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

Abstract

Seafloor depressions (SD) are features commonly observed on the ocean floor. They often occur as circular, small-sized (up to 10 s of m) incisions caused by fluid expulsion. Larger depressions (100s m to km) are considerably less abundant, and their origin and development have been scarcely studied. This study investigated two giant morphological depressions (>5 km) using recently acquired multibeam bathymetry and backscatter, sediment echosounder, and high-resolution seismic data. An arc-shaped (SD-N) and a sub-circular depression (SD-S) are located on the Ewing Terrace at the Argentine Continental Margin north and south of the Mar del Plata Canyon, respectively. The study area is influenced by the Brazil-Malvinas Confluence, where major counterflowing ocean currents affect sedimentation, and northward flowing currents form a large contourite depositional system. Using an existing seismo-stratigraphy, the onset of SD-N was dated to the middle Miocene (∼15–17 Ma), whereas SD-S started developing at the Miocene/Pliocene boundary (∼6 Ma). Acoustic anomalies indicate the presence of gas and diffuse upward fluid migration, and therefore seafloor seepage is proposed as the initial mechanism for SD-S, whereas we consider a structural control for SD-N to be most likely. Initial depressions were reworked and maintained by strong and variable bottom currents, resulting in prograding clinoform reflection patterns (SD-N) or leading to the build-up of extensive cut-and-fill structures (SD-S). Altogether, this study highlights the evolution of two unique and complex seafloor depressions throughout the geologic past under intense and variable bottom current activity in a highly dynamic oceanographic setting.

Channel inception through bottom‐current erosion of pockmarks revealed by numerical simulation

“…In the present study, we focus on the interaction between bottom currents and depressions formed by fluid escape, but similar results could apply to other kind of negative-relief bedforms formed by other factors, such as faulting (Berndt et al, 2012;Gay et al, 2021) and sediment dissolution (Cavailhes et al, 2022;Kluesner et al, 2022). On a nearly aclinal seafloor, the bottom-current erosion would be stronger at the downstream flanks (or reaches), shown as the erosion of single pockmark (Figure 6) or pockmark train (Figure 7), which is consistent with the current erosion mainly occurred at the downstream of an arc-shaped and elongated depression (with a length of 30 km), at the northern Argentine continental margin (Warnke et al, 2023). In the Grenada Basin (Gay et al, 2021) and the Hatton Basin (Berndt et al, 2012), the wide development of giant polygonal faults on the seabed may induce a stronger bottom-current erosion between the neighbouring polygons, forming seafloor furrows with a flat bottom.…”

The diverse morphology of pockmarks around Aotearoa New Zealand

“…In this study we also consider processes other than fluid escape that may create enclosed depressions at the seafloor, and that the formation of pockmarks may result from a complex interplay between fluid seepage, biological activity, ocean currents and other factors. For example, turbidity currents scouring the seafloor, and the infilling of abandoned canyons can both generate semi-circular to elongated depressions, and the action of oceanic currents may significantly alter crater-like features formed by alternative mechanisms (Loncke et al, 2004;Heiniö and Davies, 2009;Hillman et al, 2015;Hillman et al, 2018;Wenau et al, 2021;Maier et al, 2022;Warnke et al, 2023;Yu et al, 2023).…”