High-Resolution Seismic Study as a Tool for Sequence Stratigraphic Evidence of High-Frequency Sea-Level Changes: Latest Pleistocene-Holocene Example from the Korea Strait

ABSTRACT Sequence stratigraphic analysis of high-resolution seismic reflection profiles and sediment data reveals that the latest Pleistocene-Holocene deposits in the Korea Strait shelf off the southeastern Korean Peninsula form a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 kyr) sea-level cycle. Eight depositional systems, each with different seismic facies, constitute the systems tracts. The lowstand systems tract, consisting of sandy mud, forms a deltaic wedge that pinches out updip near or at the relict shelf edge. The transgressive systems tract, consisting mainly of sands, includes six depositional systems: (1) inner-shelf transgressive layer, (2) transgressive estuarine-deltaic complex, (3) transgressive sand ridge, (4) mid-shelf transgressive layer, (5) incised-channel fill, and (6) beach-shoreface complex. Although the transgressive systems tract is widely distributed, it is much thinner than the lowstand and highstand systems tracts. The highstand systems tract is composed of a prodelta-shelf complex consisting almost exclusively of Holocene muds. The distribution and geometry of the systems tracts in the latest Pleistocene-Holocene sequence in the Korea Strait shelf is different from that of Vail's model in that: (1) the lowstand systems tract consists only of the lowstand deltaic wedge, which forms an elongated sediment body along the paleoshelf edge, and (2) the highstand systems tract is completely confined to the inner shelf and forms a nearshore belt parallel to the coastline. High-frequency (20 kyr), high-amplitude (magnitude of about 130 m) sea-level change, together with strong currents flowing northeastward along the southeastern coast of the Korean Peninsula and varying sediment supply, have resulted in this rather unusual stratigraphic architecture.

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