Browsing by Subject "Mass transport deposits"

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Failure mechanics, transport behavior, and morphology of submarine landslides
(2010-12) Sawyer, Derek Edward; Flemings, Peter Barry, 1960-; Mohrig, David; Lavier, Luc; Hornbach, Matthew; Shipp, R. Craig; Nikolinakou, Maria
Submarine landslides retrogressively fail from intact material at the headwall and then become fluidized by strain weakening; the final deposits of these flows have low porosity, which controls their character in seismic reflection data. Submarine landslides occur on the open slope and also localized areas including margins of turbidite channel-levee systems. I develop and quantify this model with 3-D seismic reflection data, core and log data from Integrated Ocean Drilling Program Expedition 308 (Ursa Basin, Gulf of Mexico), flume experiments, and numerical modeling. At Ursa, multiple submarine slides over the last 60 ky are preserved as mass transport deposits (MTDs). Retrogression proceeded from an initial slope failure that created an excavated headwall, which reduced the horizontal stress behind the headwall and resulted in normal faults. Fault blocks progressively weakened until the gravitational driving stress imposed by the bed slope exceeded soil strength, which allowed the soil to flow for more than 10 km away from the source area. The resulting MTDs have lower porosity (higher bulk density) relative to non-failed sediments, which ultimately produces high amplitude reflections at the base and top of MTDs. In the laboratory, I made weak (low yield strength) and strong flows (high yield strength) from mixtures of clay, silt, and water. Weak flows generate turbidity currents while moving rapidly away from the source area. They create thin and long deposits with sinuous flow features, and leave behind a relatively smooth and featureless source area. In contrast, strong flows move slowly, do not generate a turbidity current, and create blocky, highly fractured source areas and short, thick depositional lobes. In Pleistocene turbidite channels of the Mississippi Fan, deep-seated rotational failures occurred in the flanking levees. The rotational failures displaced material into the channel from below where it became eroded by turbidity flows. This system achieved a delicate steady state where levee deposition and displacement along the fault into the channel was balanced by erosion rate of turbidity flows. This work enhances our understanding of geohazards and margin evolution by illuminating coupled processes of sedimentation, fluid flow, and deformation on passive continental margins.
Geometry and nature of modern and ancient mass transport deposits worldwide
(2010-05) Singh, Kadira Analisa, 1986-; Wood, Lesli J.; Fisher, W. L. (William Lawrence), 1932-; Moscardelli, Lorena; Kerans, Charles
Mass transport deposits form a significant portion of the rock record in both modern and ancient basins. Their geometry, composition, distribution and genesis are poorly understood, making it difficult to predict anything about these deposits in assessing subsurface basin stratigraphy or modern seafloor hazards. A tremendous effort has been made in the last few years to characterize and better understand seafloor failures in numerous margins of the world. These mass failures have triggered the interests of geologists, particularly in the oil and gas industry, as they can form prominent seals and reservoirs. To increase our knowledge base of mass transport complexes (MTCs), the characteristics of 259 siliciclastic deposits worldwide, were analyzed in terms of their volume, area, length, thickness, lithology, and tectonic settings. In some instances, MTCs were geo-referenced and digitized into ArcGIS and their dimensions were calculated. These data reveal several interesting points and suggest a number of statistically significant predictive relationships. Sand-rich mass transport deposits show a propensity to be short and thick. Muddy MTCs show a propensity to be longer and thinner. The highest number and largest volume of clastic mass transport deposits occur along passive margins. These mega-MTCs are typically muddy with lengths up to 800 km and volumes up to 5000 km3. Sandy and gravelly Quaternary-age MTCs show maximum lengths of less than 300 km and with volumes less than 2000 km3. Pre-Quaternary MTCs are systematically under-documented in literature, but known occurrences are found in passive, active and convergent margins. The largest (30,000 to 40,000 sq km) occur along the older Tertiary margin of West Africa. To date, 41 separate mass transport deposits composed dominantly of carbonate material have been identified in literature. The most extensive and voluminous (7000 km3) carbonate mass transport complexes occur in the Citronens Fjord, Offshore Greenland. They are 200m thick, Silurian-age mega-breccias that were deposited in a convergent margin setting. On comparison carbonate MTCs tend to show longer flows with coarser grain sizes, while clastics show coarser grained deposits to be of more limited length. The Mad Dog area, Gulf of Mexico is a region of active salt tectonics and mass transport processes. Consequently, it was selected to form a focus study area to test the relationships developed during this project. MTCs in this region were grouped into four main types based on their size, geomorphology and internal structure. Their geometries indicate they are comparable to MTCs found offshore Oregon and New Jersey and are most likely muddy in nature.
Mass transport deposit and turbidite interaction in the Mio-Pliocene Gulf of California : Fish Creek-Vallecito Basin, Salton Trough
(2015-05) Slaugenwhite, Jeremy Scott; Steel, R. J.; Mohrig, David; Olariu, Cornel
Mass transport deposits represent a significant component of modern and ancient deep-water depositional systems. However, geophysical data lack the resolution needed to identify meso-scale (meters to tens of meters) interactions between mass transport deposits and the underlying and overlying sediment. An exposed section of supra- detachment rift basin sedimentary deposits containing subaerial and subaqueous debris flows and coarse-grained turbidites provides an opportunity to examine both the variability related to debris flow emplacement and the unique type of debris flow known as a sturzstrom. The Fish Creek -- Vallecito Basin, part of the larger Salton Trough region of southern California, contains a late Miocene to Pliocene stratigraphic section that records the opening of the rift basin, marine flooding by the Gulf of California, and the arrival of the Colorado River. The lower Split Mountain Group debris flow (up to 50 m thick) was deposited subaerially and was extensive enough to partially cover the previously deposited alluvial fans. At this time it is likely that the subaerial basin floor had subsided below sea-level, much like the floor of the Salton Sea today. Breaching of the basin walls then led to a rapid marine incursion into an already deep basin, such that the lower debris flow was immediately and conformably overlain by gypsum, mudstones, and coarse- grained Lycium member turbidites of the Imperial Group. A second major debris flow (up to 45 m thick), this one a subaqueous flow, severely deformed, scoured, and truncated the underlying Lycium member turbidites, and profoundly impacted the routing and deposition of the overlying Wind Caves member turbidites that signal the arrival to the basin of the Colorado River. Each of the turbidite successions thus follows an event of catastrophic mass transport. This thesis describes and documents the variable meso-scale erosion of the underlying turbidite deposits by the younger debris flow, the impact of variable upper debris flow surface bathymetry on subsequent turbidite deposition and connectivity, and links these findings to observations made by other workers studying similar deep-water deposits in outcrop and in seismic-reflection data. Building on the efforts of previous workers, this thesis also describes the characteristics of the subaerial lower and subaqueous upper sturzstroms, investigates emplacement mechanism implications of micro-scale features, and provides the first paleogeographic reconstruction of the basin during the time of subaerial to marine transition and the arrival of the Colorado River into the region.