Growth of triangle zone fold-thrusts within the NW Borneo deep-water fold belt, offshore Sabah, southern South China Sea

Abstract

The NW Borneo deep-water fold-and-thrust belt, offshore Sabah, southern South China Sea, contains a structurally complex region of three to four seafloor ridges outboard of the shelf-slope break. Previous studies have suggested the seafloor ridges formed either above shale diapirs produced by mass movement of overpressured shales (i.e., mobile shale) or above an imbricate fold-and-thrust array. Here, we performed tectonostratigraphic analyses on a petroleum industry three-dimensional (3-D) seismic volume that imaged the full growth stratal record. We show fold growth history, deformation styles, along-strike structural variabilities, and synkinematic sedimentation during triangle zone–style fold growth. Nine seismic horizons within growth strata were mapped and correlated to petroleum industry seismostratigraphy. Synkinematic sedimentation interactions with growing folds and near-surface strains were analyzed from seismic attribute maps. We interpret that the seafloor structures were formed by imbricate thrusts above multiple detachments. We estimate ∼8 km minimum shortening since the late Miocene ca. 10 Ma. The folds show oversteepened fold forelimbs, back-rotated backlimbs, and forward-vergent (NW to NNW) “blind” thrust ramps that terminate within the growth strata. Fold cores show evidence of internal shear. Immature folds show detachment fold geometries, whereas mature folds show forelimb break thrusts, type I triangle zones, and rotated forward-vergent roof thrusts. Thrust linkages spaced ∼10 km apart were exploited as thrust top synkinematic sedimentation pathways; the linkages also partition near-surface strains. Our comprehensive, three-dimensional documentation of triangle zone fold growth and sedimentation in a deep-water fold belt highlights internal shear, multiple detachments, and opposite thrust vergence; mobile shales are not required to explain the deformation.

Foreshock–mainshock–aftershock sequence analysis of the 14 January 2021 (Mw 6.2) Mamuju–Majene (West Sulawesi, Indonesia) earthquake

“…The development of fold and thrust belts in a highly compressive tectonic regime such as in Sulawesi is commonly known (Bergman et al 1996;Puspita 2005;Morley et al 2011;Wu et al 2020). This fold and thrust belt may form a series of imbricated synthetic thrust faults (roof ) seated on larger decollement thrust fault (floor thrust) (Yan et al 2016).…”

Gas Hydrate Resource Potential Of Deepwater Sabah, Malaysia: A Preliminary Assessment

“…A dataset acquired later by BGR in 2001 (BGR-01) also showed the presence of BSR between 250 and 350 m below the seafloor in the fold-thrust belt area (Behain et al, 2003;Behain, 2005;Franke et al, 2008). More recent works have also mentioned or reported the presence of BSR and/ or gas hydrates in offshore NW Sabah (e.g., Warren et al, 2010;Laird & Morley, 2011;Dan et al, 2014;Paganoni et al, 2016Paganoni et al, , 2018Goh et al, 2017;Jong et al, 2020;Wu et al, 2020).…”

Mud volcanoes guided by thrusting in compressional settings

“…This assumption is common in structural restorations, although we are thus ignoring possible deformation-related changes, due for example to dissolution, pore reduction, shale flow, and horizontal compaction during shortening (see Fig. 1; e.g., Butler and Paton, 2010;Groshong et al, 2012;Eichelberger et al, 2015;Totake et al, 2018;Wu et al, 2020). In consequence, the values we estimated represent a minimum value of the shortening magnitude.…”