Microconchids from microbialites near the Permian-Triassic boundary in the Zuodeng Section, Baise area, Guangxi Zhuang Autonomous Region, South China and their paleoenvironmental implications

Abundant isolated specimens of microconchid tubes have been extracted from a microbialite deposit near the Permian-Triassic boundary (PTB) in the Dajiang section, southern Guizhou Province, South China. They are assignable to Microconchus aff. utahensis, M. aff. aberrans and Helicoconchus aff. elongatus, all of which possess micro-lamellar tube walls. Quantitative analysis of bulk samples indicates that most microconchids occur in the upper part of the PTB microbialite deposit and show substrate selectivity for bioclastic grainstone-packstones. In contrast, very few microconchids were found in the rocks bearing well-developed microbialite structures. Both stratigraphical and substrate preferences indicate proliferation of microconchids coincided with an ebb of microbialite development. Microconchids therefore only proliferated in local niches in which microbial activities were not very active within the PTB microbialite ecosystem. The presence of abundant microconchids further strengthens the impression that PTB microbialite metazoans are much more diverse than previously thought. The end-Permian mass extinction is calibrated to the base of microbialite deposit in South China. Thus, abundant microbialite metazoans, such as ostracods, lingulid brachiopods, microgastropods and microconchids, together with the considerable, temporarily surviving faunas reported from non-microbialite PTB sections in South China, indicate that metazoans diversified immediately after the first episode of the end-Permian mass extinction, supporting the scenario that marine ecosystems underwent episodic collapses during the devastating biocrisis over the

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“…; Yang et al . ). Thus, the microbialite ecosystems are characterized by the participation of abundant ‘disaster forms’ (Yang et al .…”

Section: Discussionmentioning

confidence: 97%

Palaeoecology of microconchids from microbialites near the Permian–Triassic boundary in South China

Yang

Chen

Wang

et al. 2015

LET

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“…Yang et al . () described these morphologies from the microbialites at the Dajiang section that were helically coiled were either assigned to the microconchids Helicoconchus aff. elongatus or Microconchus aff.…”

Section: Microconchus Aberrans Hohenstein Figure Q–smentioning

confidence: 99%

Early Triassic benthic invertebrates from the Great Bank of Guizhou, South China: systematic palaeontology and palaeobiology

Foster

Lehrmann

Hirtz

et al. 2019

Papers in Palaeontology

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To further our understanding of the evolution, selectivity and ecological composition of marine communities following the latest Permian mass extinction, new collections from underrepresented regions in the immediate extinction aftermath are required. Here, we provide new systematic data and the first palaeobiological account of the benthic invertebrate community from the Great Bank of Guizhou, South China. We systematically describe three brachiopod species, 26 bivalve species, 11 gastropod species, 1 microconchid and 1 crinoid species. The descriptions include 5 new species; 2 bivalve species (Hoernesia? danisae, Atomodesma? hautmanni) and 3 gastropod species (Donaldina erwini, Cossmannina alfischeri and Vernelia samae). This is the most species-rich benthic community known so far from the extinction aftermath, which is typically characterized by a high proportion of Permian holdover genera and cosmopolitan taxa. Taxonomically, this community is different from coeval faunas with dissimilarity values >60%. Ecologically, however, this fauna is similar to faunas from the Dolomites (Italy) and East Greenland. This new data, therefore, suggests that the lower Griesbachian invertebrate faunas were taxonomically heterogeneous, whereas ecologically they were relatively homogenous. The marine community on the Great Bank of Guizhou records genera that survived the mass extinction event with some, but not all, recording a size reduction, that is, the Lilliput effect. The absence of large body fossils and the preferential survival of small species suggest that the mass extinction event was size-selective.

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“…Small-sized gastropods, thin-shelled bivalves, and ostracods are abundant in the groundmass, while serpulid worm tubes (assigned to microconchids, Zaton et al, 2013;Yang et al, 2015aYang et al, , 2015b are present mostly in the sparite-filled cavities. Ezaki et al (2008), Lehrmann et al (2015a) and Baud et al (2005) described a similar facies in earliest Triassic microbialites from the Nanpanjiang Basin and from western Taurus (SW Turkey).…”

Section: Nanemmentioning

confidence: 99%

Onset, development, and cessation of basal Early Triassic microbialites (BETM) in the Nanpanjiang pull-apart Basin, South China Block

et al. 2017

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New investigations in the Nanpanjiang Basin indicate that the onset of the iconic microbialites associated with the Paleozoic-Mesozoic boundary was Early Triassic in age. Bathymetry (water agitation, oxygenation, light penetration) and clastic load are shown to have exerted a direct control on the growth of microbialites. Carbonate supersaturation is also required for the deposition of the microbialites. Bathymetric control is further corroborated by the topographic inheritance of a latest Permian pull-apart basin into Early Triassic times, with a distribution of basal Early Triassic microbialites (BETM) restricted to uplifted blocks. This control is also reflected by the accumulation of carbonaceous black shales in adjacent troughs. The geographically most extensive Nanpanjiang BETM bloomed on a large NW-SE trending uplifted block exceeding 12,000 km2 (Luolou Platform) centered on northwestern Guangxi. Post-Triassic displacements along the Youjiang Fault obscure the paleogeographic relation of BETM exposed west of this fault. Triassic foraminifers occur in the basal most BETM episode, which is locally bracketed by high-energy grainstones made of reworked Permian foraminifers. Therefore, the Permian-Triassic boundary (PTB) is within the unconformity that separates the Late Permian Heshan Fm. from the basal most BETM. Where accommodation space was sufficient, up to five event surfaces are associated with the unconformity. Microfacies analysis supports chemical dissolution but did not reveal evidence for subaerial erosion, although intercalated grainstone made of Permian foraminifers indicate reworking. Chemical dissolution and mechanical erosion both conceivably contributed to the genesis of the unconformity. The upward shift from tabulated to domical microbial build-ups is accompanied by accumulation of coquinoid lenses between domes, which indicates deepening of the Luolou Platform BETM. The main drowning resulting from both regional tectonic subsidence and a global sea-level rise led to the cessation of the BETM that were buried under predominant fine siliciclastics. Any concomitant change in sea water chemistry appears unlikely.

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Microconchids from microbialites near the Permian-Triassic boundary in the Zuodeng Section, Baise area, Guangxi Zhuang Autonomous Region, South China and their paleoenvironmental implications

Cited by 28 publications

References 51 publications

Palaeoecology of microconchids from microbialites near the Permian–Triassic boundary in South China

Palaeoecology of microconchids from microbialites near the Permian–Triassic boundary in South China

Early Triassic benthic invertebrates from the Great Bank of Guizhou, South China: systematic palaeontology and palaeobiology

Onset, development, and cessation of basal Early Triassic microbialites (BETM) in the Nanpanjiang pull-apart Basin, South China Block

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