Initiation of Upward-Moving Gravity Structures
1984. "Initiation of Upward-Moving Gravity Structures", Structural and Depositional Styles of Gulf Coast Tertiary Continental Margins: Application to Hydrocarbon Exploration, Martin P.A. Jackson, William E. Galloway
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True (Newtonian) liquids will rise spontaneously by buoyancy if a density inversion exists even from a perfectly flat source layer. But for solids to rise, some kind of imperfection is required to trigger growth, even though the source layer is potentially mobile.
This heterogeneity can be either in the source layer (the mother layer of buoyant material) or in its overburden. Lateral variations in thickness, density, viscosity, or temperature can all initiate upward movement of a buoyant source layer. Some geologic heterogeneities in the source layer are listed below.
Initial heterogeneities can be present in a salt layer as a result of accumulation in a graben in a rifted terrane or as a result of lateral facies changes (fig. 1). Heterogeneities may be imposed by faulting or folding of the source layer. Faulting can be basement involved or thin-skinned, as discussed in unit 10 (fig. 1). In each case the diapir is likely to form on the upthrown side of the fault where the load is less. Detached faults usually sole out within the ductile source layer, whether this is salt or shale.
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Structural and Depositional Styles of Gulf Coast Tertiary Continental Margins: Application to Hydrocarbon Exploration
The structure and genetic stratigraphy of the Gulf of Mexico continental margin are inextricably intertwined. As hydrocarbon exploration and exploitation advance into the deeply buried Tertiary basin fill, interpretation of the complex depositional and structural styles of the outer shelf and upper slope setting will increasingly challenge the interpreter. This publication provides a coherent summary of the key concepts, models, and tools that are needed to meet this exploration challenge, and includes chapters on: basic principles, submarine slope systems, models of growth faults, mechanics of diapir growth, petroleum traps, and techniques on analyzing normal faults and balancing cross sections with extended strata.