Abstract

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 palaeosols 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.

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