Browsing by Author "Minisini, D."

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    Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)
    (European Association of Geochemistry, 2022) Yobo, L. Nana; Brandon, A.D.; Lauckner, L.M.; Eldrett, J.S.; Bergman, S.C.; Minisini, D.
    The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187Os/188Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187Os/188Os) at the onset of the MCE interval argues against LIP involvement in the event’s initiation. Rather, more radiogenic 187Os/188Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187Os/188Os from the middle of the MCE onward, coincident with a 40Ar/39Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.
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    Rhenium Isotopes Record Oxidative Weathering Intensity in Sedimentary Rocks
    (Wiley, 2024) Dickson, A. J.; Hilton, R. G.; Prytulak, J.; Minisini, D.; Eldrett, J. S.; Dellinger, M.; Stow, M.; Wang, W.
    Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic-rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.