Erosional truncation of uppermost Permian shallow-marine carbonates and implications for Permian-Triassic boundary events

Abstract

On shallow-marine carbonate buildups in south China, Turkey, and Japan, uppermost Permian skeletal limestones are truncated by an erosional surface that exhibits as much as 10 cm of topography, including overhanging relief. Sedimentary facies, microfabrics, carbon isotopes, and cements together suggest that erosion occurred in a submarine setting. Moreover, biostratigraphic data from south China demonstrate that the surface postdates the uppermost Permian sequence boundary at the global stratotype section and truncates strata within the youngest known Permian conodont zone. The occurrences of similar truncation surfaces at the mass-extinction horizon on carbonate platforms across the global tropics, each overlain by microbial buildups, and their association with a large negative excursion in δ 13 C further suggest a causal link between erosion of shallow-marine carbonates and mass extinction. Previously proposed to account for marine extinctions, the hypothesis of rapid carbon release from sedimentary reservoirs or the deep ocean can also explain the petro-graphic observations. Rapid, unbuffered carbon release would cause submarine carbonate dissolution, accounting for erosion of uppermost Permian skeletal carbonates, and would be followed by a pulse of high carbonate saturation, explaining the precipitation of microbial limestones containing upwardgrowing carbonate crystal fans. Models for other carbon-release events suggest that at least 5 × 10 18 g of carbon, released in <100 k.y., would be required. Of previously hypothesized Permian-Triassic boundary scenarios, thermogenic methane production from heating of coals during Siberian Traps emplacement best accounts for petrographic characteristics and depositional environment of the truncation surface and overlying microbial limestone, as well as an associated carbon isotope excursion and physiologically selective extinction in the marine realm.

Calcium isotope constraints on the end-Permian mass extinction

“…S2). The global scenario is consistent with the greater relative abundance of aragoniteversus calcite-producing skeletal animals globally in the Lower Triassic (48), with petrographic evidence for an originally aragonitic mineralogy for Early Triassic ooids and carbonate crystal fans (5), and with the similarity of Lower Triassic carbonate strata across the global tropics (8).…”

“…First, the synchronous deposition of microbialites and oolites across the global tropics within the H. parvus conodont zone (7,8) could reflect rapid carbonate deposition resulting from enhanced silicate and carbonate weathering in the aftermath of a CO 2 release event. The weathering hypothesis can explain why synchronous, widespread deposition of these facies is confined to the earliest Triassic, despite the persistence of ocean anoxia (55) and skeleton-poor carbonate sediments (34) through much of Early Triassic time.…”

“…Microbialites and oolites overlie diverse, fossiliferous limestones of the latest Permian age in carbonate strata deposited across the tropical Tethys (1)(2)(3)(4)(5)(6)(7)(8) and in the Panthalassa Ocean (8,9) (Fig. S1).…”

“…Upwelling of these alkaline deep waters would have triggered carbonate precipitation on the shelves (2,5,15,16) and caused mass extinction through combined stresses of hypercapnia, anoxia, and hydrogen sulfide poisoning (14,15,17). Third, the ocean acidification model proposes that massive release of 13 C-depleted carbon from a reservoir in the crust (e.g., methane clathrates, coal, and magma) (18)(19)(20)(21)(22) acidified the ocean, reducing carbonate sedimentation and potentially leading to dissolution of carbonate sediments (8). Subsequently enhanced continental weathering and consequent delivery of carbonate alkalinity to the oceans would account for the widespread deposition of microbialites and oolites above the extinction horizon (8).…”

Discovery of an earliest Triassic, post-extinction foraminiferal assemblage above the Permian-Triassic boundary, Strandzha nappes, northwest Turkey.

“…mahajeri and Rectocornuspira kalhori be long to the same ge nus and in tro duced the taxon as Postcladella kalhori n. comb. The known strati graphic dis tri bu tion of Postcladella kalhori is from lat est Mid dle Perm ian to ear li est Tri as sic strata; it is es pe cially com mon and char acter is tic of Induan (ear li est Tri as sic) strata glob ally, for in stance, in South China (Ezaki et al, 2003;Song et al, 2007Song et al, , 2009bGalfetti et al, 2008), south ern Tur key (Crasquin-Soleau et al, 2004;AltÏner et al, 2005;Payne et al, 2007) and north ern It aly (Groves et al, 2007). Some ques tionable oc cur rences of this taxon are in di cated in the Olenekian (late Early Tri as sic; Krainer and Vachard, 2011).…”