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<p>Along the macrotidal southwestern coast of Korea, roughly a thousand rocky islands are scattered across the nearshore. Diverse tidal flats have developed along the margins of this rocky archipelago. Because these bedrock islands are non-migrating, the associated tidal flats differ greatly from classical tidal flats in their sedimentation patterns and long-term evolution. In this study, we characterize the island-type tidal flat and document distinct sedimentation pattern and stratigraphic evolution during the late Quaternary. For this purpose, we collected about 40&#xa0;m long borehole core from the mud flat of Imja Island. Sedimentary facies and grain-size analyses have been conducted. Diatom assemblages have been additionally obtained. For the chronostratigraphy of the archipelago tidal flat, <sup>14</sup>C-AMS and OSL age dating methods were applied. Imja Island tidal flat deposits are divided into four unconformity-bounded units, the units directly overlying volcanic basement. The lowermost unit A, a sandy-silty fluvial package dated to 97 ± 8&#xa0;ka (Unit A) is overlain by lacustrine floodplain mud (Unit B1) and peat-rich swamp deposits (Unit B2) that accumulated at 55–52&#xa0;ka during the lowstand of sea level. Early-Holocene transgression produced a 7.9&#xa0;m-thick, finely laminated salt-marsh sequence (Unit C) between 10 and 8.5&#xa0;ka. The uppermost unit D comprises about 17&#xa0;m-thick of heterolithic sand–mud couplets and bioturbated mud, showing nine stacked channel fills emplaced since ~ 2.3&#xa0;ka. Age–depth modelling indicates rapid accumulation during the early Holocene, a reduced rate through much of the middle to late Holocene, and renewed acceleration during the late Holocene. The late increase in sediment accumulation, despite relatively limited regional sea-level rise, suggests that autogenic tidal-channel migration and vertical stacking played an important role in controlling sedimentation within the bedrock-confined archipelago setting.</p>

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Archipelago tidal flats in Shinan, Southwestern Korea – sedimentary facies characteristics, sedimentation pattern and holocene rapid accretion

  • 期刊论文

  • 发表日期：

    2026年5月18日

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  • Hyun Ho Yoon,
  • Tae Soo Chang,
  • Ara Cho,
  • Seung Young Ju,
  • Seoung Soo Chun

摘要

Along the macrotidal southwestern coast of Korea, roughly a thousand rocky islands are scattered across the nearshore. Diverse tidal flats have developed along the margins of this rocky archipelago. Because these bedrock islands are non-migrating, the associated tidal flats differ greatly from classical tidal flats in their sedimentation patterns and long-term evolution. In this study, we characterize the island-type tidal flat and document distinct sedimentation pattern and stratigraphic evolution during the late Quaternary. For this purpose, we collected about 40 m long borehole core from the mud flat of Imja Island. Sedimentary facies and grain-size analyses have been conducted. Diatom assemblages have been additionally obtained. For the chronostratigraphy of the archipelago tidal flat, 14C-AMS and OSL age dating methods were applied. Imja Island tidal flat deposits are divided into four unconformity-bounded units, the units directly overlying volcanic basement. The lowermost unit A, a sandy-silty fluvial package dated to 97 ± 8 ka (Unit A) is overlain by lacustrine floodplain mud (Unit B1) and peat-rich swamp deposits (Unit B2) that accumulated at 55–52 ka during the lowstand of sea level. Early-Holocene transgression produced a 7.9 m-thick, finely laminated salt-marsh sequence (Unit C) between 10 and 8.5 ka. The uppermost unit D comprises about 17 m-thick of heterolithic sand–mud couplets and bioturbated mud, showing nine stacked channel fills emplaced since ~ 2.3 ka. Age–depth modelling indicates rapid accumulation during the early Holocene, a reduced rate through much of the middle to late Holocene, and renewed acceleration during the late Holocene. The late increase in sediment accumulation, despite relatively limited regional sea-level rise, suggests that autogenic tidal-channel migration and vertical stacking played an important role in controlling sedimentation within the bedrock-confined archipelago setting.