Distribution and environmental significance of live and dead benthic foraminiferal assemblages in surface sediments of Laizhou Bay, Bohai Sea

Surface sediment samples at 80 stations were collected from Laizhou Bay in the Bohai Sea, and the live and dead foraminifera were analyzed in order to understand the relationship between foraminiferal assemblages and environmental factors. Four representative zones (A, B, C and D) of natural stations were classified by the Hierarchical Cluster Analysis (HCA), based on the total (live plus dead) relative abundances of 25 species commonly observed in the study area. The distribution patterns of benthic foraminifera, especially the characteristic species, responded well to the slightly varying environment. In Zone A, the nearly consistent structural components of live and dead foraminifera indicate that there was no massive transportation process. Their distribution was mainly controlled by the deeper water depth, a higher bottom salinity and coarse sandy silt (ST) content. In Zone B, the high proportion of living miliolid tests might be related to the high-salinity tongues along the southern Laizhou Bay towards its center. The dilution effect of high sedimentation rate along the southern Yellow River (Huanghe) mouth led to the sparse amount of foraminiferal tests in Zone C. However, complex environmental factors limited the distribution and postmortem taphonomic process of the benthic foraminifera in Zone D. Under the coactions of large amounts of freshwater and nutrient from the Yellow River and some small rivers located in the western study area, and silt (T) substrates mainly from the suspended sediments of the Yellow River, the living group Cribrononion subincertum (Asano) and agglutinated species dominated in Zone D. Besides, part of the allochthonous miliolid tests from Zone B might have been transported and reburied along with the autochthonous species in Zone D due to the bottom circulation. Moreover, the small- and thin-shelled species C. subincertum that dominated in the living assemblages was poorly preserved or totally absent in the dead groups. It may have been transported as suspended load and redeposited by the circulation flowing towards the outer bay. (C) 2016 Elsevier B.V. All rights reserved.