Characteristics, classification and genetic mechanism of pockmarks

Abstract

Pockmarks are a kind of negative geomorphology formed by overpressure fluid spilling from the seabed. They are widely distributed in various underwater tectonic environments (such as continental margin basins and accretion wedges). Based on the recent research progress and achievements of pockmarks, this paper systematically divides the types of pockmarks according to their shapes, diameters, length width ratios, distribution characteristics and vertical filling modes. Moreover, this paper detailed introduces the main conditions and influence factors (such as diapir and fault)and deeply analyzes the genetic mechanisms of pockmarks. The local abnormal fluid pressure (overpressure) is the key factor to trigger the formation of pockmarks. According to the formation and leakage speed of overpressure during pockmark formation, the genetic mechanisms of pockmarks can bedivided into progressive, sudden and transitional three types. In the progressive formation model, both the formation and leakage processes of overpressure are slow. Whilst in the sudden formation model, the formation and leakage processes of overpressure are fast. For the transitional model, the formation and leakage processes of overpressure are faster than those of the progressive model but slower than those of the sudden model. The formation of pockmarks is affected by many factors, such as seawater and underlying strata. The physical and numerical simulation of dynamic overpressure formation and vertical migration to the seabed may be the future study directions of pockmarks.

Keywords

• pockmark
• classification
• influencing factor
• genetic mechanism