Phytoplankton evidence for the timing and correlation of palaeoceanographical changes during the early Toarcian oceanic anoxic event (Early Jurassic)

Abstract

The causes and duration of the early Toarcian anoxic event are controversial. Integration of data from calcareous and organic phytoplankton provides a biochronological framework that allows precise correlations across the western Tethys. In particular, the Carinolithus superbus nannofossil Zone can be used to correlate the levels enriched in organic matter and the related δ 13 C negative excursion. Although a variable duration is given in the literature for this negative excursion, it is likely that it lasted between 520 and 650 ka. Increased atmospheric p CO 2 , related to excess volcanic emissions (magmatic activity in the Karoo and Ferrar Provinces), had an impact on climate and ocean chemistry, and marked the inception of a biotic crisis affecting many organisms. The beginning of the crisis within shallow carbonate platforms, documented at southern latitudes, predates the levels enriched in organic matter. Dinoflagellate cysts experienced a decrease in abundance in the C. superbus Zone, until they temporarily disappeared. The nannoplankton crisis was twofold: a decrease in size and low calcified specimens are observed in addition to a drastic decrease in absolute abundance. The increased atmospheric p CO 2 , as a result of the magmatic activity and temporarily amplified by transient methane release, could have been the trigger for the biocalcification crisis, which first affected the probably more reactive neritic system, and eventually the nannoplankton community.

An open ocean record of the Toarcian oceanic anoxic event

“…The excursion has been recognized in marine inorganic and organic matter (Jenkyns and Clayton, 1986;Schouten et al, 2000;Kemp et al, 2005;Suan et al, 2008), and terrestrial plant material (Hesselbo et al, 2000(Hesselbo et al, , 2007. Associated with the T-OAE is concomitant evidence for: a threefold increase in atmospheric CO 2 levels (McElwain et al, 2005), a rise in seawater palaeotemperatures (Rosales et al, 2004;, an increase in silicate weathering rates (Cohen et al, 2004;Waltham and Gröcke, 2006) and a biotic crisis affecting marine invertebrates and biocalcifying microorganisms (Little and Benton, 1995;Mattioli et al, 2004;Tremolada et al, 2005).…”

New deep-water brachiopod resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its significance for the brachiopod adaptive strategies around the Early Toarcian Mass Extinction Event

“…Coccolith distributions (Reolid et al 2014a) allow calibration according to the scheme of Mattioli & Erba (1999) for the South-Tethyan region. Other recent biochronological data (Mattioli et al 2004(Mattioli et al , 2013) are also applied. Stable isotopic records from Reolid et al (2014a) are used for determining the position of the negative CIE in the section.…”

“…2) from bed 30 upwards, assigning this interval to the NJT6 Zone (CNZ). This zone usually contains the T-OAE record (Mattioli et al 2004(Mattioli et al , 2009Casellato & Erba 2015), and, in other Tethyan basins, it spans the uppermost polymorphum -lower serpentinum ammonite zones.…”

“…Globally, the ETMEE is typified by a crisis of carbonate production in shallow-marine settings, an increase in organic matter content and a negative carbon isotope excursion (Jenkyns & Clayton 1997;Mattioli et al 2004Mattioli et al , 2009Hesselbo et al 2007;Suan et al 2008;Hermoso et al 2009;Al-Suwaidi et al 2010Littler et al 2010;Caruthers et al 2011). This event, so-called T-OAE (Toarcian Oceanic Anoxic Event) was originally considered as global on the basis of the prevailing record of organic-rich facies and anoxic conditions (Jenkyns 1988).…”

New data on internal morphology of exceptionally preserved Nannirhynchia pygmaea (Morris, 1847) from the Lusitanian Basin (Brachiopoda, Early Jurassic, Portugal)

“…Beds with the high pyrite content are marking the onset of the Toarcian anoxic event resulting in a mass extinction which, e.g., the spiriferid and athyrid brachiopods did not survive (Wignall et al 2005). The appearance of the Karoo Ferrar flood basalt Province is regarded as the cause for the increase of warming volcanic CO 2 resulting in an acidification of oceanic surface waters (Cohen et al 2004;Mattioli et al 2004), however, this theory is still a matter of debate (Jourdan et al 2005). The pyrite content in this time interval occurs only in the Tethyan but not in the Boreal Realm, where the Early Toarcian mass extinction event is described by the onset of a phase of black shale deposition (Hallam 1986;Little & Benton 1995;Wignall et al 2005).…”