Growth and demise of Permian biogenic chert along northwest Pangea: evidence for end-Permian collapse of thermohaline circulation

Abstract

The Permian Chert Event (PCE) was a 30 Ma long episode of unusual chert accumulation along the northwest margin of Pangea, and possibly worldwide. The onset of the PCE occurred at about the Sakmarian^Artinskian boundary in the Sverdrup Basin, Canadian Arctic, where it coincides with a maximum flooding event, the ending of high-frequency/high-amplitude shelf cyclicity, the onset of massive biogenic chert deposition in deep-water distal areas, and a long-term shift from warm-to cool-water carbonate sedimentation in shallow-water proximal areas. A similar and coeval shift is observed from the Barents Sea to the northwestern USA. A landward and southward expansion of silica factories occurred during the Middle and Late Permian at which time warm-water carbonate producers disappeared completely from the northwest margin of Pangea. Biotically impoverished and increasingly narrow cold-water carbonate factories (characterised by non-cemented bioclasts of sponges, bryozoans, echinoderms and brachiopods) were then progressively replaced by silica factories. By Late Permian time, little carbonate sediments accumulated in the Barents Sea and in the Sverdrup Basin, where the deep-to shallow-water sedimentary spectrum was occupied by siliceous sponge spicules. By that time, biogenic silica sedimentation was common throughout the world. Silica factories collapsed in the Late Permian, abruptly bringing the PCE to an end. In northwest Pangea, the end-Permian collapse of the PCE was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions. Chert deposition resumed in the distal oceanic areas during the early Middle Triassic (Anisian) after a 8^10 Ma interruption (Early Triassic Chert Gap). The conditions necessary for the onset, expansion and zenith of the PCE were provided by the thermohaline circulation of nutrient-rich cold waters along the northwestern and western margin of Pangea, and possibly throughout the world oceans. These conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area, created a nutrient-and oxygen-rich environment favouring siliceous biogenic productivity, established cold sea-floor conditions, hindering silica dissolution, while increasing calcium carbonate solubility, and provided conditions adverse to organic and inorganic carbonate production. The northwest margin of Pangea was, for nearly 30 Ma, bathed by cold waters presumably derived from the seasonal melting of northern sea ice, the assumed engine for thermohaline circulation.This process started near the Sakmarian^Artinskian boundary, intensified throughout Middle and Late Permian time and ceased suddenly in latest Permian time. It led to oceanic conditions much colder than normally expected from the palaeolatitudes, and the influence of cold northerly-derived water was felt as far south southern Nevada. The demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warm...

Stratigraphical and palaeogeographical significance of the continental sedimentary transition across the Permian–Triassic boundary in Spain

“…Iberian Plate was located north of the equator and south of the tropic Beauchamp and Baud, 2002) acting as a main doorway for the defmitive westward propagation of the Neotethys reaching the plate during the Anisian. The equatorial seaway between the Palaeotethys and western oceans had been previously eliminated due to continued closure between the gondwanan and laurasian elements of Pangea (Ford and Golonka, 2003).…”

Facies arrangement and cyclostratigraphic architecture of the Templet Member and the Kapp Starostin Formation (Permian) on Spitsbergen, Svalbard

“…4). The presence of glauconite suggests a low sedimentation rate, most likely below the SWWB, and the presence of burrows is indicative of aerobic conditions (Beauchamp & Baud, 2002). The occurrence of shale horizons and a lime-mud matrix might have led to the dark colour of the bedded cherts (Gates et al, 2004).…”

“…The presence of glauconite and silica deposits specifically in the mid-to outer-ramp microfacies is related to upwelling currents, which could have brought substantial amounts of nutrients onto the ramp (Beauchamp & Baud, 2002;Gates et al, 2004). Seasonal thawing of northern seaice sheets led to the production of dense, cold water in the deep northern Panthalassan Ocean, displacing nutrients and silica-rich water to the western and northern shelfal areas of Pangea via upwelling.…”

“…Seasonal thawing of northern seaice sheets led to the production of dense, cold water in the deep northern Panthalassan Ocean, displacing nutrients and silica-rich water to the western and northern shelfal areas of Pangea via upwelling. This process created an environment favouring siliceous biogenic productivity (Beauchamp & Baud, 2002). Additionally, the closure of the Uralian seaway during the Kungurian caused the cutoff of the supply of warm waters of the Tethys (Blomeier et al, 2011).…”

“…The Permian was a time of extensive spiculitic chert accumulation along the northern margin of Pangea, and several seismic-based sequencestratigraphic studies have resulted in findings of reservoir rocks for hydrocarbon exploitation, e.g., the Finnmark Platform (Norwegian Barents Sea) (Ehrenberg et al, 1998(Ehrenberg et al, , 2001Beauchamp & Baud, 2002;Larssen et al, 2002;Gates et al, 2004;Colpaert et al, 2007). Therefore, the study presented here will be of benefit to our understanding of the depositional environment and bedscale, lateral and vertical, microfacies variations in the source and reservoir rocks of the Barents Sea oil and gas plays.…”