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1.
Introduction
Abundant red-bed facies, with evaporites, aeolian sands and evidence of ephemeral lakes, rivers and extreme seasonality, has led to a long-held prevailing view that the climate through much of the Triassic Period was predominantly arid or semi-arid at least across Europe and North America (Crowley, 1994; Lucas & Orchard, 2013). In 1989 two of us (MJS, AR) collated evidence, from published sources as well as our own observations, for a significant increase in humidity during the early Julian to Tuvalian of the Carnian Age. The onset and cessation of this humid episode appeared to be broadly synchronous with significant biotic changes, both as extinctions and diversifications (Simms & Ruffell, 1989, 1990). Despite increased interest in palaeoclimate studies through the 1990s, this hypothesis was not immediately embraced by the geological community and aroused significant opposition in some quarters both in Europe (Visscher et al. 1994) and North America (P. Olsen, pers. comm. 1995). However, the ensuing two decades has seen a growing body of evidence (summarized below) in support of our original hypothesis that the Carnian was significantly more humid than at other times during the Triassic Period.
2.
Challenges to the humid episode theory
Following the publication of Simms & Ruffell (1989, 1990), there have been more than 20 publications that have supported the hypothesis (the key 12 works are included in Table 1) and one publication, and a website, that have cast doubt on the theory. The key works that were negative, positive or modified the theory are summarized in Table 1. However, some of the publications misinterpret what Simms & Ruffell (1989) suggested this episode to be and, furthermore, the two more critical works include information that supports our hypothesis. The desire on our part to clarify some issues drove us to write this review article. Visscher et al. (1994) rather provocatively entitled their paper 'Rejection of a Carnian (Late Triassic) "pluvial event" in Europe'. Significantly they substituted the word 'event' in place of 'episode', as was used in Simms & Ruffell (1989) or 'phase', as in Simms & Ruffell (1990). In summary, Visscher et al. (1994) suggested that a widespread inundation was not necessary in order to explain the...