Fossil Benthic Foraminifera in the Nakdong River Delta (Southeast Korea) during the Early to Middle Holocene

Abstract

Abstract. We investigated early to middle Holocene benthic foraminifera from four borehole cores in the Nakdong River Delta (southeast Korea) to document faunal associations and the transition of benthic foraminifera in coastal areas along the Tsushima Warm Current. We recognized four varimax factor assemblages. The varimax factor 1 assemblage (characterized by Pseudoparrella naraensis with Eilohedra nipponica) is common throughout core ND-02, which is seaward in the delta, whereas the varimax factor 2 assemblage (characterized by Haynesina sp. A) is dominated by low evenness in core 16ND-C02, which is landward in the delta. The varimax factor 4 assemblage (characterized by Buccella frigida) is generally common at the bottom and/or top part of the studied cores, whereas the varimax factor 3 assemblage (characterized by Elphidium somaense) tends to be common in the upper part of the three cores in the delta's seaward area. Both the contrasting high diversity and low diversity with low evenness of benthic foraminifera (varimax factor 1 and 2 assemblages, respectively) were present between the seaward and landward portions of the delta during the same period (∼7–6 ka), respectively. The combination of these contrasting faunas tended to appear in the delta with the intensification of the Tsushima Warm Current during ∼8–6 ka in addition to the sea-level rise. Common taxa in the Nakdong River Delta are largely neritic species of the temperate region in the East Asian margin, whereas some upper bathyal species, such as Angulogerina ikebei, Bolivina decussata, and E. nipponica, were subordinated in the delta's seaward portion. Such faunal features in the Nakdong River Delta are distinguishable from other coastal areas in the Japanese Islands.