Distribution and growth styles of isolated carbonate platforms as a function of fault propagation

Abstract

Fault control on the position and distribution of isolated carbonate platforms is investigated in Northwest Australia using high-quality 3D seismic and borehole data from the Bonaparte Basin. Specifically, we address the relationship between carbonate productivity and fault growth so as to understand what are the primary controls on the growth of isolated carbonate platforms. Throw-depth (T-Z) and throw-distance (T-D) profiles for normal faults suggest they formed fault segments that were linked at different times in the study area. This caused differential vertical movements; some of the normal faults propagated to the surface, while others have upper tips that are 19–530 ms two-way-time below the sea floor, with the largest throw values comprising faults underneath isolated carbonate platforms. As a result, four distinct zones correlate with variable geometries and sizes of carbonate platforms, which are a function of the topographic relief generated by underlying propagating faults. Some relay ramps form the preferred location for the initiation and development of carbonate platforms, together with adjacent structural highs. Due to the complex effect of fault propagation to the palaeo-seafloor, and soft-linkage through relay ramps, three distinct ICP types are proposed: (1) in the first type, fault throw is larger than carbonate productivity; (2) the second type considers fault throw to be equal or less than carbonate productivity; and (3) in the third type, fault throw post-dates the growth of the carbonate platform(s). The analysis of fault propagation vs. carbonate platform growth shown here is important, as the three ICP types proposed, potentially correlate with variable fracture densities and distributions within the carbonate platforms. Based on our results, types 2 and 3 above enhance fracture- and fault-dominated porosity and permeability to a greater degree, making them favourable targets for hydrocarbon exploration.