analyzed for palynology and for bulk carbon isotope values covering a 450 m thick succession. A known − 3‰ bulk organic carbon isotope excursion, possibly as a result of the eruption of large amounts of volcanogenic material, in the Göstling Member and the basal Reingraben Formation has been confirmed. A total of five distinctive palynology assemblages were recognized and correlated regionally. While the under- and overlying formations yield terrestrial and subordinate also marine palynomorphs, the palynoflora of the Lunz Formation is near wholly terrestrial in origin. Climate trends were inferred from multivariate statistical analysis (PCA) of the palynofloral record. Palynomorphs show a general trend from a dry climate during the Julian 1 to wetter conditions during the Julian 2. The wetter conditions were periodically interrupted by shorter periods of dryer climate. In terms of temperature trends the climate was warmer during the early Julian 2 which corresponds with the deposition of the Reingraben Formation, temperature decreased again and remained fairly stable during most of later part of the Julian 2, which corresponds to the deposition of the Lunz Formation. This study correlates with similar observations from other locations from the western Tethys region that support the theory of a wide-ranging to global Carnian Pluvial Phase.

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