New data from Oman indicate benthic high biomass productivity coupled with low taxonomic diversity in the aftermath of the Permian–Triassic Boundary mass extinction

Abstract

A new Early Triassic marine fauna is described from an exotic block (olistolith) from the Ad Daffah conglomerate in eastern Oman (Batain), which provides new insights into the ecology and diversity during the early aftermath of the Permian–Triassic Boundary mass extinction. Based on conodont quantitative biochronology, we assign a middle Griesbachian age to the upper part of this boulder. It was derived from an offshore seamount and yielded both nektonic and benthic faunas, including conodonts, ammonoids, gastropods and crinoid ossicles in mass abundance. This demonstrates that despite the stratigraphically near extinction at the Permian–Triassic Boundary, Crinoidea produced enough biomass to form crinoidal limestone as early as middle Griesbachian time. Baudicrinus, previously placed in Dadocrinidae, is now placed in Holocrinidae; therefore, Dadocrinidae are absent in the Early Triassic, and Holocrinidae remains the most basal crown‐group articulates, originating during the middle Griesbachian in the Tethyan Realm. Abundant gastropods assigned to Naticopsis reached a shell size larger than 20 mm and provide another example against any generalized Lilliput effect during the Griesbachian. Whereas the benthic biomass was as high as to allow the resumption of small carbonate factories, the taxonomic diversity of the benthos remained low compared to post‐Early Triassic times. This slow benthic taxonomic recovery is here attributed to low competition within impoverished post‐extinction faunas.

Bioindicators of severe ocean acidification are absent from the end-Permian mass extinction

“…None of the described or figured specimens record bioindicators consistent with severe ocean acidification. In partially silicified assemblages from Oman 51 , 52 , the apices of high-spired gastropods are intact, which would not be expected if they experienced severe ocean acidification. Examples where protoconchs are missing and shell apertures are not fully preserved are most likely the result of the coarse silicification 51 , 52 and not ocean acidification.…”

A diverse gastropod fauna from the shallow marine carbonate platform of the Yangou section (south China) in the immediate aftermath of the Permian–Triassic mass extinction

“…Typical Griesbachian gastropod faunas, such as those from east Greenland or the Nanpanjiang basin, have very low diversities and are composed of a few dominant species and genera such as Naticopsis (Brayard et al, 2015; Hautmann et al, 2015). Only at a handful of localities is the fauna more diverse, such as in the case of the Wadi Wasit section in Oman (Brosse et al, 2019; Wheeley & Twitchett, 2005). The Yangou gastropod fauna has a higher diversity and a higher dominance than the Oman fauna.…”

“…In addition, in the immediate aftermath of the PTME, PTBM proliferation occurred rapidly all over the world (e.g., Kershaw et al, 2009). The anoxia was extensively recorded across the extinction horizon, whereas oxygenation has only been recorded in south China, Arctic Canada, and Oman (Bond & Wignall, 2010; Brosse et al, 2019; Wignall et al, 2020; Xiao et al, 2018). However, although these studies discovered this oxygenation event in the microbialites‐bearing sections, the redox conditions of PTBMs were still dysoxic rather than fully oxic, which were insufficient for the inhabitation of many metazoans (e.g., Song et al, 2014).…”

The main stage of recovery after the end-Permian mass extinction: taxonomic rediversification and ecologic reorganization of marine level-bottom communities during the Middle Triassic

“…(1) benthic communities from various environmental settings and palaeogeographically distant regions show little indications for unusual environmental stress (Twitchett et al, 2004;Hautmann et al, 2011;Hautmann et al, 2015;Hofmann et al, 2014); (2) ichnofaunas were diverse and complex soon after the extinction event in different palaeolatitudes (Beatty, Zonneveld & Henderson, 2008;Hofmann et al, 2011); (3) shell sizes of many Early Triassic gastropods reached large sizes (Brayard et al, 2010;Brayard et al, 2011a;; (4) the diversification of ammonoids was extremely rapid and displayed a cyclic pattern in time (Brayard et al, 2009;. (5) biomass productivity of marine benthos was high in spite of low taxonomic diversity (Brosse et al, 2019) and ( 6) marine apex predators were present throughout the Early Triassic (Scheyer et al, 2014). This criticism does not deny the existence of environmental stress in the Early Triassic, but it suggests that it was locally and temporarily restricted and had differential impacts on the benthos and nekton.…”