Nitrogen and carbon cycle perturbations through the Cenomanian-Turonian oceanic anoxic event 2 (~94 Ma) in the Vocontian Basin (SE France)

Interpretation of Nitrogen Isotope Profiles in Petroleum Systems: A Review

“…Sedimentary δ 15 N profiles have also been used to identify intervals and locations where the nitrogen cycle and nutrient regimes appear to have been significantly altered from that for the modern-day, including Precambrian conditions and Mediterranean sapropel deposits (e.g., Godfrey and Falkowski, 2009;Higgins et al, 2010;Ader et al, 2016). These evaluations of paleoredox conditions and changes in the nitrogen cycle can provide critical evidence for the occurrence of larger biogeochemical cycle changes or geological events, such as emplacement of large igneous provinces, climate change, changes in export production, or the timing of the Great Oxygenation Event (e.g., Holloway and Dahlgren, 2002;Meyers et al, 2009;Algeo et al, 2014;Ader et al, 2016;Danzelle et al, 2020).…”

The Plenus Cold Event Record in the Abyssal DSDP Site 367 (Cape Verde, Central Atlantic): Environmental Perturbations and Impacts on the Nitrogen Cycle

“…The geological evidence of this event lies primarily on the occurrence of black laminated organic-rich sediments (e.g., black shale) across a wide range of marine settings, ranging from deep ocean basins to shallow shelfal seas. The widespread deposition of these black shales is associated to a short-term (<1 Myr) perturbation of the carbon cycle marked in the case of OAE-2 by a positive carbon-isotope excursion (CIE) recorded in both the organic (δ 13 C org , up to 6.0‰) and inorganic (δ 13 C carb , up to 2.5‰) reservoirs (e.g., Scholle and Arthur, 1980;Schlanger et al, 1987;Arthur et al, 1988;Jenkyns et al, 1994;Kuypers et al, 2002;Tsikos et al, 2004;Bowman and Bralower, 2005;Erbacher et al, 2005;Sageman et al, 2006;Jarvis et al, 2011;Gale et al, 2019;Danzelle et al, 2020). The positive CIE, resulting from preferential burial of 12 C-rich organic carbon in marine sediments and observed in many marine DSDP-ODP-IODP sites and continental sections and cores, is used to define the extent of the biogeochemical OAE-2 (Gale et al, 1993;Kuypers et al, 2002).…”

“…The global distribution of this isotopic carbon anomaly argues for a global change of the carbon cycle. Based on pCO 2 -dependent proxies (Δ 13 C; stomatal index, leaf-wax δ 13 C), the P-CIE has been interpreted as a short episode of pCO 2 rise during the δ 13 C fall, followed by a decrease in pCO 2 up to the δ 13 C maximum value (Kuypers et al, 1999;Sinninghe Damsté et al, 2008;Barclay et al, 2010;Sinninghe Damsté et al, 2010;Jarvis et al, 2011;Danzelle et al, 2020). These rapid oscillations of CO 2 concentration are thought to be linked to changes in temperature and oxygenation in oceanic domain.…”

“…These rapid oscillations of CO 2 concentration are thought to be linked to changes in temperature and oxygenation in oceanic domain. Geochemical evidences of oscillations in the oxygenation state of the water column include decrease in OM content and changes in the concentrations of redox-sensitive trace elements (RSTE: Mo, U, V, Cu) recorded within the P-CIE (Jarvis et al, 2011;van Helmond et al, 2014a;Clarkson et al, 2018;Danzelle et al, 2018Danzelle et al, , 2020Gale et al, 2019). The reoxygenation interval is usually termed the benthic oxic zone and marked by repopulation of benthic fauna (Friedrich et al, 2006;Keller et al, 2008;Eldrett et al, 2014).…”

“…This event, initially highlighted by the incursion of boreal marine fauna into the mid-latitudinal basins (Vocontian Basin, SE France; Jefferies, 1962, Jefferies, 1963, is now well defined in several basins and at all latitudes (see review of O'Connor et al, 2020 and references herein). The PCE is coeval to the second buildup of the δ 13 C signal within the positive CIE and has been geochemically characterized by positive isotopic excursion of the δ 18 O signal and by a decrease of dedicated biomarkers concentrations, such as the crenarchaeotal membrane lipid, linked to the TEX 86 , a sea-surface temperature proxy (Jenkyns et al, 1994;Paul et al, 1999;Tsikos et al, 2004;Forster et al, 2007;Sinninghe Damsté et al, 2008;Takashima et al, 2009;Danzelle et al, 2020). The origin of this short-term carbon cycle event is still debated (atmospheric vs. oceanographic; regional vs global processes) because the triggering factors of CO 2 change are difficult to identify.…”