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

Abstract

The generally arid Late Triassic climate was interrupted by a wet phase during the mid Carnian termed Carnian Pluvial Episode (CPE). Quantitative palynological data from the Mercia Mudstone Group in the Wessex Basin (UK), reveals vegetation changes and palaeoclimate trends. Palynostratigraphy and bulk organic carbon isotope data enable 9 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 also reported from the Schilfsandstein in Germany. Hounslow et al. (2002) suggested that the Ladinian-Carnian boundary may be in the upper part of the Sidmouth Mudstone Formation and the Carnian-Norian boundary near the boundary between the DMF and overlying Branscombe Mudstone Formation, however, this was based on hitherto unpublished magnetostratigraphic data. The DMF crops out along coastal cliffs between Higher Dunscombe Cliff and Strangman`s Cove and has a wide distribution in the sub-surface of the Wessex Basin (Gallois & Porter 2006; Porter & Gallois 2008) (Fig. 1). The DMF was cored in two boreholes Wiscombe Park 1 and 2 (WP-1 and 2) about 5 km north of the coastal outcrop (Porter & Gallois 2008) (Fig. 1). 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. However, 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.

Carnian (Late Triassic) C-isotope excursions, environmental changes, and biotic turnover: a global perturbation of the Earth's surface system

“…This is an extremely interesting finding. Indeed, a second negative carbon isotope excursion within the Julian 2 has been recently found also in organic carbon from marine sections of northwestern Tethys realm (Italy and Hungary), and in successions from continental Pangea (Miller et al 2017;Baranyi et al 2018;Dal Corso et al 2018b), as well as in carbonate carbon from a marine succession in Southwest China (Sun et al 2016). During the Carnian Oman was located c. 30°S, and these new data from the southern hemisphere add a precious tessera in our understanding of Carnian carbon cycle changes.…”

“…Franz et al documented a clear deviation of the clay chemistry and type of palaeosols in the Shilfsandstein with respect to previous and subsequent units of the Central European Basin that could be explained, however, without changes of rainfall. This work should be compared with Barrenechea et al (2018), Lucas & Tanner (2018) and Baranyi et al (2018), who studied similar continental successions and found evidence for climate change, albeit less intense than suggested by Simms & Ruffell (1989) and recorded in most marginal marine successions of Tethys. The debate is still open.…”

“…The debate is still open. Baranyi et al (2018) continue the reliable tradition of studying Carnian palynofloras with an examination of the Mercia Mudstone Group (syn: Keuper facies) in southern England. New organic carbon isotope data from outcrop material from Strangman's Cove (Devon) are also presented and integrate previous data from core material of the Mercia Mudstone Group (Miller et al 2017).…”

“…This is particularly important, because the negative δ 13 C shifts during the CPE interval have been so far detected mainly through the analysis of bulk organic matter and biomarkers (leaf wax n-alkanes, and algae isoprenoid lipids and n-alkanes; e.g. Dal Corso et al 2012Corso et al , 2018bMiller et al 2017;Baranyi et al 2018). In the reference sections of the Dolomites, the bulk carbonate carbon isotope record does not parallel the organic carbon isotope record and does not record negative δ 13 C shifts (Dal Corso et al 2015).…”

Dryland continental mudstones: Deciphering environmental changes in problematic mudstones from the Upper Triassic (Carnian to Norian) Mercia Mudstone Group, south‐west Britain

“…alluvial sheet sandstones, evaporite pseudomorphs, tepees and sulphates) recognized in sheet sandstone facies. This culminated in deposition of the widespread, and relatively thicker, fluvial sands of the Arden Sandstone Formation and its wider correlatives that form a key line of evidence for the Carnian Pluvial Episode, a period of globally enhanced precipitation (Simms & Ruffell, ; Ruffell et al ., ; Baranyi et al ., , ).…”