Seabed geomorphology and associated precondition for ferromanganese crust and nodule exploration in the southwestern part of central oceanic basin of the East Vietnam Sea

Vu Le Phuong*, Le Dinh Nam, Nguyen Nhu Trung, Phan Dong Pha, Tran Hoang Yen, Bui Van Nam
Received: 3 September 2020; Accepted: 26 November 2020

Abstract
The ferromanganese crusts and nodules are exposed deep-water deposits on the seafloor and have numerous significant scientific values and economic prospects. The southwest deep water basin of East Vietnam Sea has a complex terrain and geologic structure, which is considered auspicious for bearing ferromanganese deposits. The ferromanganese deposits are concrete ore precipitated on a hard substrate such as outcrops or debris (nucleus), hence the local seafloor geomorphology is fundamental for delineation and prediction of the distribution probability of deposits. An integrated set of 6 criteria was used to establish the seafloor geomorphological map and to evaluate the preconditions of crust and nodule bearing landform using the simple matrix and qualitative assessment in the study area. 6 criteria - including (1) underwater depth of seafloor referred to oxygen minimum zone (OMZ) and carbonate compensation depth; (2) slope rating into 4 grades of 0-4o; 4-7o; 7-15o and above 15o; (3) near-bed current; (4) hard substrate availability or landform proximity to surrounding terrain; (5) landform ages; and (6) seabed sediment characteristics, were applied with initial assumption of having the same contribution in the formation and preservation of the ferromanganese deposits. The final seafloor geomorphological map included 26 morphogenesis units belonging to 4 zones including the continental shelf, the continental slope, the continental rise and the deep water basin. Predictive evaluation using 6 criteria on 26 geomorphological units revealed 5 and 8 units classified as eligible for probing ferromanganese crust and nodule distribution, respectively. These preliminary results could be applied as precondition in ferromanganese deposit reconnaissance in the East Vietnam Sea and adjacent areas.
Keywords: seafloor geomorphology, ferromanganese, crust, nodule, East Vietnam Sea.