An exceptional window into the Triassic-Jurassic boundary on the margins of the Ardenno-Rhenish Massif: stratigraphy and palaeontology of the Irrel section (Rhineland-Palatinate, Germany)

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The Triassic-Jurassic (T/J) boundary witnessed one of the five major mass extinctions during the Phanerozoic, paving the way towards the evolution of modern ecosystems. However, the study of biotic change during this interval is hampered by the scarcity of outcrops exposing the T/J-boundary without major interruptions or abrupt facies change. Here, we present a previously undocumented succession of Rhaetian (Upper Triassic) to Hettangian (Lower Jurassic) strata, exposed on two sections along the banks of the river Prüm near the town of Irrel, Rhineland-Palatinate, Germany. The new succession holds an unusual palaeogeographic position squeezed between the Rhenish and London Brabant (including the Ardennes) massifs, thus filling a gap in the T/J-boundary record of the Central European Basin. It includes some unusual facies such as a thick and highly fossiliferous, conglomeratic bonebed close to the top of the middle Rhaetian and bituminous black claystones in the middle Hettangian. Finally, it stands out in yielding well preserved fossils of taxa that are rare or undocumented in the region. We provide a comprehensive account of the lithostratigraphy of the new succession and assess its biostratigraphic framework using ammonite, ostracod and palynomorph occurrences.