Abstract:

We used an AMS 14C and OSL dated core (QX01) from the coastal lowland of Bohai Bay to decipher the late Pleistocene paleo environment change and river channel infilling. Sedimentary facies, grain size, large amplitude changes in benthic foraminifers assemblage and diatom assemblage composition indicate that the major environmental changes occurred during the last 40000 years in the study area. The results show that 6 sedimentary stages were identified, which is (1) 3029.72 m: fluvial deposition; (2) 29.7229.4 m: transgression deposition, >43.5 ka; (3) 29.417.7 m: sandy sediments, river channel filling, ~37.929.7 ka; (4) 17.713.2 m: sediments finning from sand to clay, ~29.78 ka, the environments from river channel infilling to swamp; (5) 135 m: 84 ka, Holocene transgression deposits, the environments from fresh water swamp, to brackish swamp or salt mash, to shallow sea, to salt marsh, most strongest marine influence happened during 60005750 cal BP, then retreat; (6) 50 m: since 1.7 ka, the environment was controlled by river, and it is flood plain deposits during this period. The sedimentary changes were correlated with sea level change very well. During MIS 4 or 6, the sea level was relatively lower, the river cut down and river channel formed, then the river channel was infilling during 37.929.7 ka of MIS 3, when the sea level was relatively higher, the height of the river channel were infilled from -24.2 m to -11.8 m of Huanghai 85 highness. Then the last glacial maximum came, the sea water retreated out of Bohai Sea and the study area was swamp or shallow lake; the sedimentation stopped or at a very low level till the early Holocene, 8 ka. With the end of the last glacial maximum, the sea water came back again during 84 ka, represented by fresh swamp, salt marsh, and shallow sea deposits. Then the deposition stopped again, till 1.7 ka, with the role of the river, the environments became floodplain deposits. Moreover, two sedimentary break were identified, which is the break during last glacial of low sea level, and the break during 41.7 ka, when the marine influence finished or sea water retreated from the study area, but the role of the river had not started.

Key words: palaeochannel, environmental change, coastal lowland, Bohai Bay