Discussion on  Provenance Systems in Yingcheng Formation in Shiwu Area of Shiwu Fault Depression,  Songliao Basin

Key words: 
•   /
• provenance analysis /
• clastic particles component /
• heavy minerals

Abstract: Several provenances deposition is the result of mixed deposition of detrital materials that came from different provenances and different types of parent rocks.We may neglect the diversity of different provenances if we simply analyse the indexes that can indicate the characteristic of mother rock by calculating the average value. So we should classify the samples which belong to the same provenance at first, then analyze the direction and characteristics of every provenance.
  This article discussed the provenance system characteristics of Yingcheng Formation in Shiwu fault depression by comprehensive analysis of clastic grain combination, heavy minerals combination, sandy conglomerate distribution, dip logging and other materials. Clastic grain combination can indicate parent  rock characteristics of the provenance area, and clastic grain maturation can help to distinguish the transportation direction of fragmentary material. The authors determined three kinds of provenances by classification of the same provenance for clastic grain combination materials of all wells in the study area. The samples of the first kind provenance have the characteristics of " low quartz content, high feldspar and cuttings content, and magmatite is the main cuttings type";  the samples of the second kind provenance have the characteristics of " high quartz content, low cuttings content, and magmatite and metamorphic are the main cuttings types"; the samples of the third kind provenance have the characteristics of "quartz, feldspar, and cuttings' contents are nealy the same, and sedimentary and magmatite rock are the main cuttings types".Then the three provenance directions above have been determined, and the result are northern provenance, eastern provenance, and northwest provenance respectively.
  Heavy minerals analysis is also one of the methods of study provenance direction and parent  rock characteristics. Three heavy minerals combination areas have been identified by heavy minerals content statistics and combination classification of study area. There are "high zircon content area" in the north, "zircon, garnet, and green shade stone combination area" in the east, and "zircon and garnet combination area" in the westnorth. They stand  for the three provenance systems,  respectively.These areas indicated that there were three provenance systems exist in Yingcheng Formation of Lishu area.
  The transport direction and path of detrital material that derived from provenance can be pointed out by analyzing sand bodies distribution characters, and the palaeocurrent can be indicated by dipmeter. It were found that there were high content regions of  sandy conglomerate  in the north, the east and the northwest of the research area, and the direction of sandy conglomerate  content declining was the same as the direction of palaeocurrent that indicated by dipmeter. The results confirm three provenances which have been identified by analysis all above 
  After analyzing all above, three provenance systems were identified in Shiwu area of Yingcheng Formation.The mother rock in the northwest provenance system are sedimentary rocks and magmatic rocks, mother rock in northern slope provenance is magmatic rocks and mother rock in eastern slope are magmatic rocks and metamorphic rocks. The forming and distribution of sand bodies in Yingcheng Formation of Shiwu area were jointly controlled by the three provenances all above. Consequently, hybrid sedimentation were formed under the control of "multiprovenance, differences existed between each other provenance, and the characteristics of every provenance were inherited between each phase” in Shiwu area.