A preliminary study on geomorphological characteristics and genetic mechanism of pockmarks in the Makran accretionary prism, northern Arabian Sea

摘要

Submarine pockmarks are residual negative geomorphologic features on the seafloor, which are generally considered to be related to fluid escape. In this paper, the geomorphological characteristics and genetic mechanism of pockmarks in the Makran accretionary prism are analyzed by using multi-beam bathymetric data and multichannel seismic data. Dozens of pockmarks have been found on the upper continental slope, middle continental slope, and lower continental slope of the Makran accretionary prism. Most of the pockmarks are characterized as giant and mega pockmarks. They display circular, semicircular, crescent, elongated, comet, and irregular shapes. Some show isolated distribution, while most show composite or chain-like distribution. Faults, gas chimneys, and mud diapirs act as main migration pathways through the fine-grained seabed surface sediments. Prevailing bottom currents clearly affect the morphology and development of the pockmarks. Fluid escape activities are the key factors for the development of pockmarks in the Makran accretionary prism. Due to the erosion and deposition of the submarine canyons, the pockmarks are mainly distributed on anticline ridges of the upper-middle slope on both sides of the canyons. During the development of pockmarks, their planar shapes may change, and the semicircular, elongated, and irregular pockmarks on the anticline ridges may cause seafloor collapse.