Investigating the role of Large Igneous Provinces (LIPs) in the Mid-Cenomanian Event (MCE): Nd, Sr, and Os isotope evidence from the Iona-1 core



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Based on Earth’s climate cycling history of icehouse to greenhouse states and isotopic proxies for paleoclimate and environmental conditions, there is a direct relationship between volcanism, weathering, ocean circulation, and the carbon perturbations that define these cycles. Ocean anoxic events (OAEs) occur during Earth’s greenhouse states. The OAEs are defined as periods of increased oxygen depletion (anoxia) in the global ocean and are identified in lithostratigraphy as globally traced units of black shale. While geochemical constraints of ocean anoxia are well documented, the biogeochemical triggers of these anoxic events are not well understood. It is theorized that the Cenomanian-Turonian Ocean Anoxic Event 2 (OAE2; ca 94 Ma) was at least partly triggered by the emplacement of a large igneous province (LIP) based on Nd isotope data indicating enhanced nutrient content in seawater from increased hydrothermal activity (Eldrett et al., 2014; Jenkyns et al., 2010). The Mid-Cenomanian OAE (MCE; ca 96.5 Ma) may have been a prelude to OAE2 (Coccioni and Galotti, 2003). Understanding the paleoclimate of the MCE would contribute to a better understanding of OAE2 and how OAEs may be related. However, there is scarce evidence for the MCE’s environmental conditions. This study reconstructs the mid-Cenomanian Cretaceous Western Interior Seaway (KWIS) seawater εNd, 87Sr/86Sr and 187Os/188Os from Shell’s Iona-1 research core of southwest Texas to test the role of changes in ocean circulation and the emplacement of a LIP in triggering the MCE. The modern ocean ranges in εNd values of -14.340.13 to -8.00.3 (Flierdt et al., 2016). The MCE data from this study show a positive εNd excursion (-4.14 to -0.56) likely as a result of a highly radiogenic εNd input from submarine volcanism. The emplacement of the Caribbean large igneous province (CLIP; 98.7 Ma) was carried northward into the KWIS by the migration of the equatorial Atlantic Tethyan water mass during the early Cenomanian (Serrano et al., 2011; Eldrett et al., 2017). This northward migration of the Tethyan water mass with high nutrient contents from volcanic input may explain the positive εNd excursion and contribute to the onset of ocean anoxia observed in the MCE.



OAE, Mid-Cenomanian, ocean, anoxia, carbon cycle, greenhouse, climate, isotope, environmental, proxy, Neodymium, Strontium, Osmium, Geochemistry, paleoclimate, paleocirculation, shale, Iona-1 core, Eagle Ford group