A preliminary study on morphology and genesis of giant and mega pockmarks near Andu Seamount, Nansha Region (South China Sea)

Abstract

Pockmarks consists of depressions on the seafloor and are often considered to originate from fluid escape activities. In this study, we report 125 pockmarks near the Andu Seamount in the southern margin of the South China Sea (SCS) and preliminarily investigate their genesis based on multi-beam bathymetry and multichannel seismic reflection data. Most of them are giant and mega pockmarks and display circular, elliptical, elongated, crescent, comet and irregular shapes on a plan-view. The mapped pockmarks cover a total surface of 291.354 km 2 . Most of them occur in strings or clusters, while some are isolated. The filled volume of pockmark is calculated for the first time in this region, which may have significant implications for sedimentary process. Beneath most of the pockmarks, high-angle faults, high-amplitude reflections, filled-up structures and other fluid escape features are imaged on seismic sections. The structural settings, especially the fault systems, may control the genesis and development of pockmarks in this area. We also speculate that seabed gradients may contribute to generation of crescent pockmarks. According to seismic sections, sediment types and morphological analysis, we finally proposed that the genesis of these pockmarks may mainly be triggered by gas escape activities in the study area. This work may have important implications for the gas exploration in the Nansha Region, southern South China Sea.

Evolution of complex giant seafloor depressions at the northern Argentine continental margin (SW Atlantic Ocean) under the influence of a dynamic bottom current regime

“…Seafloor depressions are common geomorphological features in marine and lacustrine environments around the globe. Among them, large-scale depressions are characterized by hundreds of meters in diameter and several tens of meters in depth as described, e.g., for the Lower Congo Basin (e.g., Pilcher and Argent, 2007;Sahling et al, 2008;Nöthen and Kasten, 2011;Kasten et al, 2012;Wenau et al, 2017), Chatham Rise off New Zealand (Davy et al, 2010;Collins et al, 2011;Klaucke et al, 2018), the South China Sea (Zhang et al, 2020), and the Korean Peninsula shelf (Cukur et al, 2019). The origin and preservation mechanisms of seafloor depressions, in general, are ascribed to several different processes; however, especially for complex, large-scale depressions, these are often elusive (King and MacLean, 1970;Hovland and Judd, 1988;Judd and Hovland, 2007;León et al, 2010;Cukur et al, 2019).…”

Geophysical and Geochemical Exploration of the Pockmark Field in the Gulf of Patras: New Insights on Formation, Growth and Activity

“…The good coherence in orientation between collinear pockmarks and faults further supports the close relationship between the regional structural setting and the local fluid escaped patterns, which, in turn, control pockmark configuration and spatial distribution. At similar sites where the structural setting dominates, a pockmark field configuration has been reported, such as in the Barents Sea [27], Ireland [29] and the Nasha Region of the South China Sea [105].…”

Seabed fluid flow in the China Seas

“…In addition to the northern slope of the South China Sea, a few possible cold seeps are indicated in the southern South China Sea, e.g., methane seepage is inferred from the porewater geochemistry of shallow sediments in the Beikang basin . Zhang K et al (2020) reported 125 pockmarks close to the Andu seamount in the southern margin of the South China Sea. To date, cold seeps remain poorly investigated in the southern South China Sea.…”