Spatial variability of watermass conditions within the European Epicontinental Seaway during the Early Jurassic (Pliensbachian–Toarcian)

Abstract

In order to constrain spatial variability in watermass conditions within the European Epicontinental Seaway prior to, during and after the Toarcian Oceanic Anoxic Event, carbon (δ13Cbel, δ13Ccarb) and oxygen (δ18Obel, δ18Ocarb) isotope records were obtained from three sections in the Grands Causses Basin (southern France). These data were then compared with similar records along a north–south transect across the European Epicontinental Seaway. As the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes, an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite. Intra‐rostral carbon and oxygen‐isotope data from six belemnite specimens belonging to the genus Passaloteuthis were collected. Intra‐rostral carbon‐isotopes are influenced by vital effects, whereas oxygen‐isotopes reflect relative changes in temperature and salinity. Palaeotemperatures calculated from δ18Obel‐isotope records from the Grands Causses Basin confirm relatively low temperatures throughout the Late Pliensbachian. Similar cool water conditions have previously been shown in Germany, England, Spain and Portugal. A temperature increase of up to 6 °C is observed across the Pliensbachian–Toarcian boundary. A pronounced negative shift of at least −3‰ (Vienna‐Pee Dee Belemnite) is recorded in bulk carbonate carbon during the lower Harpoceras serpentinum zone, typical of the Toarcian Oceanic Anoxic Event. Before and after the Toarcian Oceanic Anoxic Event, a good correlation between δ13Ccarb and δ13Cbel exists, indicating well‐ventilated bottom‐waters and normal marine conditions. Instead, data for the Toarcian Oceanic Anoxic Event indicate the development of a strong north–south gradient in salinity stratification and surface‐water productivity for the Western Tethyan realm. This study thus lends further support to a pronounced regional overprint on carbon and oxygen‐isotope records in epicontinental seaways.

Calcium isotope evidence for dramatic increase of continental weathering during the Toarcian oceanic anoxic event (Early Jurassic)

“…The Mg and Fe contents show trends similar to those reported by Hermoso et al (2009), albeit showing somewhat lower values in the basal levisoni Zone (Fig. 3).…”

Palaeoclimatic oscillations in the Pliensbachian (Early Jurassic) of the Asturian Basin (Northern Spain)

“…This narrow excursion was described by Hesselbo et al (2007) in bulk rock samples in Portugal, and tested by Suan et al (2010) in the same basin and extended to the Yorkshire (UK) by Littler et al (2010) and by Korte and Hesselbo (2011). If this perturbation of the carbon cycle is global, as Korte and Hesselbo (2011) pointed out, it could correspond with the negative δ 13 C peak recorded in the upper part of the Spinatum Chronozone in the Asturian Basin (present paper); with the negative δ 13 C peak reported by Quesada et al (2005) in the same stratigraphical position in the Basque-Cantabrian Basin, and with the δ 13 C negative peak reported by van de Schootbrugge et al (2010) and Harazim et al (2013) in the French Grand Causses Basin.…”

“…McArthur et al, 2000;Jenkyns et al, 2002;van de Schootbrugge et al, 2010;Gómez and Goy, 2011;Armendáriz et al, 2012;Harazim et al, 2013).…”

“…To calculate palaeotemperature, it has been assumed that the δ 18 O values, and consequently the resultant curve, essentially reflect changes in environmental parameters (Saelen et al, 1996;Bettencourt and Guerra, 1999;McArthur et al, 2007;Price et al, 2009;Rexfort and Mutterlose, 2009;Benito and Reolid, 2012;Li et al, 2012;Harazim et al, 2013;Ullmann et al, 2014, Ullmann andKorte, 2015), as the sampled non-luminescent biogenic calcite of the studied belemnite rostra precipitated in equilibrium with the seawater.…”

Lower Jurassic Radiolarian Biochronology and Evolutionary Rates

“…Our major arguments refer to an important emersion topography observed on seismic images of the North Sea (Marjanac and Steel 1997), to the evidence for polar ice storage (Price 1999) and to the deposition of thick conglomerates Dunlap Formation in Nevada (USA) (Muller and Ferguson 1939) and Ururoa-Kawhia area, New Zealand (Hudson 2003). The cooling model is supported by recent δ 18 O data on belemnites (Gomez et al 2008a, b;Harazim et al 2012) and by the discovery of glendonites in the upper part of the Pliensbachian (Suan et al 2011). The origin of the major cooling is probably related to huge volcanogenic SO 2 degassing during the Late Pliensbachian preceding the major CO 2 emissions of the Early Toarcian (Guex et al 2001; see also Sect.…”