Browsing by Author "Marroquin, Selva M."

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    A new Early Jurassic (ca. 183 Ma) fossil Lagerstatte from Ya Ha Tinda, Alberta, Canada
    Martindale, Rowan C.; Them, Theodore R.; Gill, Benjamin C.; Marroquin, Selva M.; Knoll, Andrew H. (Geological Society of America, 2017-03-01)
    Lagerstatten-deposits of exceptionally preserved fossils-offer vital insights into evolutionary history. To date, only three Konservat Lagerstatten are known from Early Jurassic marine rocks (Osteno, Posidonia Shale, and Strawberry Bank), all located in Europe. We report a new assemblage of exceptionally preserved fossils from Alberta, Canada, the first marine Konservat-Lagerstatte described from the Jurassic of North America. The Ya Ha Tinda assemblage includes articulated vertebrates (fish, ichthyosaurs), crinoids, crustaceans, brachiopods, abundant mollusks (coleoids with soft tissues, ammonites, gastropods, bivalves), wood, and microfossils. Paired bio-and chemostratigraphies show that Lagerstatte deposition occurred during the late Pliensbachian through early Toarcian, capturing the carbon isotope excursion associated with the Toarcian Oceanic Anoxic Event. Therefore, the Panthalassan Ya Ha Tinda biota is coeval with Toarcian Lagerstatten from the Tethys Ocean (Posidonia Shale and Strawberry Bank). Comparisons among these deposits permit new insights into the diversity, ecology, and biogeography of Jurassic marine communities during a time of pronounced biological and environmental change (e.g., expanded subsurface anoxia, warming, and extinctions). They also highlight the possibility that Mesozoic Oceanic Anoxic Events are temporal foci of exceptional preservation.
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    Thallium isotopes reveal protracted anoxia during the Toarcian (Early Jurassic) associated with volcanism, carbon burial, and mass extinction
    Them, Theodore R.; Gill, Benjamin C.; Caruthers, Andrew H.; Gerhardt, Angela M.; Grocke, Darren R.; Lyons, Timothy W.; Marroquin, Selva M.; Nielsen, Sune G.; Alexandre, Joao P. Trabucho; Owens, Jeremy D. (National Academy of Sciences, 2018-06-26)
    For this study, we generated thallium (Tl) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) of the Early Jurassic. The T-OAE, like other Mesozoic OAEs, has been interpreted as an expansion of marine oxygen depletion based on indirect methods such as organic-rich facies, carbon isotope excursions, and biological turnover. Our Tl isotope data, however, reveal explicit evidence for earlier global marine deoxygenation of ocean water, some 600 ka before the classically defined T-OAE. This antecedent deoxygenation occurs at the Pliensbachian/Toarcian boundary and is coeval with the onset of initial large igneous province (LIP) volcanism and the initiation of a marine mass extinction. Thallium isotopes are also perturbed during the T-OAE interval, as defined by carbon isotopes, reflecting a second deoxygenation event that coincides with the acme of elevated marine mass extinctions and the main phase of LIP volcanism. This suggests that the duration of widespread anoxic bottom waters was at least 1 million years in duration and spanned early to middle Toarcian time. Thus, the Tl data reveal a more nuanced record of marine oxygen depletion and its links to biological change during a period of climatic warming in Earth’s past and highlight the role of oxygen depletion on past biological evolution.