Microbialites as disaster forms in anachronistic facies following the end-Permian mass extinction: a discussion

Latest Permian carbonate carbon isotope variability traces heterogeneous organic carbon accumulation and authigenic carbonate formation

“…While conditions favoured the formation of these structures, poorly buffered calcified metazoans (e.g., brachiopods and corals) were proportionally more affected by the end-Permian mass extinction (Knoll et al, 2007). This biotic shift has been interpreted as a prevalent carbonate factory turnover from skeletal to microbial (e.g., Kershaw et al, 2009).…”

“…However, δ 13 C variability complies most compellingly with at least continuing OC accumulation over the studied interval and thereby largely undermines scenarios of reduced primary productivity (e.g., Rampino and Caldeira, 2005). On the other hand, the proliferation of post-extinction authigenic sea-floor precipitates (e.g., thrombolites, stromatolites and fan-shaped structures) likely represents a symptom of reduced sediment disturbance and elevated carbonate saturation (Kershaw et al, 2009). Since some of the more conspicuous post-extinction sea-floor structures have been connected with microbial communities and distinct metabolism-mediated isotope signatures (e.g., Heindel et al, 2013), they might be equally important constituents of the observed spatial δ 13 C variability.…”

“…This does not, however, exclude local departures from this dynamic equilibrium or depth-related isotope differences, such as those forced by the biological pump (Kump and Arthur, 1999;Rampino and Caldeira, 2005). High carbonate ion concentrations are invoked to explain the advent of (microbial) carbonate sea-floor structures (e.g., thrombolites, stromatolites and fan-shaped structures) in the extinction aftermath and the ensuing Early Triassic recovery phase (Baud et al, 1997;Rampino and Caldeira, 2005;Riding and Liang, 2005;Pruss et al, 2006;Kershaw et al, 2007Kershaw et al, , 2009Leda et al, 2014). While conditions favoured the formation of these structures, poorly buffered calcified metazoans (e.g., brachiopods and corals) were proportionally more affected by the end-Permian mass extinction (Knoll et al, 2007).…”

Permian–Triassic boundary microbialites (PTBMs) in southwest China: implications for paleoenvironment reconstruction

“…Analysis of conodont biostratigraphy, mega-to microscopic microbialite structures, stratigraphic variations in abundance and size of metazoan fossils, and total organic carbon (TOC) and total sulfur (TS) contents within the PTBM reveals the following results: (1) the microbialites occur mainly in the Hindeodus parvus Zone but may cross the Permian-Triassic boundary, and are comprised of, from bottom to top: lamellar thrombolites, dendritic thrombolites and lamellarreticular thrombolites; (2) most metazoan fossils of the microbialite succession increase in abundance upsection, so does the sizes of bivalve and brachiopod fossils; (3) TOC and TS values of microbialites account respectively for 0.07 and 0.31 wt% on average, both of which are very low. The Kershaw et al 2007Kershaw et al , 2009Kershaw et al , 2011Yang et al 2011;Forel et al 2013;Kershaw et al 2012;Loope et al 2013;Jiang et al 2014;Wu et al 2014;Lehrmann et al 2015;Wu et al 2016). Microbialites also occur later in the Early Triassic (Schubert and Bottjer 1992;Lehrmann 1999;Pruss and Bottjer 2004;Pruss et al 2006;Mary and Woods 2008;Mata and Bottjer 2011;Marenco et al 2012;Chen et al 2014;Vennin et al 2015), where they are commonly described as having formed in anoxic, harsh environments (e.g., Pruss and Bottjer 2004;Pruss et al 2006;Mary and Woods 2008;Mata and Bottjer 2011).…”

“…The models for their generation consist of a series of viewpoints, including: (1) reduced benthic grazing pressure; (2) upwelling of anoxic alkaline waters; (3) elimination of skeletal CaCO 3 sinks; (4) increased nutrient levels from erupted volcanic ash; and (5) a rebound in carbonate saturation following a transient ocean acidification event (Lehrmann et al 2015 and references therein). The upwelling model, in particular, has been applied by numerous workers in the Early Triassic (Kershaw et al 1999;Ezaki et al 2003;Lehrmann et al 2003;Pruss and Bottjer 2004;Pruss et al 2005;Kershaw et al 2007Kershaw et al , 2009Kershaw et al , 2011Ezaki et al 2008;Mary and Woods 2008;Mata and Bottjer 2011;He et al 2013;Woods 2014). Lehrmann et al (2003) also drew attention to the possibility of PTBM formation in oxygenated seawater conditions.…”