Browsing by Subject "Mass transport deposit"
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Item Controls on late Neogene deep-water slope channel architecture in a bathymetrically complex seafloor setting : a quantitative study along the Southeastern Caribbean Plate Margin, Columbus Basin, Trinidad(2013-12) Ramlal, Kristie Anuradha; Wood, Lesli J.Slope-channels act as conduits that transport sediments from the shelf staging area to the basin floor. The Pliocene-Pleistocene section of the Columbus Basin in the deep-water slope offshore eastern Trinidad provides an opportunity to study slope-channel morphology and evolution, as well as any association between deep-water deposits, palaeo-seafloor bathymetry, shelf sediment feeder mechanism and changes in sediment supply types and volumes. Approximately 3250 km2 of 3D seismic data allow imaging and interpretation of channels within an interval between two regional surfaces termed P30 and P40. Observations of seismic cross-sections and stratal slices reveal a number of features including channels, mud diapirs, mass transport deposits (MTDs), and faulted anticlinal ridges. Channels appear leveed and unleveed, and alternate with MTDs in a cyclic vertical succession. Nineteen channels were mapped and divided into two groups based on their degree of levee development and stratigraphic position relative to MTDs. Group 1 channels, positioned below MTDs near the base of the interval, are shallowly incised, and show limited levee development. Group 2 channels, situated above MTDs, are relatively deeply incised, and have comparatively larger, well-developed levees throughout their lengths. Morphometric data from these channel groups reveal significant variability in channel width, channel depth, meander belt width, and sinuosity downslope. This variability is associated with influences of temporally equivalent local features and regional sea-floor slope changes. Increased slope gradient causes a marked increase in sinuosity. Diapirs and anticlinal ridges confine channel paths, divert their flow, and cause post-depositional deformation of both levees and channels. Levee height decreases downslope while levee width shows considerable asymmetry, which is related to occurrences of mud diapirism and MTDs. Irregularities on the upper surface of MTDs create accommodation space that confines turbidity flows, enabling ponding of sediments and volumetrically large levee construction. This accounts for dispersion of turbidity flows below the MTD which creates a series of small channels spread over a wide area, and comparatively fewer, confined channels above the MTDs with large levees.Item The origin and properties of mass transport deposits, Ursa Basin, Gulf of Mexico(2009-12) Strong, Hilary Elizabeth; Flemings, Peter Barry, 1960-; Day-Stirrat, Ruarri; Mohrig, DavidUniaxial consolidation experiments on Mass Transport Deposit (MTD) and non-MTD core samples from Ursa Basin, Gulf of Mexico, show MTDs have a lower porosity at a given effective stress compared to adjacent non-MTD sediments; a behavior observed in additional experiments on lab remolded Ursa core and resedimented Boston Blue Clay (BBC). I hypothesize debris flow action remolded the sediment: removing its stress history through shearing action, resulting in dense sediments at shallow depth. I supplement testing this hypothesis through lab remolding of BBC (in addition to Ursa clay) due to the greater availability and knowledge of this material. Ursa MTDs record multiple submarine slope failure events within the upper 200 meters below sea floor (mbsf); the most prominent is labeled MTD-2. MTDs have lower porosity and higher bulk density than surrounding, non-MTD, sediment. Porosity ([phi]) is 52% at 125mbsf – immediately below MTD-2; whereas [phi] is 46% at 115mbsf – within MTD-2. Comparison of non-MTD samples to MTD-2 samples, and intact to remolded samples, shows a decrease in sediment compressibility (Cc) within the MTD-2 and remolded sediments. Permeability within Ursa mudstones also declines with porosity according to: log (k) = A[phi] - B. Permeability is slightly higher within MTD-2; however grain size analysis indicates lower clay content in MTD-2 versus the non-MTDs. Pre-consolidation stress interpretations from the experiments show a linear trend in both MTD and non-MTD sediments, indicating both geologic units depict the same pore pressure profile. Remolding via debris flow explains the origin of MTDs at Ursa and governs the evolution of this geologic unit to its dense, highly consolidated, state today. At some point, slope failure triggered movement of the sediment down slope in form of a debris flow. The shearing action of the debris flow weakened the sediment, reducing its ability to support the overburden. As consolidation resumed, the remolded sediment followed a new, less steep, Cc curve. Within the geologic record, a distinctive dense, shallow unit is preserved; evidence for historical slope failure.