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Investigations Into the Mechanics and Kinematics of Extensional Fault Systems


The extensional structures that compose rift margins and passive margin gravitational systems form hydrocarbon traps that represent significant petroleum reserves and future resources, and thus, understanding the processes that control the formation of extensional structures and validating their interpretation is of fundamental importance to petroleum geoscience. The interpretation of extensional structures in these environments is often placed into one of two conceptual frameworks—extensional fault-related folding through inclined shear, and domino-style fault arrays—though in some cases more complexities exist. Motivated by the desire to validate the geologic circumstances in which these models are applicable, and a need to find a framework for the interpretation of additional, more complex structures, a suite of 2D forward mechanical models of extensional structures using the discrete element modeling approach were generated. In this suite of models, the impact of various mechanical layering and layer strength scenarios (for example, a weak detachment layer of finite thickness with overlying layered sediments) and boundary conditions were tested, with the intent of representing a range of realistic geologic circumstances in which these structures form. These model results lend insight into the conditions that control structural style, and the mechanical circumstances that give rise to important deviations from conceptual end-members. A comparison with structures imaged in seismic reflection profiles from various representative basins demonstrates the utility of the results, providing a useful framework within which exploration geologists and geophysicists may improve the application of geologic models to the interpretation of extensional structures.