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

Détails

ID Serval
serval:BIB_C07C39706911
Type
Article: article d'un périodique ou d'un magazine.
Sous-type
Etude de cas (case report): rapporte une observation et la commente brièvement.
Collection
Publications
Titre
Onset, development, and cessation of basal Early Triassic microbialites (BETM) in the Nanpanjiang pull-apart Basin, South China Block
Périodique
Gondwana Research
Auteur(s)
Bagherpour Borhan, Bucher Hugo, Baud Aymon, Brosse Morgane, Vennemann Torsten, Martini Rossana, Guodun Kuang
ISSN
1342-937X
Statut éditorial
Publié
Date de publication
2017
Volume
44
Pages
178-204
Langue
anglais
Résumé
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 inheritance of the topography of a latest Permian pull-apart basin into Early Triassic times, with a distribution of basal Early Triassic microbialites (BETM) restricted to uplifted blocks and 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 12,000km2 (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.
Mots-clé
Permian-Triassic boundary, Microbialites, Bathymetry, Oxygen, Alkalinity
Création de la notice
30/10/2019 18:17
Dernière modification de la notice
31/10/2019 17:18
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