A continental record of the Carnian Pluvial Episode (CPE) from the Mercia Mudstone Group (UK): palynology and climatic implications

Viktória Baranyi,Mark W Hounslow,Alastair Ruffell,Wolfram M Kürschner,Charlotte S Miller

doi:10.1144/jgs2017-150

Abstract

The generally arid Late Triassic climate was interrupted by a wet phase during the mid-Carnian termed the Carnian Pluvial Episode (CPE). Quantitative palynological data from the Mercia Mudstone Group in the Wessex Basin (UK) reveal vegetation changes and palaeoclimate trends. Palynostratigraphy and bulk organic carbon isotope data allow correlation to other Carnian successions. The palynostratigraphy indicates that the Dunscombe Mudstone is Julian and the lowest part of the overlying Branscombe Mudstone Formation is Tuvalian. The Aulisporites acme characterizing the CPE in Tethyan successions and the Germanic Basin is missing in the UK. The quantitative palynological record suggests the predominance of xerophyte floral elements with a few horizons of increased hygrophytes. A humidity signal is not seen owing to the dry climate in central Pangea. Also, the signal might be masked by the overrepresentation of xerophyte regional pollen and the predominance of xerophyte hinterland flora. The bias towards regional pollen rain is enhanced by the potential increase in continental runoff related to seasonally humid conditions and differences in pollen production rates and transport mechanisms. The vegetation of British CPE successions suggests a more complex climate history during the Carnian, indicating that the CPE is not recognized by the same changes everywhere. Supplementary material: A detailed lithological log of the Strangman9s Cove (Devon) outcrop with the description of the Mercia Mudstone Group lithostratigraphical units, a description of the laboratory techniques, seven photoplates with selected spores and pollen grains, a list of all identified palynomorphs, Excel sheets with the palynological and palynofacies counts, bulk organic carbon isotope ratios and total organic carbon values of the Strangman9s Cove outcrop are available at https://doi.org/10.6084/m9.figshare.c.4138085

Highlights

Laxitexella multireticulata within the Lincombe Member in the coastal sections which is indicative of the early Carnian L. mucroreticulata Zone (Kozur & Weems 2010)
Here we provide quantitative palynological data from four terrestrial successions of the Dunscombe Mudstone Formation from the UK and interpret the vegetation changes and palaeoclimate trends
The shift to relatively more humid conditions is manifested in the expansion of hygrophyte vegetation in many locations worldwide (Roghi et al 2010)

Summary

Introduction

Laxitexella multireticulata within the Lincombe Member in the coastal sections which is indicative of the early Carnian L. mucroreticulata Zone (Kozur & Weems 2010). This species is common in the early Carnian ‘Estheria Beds’ (in the upper Grabfeld Formation in Germany), but is reported from the Schilfsandstein in Germany. Further north in Somerset, several lenticular sandstone units of the Arden Sandstone Fm can be found around Taunton, North Curry and Sutton Mallet areas (Fig. 1), similar to the Lincombe Member of the Dunscombe Mudstone Fm. the stratigraphic correlation of these arenaceous units remains uncertain (Gallois 2003; Gallois & Porter 2006). On lithostratigraphical and palaeoenvironmental grounds, Howard et al (2008) argued that the sandstone bodies in Somerset are contemporaneous with the Lincombe Member, but Gallois (2001) suggested they might occur in a higher stratigraphic position within the DMF compared to the Lincombe Member

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Conclusion