THE SEDIMENTARY CHARACTERISTICS AND ENVIRONMENTAL EVOLUTION IN THE COASTAL AREA OF THE LIAODONG BAY IN QUATERNARY

In the low mountain and hill area on the east and the west coast of the Liaodong Bay. owing to long period of slow crustal uplifting, the Quaternary loose sediment is very thin or even absent; in coastal plains near river mouths, Quaternary system, generally speaking, is 20- 50 metres thick. But in the top of Liaodong Bay, the depth of Quaternary sediment in the lower Liaohe River plain whose foundation has been continuelly descending can reach 359 metres.Lower Liaohe River plain was the centre of Quaternary sedimentation in the province of Liaoning.Inthe plain, from north to south, from the two sides to the centre line, the depth of Quaternary sediments gradually accreted, the grain size changed from coarse to fine and the number of lithological units accreted also. In the vertical sections, the grain size of Quaternary sediments changed from pebble and cobble mingled with clay in the bottom to pebble, coarse sand find sand in the middle part, and silt on the top. The evolution of sedimentary environment along the Liaodong Bay was controlled by the changes of paleoclimate, sea level changes, neotectonic movement and geomorphologic condition.The developing process of the fans of the Dalinhe River and the Xiaolinhe River, formed in middle and late pleistocene, could reflected the evolution trend of sedimentary environment of the studied area. In glacial period the product of mechanical weathering in the low mountain and hill area was mainly coarse-grained and owing to the descending of sea level, the increase of hydraulic gradient and surface water transportation, a large quantity of fragments by mechanical weathering were transported to the plain area in which a series of coarse grained sediments were formed.In western Liaoning, diluvial fan in pediment area stretched to the plain area in glacial period and retread to the mountain area in intergracial period, In intergracial period, besides mechanical weathering, chemical and biological weathering increased in this period produced a large quantity of fine- grained material and a series of fine-grained sediments were formed in the plain area.The descending scale of the lower Liaohe River plain after late pleistocene was smaller than before and the master rivers of the Dalinhe River and the Xiaolinhe River transferred to west, so that the fan of the Dalinhe River and the Xiaolinhe River moved and incressed.Three times of transgression which were different in their extent occurred in the coastal area of the Liaodong Bay in Quaternary and marine formation and marine-continental formation devclopped in the area.The alternation of transgression and regression resulted in the changes of sedimentary environments and sedimentary facies.