Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: implications for tempo and mode of biotic recovery from the end-Permian mass extinction

Abstract

Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems.

High-precision timeline for Earth’s most severe extinction

“…This record represents a potentially characteristic δ 13 C (carb) topology for the end-Permian event, which will stimulate refined comparison with other Permian-Triassic sections, although the highly condensed nature of the Meishan section makes comparison with other sections difficult. The timing of the extinction and associated changes in environmental conditions are consistent with a very rapid biological response to environmental change followed by a complex recovery/restructuring period that took some 10 Ma for many species (38)(39)(40)(41) and established the ecosystems that would dominate the Mesozoic. Further integration of the extinction timescale with detailed chemostratigraphic, cyclostratigraphic, and paleobiological data should allow many more insights into the dynamics and timing of extinction and restructuring.…”

“…However, whether the temperature increase leads, is synchronous with, or postdates the extinction is not yet known with sufficient precision. Although recovery and diversification in Ammonoids began in the earliest Triassic, the broad effects of this short-lived extinction or ecological restructuring persist for 5-10 My after the main extinction interval, emphasizing the evolutionary irreversibility of the event (38)(39)(40)(41).…”

An early Middle Anisian (Middle Triassic) Tubiphytes and cement crusts-dominated reef from North Dobrogea (Romania): facies, depositional environment and diagenesis

“…The North Dobrogean Tubiphytes-dominated framework, with a high volume (30-50%) of penecontemporaneous and early-diagenetic cements and a considerable amount of automicrite, corresponds well to other Tubiphytes-dominated reefs, known from the Late Palaeozoic to Mesozoic: the Permian reefs of the Urals in Russia (Chuvashov 1983;Antoshkina 1998), the Permian Capitan Reef in the United States (Tinker 1998;Saller et al 1999;Weidlich 2002), and the Middle Triassic (Anisian-Ladinian) reefs, such as the Great Bank of Guizhou, in south China (Enos et al 1997(Enos et al , 2006Lehrmann 1999;Payne et al 2006Payne et al , 2011Lehrmann et al 2007), the Camorelli Bank and Concarena platform in the Italian Lombardic Alps (Gaetani and Gorza 1989;Berra et al 2005;Seeling et al 2005), the Latemar platform in the Italian Dolomites (Harris 1993(Harris , 1994Emmerich et al 2005;Marangon et al 2011;Preto et al 2011), and the Aggtelek reef in Hungary (Velledits et al 2011(Velledits et al , 2012. Microbial boundstones, as Tubiphytes-dominated facies, are also the main constituents of the Carboniferous upper slopes in the Cantabrian Mountains in northern Spain (Della Porta et al 2003;2004;Kenter et al 2005;Bahamonde et al 2007).…”

Early Jurassic foraminiferal assemblages in platform carbonates of Mt. Krim, central Slovenia

“…The biodiversity of each sample was estimated on the basis of the Shannon-Wiener diversity index H´ (Ham- HarPer, 2006). In addition to calculating diversity, the maximum specimen size from each biozone was measured (see Payne et al, 2011). We also measured the largest specimen of the most common and widespread species, Meandrovoluta asiagoensis, in different facies types.…”

“…Such stability might have been related to stabilization of the physical environment (e.g., ocean chemistry, sea temperature) after the end-Triassic extinction, or to the increasing interactions among organisms, but it might also have come with the transition from highly fluctuating peritidal conditions where there are drastic changes in light intensity, salinity and temperature, to predominantly subtidal and thus more physically stable conditions (see HallocK, 1988). Furthermore, although a steady increase in the size of foraminifera has been recorded after the Permian-Triassic boundary extinction and used as an argument for a true (i.e., not facies-change related) recovery of foraminifera (Payne et al, 2011;reGo et al, 2012), it is not known whether such an increase in size is possible also during the time of rising sea level (Wilmsen & neuWeiler, 2008). In other words, the increased complexity of foraminiferal assemblages in transgression-affected succession should not be attributed solely to post-extinction biotic recovery and diversification, but may instead reflect a rather local re-establishment of suitable habitat.…”