Deepwater folding and thrusting offshore NW Borneo, SE Asia

Abstract

Abstract The slope and deepwater portion of the offshore NW Borneo continental margin hosts a number of proven hydrocarbon accumulations. Reprocessed and post-stack depth-migrated regional 2D seismic data reveal the occurrence of an extensive series of deepwater folds located at the leading edges of imbricate thrusts. Typical thrust-top folds include (1) anticlines characterized by large interlimb angles that lack a sea-floor expression; (2) anticlines with medium interlimb angles that show a clear sea-floor expression and normal faulting in the crest; and (3) anticlines with small to medium interlimb angles, a clear sea-floor expression and intensive crestal faulting associated with partial crestal failure. The different fold types occur at specific locations within the fold–thrust system, the widest and youngest anticlines near the present-day thrust front, and the narrowest and oldest folds in the most landward parts of the fold–thrust belt. Geometric restoration of the deepwater fold–thrust system along six regional shelf-to-basin cross sections provides incremental measurements of fault- and fold-related shortening for the time between the Miocene and present day in deepwater NW Borneo. Across the study area, the main thrust and fold activity appears to be largely of Pliocene–Holocene age. An apparent maximum of both incremental and total shortening is located in the central part of the study area. This location coincides with the maximum width of the fold–thrust belt and the preferential location for the development of the most recent deepwater anticlines.