Diversity and systematics of Middle-Late Ordovician calcified cyanobacteria and associated microfossils from Ordos Basin, North China

Abstract

Calcified cyanobacteria are of considerable research value for reconstructing the ecology of Paleozoic and Mesozoic benthic communities on carbonate platforms due to their ability to produce oxygen and fix nitrogen and CO2. The diversity and abundance of calcified cyanobacteria was initially suggested to have declined in the Middle and Late Ordovician, although more recent work suggests that complex and diverse assemblages persisted throughout the Ordovician. Here, calcified cyanobacteria and associated microfossil flora from the Middle and Late Ordovician of the Ordos Basin, North China Block, are systematically described for the first time based on 1330 thin sections from seven outcrop profiles and four drill cores. In total, there are 18 species belonging to 16 genera, including a new species, Proaulopora ordosia n. sp. Girvanella, Subtifloria, Acuasiphonoria, Xianella, and Oscillatoriaceae gen. indet. are assigned to Osillatoriales of cyanobacteria; Ortonella, Hedstroemia, Cayeuxia, Zonotrichites, Proaulopora, and Phacelophyton are assigned to Nostocales of cyanobacteria; and Garwoodia, Renalcis, Izhella, Rothpletzella, and Wetheredella are assigned to calcified Microproblematica. A literature survey of Ordovician microfloral assemblages shows that cyanobacteria and associated microfossils occur in reef, open platform, lagoon, and tidal facies. Most genera occur on at least two independent blocks, and many have a cosmopolitan distribution in similar sedimentary facies. Our research suggests that calcified cyanobacteria and associated microfossils formed complex ecosystems and played greater ecological roles on carbonate platforms during the late Middle and Late Ordovician than was previously thought. UUID: http://zoobank.org/1812ccf8-136c-4cff-92ba-faeaf06523ef

Palaeoecology of calcified microfossils from the Lower Devonian (Pragian-Emsian) of Sierra Morena (SW Spain)

“…A is similar to the species G. kasakiensis Maslov, 1949, whereas the form G. sp. B is similar to the species G. problematica Nicholson and Etheridge, 1878, as described in Liu et al (2021).…”

“…A. Similar joint occurrences of Girvanella and Rothpletzella are quite common in reefal sediments (e.g., Tsien 1979; Liu et al 2016Liu et al , 2017Liu et al , 2021.…”

“…Although abundant and diverse in marine environments (Hoffman 1999), modern calcimicrobes experience intensive calci cation mostly in fresh water, rarely in subtidal marine environments (e.g., Flügel 2010). In contrast, the fossil representatives of this group are found in tidal and subtidal biotopes, often in reefs, as, for example, shown for the Ordovician occurrences (Liu et al 2021), or in the Devonian (Stephens and Sumner 2003). Rothpletzella is suggested to occur in shadowed, protected environments like lagoons, but also in reefs and open platform habitats (e.g., Chuvashov and Riding 1984;Antoshkina 1996;Wood 2000Wood , 2004.…”

Amsassia(calcareous alga) from the Lower Ordovician (Tremadocian) of western Newfoundland, and the biologic affinity and geologic history of the genus

“…Some calcimicrobes have a modular appearance and branching tubules. Garwoodia Wood, 1941, for example, has been regarded by some authors as green algal rather than cyanobacterial, because of its relatively large tubules with diameters up to 0.07 mm (Liu et al, 2021). Modules attain even larger sizes in Amsassia, with the smallest and largest species having maximum module diameters of 0.28 mm and 1.66 mm, respectively (M. Lee et al, 2016, fig.…”