Terrestrial paleoenvironment characterization across the Permian–Triassic boundary in South China

Abstract

a b s t r a c tWell-preserved marine fossils in carbonate rocks permit detailed studies of the end-Permian extinction event in the marine realm. However, the rarity of fossils in terrestrial depositional environments makes it more challenging to attain a satisfactory degree of resolution to describe the biotic turnover on land. Here we present new sedimentological, paleontological and geochemical (X-ray fluorescence) analysis from the study of four terrestrial sections (Chahe, Zhejue, Mide and Jiucaichong) in Western Guizhou and Eastern Yunnan (Yangtze Platform, South China) to evaluate paleoenvironmental changes through the Permian-Triassic transition.Our results show major differences in the depositional environments between the Permian Xuanwei and the Triassic Kayitou formations with a change from fluvial-lacustrine to coastal marine settings. This change is associated with a drastic modification of the preservation mode of the fossil plants, from large compressions to small comminuted debris. Plant fossils spanning the Permian-Triassic boundary show the existence of two distinct assemblages: In the Xuanwei Formation, a Late Permian (Changhsingian) assemblage with characteristic Cathaysian wetland plants (mainly Gigantopteris dictyophylloides, Gigantonoclea guizhouensis, G. nicotianaefolia, G. plumosa, G. hallei, Lobatannularia heinanensis, L. cathaysiana, L. multifolia, Annularia pingloensis, A. shirakii, Paracalamites stenocostatus, Cordaites sp.) is identified. In the lowermost Kayitou Formation, an Early Triassic (Induan) Annalepis-Peltaspermum assemblage is shown, associated with very rare, relictual gigantopterids. Palynological samples are poor, and low yield samples show assemblages almost exclusively represented by spores. A 1 m thick zone enriched in putative fungal spores was identified near the top of the Xuanwei Formation, including diverse multicellular forms, such as Reduviasporonites sp. This interval likely corresponds to the PTB ''fungal spike'' conventionally associated with land denudation and ecosystem collapse. While the floral turnover is evident, further studies based on plant diversity would be required in order to assess contribution linked to the end-Permian mass extinction versus local paleoenvironmental changes associated with the transition between the Xuanwei and Kayitou formations.

Fungal decomposition of terrestrial organic matter accelerated Early Jurassic climate warming

“…Observed fungal spores represent various morphotypes (Fig. 5a–e): amerospores - unicellular, aseptae, sphaerical or sack-shaped spores with a highly variable size; phragmospores - spores with transverse septa, and dictyospores - multicellate spores383940. Superficially, some sphaerical fungal spores can resemble other palynomorphs – i.e.…”

Reply to the comment on “Terrestrial Permian-Triassic boundary in southern China: New stratigraphic, structural and palaeoenvironment considerations” by H. Zhang, Z. Feng, J. Ramezanik, S-Z Shen

“…4B of Zhang et al, 2016), but as for mud clast nodules of the upper part of the Kayitou Formation, these are in fact loose samples that are not located on the general outcrop picture. Moreover, the previously published sedimentological sections (Peng et al, 2005(Peng et al, , 2006Bercovici et al, 2015) did not describe such pedogenic features within the Kayitou and Dongchan formations. In any case, provided that in the Chahe section, the top of the Kayitou and the base of the Dongchuan formations display some pedogenic features, these, as described by Zhang et al (2016), can only be found in what appears to be a folded and faulted transition area (Fig.…”

“…Liu et al, 2012;Deng et al, 2015;Faure et al, 2016). A large number of published studies consider that field areas in Southwest China, and especially the Chahe and Zhejue sections, represent key reference sections to study the terrestrial PTB, the end-Permian mass extinction on land, the gradual transition from terrestrial to marine facies from Permian to Triassic, and to provide correlations with the Meishan marine reference section across the Yangtze Platform (Peng et al, 2005(Peng et al, , 2006Yu et al, 2007Yu et al, , 2008Peng and Shi, 2008;Shen et al, 2011;Bercovici et al, 2015Bercovici et al, , 2016Zhang et al, 2016;Cui et al, 2017). All these studies are based on sedimentological sections considered as stratigraphically continuous across the PT boundary and laterally continuous from the terrestrial environments to the west to the marine deposits in the east.…”

“…Furthermore, there is no indication whether the zircon grains contained in that sediment belong to syn-sedimentary volcanic ashes (i.e., from volcanic ashes deposited directly within the sedimentary sequence without subsequent reworking by alluvial processes) or to reworked tuff deposits. Finally, even if Bed 68 is late Permian in age (assuming that the dated zircon grains belong to syn-sedimentary volcanic ashes), no further argument is provided by Yu et al (2008), Shen et al (2011), Bercovici et al (2015 nor Cui et al (2017) to consider the location of the PTB above Bed 68 (see Fig. 4 in Bourquin et al, 2018).…”

The Triassic to Early Jurassic palynological record of the Tarim Basin, China

“…These Olenekian wetland communities are possibly a response of an allogenic succession of early pioneers represented by bryophytes and lycophytes that produced spores such as Limatulasporites limatulus and Densoisporites spp. This spore-producing vegetation was thriving globally following the end-Permian mass extinction, forming a marker for the recovery successions in continental environments (Looy et al 1999;Grauvogel-Stamm and Ash 2005;Vajda and McLoughlin 2007;Bercovici et al 2015).…”