Microbial mounds prior to the Frasnian-Famennian mass extinctions, Hantang, Guilin, South China

Abstract

Late Frasnian mounds of the Yunghsien Formation, Guilin, South China, developed as part of the Guilin platform, mostly in reef‐flat and platform margin settings. Microbial mounds in platform margin settings at Hantang, about 10 km west of Guilin, contain Frasnian biota, such as Stachyodes and Kuangxiastraea and, thus, occur below the Frasnian‐Famennian mass extinction boundary. Platform margin facies were dominated by microbes, algae and receptaculitids. Massive corals and stromatoporoids are not common and rarely show reef‐building functions as they did in Givetian time. The margin mounds are composed of brachiopod‐receptaculitid cementstone, and a variety of boundstones that contain Rothpletzella, Renalcis, thrombolite and stromatolite. Other microbial communities include Girvanella, Izhella, Ortonella and Wetheredella. Solenoporoid algae are abundant locally. Zebra structures and neptunian dykes are well‐developed at some intervals. Pervasive early cementation played an important role in lithification of the microbial boundstones and rudstones. Frasnian reefs of many regions of the world were constructed by stromatoporoids and corals, although a shift to calcimicrobe‐dominated frameworks occurred before the Famennian. However, the exact ages of many Frasnian margin outcrops are poorly constrained owing to difficulties dating shallow carbonate facies. The Hantang mounds represent a microbe‐dominated reef‐building community with rare skeletal reef builders, consistent with major Late Devonian changes in reef composition, diversity and guild structure occurring before the end of the Frasnian. A similar transition occurred in the Canning Basin of Western Australia, but coeval successions in North America, Western Europe and the northern Urals are either less well‐known or represent different bathymetric settings. The transition in reef‐building style below the Frasnian‐Famennian boundary is documented here in the two best exposed successions on two continents, which may have been global. Set in the larger context of Late Devonian and Mississippian microbial reef‐building, the Hantang mounds help to demonstrate that controls on microbial reef communities differed from those on larger skeletal reef biota. Calcimicrobes replaced stromatoporoids as major reef builders before the Frasnian‐Famennian extinction event, and increasing stromatoporoid diversity towards the end of the Famennian did not result in a resurgence of skeletal reef frameworks. Calcimicrobes dominated margin facies through the Famennian, but declined near the Devonian‐Carboniferous boundary. Stromatolite and thrombolite facies, which occurred behind the mound margin at Hantang, rose to dominate Mississippian shallow‐water reef frameworks with only a minor resurgence of the important Frasnian calcimicrobe Renalcis in the Visean when well‐skeletonized organisms (corals) also became volumetrically significant frame builders again.

Global microbial carbonate proliferation after the end-Devonian mass extinction: Mainly controlled by demise of skeletal bioconstructors

“…4). During the Frasnian, carbonate platforms were widely occupied by stromatoporoid-coral bioconstructions with fewer microbe-dominated bioconstructions3334 (Fig. 4).…”

Microbes and mass extinctions: paleoenvironmental distribution of microbialites during times of biotic crisis

“…Of note is that algae represent the only skeletal component within these reefs, while calcimicrobes, dominantly Renalcis , are the main constructors (Shen & Webb, 2004a,b). A pre‐extinction microbialite reef has been documented in latest Frasnian strata, also within the Yunghsien Formation, and is associated with receptaculitid‐brachiopod cementstone (Shen et al. , 2010).…”

“…, 2010). Yet, while similar in character to Famennian‐age reefs of the Yunghsien Formation, it differs in that it still contains framework metazoans including receptaculitids, massive corals, spiculate sponges, and stromatoporoids, although not in great abundance (Shen et al. , 2010).…”

A Review on Microbialites: a Korean Perspective

“…당시의 미생물초에는 Renalcis와 Epiphyton 등의 다양한 석회화된 미생물이 대량으로 나타나며, 이는 데본기 후기 대멸종 때문에 다량의 생물들이 멸종한 결과 미생물들이 번성할 수 있었기 때문으로 생각된다 (Riding, 2006b). 그러나 데본기 후 기 대멸종 이전에도 상당수의 미생물초가 존재하였기 때문에, 이 시기에 미생물초가 번성했던 것에는 대멸 종 이외에도 다른 이유가 있을 수 있다 (Feng et al, 2010;Shen et al, 2010). 페름기 말 대멸종 직후 약 150만 년에서 500만 년에 걸쳐 주로 Renalcis 그룹 또는 Microcystis로 생각되는 미생물과 미크라이트로 구성된 미생물암이 전 세계적으로 널리 나타났다 (Kershaw et al, 1999(Kershaw et al, , 2012Ezaki et al, 2003;Wu et al, 2014).…”