Load structures: gravity-driven sediment mobilization in the shallow subsurface
Published:January 01, 2003
Geraint Owen, 2003. "Load structures: gravity-driven sediment mobilization in the shallow subsurface", Subsurface Sediment Mobilization, P. Van Rensbergen, R. R. Hillis, A. J. Maltman, C. K. Morley
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Load structures are a type of soft-sediment deformation structure comprising synforms (load casts and pseudonodules) and antiforms (flame structures and diapirs) at an interface. They form in response to unstable density contrasts (density loading) or lateral variations in load (uneven loading) when sediment becomes liquidized or otherwise loses strength. They are here classified into five varieties: simple and pendulous load casts, in which the upper (denser) layer is laterally continuous; and attached pseudonodules, detached pseudonodules and ball-and-pillow structure, in which discrete masses of the upper layer are separated by matrix. Conceptual models demonstrate that there are several possible modes of formation for each type of load structure. One interpretation of the variation of load structure morphology is as a deformation series representing varying degrees of deformation, controlled by the magnitude of the driving force and/or the duration of its effective action. An interpretation of the commonly observed pattern of wide load casts and narrow flame structures is presented in terms of their differential growth. Fluidization has an important influence on the development of load structures and their relationship to other products of sediment mobilization.
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Subsurface Sediment Mobilization
Sedimentary facies in the subsurface are usually interpreted from a epositional/stratigraphical perspective: the depositional layering is generally considered to remain undisturbed, except in a few settings. But, there is growing evidence that subsurface sediment mobilization (SSM) is more widespread than previously thought, as new observations arise from the ever-increasing resolution of subsurface data. Many examples are from hydrocarbon provinces but studies elsewhere, for example in preparation for the underground storage of hazardous waste, have yielded unexpected examples. Although until now the different aspects of SSM, including soft sediment deformations, sand injections, shale diapirs, mud volcanoes, etc, have been separated, the new discoveries emphasize their inter-connection, regardless of scale, depth, location, grain size or trigger mechanism. This volume integrates the different aspects of sediment mobilization in the subsurface and their structural consequences, allowing a more generaland a more coherent view of the subject.