Abstract
AbstractThe Late Triassic deposits of the Sichuan Basin, southwestern China are significant for hosting abundant and diverse fossil assemblages including plants (containing spores and pollen), bivalves and insects. However, the Late Triassic palaeoecological variations are still poorly documented in this region. Here we present results from a palynological study from the Upper Triassic Xujiahe Formation in Hechuan of Chongqing, southern Sichuan Basin. The palynological analysis revealed a well-preserved terrestrial palynoflora of high diversity, comprising 184 species in 75 genera of spores and pollen. Three palynological assemblages were recognized, reflecting terrestrial successions throughout the entire interval with significant changes in the vegetation. Cycads/bennettites/ginkgophytes and conifers show an increasing trend into younger deposits, while ferns and lycopsids decrease in relative abundance. The Late Triassic vegetation underwent changes from lowland fern forest to a mixed forest with more canopy trees. We applied the Spore-pollen Morphological Group (SMG) method and Sporomorph EcoGroup (SEG) model to interpret the palaeoclimate features. The results reveal that the lower part of the Xujiahe Formation was deposited under relatively warm and humid conditions with an overall cooling and drying trend from latest Norian to Rhaetian time, accompanied by a general decrease of ferns and simultaneous increase of gymnosperms, and a decline in diversity of miospores. This study presents data on variations within the terrestrial ecosystem prior to the end-Triassic extinction event in the Sichuan Basin, and therefore provides important information for understanding the changes in the vegetation preceding the end-Triassic event.
Highlights
IntroductionThe end-Triassic mass extinction (201.36 ± 0.17 Ma; Schoene et al 2010; Wotzlaw et al 2014) is considered as one of the five largest Phanerozoic extinction events (Raup & Sepkoski, 1982; Sepkoski, 1996; Hesselbo, McRoberts & Pálfy, 2007), and massive biotic crises occurred in both the marine and terrestrial realms (Colbert, 1958; Pálfy et al 2000; Hallam, 2002; Hesselbo et al 2002; Olsen et al 2002; Akikuni et al 2010)
The SMG (Spore-pollen Morphological Group) method outlined by Visscher & Van der Zwan (1981) and the Sporomorph EcoGroup model (SEG) (Sporomorph EcoGroup) model established by Abbink (1998) and Abbink, van Konijnenburg-van Cittert & Visscher (2004) were applied in this study to reconstruct the palaeoclimatic variations
The above outlined climate change is consistent with macrofloral studies of the Xujiahe Formation, which implied a palaeoclimatic trend from humid to arid conditions (Huang & Lu, 1992)
Summary
The end-Triassic mass extinction (201.36 ± 0.17 Ma; Schoene et al 2010; Wotzlaw et al 2014) is considered as one of the five largest Phanerozoic extinction events (Raup & Sepkoski, 1982; Sepkoski, 1996; Hesselbo, McRoberts & Pálfy, 2007), and massive biotic crises occurred in both the marine and terrestrial realms (Colbert, 1958; Pálfy et al 2000; Hallam, 2002; Hesselbo et al 2002; Olsen et al 2002; Akikuni et al 2010). The most commonly accepted killing mechanism is rapid global warming driven by outgassing of CO2 and release of methane (McElwain, Beerling & Woodward, 1999; Tanner, Lucas & Chapman, 2004; Bonis, Ruhl & Kürschner, 2010; Whiteside et al 2010; Ruhl et al 2011; Schaller, Wright & Kent, 2011; Steinthorsdottir, Jeram & McElwain, 2011; Schaller et al 2012), and acidification of surface waters and terrestrial environments (van de Schootbrugge et al 2009; Greene et al 2012; Hönisch et al 2012; Richoz et al 2012; Callegaro et al 2014; Ikeda et al 2015; Bachan & Payne, 2016; van de Schootbrugge & Wignall, 2016).
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