Sequence stratigraphic model and Evolution of the Channelized depositional systems during Miocene in Ulleung Basin southeastern margin, East Sea

Abstract:

The southwestern margin of Ulleung Basin consists of broad and gentle slope continental shelf and shelf break. The sedimentary succession of the continental shelf is divided into nine sequences (S1-S9). The sedimentary succession is consists of the lower pro-graded sequences (from S2 to S6; 16.5-8.2 Ma) and upper channelized depositional sequences (S7 and S8; 8.2-5.5 Ma) in the Miocene. It progressively thickens northeast ward, suggesting a significant contribution of sediments into the basin margin. The channelized depositional system of S7 is divided into two subunits in which lower boundaries of each subunit are indicated by erosional truncation and channel incision. The underlying subunit 1 has two main streams; the progressive directions are to the NNE (a) and ENE (b). The main stream of subunit 2, developed after giving rise to the low-relief topography of the subunit 1, is only overlapping main stream (a) of subunit 1. The gentle sloped proximal-middle zone has different internal reflector, subunit 1 is characterized by parallel to chaotic reflections, whereas the subunit 2 is dominated by continuous and inclined reflectors, which can be interpreted that sediments supply is increase in subunit 2 than subunit 1. The steep sloped distal zone of channelized depositional systems connected the shelf break. The slope gradient is more slanted subunit 2 than 1. The internal structures are dis-continuous and inclined chaotic internal reflectors, which is interpreted mass transport deposits (MTDs). The slope failures commonly start near the shelf break, but some others are connected perpendicular to the main stream. The upper boundary of subunit 2 is truncated by transgressive surface. The stacking pattern of sequence 7 suggests the type-1 sequence controlled by sea level change, and the internal erosional surface in the channelized depositional systems can be interpreted that formed by tectonic or relative sea level flocculation during late Miocene in East Sea.