Discovery of numerous pingos and comet-shaped depressions offshore southwestern Taiwan

Abstract

High-resolution bathymetry collected with an autonomous underwater vehicle (AUV) along the flanks of three ridges of the accretionary prism offshore southwestern (SW) Taiwan revealed more than 650 elongated depressions in water depths ranging from 1155 to 1420 m. The depressions are between 12 and 129 m long, 5 to 70 m wide, and up 9 m deep at their center and shallowing downslope to about 1-m depth. Due to their shape in downslope cross section, they are termed comet-shaped depressions (CSD). The CSD occur in patches of more than 100 with densities of 53 to 98 CSD/km 2. In addition, seven topographic mounds were mapped and interpreted as pingos, which remotely operate vehicle (ROV) observations and sampling show to be covered with authigenic carbonate. These features overlie areas where multichannel seismic reflection (MCS) profiles show bottom simulating reflectors (BSR) and dipping strata extending from below the BSR to near the seafloor. We consider comet-shaped depression, a new type of pockmark, forms on a sloping seafloor where fluids expulsion occurred. We also suggest that the two types of distinctive geomorphic features are attributed to fluid venting which occurs at different rates, with the mounds developing slowly over time, but the CSD forming in discrete events perhaps associated with large earthquakes.

Barren ground depressions, natural H2 and orogenic gold deposits: Spatial link and geochemical model

“…The comet-shaped white spots observed here in Madagascar, Tanzania, Zimbabwe and Burkina Faso occur on the slope of small hills with circular white spots at the top of the hill. The tail of the comet-shaped features is oriented downslope, which is consistent with the model proposed by Chen et al (2020) for similar structures on the seafloor in association with gas venting. Moreover, elliptical pockmarks on the seafloor can have their main axis progressively rotating with distance (Hillman et al, 2015), leading to patterns similar to the "peacock feather-like" appearance described here (Figure 3 D).…”

“…Jürgens et al (2021) noted the same relationship in their point pattern analysis of fairy circles in Angola with small g max values for large mean nearest-neighbor distance. Comet-shaped and elliptical depressions are also described on the seafloor (Chen et al, 2015(Chen et al, , 2020 and formed by a combination of gas venting generating pockmarks and surface properties such as bottom current direction or slope leading to the comet shape (Berton and Vesely, 2018). The comet-shaped white spots observed here in Madagascar, Tanzania, Zimbabwe and Burkina Faso occur on the slope of small hills with circular white spots at the top of the hill.…”

Incision of Submarine Channels Over Pockmark Trains in the South China Sea

“…Interactions between gravity‐driven processes and fluid escape in pockmarks can reshape the latter to form comet‐shaped pockmarks oriented perpendicularly to the slope (Chen et al., 2019), ultimately forming across‐slope channels (Gay et al., 2006; Nakajima et al., 2014; Pilcher & Argent, 2007). Several pockmark trains are perpendicular to the slope gradient north and south of the GH, effectively comprising circular, comet‐shaped, and elongated pockmarks (Figure 1b).…”

Authigenic Carbonate Precipitation at Yam Seep Controlled by Continuous Fracturing and Uplifting of Four‐Way Closure Ridge Offshore SW Taiwan

“…Chen et al., 2014; T.‐T. Chen et al., 2020; Lim et al., 2011). To the south of the Manila Trench where the South China Sea lithosphere is subducted, chains of active volcanoes above the subduction zone are aligned parallel to the trench on Luzon Island (Ku et al., 2009; Wei et al., 2003).…”