Multiproxy geochemical analysis of a Panthalassic margin record of the early Toarcian oceanic anoxic event (Toyora area, Japan)

Abstract

a b s t r a c tThe early Toarcian oceanic anoxic event (OAE) was a significant palaeoenvironmental perturbation that led to marked changes in ocean chemistry and climate, and which also had a long-lasting impact on marine ecosystems. The global significance of the event has been recognised from the widespread occurrence of a~3-7‰ negative excursion in the carbon-isotope (δ 13 C) composition of marine organic and inorganic matter and terrestrial plant material. This feature of the event is indicative of a pronounced perturbation to the global carbon cycle; an inference further supported by widespread evidence for seawater deoxygenation and elevated rates of organic carbon burial. Nevertheless, the precise palaeoenvironmental impacts of this event from sections outside of the Boreal and Tethyan realms are uncertain. Here, we present the results of a multiproxy geochemical study of an expanded record of the early Toarcian event from the northwest Panthalassa Ocean margin exposed in southwest Japan (Toyora area, Yamaguchi prefecture). Our results indicate that in the studied succession, organic matter enrichment persisted through the early Toarcian event, but elemental redox proxies do not support persistent seawater anoxia. Analyses of terrigenously derived major and trace element abundances coupled with sedimentological observations reveal an increase in coarse-grained sediment close to the onset of a~−4‰ excursion in δ 13 C org , and coincident with an inferred increase in terrestrial organic matter flux. These observations are consistent with previously published evidence for a marked strengthening of hydrological cycling and increased runoff that occurred contemporaneously with abrupt warming at the onset of the carbon isotope event.

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

“…In addition, other coastal basins with high organic carbon burial may have existed elsewhere on Earth, as published sections are currently geographically limited. However, several sites with high organic carbon during the T‐OAE have been found in, for example, the Neuquén Basin and Yakon River (Argentina; Al‐Suwaidi et al, , ), Haida Gwaii (British Columbia, Canada; Caruthers et al, ), and Toyora (Japan; Kemp & Izumi, ). In addition, other anoxic basins in which sediments are no longer preserved may have developed during the T‐OAE.…”

Tracking the redox history and nitrogen cycle in the pelagic Panthalassic deep ocean in the Middle Triassic to Early Jurassic: Insights from redox-sensitive elements and nitrogen isotopes

“…In addition to sea level changes (e.g., Hallam and Wignall, 1999), anomalous events occurred in both marine and terrestrial environments, such as global-scale intense volcanism and bolide impacts within less than a few million years (Cohen et al, 1999;Coe, 2002, 2007;Olsen et al, 2002aOlsen et al, , 2002bCohen et al, 2004;Tanner and Kyte, 2005;Tanner et al, 2008;Kuroda et al, 2010). The evidence for widespread anoxia in Middle Triassic and Early Jurassic shelf sedimentary rocks has been independently confirmed by multigeochemical proxies and lithological changes (e.g., Jenkyns, 1988;Quan et al, 2008;Bonis et al, 2010;Mazzini et al, 2010;Izumi et al, 2012;Pálfy and Zajzon, 2012;Song et al, 2012;Richoz et al, 2012;Jaraula et al, 2013;French et al, 2014;Kemp and Izumi, 2014;Kasprak et al, 2015).…”

“…This interval was also a period of global-biotic changes, such as the mass extinction at the Triassic-Jurassic (Tr-J) boundary, and the Toarcian Oceanic Anoxic Event (T-OAE) (e.g., Jenkyns, 1988Jenkyns, , 2010Alroy, 2010). These events were likely linked to major redox changes in the Tethys (McArthur et al, 2008;Pearce et al, 2008;Quan et al, 2008;Bonis et al, 2010;Pálfy and Zajzon, 2012;Richoz et al, 2012;Jaraula et al, 2013;French et al, 2014;Kemp and Izumi, 2014;Kasprak et al, 2015) and Panthalassic Oceans (Hori, 1993;Hori et al, 2007). In addition to sea level changes (e.g., Hallam and Wignall, 1999), anomalous events occurred in both marine and terrestrial environments, such as global-scale intense volcanism and bolide impacts within less than a few million years (Cohen et al, 1999;Coe, 2002, 2007;Olsen et al, 2002aOlsen et al, , 2002bCohen et al, 2004;Tanner and Kyte, 2005;Tanner et al, 2008;Kuroda et al, 2010).…”

Calibrating the magnitude of the Toarcian carbon cycle perturbation

“…In NW Europe and N Siberia, the organic-rich strata occur stratigraphically both within and well above the CIE (up to the top of the bifrons ammonite zone) [Röhl et al, 2001;Suan et al, 2011;Hermoso et al, 2013], whereas in S Europe, when present, they are generally bound to strata recording the CIE [Sabatino et al, 2009;Kafousia et al, 2011]. In most known successions, however, strata recording the negative CIE exhibit dramatic changes in geochemical, sedimentological, and micropaleontological composition [Hesselbo et al, 2007;Mattioli et al, 2009;Hermoso et al, 2012Hermoso et al, , 2013Kemp and Izumi, 2014], suggesting that the carbon cycle perturbation was intimately linked with profound climatic and oceanographic disturbances. SUAN [Kemp et al, 2005;Cohen et al, 2007], thermogenic methane emissions from the intrusive eruption of the Karoo-Ferrar province [Svensen et al, 2007], or the local recycling of remineralized carbon into superficial waters in restricted basin [Küspert, 1982;Saelen et al, 2000;Röhl et al, 2001;van de Schootbrugge et al, 2005].…”