Response to sea-level change in a non-deltaic coastal plain: Insights from cores chronologies

Abstract

The North coastal South China Sea (SCS) contains densely populated deltaic and non-deltaic plains. While recent dating has advanced knowledge on land-sea interactions in deltaic areas, chronological data for non-deltaic plains remain lacking, hindering a full understanding of coastal evolution. This study establishes the first chronological framework since late-Pleistocene for Longjiang plain, a non-deltaic coastal plain shaped by wind, ocean and fluvial forces. Using quartz Optically Stimulated Luminescence (OSL) and radiocarbon (¹⁴C) dating on two cores, combined with Bayesian age-depth modeling, we identified depositional hiatuses between >123 ± 8 ka and ${7.6}_{-0.6}^{+0.7}$ ka and between >72 ± 4 ka and ~${5.1}_{-0.9}^{+1.2}$ ka, respectively. These hiatuses were attributed to intensive erosion during last glacial sea-level fall/low stands. Below the hiatuses are strongly weathered sediments. Post-hiatus aeolian deposition during ${7.6}_{-0.6}^{+0.7}$ ka–${6.5}_{-0.5}^{+0.7}$ ka is linked to post-glacial sea-level rise. By contrast, aeolian deposition after ${2.14}_{-0.48}^{+0.69}$ ka successive to tidal deposition is likely triggered by local regression caused by increased sediment supply, favored by human activity since ~2.5 ka. Erosion during last glacial sea-level fall/low stands and aeolian deposition during the latest interglacial (Holocene) sea-level high stands, support the view that aeolian dunes preserved in modern coastal areas are mainly formed at sea-level high stands, rather than low stands. They also indicate that coastal erosion-accumulation cycles, controlled by eustatic sea-level fluctuation are not limited to deltas but may prevail in non-delta coasts. Quartz OSL sensitivity variations are observed in both cores and linked to provenance change, rework/redeposition by wind or Long-term chemical weathering.