Abstract

Extensive studies of Quaternary transgressions have been conducted in Bohai Sea, but debates continue regarding the sedimentary evolution and timing of transgressions, especially in the Pleistocene section. Benthic foraminifers and ostracodes from three boreholes (GK138, GK111, GK95) at Laizhou Bay, Bohai Sea, were utilized to interpret the paleoenvironments of deposition and elucidate the coastal response to global sea-level changes since the late Quaternary. Benthic foraminiferal species identified included 32 species from 15 genera; ostracodes included 28 species from 16 genera. Three marine sedimentary beds were recognized based on sedimentary characteristics, down-core changes in environmental proxies (benthic foraminifers and ostracodes), accelerator mass spectrometry (AMS) 14C, and optically stimulated luminescence (OSL) dates. These three beds were interpreted as: marine sedimentary bed 3 (M3), deposited in the late-middle Pleistocene; marine sedimentary bed 2 (M2), deposited during the late Pleistocene; and marine sedimentary bed 1 (M1), deposited during the Holocene. Three microfossil assemblages were identified, all indicating nearshore conditions. Assemblage III indicated a fluvially influenced or paralic environment during a relatively small-scale late-middle Pleistocene transgression that produced bed M3. Assemblage II indicates an intertidal-subtidal environment where bed M2 was deposited during the late Pleistocene transgression. Assemblage I indicates somewhat more marine influence in a subtidal environment where bed M1 was deposited during the Holocene marine transgression.

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