Palaeoecology of a post‐extinction reef: Famennian (Late Devonian) of the Canning Basin, north‐western Australia

Abstract

ABSTRACT. Reefs were decimated by the Frasnian/Famennian (Late Devonian) mass extinction event (371 Ma), and are assumed to have survived only as depauperate calcimicrobial communities dominated by disaster taxa. Description of Famennian proximal reef-slope communities within the Windjana Limestone, Canning Basin, north-western Australia, shows that, notwithstanding the loss of large metazoans, novel ecologies were established in this setting by a rich biota of survivor and progenitor taxa. Diverse calcimicrobes together with algae, crinoids, bryozoans, brachiopods, and abundant sponges (stromatoporoids, inozoans, sphinctozoans, lithistids and hexactinellids) formed a reef framework of either elevated platy structures up to 4 m in diameter and 0·35 m thick, or mounds up to 15 m in diameter. This framework was dominated by a complex intergrowth of calcimicrobes, where Rothpletzella formed the primary framework, Ortonella, and Girvanella were secondary encrusters, and Shuguria spp. occupied small crypts 2-30 mm in diameter. Contiguous columnar stromatolites up to 50 mm in height and 1 m in width grew upwards from substrate sheltered beneath large sheltered primary cavities: based on minimum growth rates of 50-100 mm/year these are estimated to have been between 500 and 1000 years old. The elevated platy community is inferred to have grown in conditions of episodic siliciclastic sediment input; the reef mounds grew during either episodes, or in localised areas, of low sedimentation. At least 14 morphospecies of spicular sponges are now identified from the Windjana Limestone, where only two were previously documented. These fore-slope reef communities exposed in Windjana Gorge flourished in high-energy carbonate environments dominated by coated grain sediments, and where rapid, early lithification was pervasive.Such observations demonstrate that no protracted interval of time was necessarily required for post-extinction 'recovery' in regions where some reef-building taxa survived and suitable carbonate habitats persisted or returned. Moreover, they show that new ecologies, rather than remnants of the pre-extinction community, could be established rapidly. The reef-slope communities of the Windjana Limestone offer little evidence to support the ideas of resurgence or invasion of taxa from deeper waters after the Frasnian/Famennian extinction. Indeed, there is evidence to suggest that similar microbial-sponge communities were already established in margin and reef slope communities in the latest Frasnian. As such, the most dramatic ecological changes caused by the extinction occurred in back-reef communities.

Patterns of extinction and recovery of phacopid trilobites during the Frasnian–Famennian (Late Devonian) mass extinction event, Canning Basin, Western Australia

“…They form part of a major reef complex that became established on the Lennard Shelf on the northern side of the Canning Basin during the latest Givetian to Famennian (Playford, 1980(Playford, , 1981(Playford, , 1984Playford & Lowry, 1966;Becker et al 1991;George & Chow, 2002). The reef complex was dominated by stromatoporoids in the Givetian and Frasnian, being replaced in the Famennian by cyanobacterial reefs (Playford, 1980;George & Chow, 2002;Wood, 2004). Trilobites have only been collected from the marginal slope facies, the Virgin Hills Formation, that may have been deposited at depths of several tens to at least 200 m (Becker et al 1991).…”

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

“…Important Middle Devonian reef constructors, such as stromatoporoids and rugose and tabulate corals, were scarce and volumetrically insignificant on reef margins by the Famennian, leaving calcimicrobes, micritic microbialite and biocementstone to dominate documented reef frameworks (Kerans, 1985; Boulvain et al. , 2001; Webb, 2001b; Copper, 2002a; George & Chow, 2002; Wood, 2004; Antoshkina, 2006). Subsequent development of non‐skeletal, micrite‐dominated buildups from the Famennian (e.g.…”

“…, 2008). Early Famennian communities are very similar to the latest microbe‐dominated Frasnian communities, even including minor thin stromatoporoids in some cases (Wood, 2000a, 2004; Webb, 2001b). In the Guilin area of South China, most reef‐building corals disappeared in the early Frasnian, and the growth forms of stromatoporoids changed from frame‐building morphologies (tabular, massive and dome‐shaped) to non‐frame‐building forms (branching, bulbous and irregular) (Shen & Zhang, 1997).…”

“…However, it also reflects the scarcity of well‐documented, in situ Frasnian microbe‐dominated shelf‐margin facies. In situ Famennian microbe‐dominated reef facies have been described from several regions (Kerans, 1985; Tsien, 1994; Wood, 2000a,b, 2004; Webb, 2001b; Stephens & Sumner, 2003; Shen & Webb, 2004a,b) but upper Frasnian shelf‐edge microbial facies are known primarily from fore‐reef debris.…”

Facies and platform development of a microbe‐dominated carbonate platform: The Zhangxia Formation (Drumian, Cambrian Series 3), Shandong Province, China

“…It was due to the rise of metazoans either as grazers and carbonate producers (Pratt, ; Walter & Heys, ). Microbes acted rather cryptically to form lime mud fraction of the carbonate platform (Pratt, ), and the microbialites resurged in the specific time periods such as aftermath of the mass extinctions (e.g., Baud, Cirilli, & Marcoux, ; Ezaki, Liu, & Adachi, ; Vennin et al, ; Wood, ). Microbial sediments have been increasingly recognized as an important player for the Phanerozoic carbonate production (Riding, ).…”