Michael J. Benton, Massimo Bernardi and Cormac Kinsella (2018)
The Carnian Pluvial Episode and the origin of dinosaurs.
Journal of the Geological Society (advance online publication)
We present new evidence for a major inflection point in the history of tetrapods on land, a jump in the diversification of archosauromorphs, primarily dinosaurs, at 232â230âMa. This corresponds to a long-noted changeover in Triassic terrestrial tetrapod faunas from those dominated by synapsids, many of them holdovers from the Permian, to those dominated by dinosaurs. The dinosaur explosion is shown here to correspond in timing to the Carnian Pluvial Episode (CPE), dated at 232âMa, a time of increased rainfall and perturbation of oceans and atmospheres, followed by substantial aridification. The rock record through the CPE confirms that this event shared many characters with other mass extinctions driven by eruption of large igneous provinces, in this case the Wrangellia flood basalts of the west coast of North America. If this was a catastrophic extinction event, then the environmental perturbations of the CPE explain the sharp disappearance of various terrestrial tetrapods, and the subsequent sharp rise of dinosaurs and perhaps other clades too, especially those that constitute much of the modern terrestrial faunas, such as lissamphibians, turtles, crocodiles, lizards, and mammals.
==
NOT free:
Spencer G. Lucas and Lawrence H. Tanner (2018)
Record of the Carnian wet episode in strata of the Chinle Group, western USA.
Journal of the Geological Society (advance online publication)
The Late Triassic Carnian wet episode was an interval of humid climate evident in the lowermost strata of the Upper Triassic Chinle Group in the western USA. Chinle deposition began with the development of major river systems of the Shinarump Formation and equivalents, laterally equivalent to and/or overlain by floodplain deposits containing kaolinitic gleyed to spodic paleosols and local coal beds. The Chinle strata immediately above these wet episode strata are deposits of smaller rivers that lack coal or carbonaceous strata and contain non-kaolinitic palaeosols that are locally calcareous and vertic, indicative of drier but strongly seasonal climates. The lowermost Chinle strata contain fossil tetrapods, palynomorphs and conchostracans that are consistent with other data that indicate that the basal Chinle strata are of Julian age and immediately overlying lower Chinle strata are early Tuvalian, so these strata are the age of the Carnian wet episode. Identification of a 'long Norian' stage places the Norian base in the Chinle Group near the top of the strata of the wet episode, which means that Norian strata sit directly on early Carnian strata, but there is no unconformity at this level to support recognition of such a long Norian in the Chinle section.
====