Abstract
New high-resolution geochemical and sedimentological data from Fiskegrav, East Greenland, reveal fluctuations in marine redox conditions associated with the final disappearance of bioturbating organisms during the latest Permian mass extinction (LPME). Sedimentological observations imply a transgressive episode, and associated geochemical evidence for decreasing oxygen availability and the establishment of persistently ferruginous (Fe2+-rich) conditions implies the shoreward migration of oxygen deficient waters. The long-term decline in dissolved oxygen (DO) availability could have been exacerbated by increasing water temperatures, reducing the solubility of oxygen and promoting thermal stratification. Mixing of the water column could have been further inhibited by freshwater influxes that could have generated salinity contrasts that reinforced thermal stratification. Enhanced runoff could also have increased the delivery of nutrients to the marine shelf, stimulating biological oxygen demand (BOD). During the transition to persistently ferruginous conditions we identify intervals of intermittent benthic meiofaunal recolonization, events that we attribute to small transient increases in DO availability. The mechanism controlling these fluctuations remains speculative, but given the possible centennial- to millennial-scale frequency of these changes, we hypothesise that the mid-latitude setting of Fiskegrav during the Late Permian was sensitive to changes in atmospheric circulation patterns, which may have influenced local precipitation and intermittently modulated some of the processes promoting anoxia.
Highlights
The latest Permian mass extinction (~252 Ma) was the greatest biological catastrophe of the Phanerozoic (Benton and Twitchett, 2003; Erwin, 2006; Bottjer et al, 2008; Burgess et al, 2014)
Our aim is to resolve the stratigraphic relationship between changes in redox conditions and the transition from bioturbated sediments that record the activities of marine benthos, to laminated horizons that are devoid of evidence of macroscopic marine animals or bioturbation (Twitchett et al, 2001)
Increased carbonate abundance in laminated horizons could reflect authigenic carbonate cements produced in association with anaerobic oxidation of methane coupled to microbial sulphate reduction (MSR) (Hovland et al, 1987; Peckmann et al, 2001)
Summary
The latest Permian mass extinction (~252 Ma) was the greatest biological catastrophe of the Phanerozoic (Benton and Twitchett, 2003; Erwin, 2006; Bottjer et al, 2008; Burgess et al, 2014). One of the associated environmental changes that has been invoked as a factor in the marine crisis is ocean stratification and the expansion of anoxic or even euxinic waters during a ‘superanoxic’ event (Wignall and Twitchett, 1996; Isozaki, 1997; Grice et al, 2005; Riccardi et al, 2006; Shen et al 2016), or the expansion of oxygen minimum zones (OMZs) onto continental shelves (Stüeken et al 2015; Clarkson et al, 2016; Lau et al 2016) Such studies are, biased towards low (tropical) palaeolatitudinal, carbonate-dominated successions of the Palaeo- and Neo-Tethys (Foster and Twitchett, 2014), and condensed sections including the Permian-Triassic boundary global stratotype section and point (GSSP) in Meishan, South China. The transition from bioturbated sediments containing macroscopic shelly fossils to laminated sediments mostly devoid of fossil evidence of marine animals (Stemmerik et al, 2001; Twitchett et al, 2001) appears to predate the onset of anoxia (Fenton et al, 2007; Neilsen et al, 2010)
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