Stratigraphic Organization of the Late Quaternary Deposits in the Inner Shelf off the Nakdong River, SE Korea

Sequence stratigraphic analysis of high-resolution seismic profiles and borehole data reveals that the late Quaternary deposits in the inner shelf off the Nakdong River in the SE Korea form a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts in response to a fifth-order (20 kyr) sea-level cycle. Four sedimentary units, each with different seismic facies, constitute the systems tracts: incised-channel fill (SU1), transgressive estuary deposits (SU2), transgressive sand layer (SU3), and a delta-shelf complex (SU4).

The lowermost unit (SU1), which overlies the sequence boundary, is interpreted as fluvial deposits formed during the last glacial period and belongs to the lowstand systems tract. The lower middle unit (SU2) lying below the ravinement surface represents a paralic component that consists of estuarine sandy mud or muddy sand developed between approximately 13 and 8 cal kyr BP, whereas the upper middle unit (SU3) above the ravinement surface corresponds to a marine component that consists of sand veneer produced by the shelf erosion during the ensuing sea-level rise (8 - 6 cal kyr BP). These two units (SU2 and SU3) belong to the transgressive systems tract. The uppermost unit (SU4) regarded as the highstand systems tract formed the Nakdong subaqueous delta including the proximal and distal systems developed after the highstand sea level at approximately 6 cal kyr BP. The lateral transition from the proximal to distal facies suggests a prograding delta system in the Nakdong River.