The Occurrence and Distribution of Polygonal Fault Systems in the Gulf of Mexico

Abstract

Polygonal fault systems are defined as clustered stratigraphic-bound arrays of multi-oriented extensional faults which form a polygonal pattern in plan-view. The faults are observed primarily in fine-grained sediment sequences (i.e. mudstones, chalks). These fault networks are recognized globally, in addition to being identified on other planets such as Mars. They have also been documented in offshore (e.g. Norway, South China Sea, etc.) as well as onshore environments (e.g. Niobrara Fm, Colorado, etc.). Polygonal fault systems are best identified with 3D seismic data; however, 2D discrimination is possible. The first published account was by Henriet et al. (1991) on 2D seismic data in the North Sea. While the definition of polygonal fault systems is widely agreed upon, the origin of these fault arrays remains debatable. A swath of literature is dedicated to the formative mechanisms and the few outcrop-based studies to date have yet to resolve the debate (Hibsch et al., 2003, Verschuren, 1992, Dehandschuter et al., 2005, Tewksbury et al., 2014, Cartwright, 2014). The faults appear to be constrained to specific stratigraphic horizons, often referred to as ‘tiers’ in literature, which may be subsequently divided by non-deformed stratigraphic units (Cartwright, 2014). It is postulated that the faults are non-tectonic in origin, given their intrinsic coupling with specific stratigraphic units possibly controlled by host-rock lithology and mechanical strength (Berndt, in press, Cartwright, 2003). Polygonal fault systems are of particular interest to regional geologists and petroleum geoscientists due to their large areal extent, ambiguous process of formation, and observed link to lithology. The presence of polygonal fault arrays has implications regarding paleo-stress field, fluid flow, and host rock lithology, mineralogy and mechanical properties, all of which are critical to exploration and development activities. Polygonal fault arrays have been observed in the Gulf of Mexico from the shelf to the outer abyssal plain. While many authors have noted the widespread occurrence of polygonal fault systems in the Gulf of Mexico, their stratigraphic occurrence and areal distribution, as well as the potential implications for basin exploration, are not well understood. Using a combination of seismic mapping and published literature from other basins (e.g. North Sea), a comparative statistical analysis of polygonal fault systems is possible.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016