A 3-dimensional seismic method to assess the provenance of Mass-Transport Deposits (MTDs) on salt-rich continental slopes (Espírito Santo Basin, SE Brazil)

Provenance studies of Mass-Transport Deposits (MTDs) frequently rely on the analysis of kinematic indicators. In this work, we use seismic facies analyses, measurements of preserved blocks, and correlations between MTDs thickness and salt diapir geometry to introduce a new method to estimate the provenance of MTDs on 3D seismic data. The method, applied to a high-quality 3D seismic volume from the Espírito Santo Basin (SE Brazil), provides information on the location of source areas of MTDs, their bulk composition, and on their directions of transport. Whenever blocks of strata are found, their orthogonal axes are measured to estimate parameters such as Maximum Projection Sphericity Index (MPSI), Oblate Prolate Index (OPI), and ratio of short and intermediate axes (ds/di). These parameters are used to quantify the relative degrees of remobilization and transport of MTDs. Statistical data of importance include the variation of MTDs thickness with the diameter and distance from the centre of growing salt diapirs. In addition, the presence of cubic or equant blocks with c/a > 0.4 and c/b > 0.65 ratios are typical of proximal areas in MTDs, reflecting small transporting distances. Our work is important because it shows that distinct correlation coefficients exist between the thickness of MTDs and diameter of salt diapirs. Positive coefficients of correlation between diapir diameter and MTD thickness characterise active diapirism during the deposition of MTDs. This quantification allows the interpreters to distinguish MTDs sourced from local diapirs from MTDs sourced from more distal regions on the continental slope. Thus, the new method used in this research provides an alternative technique to kinematic indicators for determining the provenance of mass transport deposits on continental margins.

► MTD seismic facies include rafted, coherent, deformed blocks and debrites.
► Homogeneous MTD started as slides or slumps and end up as debris flow deposits.
► Proximal blocks have c/a > 0.4 and c/b > 0.65.
► Blocky debris flow deposits are poorly sorted.
► Positive correlation coefficients between diapir diameter & MTD thickness imply diapirism during deposition.