Biostromal unit from the Middle Devonian Jinbaoshi Formation, Sichuan, Southwest China: Implications for ecological structure of coeval reef communities

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2022-12, Vol.608, p.111272, Article 111272
• Main Authors: Huang, Jiayuan, Li, Yue, Kershaw, Stephen, Guo, Wen, Liang, Kun, Qie, Wenkun
• Format: Article
• Language: English
• Subjects: Coral-stromatoporoid biostromal unit; Ecological unit; Givetian; Longmenshan area; Palaeoenvironment
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2022.111272

This study provides a comprehensive palaeontological and palaeoecological analysis of a middle Givetian (Middle Devonian) coral-stromatoporoid biostromal unit from the upper member of the Jinbaoshi Formation, northern Sichuan Province, Southwest China. The biostromal unit is 17.7 m of medium- to thick-bedded limestones, and lacks observable morphological relief in the field. Diverse shallow marine benthic fossils are common elements of the biostromal unit encompassing stromatoporoids (7 genera), tabulate corals (4 genera), brachiopods (2 genera), plus unidentified rugose corals, chaetetids, bryozoans, tubeworms, ostracods, gastropods, crinoids and calcimicrobes. In terms of the biotic composition and biostrome-building contributors, three ecological units are recognized: Alveolites–Clathrocoilona community (EU 1), Salairella–Pseudotrupetostroma community (EU 2) and Scoliopora–Idiostroma community (EU 3). High fragmentation of bioclasts partially with micritic envelopes in wackestone, packstone to grainstone matrix and the dominance of low-profile stromatoporoids indicate deposition in shallow water conditions with episodic high sedimentation rate and frequent turbulent periods. Muddy silt- to sandstone facies overlie the biostromal unit, and are interpreted to represent a shallowing-up sequence, together with terrigenous input, thus triggering termination of the biostromal unit. This biostromal unit is similar to the other early to middle Givetian reefs of South China, East Australia, West Europe, East Europe and North Africa in relation to their fossil composition and reef-building characteristics. The stability of the reef communities (i.e. no conspicuous extinction) and common occurrence of unusual reef structures (e.g. coverstone) are thus interpreted as significant biotic factors for the expansion of large-scale ecosystems during the Phanerozoic reef-building acme. •Coral-stromatoporoid biostromal unit is detailed reported in Givetian of northern Sichuan Province.•Three distinctive ecological units were identified in the biostromal unit.•Large extensive laminar stromatoporoids imply coverstone-dominated reef limestone.•Laminar stromatoporoids and fragmented bioclasts indicate a relatively turbulent environment.•Biotic contribution of reef organisms is essential in expansion of large-scale reef ecosystems.