Cenozoic mud volcano activity along the Indus Fan: offshore Pakistan

This study documents the tectono-stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two-dimensional (2D) and 3D seismic reflection data in a confined area of 50 x 65 km2. Conduits are recognized on each of these MVs connecting the pre-Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra-Middle Miocene and in the Late Miocene to Plio-Pleistocene transition. Most of the mud source (parent beds) seems to be of pre-Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5 +/- 9 km3. The location of the MV field is limited to the pre-Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo-Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived (similar to 22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present-day mud flow activity is seen on the seabed seismic reflection in the study area.