Late Quaternary transgressive deposits in a low-gradient environmental setting: Korea Strait shelf, SE Korea

摘要

Analysis of high-resolution seismic profiles and sediment data from the Korea Strait shelf reveals that the late Quaternary deposits in this area consist of five sedimentary units deposited during transgression phases of sea-level changes between about 15 and 6 ka BP: ancient beach/shoreface complex (unit P1), estuarine deposits (unit P2), mid-shelf sand sheet (unit M1), sand ridge system (unit M2), and inner-shelf sand sheet (unit M3). They are paralic and marine, separated by a ravinement surface. The lower paralic component below the ravinement surface consists of two sedimentary units (P1 and P2) preserved from shoreface erosion. The top surface of the paralic unit is truncated by a sharp erosional surface. This surface is overlain by three sedimentary units (M1, M2, and M3), which were produced by shoreface erosion that shifted landward during transgression. The transgressive deposits in this area, considering geometries and distribution patterns, can be divided into three types (Ⅰ, Ⅱ, and Ⅲ). Type Ⅰ overlying the lowstand systems tract is confined to the shelf margin, and consists of a thick paralic unit P1 and a relatively thin marine unit M1. Type Ⅱ on the mid shelf has no paralic component and the marine units M1 or M2 directly overly the sequence boundary. Type Ⅲ, found in the inner shelf, includes a thick paralic (unit P2) and a thin marine (unit M3) component. It is completely covered by the highstand systems tract.