The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms.

https://www.pnas.org/content/pnas/111/9/3316.full.pdf

High-precision timeline for Earth's most severe extinction

Current chemostratigraphical studies of the Jurassic System primarily involve the use of one sedimentary component (marine organic carbon), one divalent transition metal substituted in carbonate (manganese), and two isotopic tracers: strontium-isotope ratios ( 87 Sr/ 86 Sr) and carbon-isotope ratios (δ 13 C carb and δ 13 C org ) in carbonate and in organic matter. Other parameters such as Mg/Ca and Sr/Ca ratios in calcite, oxygen-isotope ratios (δ 18 O) in carbonate, sulphur-isotope ratios (δ 34 S) in carbonate-hosted sulphate, nitrogen-isotope ratios (δ 15 N org ) in organic matter, osmium-isotope ratios ( 187 Os/ 188 Os) in black shales and neodymium-isotope ratios ( 143 Nd/ 144 Nd) in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors. Stratigraphical patterns in total organic carbon (TOC) can be of either local or regional significance, depending on the lateral extent of the former nutrient-rich and productive water mass. Divalent manganese follows a similar pattern, being concentrated, most probably as a very early diagenetic phase, only in oxygen-depleted waters that typically underlie zones of elevated organic productivity. Shifts in Mg/Ca and Sr/Ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes. Strontium-isotope ratios from pristine skeletal calcite provide a global signal; δ 13 C values from carbonates with minimal diagenetic overprint potentially do the same, although small spatial differences in palaeo-water-mass composition may have been locally significant. Oxygen-isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful, because they reflect palaeotemperature, the evaporation–precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase. Nitrogen-isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification, and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis. Neodymium-isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems. Preliminary data on sulphur-isotope ratios in carbonates and osmium-isotope ratios in organic-rich shales, both potentially offering global correlation, indicate that these tracers may be valuable, although the records at present are not sufficiently well established to allow high-resolution regional correlation. In all cases, biostratigraphically well-dated reference sections, against which the relevant geochemical data have been calibrated, are required in the first instance. To date, studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern (Boreal) and southern (Tethyan) Europe; carbon-isotope stratigraphy has been undertaken primarily, but not exclusively, on bulk pelagic sediments from the Alpine–Mediterranean or Tethyan domain; and strontium-isotope stratigraphy has been undertaken largely on calcitic skeletal material (belemnites and oysters) from northern and southern Europe. In many sections, including those containing ammonites, multi-parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means. Strontium-isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record.

/pdf/chemostratigraphy-of-the-jurassic-system-applications-fuep9zfrjr.pdf

Chemostratigraphy of the Jurassic System: applications, limitations and implications for palaeoceanography

Paleoceanographic applications of trace-metal concentration data

Structural comparison of archetypal Atlantic rifted margins: A review of observations and concepts

Triassic seismic sequence stratigraphy and paleogeography of the western Barents Sea area

Shallow stratigraphic drilling applied in hydrocarbon exploration of the Nordkapp Basin, Barents Sea

Significant thicknesses of organic-rich shales accumulated under predominantly marine depositional conditions in the Arctic region during the Mesozoic era. Deposition of these shales was most prevalent during the Triassic and Late Jurassic, but also extended into the Cretaceous in Arctic North America. Triassic organic-rich shales are represented by the Sassendalen Group of Svalbard and its equivalents in the Barents Sea, the Schei Point and Blaa Mountain Groups of the Sverdrup Basin, and the Shublik Formation of northern Alaska and adjacent northwestern Canada. The oldest Triassic organic-rich shales are the mid-Early Triassic shales of the Barents Sea and northeastern Sverdrup Basin, whereas the youngest are the Upper Triassic shales of Canada and Alaska. Deposition of these shales was most widespread during the Middle Triassic. Organic geochemical data indicate a remarkable degree of similarity in the character of the organic matter in the Triassic shales over the entire region. Deposition of organic-rich shales occurred over a greater area during the Late Jurassic, as represented by the Hekkingen and Janusfjellet Formations of the western Barents Shelf, the Bazhenov Formation of Western Siberia and the dark shales of the Timan-Pechora Basin, the Ringnes Formation of the Canadian Arctic Islands and the Kingak Shale of Alaska. Organic-rich shales of the Pebble Shale Unit and Hue Shale of northern Alaska, the Boundary Creek and Smoking Hills Formations of the Beaufort-Mackenzie Basin and the Kanguk Formation of the Sverdrup Basin represent important potential source-rocks of Cretaceous age in the North American Arctic. The occurrence of potential hydrocarbon source-rocks in the Barents Sea and adjacent areas is controlled by both regional palaeogeography and local depositional conditions. Prediction of source-rock character is vital to the evaluation of a potential exploration area, and definition of the depositional constraints on organic-rich shale occurrence is an important objective for further work.

Mesozoic hydrocarbon source-rocks of the Arctic region

Hot acidic Late Permian seas stifle life in record time

A 750 m-thick, fully marine succession of sandstones, coarse-grained turbidites, shales, and reworked sabkha sediments has been cored on the eastern margin of the mid-Norwegian shelf. The succession has been dated as Upper Permian-Lower Triassic and is comparable to rocks of the same age exposed onshore East Greenland. These data demonstrate that the marine depositional basin between Greenland and Norway extended much farther east than previously thought. Reddish, shallow-marine sandstones in the lower 170 m of the cored succession probably represent reworking of older sedimentary rocks present to the east of the drill sites. This suggests that Upper Devonian-Lower Permian sediments were deposited on Caledonian basement east of the present-day limits of the basin. The cored succession also contains source rocks that can be stratigraphically correlated with the oil-prone source rocks of the Upper Permian Ravnefjeld Formation onshore East Greenland. Some of the cored sandstone intervals were stained with light, nonbiodegraded oil that most likely was sourced from Upper Permian or, alternatively, Lower Triassic mudstones. Reworked fragments of reef-building organisms in Upper Permian turbidites and Upper Permian carbonates encountered in an exploration well on the Nordland Ridge indicate that carbonate deposition and reef building occurred on structural highs on the Trondelag Platform. The observations from the cored successions are key elements in a new Paleozoic play model on the mid-Norwegian continental shelf and include the first evidence for the existence of an Upper Permian source rock in the area, with Upper Permian carbonates or sandstones or Triassic-Jurassic sandstones as reservoir. (Begin page 108)

Hermann M. Weiss

Papers

Shallow stratigraphic drilling applied in hydrocarbon exploration of the Nordkapp Basin, Barents Sea

Mesozoic hydrocarbon source-rocks of the Arctic region

Hot acidic Late Permian seas stifle life in record time

Upper Permian as a new play model on the mid-Norwegian continental shelf: Investigated by shallow stratigraphic drilling

Re–Os geochronology of Arctic black shales to evaluate the Anisian–Ladinian boundary and global faunal correlations