Triassic

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Abstract
"The Triassic rocks of Great Britain, if one may judge from statements in the textbooks, are among the simplest of our deposits; but a closer inspection reveals a number of very difficult and intensely interesting problems hidden behind this apparent simplicity." L. J. Wills, 1910. During latest Permian times, northerly-sourced epeiric marine environments, in which the Zechstein sequence formed, were replaced by predominantly clastic sedimentary regimes. The succeeding Triassic deposits, representing about 45 million years, are largely continental; some formed under transient marine influences but few are biogenic. They succeed Permian deposits conformably and overstep these to rest unconformably upon older rocks. Over much of the region the youngest Triassic deposits represent a transgression that re-established marine environments before the end of the Period. The region lay in Laurasia, the northern part of the Pangaean supercontinent, some 15 to 20° north of the equator and close to the northern margin of the Tethys (Tollmann & Kristan-Tollmann 1985) but separated from that ocean by the Variscan mountain chain, denudation of which continued from Permian into Triassic times. A monsoonal climate is envisaged (Robinson 1973; Parrish & Curtis 1982; Parrish et al . 1982). The principal onshore Triassic occurrences are in England and Northern Ireland; others in the British Isles are relatively minor (Warrington et al . 1980, figs 2 & 3). Concealed developments in The Netherlands (Map Tr2) and northeast France (Mégnien & Mégnien 1980; Debrand-Passard 1980; Berners et al . 1984; Maps Tr2-3b & 4c) are contiguous with the tripartite German sequence from