THE SEDIMENTARY CHARACTERISTICS OF THE LACUSTRINE FANS IN THE DALINGHE OIL BED OF LIAOHE BASIN

The Dalinghe oil bed of Liaohe Basin is in the lower part of the Shahejie-3 Formation of the Oligocene.It is distributed in the western depression of Liaohe Basin, and consists of conglomerates, pebbled sandstones, sandstones and deep-water mudstones. Coarse tailed graded bedding, normal graded bedding as well as various sole marks are well developed while traction structures are rare. Besides the typical turbidites, non-typical turbidites facies occur more frequently,such as chaotic coarse conglomerate facies, conglomerate sandstone facies with coarse tailed graded be-d ding, inverse-normal grading pebbled sandstone facies, massive sandstone facies and sandstone facies with diagonal bedding. Each facies has its special types of lithesome and sedimentary structures. The oil layer in the Baling River belongs to gravity current channel-flood turbidity of lacustrine fan system.Lacustrine fans developed in deep water area. The gravity current channel was a canal of leading the flood turbidity current into the lake basin, it began at the shore, passed through the shallow water area, and conjoined with lacustrine fans in deep water area. The lacustrine fans can be subdivided into inner-fan,mid-fan and outer-fan sub-facies. The main channel with levees was developed in the inner-fan. High-density turbidites were mainly in the channels and developed into coarse conglomerate facies with chaotic structure,while the levees located at both sides of the channel were classic turbidites mainly resulted from the lower-density turbidity current sediments. The mid-fan subfacies was lobe-shaped. The braided channels without levee were developed on the lobe near the upper-fan, and they gradually vanished along the current flowing direction and were changed into the channelless area. The braided channels were mainly the well developed coarse-tail grading pebbled sandstone facies resulted from high-density turbidity current sediments.The channelless area was characterized by the classic proximal turbidites.The topography of the lower fan area is flat, and the deposits were mainly the distal classic turbidites resulted from the lower-density turbidity current. The gravity current channel-lacustrine fan system is probably a kind of important turbidites in the faulted lake basin. Many kinds of stratum-lithological traps can be developed in the lacustrine fan, especially in the mid-fan area. Source, reservoir and cap rock complexes are well present in the lacustrine fans, so they are the important fields for petroleum exploration.