Geochemical and clay mineral characteristics of the Holocene sediments on the west coast of Bohai Bay and their implications for environmental and climatic changes

Based on the data of clay mineralogy, element geochemistry, grain size and AMS¹⁴C dating from the core of BXZK11 collected from the west coast of Bohai Bay and the correlation made with six well dated core profiles surrounding the study area, in addition to the smectite/(illite+chlorite) ratio, Al/Si ratio and Al/Na ratio analysis results, the sedimentary environmental and climatic changes since the beginning of Holocene are discussed for the region in this paper. The results suggest that owing to the rapid sea level rising during the period from the Last Glacial Maximun to 8830 cal. aBP, the sea water was quite close to the study area, the sedimentary environment had been dominated by the paleo-channel of the Yellow River, and a cool and slightly humid climate. During the period of 8830 to 6255 cal. aBP when the transgression reached its peak, the study area had been dominated by tidal flat and shallow sea and a warm and humid climate. From 6255 cal. aBP to 3650 cal. aBP, as the sea level was gradually dropping, this area had been occupied by a prodelta deposit, as one of the super lobes of the Yellow River Delta, under a cool and slightly humid climate. In the period from 3650 to 2780 cal. aBP, the sea level had remained stable to keep the delta continuously progradating as a delta front, while the climate changed to cool and dry. Since 2780 cal. aBP, the ancient Yellow River Delta has been continuously expanding, and the study area become a wide deltaic plain and the climate is cool and dry, similar to that of the present.