Recent sedimentary processes along the Makran trench (Makran active margin, off Pakistan)

Abstract

A geophysical and geological survey (CHAMAK) has been carried out on the Makran accretionary wedge off Pakistan in order to understand the structure of the margin and the recent sedimentary processes in this self-maintaining prism disconnected from the modern Indus inputs (Qayyum et al., 1997; Gaedicke et al., 2002a; Schluter et al., 2002). Morphostructural analysis, based on the interpretation of bathymetric data and backscatter imagery, as well as a 3.5 kHz echo-character mapping, allow us to distinguish three structural domains, from north to south, where sedimentary processes differ: (1) the accretionary wedge to the north, (2) the trench and (3) the northern Murray Ridge at the seaward edge of the trench. The accretionary wedge is cut by canyons responsible for an important erosion of the prism especially in the eastern part of the wedge. Within the trench, sediments transported by the canyons generate sediment waves and are transported westward, parallel to the E–W axis of the trench. The eastern part of the abyssal plain is eroded by strong turbidity currents whereas important sediment deposition occurs in the western part of the abyssal plain, as a consequence of a decrease in the current energy. Nearly no mass transport deposits are recognized in the study area except near the ridges forming the accretionary wedge. Small-scale slope failure scars are described. The prevalence of turbiditic processes and the existence of a morphological barrier formed by the Murray Ridge allow the confinement of turbidites within the trench. Migrating sediment waves seem to be common sedimentary structures in this setting. These features might be produced by important velocity decrease of turbidity currents when reaching the trench.