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Abstract ▼ AI-Helper

In order to understand the paleoceanographic change in the inner-shelf area of the northern East China Sea, benthic foraminiferal assemblages from the core sediments were analysed. Characteristically, the sedimentary facies change distinctly at about 390 cm core depth, and the result of the age dati...

In order to understand the paleoceanographic change in the inner-shelf area of the northern East China Sea, benthic foraminiferal assemblages from the core sediments were analysed. Characteristically, the sedimentary facies change distinctly at about 390 cm core depth, and the result of the age datings shows that there is a hiatus between the upper and lower parts of the depth. On the basis of foraminiferal analysis, the core sediments are divided into three benthic foraminiferal assemblages, and they indicate the paleoceanographic changes in the northern East China Sea. The lower interval (550~395 cm core depth) is represented by Ammonia beccarii-Elphidium clavatum assemblage, so it is interpreted to have been formed under the coastal/estuary environment influenced by the fresh water during the low sea-level period. It is also supported with well-developed laminar structure that is characteristic in this interval. The middle interval (380~120 cm core depth) was formed in about 5~2 ka B.P., showing the age gap with the lower deposit. This suggests that the erosional process was predominant in the study area during the transgression period, and sedimentation started again in about 6-5 ka B.P. when the sea-level reached the present level. The middle interval is represented by Bolivina robusta-Pseudorotalia gaimardii assemblage, indicating the change into the inner-shelf environment. It is characteristic that the amount of fresh water from the Chinese continent (YSCW and/or CDW) decreased as the result of the weak summer monsoon precipitation on the East Asian continent during this period. The upper interval (105~0 cm core depth) is identified with Bolivina robusta-Pseudoparella naraensis assemblage, and it was formed after 2 ka B.P. This interval well reflects the modern oceanographic environment of the northern East China Sea, where the influence of the fresh water from the continent is strong.

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