Late Quaternary high-resolution shallow seismic interpretation: Recognition of depositional sequences and systems tracts in response to sea-level changes in the northernmost part of the central Vietnam continental shelf

Abstract

This study presents the findings from a high-resolution shallow seismic profiles acquired in the northernmost part of the central Vietnam continental shelf. The purpose was to investigate the evolution of the late Quaternary succession. The seismic grid was correlated with two geotechnical boreholes and five gravity cores, providing a comprehensive understanding of the late Quaternary stratigraphy. The seismic stratigraphic interpretation reveals four major seismic facies (F1–F4) and identifies six stratigraphic unconformity surfaces, establishing their relationship with six seismo-stratigraphic sequences and the corresponding depositional system tracts within each sequence. The sequence boundaries have been erosively truncated by a series of incised channels/valleys. These boundaries were unconformably overlain by seismic facies F1 and F2. These facies comprise mostly high amplitude and discontinuous to continuous reflections. They were deposited during a period of relative sea-level fall, resulting in fluvial lowstand deposits of the lowstand systems tract (LST). Below this boundary, toplap terminations of clinoform were observed, corresponding to facies F3. This facies comprise primarily a progradational stacking pattern of the highstand systems tract (HST), transitioning downlap into thinner deposit toward the east-southeast. This suggests the eastward and southeastward transport of sediments from the edge of the Vietnamese mainland, as confirmed by the orientation of the incised channels/valleys. The transgressive systems tract (TST) is thin, and correlates with the seismic characteristics of facies F4, with low amplitude to transparent reflections. This systems tract is commonly bounded above by the highstand systems tract (HST) and below by the lowstand systems tract (LST).