Lateral variability in strain along a mass-transport deposit (MTD) toewall: a case study from the Makassar Strait, offshore Indonesia

Contractional features characterise the toe domain of mass-transport deposits (MTDs). Their frontal geometry is typically classified as frontally-confined or frontally-emergent. However, it remains unclear how frontal emplacement style and contractional strain within an MTD can vary along strike. We use bathymetry and 3D seismic reflection data to investigate lateral variability of frontal emplacement and strain within the toe domain of the Haya Slide in the Makassar Strait. The slide originated from an anticline flank collapse, and the toe domain is characterised by a radial fold-and-thrust belt that reflects southwestwards emplacement. The frontal geometry of the slide changes laterally. In the S, it is frontally-confined, associated with a deep, c. 200 mbsf, and planar basal shear surface. The frontal geometry gradually changes to frontally-emergent in the W, associated with a shallow, c. 120 mbsf, and NE-dipping, c. 3o, basal shear surface. Strain analysis shows c. 8-14% shortening, with cumulative throw of the thrusts that increases along strike westwards from c. 20-40 to c. 40-80 m. We show that even minor horizontal translation of MTDs (c. 1 km) can result in marked lateral variability in frontal geometry and strain within the failed body, which may influence their seal potential in petroleum systems.