APPROACH TO DEPOSITONAL MODEL OF ALLUVIAL FANS ON THE PERIPHERY OF LOWER LIAOHE PLAIN

River system such as Liaohe River, Hunhe River. Taizi River Dating River ctc.cntcrsinto Lower Liaohe Graben Basin form moutains, modeling the mst Lower Liaohe Plain and forming a series of buricdQuatcrnary alluvial fans on periphery area of the plain which arc perfect resources of supplyiyg water for Shcnyang, Anshan, Jinhou and othetr cities. Lower Liaohe Plain is a rift basi in Middle Cenozoic. Since Quaternary neotectonic movement is inhericed settle,The piedmont on periphery of the plain is strong place of tectonization. So the structural slope belt on the piedmont is the premise condition which buried alluvial tan is formed.The plain area not only has huge terrihenous elastic sediment(6000m一8000m) but also is the centre of Quaternary sediment in Liaoning province (more than 400m). Flowing out of mountain gaps, rivers form a series of large Quternary alluvial fans, there are Liaohc Fan. Hunhe Fan, Taizihe Fan, Dalinghe Fan. The area of only one fan is IOOOto 1500 spuare kilornctres, belong to large or middle-type.The shape and plane distribution of the fans are controlled by landform conditions which rivetrs flow out of mountain gaps.They usually distribute in the form of regular fan of tongue.The vertical shape of the alluvial fans is controlled by structure of basement.If the moutain gap has deep Fracture or step Fracture, the form of alluvial Fans is sphenoid or step; if the mountain gap is sagged slowly, the form is lens. The lithofacics structure of the alluvial fans have obvious horizontal banding.The body of fans can be further divided into sedimentary subfacies of top, middle and edge of fans according to the lithological characters, thickness and its space position.The study on grain size of sediment and electron microscope scanning of quart grain shows that dynamic mechanism of coarse elastic sediment on the top of Cans is strong hydrodynamism of rapids-type.The lithological characters of the top are gravel, grouan and sand which content is about 60-80 percent. the greatest thicknees is 100m, it is major place which water re- sources in city ezploitcd recently.The edge of fan is clay which content is 60-90 pocrcnt.Water in it is very little, so it has no meanihg of supplying water. These superposed alluvial fans formed from Late Middle Plcistoene of Late Pleistocene. The vertical variations of grain size data of the fans body reflects thqt dynamic state and sedimentary environment change with time,Φvalues of grain in Late Middle and Late Pleistocene is more coarse than in middle.lt shows that the climate was warm and the 17ow of river is large, it is the characters of flood pcriod, identical with the climate characters represntcd by data of sporo-pollen and panning.