Browsing by Author "Stright, Lisa"

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    Flow dynamics as Froude-supercritical turbidity currents encounter metre-scale slope minibasin topography
    Englert, Rebecca G.; Hubbard, Stephen M.; Romans, Brian W.; Kaempfe, Sebastian; Bell, Daniel; Nesbit, Paul R.; Stright, Lisa (Wiley, 2023-12-07)
    Seafloor topography can affect turbidity current dynamics on deep-water slopes, significantly influencing the dispersal of sediment. Despite the common occurrence of topographic complexity, there are few detailed investigations of topographic interactions and their effect on downslope flow evolution in intraslope environments. In this study, the sedimentology and architecture of an Upper Cretaceous intraslope fan succession deposited within an extensional, fault-bound minibasin are described from a rare, well-exposed, near-continuous, oblique depositional-dip outcrop of the Tres Pasos Formation, Chile. The 2 to 8 m thick studied interval transitions downslope from high-energy heterolithic strata, including metre-scale steep-faced scours, to non-amalgamated thick-bedded sandstones. Abrupt increases in sandstone percentage, sandstone bed thickness and grain size occur on the hangingwall blocks of south-east and north-east-dipping normal faults that bound the minibasin. Sandstone beds are dominated by backset or wavy low-angle stratification proximally, contain compositional banding near faults, and are characterised by increased proportions of planar laminated and structureless turbidite divisions downslope along the transect. Experimental observations of turbidity current interactions with topography are synthesised into a qualitative framework, which is used to interpret flow processes and characteristics from deposit trends. The results reconstruct the response of Froude-supercritical, stratified turbidity currents with denser basal layers when encountering metre-scale fault scarps. The analysis shows that metre-scale topographic features can substantially alter the flow properties of stratified turbidity currents, and their downslope flow evolution to include the development of transitional, depositional and flow-stripped sediment gravity currents. However, in comparison to base-of-slope settings, overall flow conditions are interpreted to be more uniform over slope breaks and zones of flow expansion in a partially confined intraslope environment. These findings have considerable implications for understanding flow response to similar scale morphological features on the seafloor and the potential for flow transformations in intraslope settings.
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    Timing of deep-water slope evolution constrained by large-n detrital and volcanic ash zircon geochronology, Cretaceous Magallanes Basin, Chile
    Daniels, Benjamin G.; Auchter, Neal C.; Hubbard, Stephen M.; Romans, Brian W.; Matthews, William A.; Stright, Lisa (2017-09-15)
    Deciphering depositional age from deposits that accumulate in deep-water slope settings can enhance understanding of shelf-margin evolutionary timing, as well as controlling mechanisms in ancient systems worldwide. Basin analysis has long employed biostratigraphy and/or tephrochronology to temporally constrain ancient environments. However, due to poor preservation of index fossils and volcanic ash beds in many deepwater systems, deducing the timing of slope evolution has proven challenging. Here, we present >6600 new U-Pb zircon ages with stratigraphic information from an ~100-kmlong by ~2.5-km-thick outcrop belt to elucidate evolutionary timing for a Campanian– Maastrichtian slope succession in the Magallanes Basin, Chile. Results show that the succession consists of four stratigraphic intervals, which characterize four evolutionary phases of the slope system. Overall, the succession records 9.9 ± 1.4 m.y. (80.5 ± 0.3 Ma to 70.6 ± 1.5 Ma) of graded clinoform development punctuated by out-of-grade periods distinguished by enhanced coarse-grained sediment bypass downslope. Synthesis of our results with geochronologic, structural, and stratigraphic data from the basin suggests that slope evolution was largely controlled by an overall decline in basin subsidence from 82 to 74 Ma. In addition to providing insight into slope evolution, our results show that the reliability of zircon-derived depositional duration estimates for ancient sedimentary systems is controlled by: (1) the proportion of syndepositionally formed zircon in a stratigraphic interval; (2) the magnitude of the uncertainty on interval-bounding depositional ages relative to the length of time evaluated; and (3) the geologic time (i.e., period/era) over which the system was active.