Browsing by Author "Minisini, Daniel"
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Item An unusual oxygen-deficient ichnofauna from the Vaca Muerta Formation: implications for the ichnofacies model(Scandinavian University Press, 2023) Paz, Maximiliano; Mángano, M. Gabriela; Buatois, Luis A.; Desjardins, Patricio R.; Minisini, Daniel; Tomassini, Federico González; Rodríguez, Maximiliano N.; Pereira, Egberto; Parada, Martin N.In most oxygen-deficient ancient successions, Chondrites and Zoophycos are typical and recurrent trace fossils that are the last to disappear during deoxygenation events. Here, we report an unusual case of an oxygen-deficient ichnofauna lacking Chondrites and showing scarce Zoophycos, from the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation of Argentina. One outcrop and cores from nine wells were analysed. The succession comprises fine-grained, mixed carbonate-siliciclastic deposits accumulated in marginal-marine, basin, drift, slope, and outer ramp environments. It displays abundant biodeformational structures mostly producing irregular-laminated and massive fabrics in fine to medium mudstone. However, discrete trace fossils can be found within interbedded coarser-grained intervals, namely (in order of decreased ichnogenera abundance), Teichichnus, Alcyonidiopsis, Coprulus, Phycosiphon, Planolites, Lockeia, Thalassinoides, Palaeophycus, Nereites, Crininicaminus, Zoophycos, Diplocraterion, and ?Skolithos. Considering all ichnotaxa, the Vaca Muerta Formation may be seen as hosting a relatively diverse ichnofauna, yet, this is misleading because most occurrences are of low diversity. This atypical ichnofauna may be explained by either a lack of strong seasonality and existence of background food-rich environments, or by salinity variations, precluding the specialized feeding style of the Chondrites and Zoophycos producers. The dominance of feeding trace fossils with spreite (Teichichnus) and the low ichnodiversity suggest that the studied ichnofauna belongs to the Zoophycos Ichnofacies. Keywords Mudstone Chondrites cryptobioturbation Zoophycos Ichnofacies ichnologyItem Centennial to millennial variability of greenhouse climate across the mid-Cenomanian event(The Geological Society of America, 2021) Ma, Chao; Hinnov, Linda A.; Eldrett, James S.; Meyers, Stephen R.; Bergman, Steven C.; Minisini, Daniel; Lutz, BrendanCentennial- to millennial-scale climate variations are often attributed to solar forcing or internal climate system variability, but recognition of such variations in the deep-time paleoclimate record is extremely rare. We present an exceptionally well-preserved, millimeter-scale laminated marlstone from a succession of precession-driven limestone-marlstone couplets deposited in the Western Interior Seaway (North America) immediately preceding and during the Cretaceous mid-Cenomanian event (ca. 96.5 Ma). Sedimentological, geochemical, and micropaleontological data indicate that individual pairs of light-dark laminae record alternations in the extent of water-column mixing and oxygenation. Principal component analysis of X-ray fluorescence element counts and a grayscale scan of a continuous thin section through the marlstone reveal variations with 80–100 yr, 200–230 yr, 350–500 yr, ∼1650 yr, and 4843 yr periodicities. A substantial fraction of the data indicates an anoxic bottom water variation with a pronounced 10,784 yr cycle. The centennial to millennial variations are reminiscent of those found in Holocene total solar irradiance variability, and the 10,784 yr anoxia cycle may be a manifestation of semi-precession-influenced Tethyan oxygen minimum zone waters entering the seaway.Item Volcanic ash as a driver of enhanced organic carbon burial in the Cretaceous(Springer Nature, 2018) Lee, Cin-Ty A.; Jiang, Hehe; Ronay, Elli; Minisini, Daniel; Stiles, Jackson; Neal, MatthewOn greater than million year timescales, carbon in the ocean-atmosphere-biosphere system is controlled by geologic inputs of CO2ᅠthrough volcanic and metamorphic degassing. High atmospheric CO2ᅠand warm climates in the Cretaceous have been attributed to enhanced volcanic emissions of CO2ᅠthrough more rapid spreading at mid-ocean ridges and, in particular, to a global flare-up in continental arc volcanism. Here, we show that global flare-ups in continental arc magmatism also enhance the global flux of nutrients into the ocean through production of windblown ash. We show that up to 75% of Si, Fe and P is leached from windblown ash during and shortly after deposition, with soluble Si, Fe and P inputs from ash alone in the Cretaceous being higher than the combined input of dust and rivers today. Ash-derived nutrient inputs may have increased the efficiency of biological productivity and organic carbon preservation in the Cretaceous, possibly explaining why the carbon isotopic signature of Cretaceous seawater was high. Variations in volcanic activity, particularly continental arcs, have the potential of profoundly altering carbon cycling at the Earth's surface by increasing inputs of CO2ᅠand ash-borne nutrients, which together enhance biological productivity and burial of organic carbon, generating an abundance of hydrocarbon source rocks.