292 / 2019-08-26 16:11:13

Concrols of Source-to-Sink System on Sand-body Distributions of the Yan’an Formation in Southeast North ShaanBei slope

Source-to-Sink System;source unit;sink unit;Sand-body

In recent years, palaeogeographic reconstruction of Source-to-Sink system is a hotspot in palaeogeography and Sedimentology. The study of sediment provenance plays an important role in the analysis of source-sink system. That is to say, the study of sediment source is helpful to restore the tectonic background of source area, the path of provenance transport, the estimation of transport distance, the reconstruction of paleo-river system and the restoration of the filling and evolution history of sedimentary basins. The Southeast of North ShaanBei Slope is located in the middle of Ordos Basin, and generally presents a westward dip monoclinic, which is characterized by an asymmetric large syncline with wide and gentle east wing but steep and narrow west wing. Based on the paleocurrent measurement, core study and well logging data of Yan 10 section, together with petrological analysis of sandstone, heavy mineral analysis, cathodoluminescence of quartz, clay mineral analysis and U/Pb dating of clastic zircon, we make clear the features of parent rocks, provenance directions and relevant tectonic setting of the Yan'an Formation in the southeastern part of northern ShaanBei slope. The results show that the parent rocks of Yan'an Formation are mainly Achaean and early Proterozoic granitoids, gneiss and epimetamorphic rocks in the northern Yinshan, northeastern Lvliang mountain and northwestern Alashan areas. Paleocurrent and provenance directions are mainly NW, WW, NE. According to the microscopic statistics of sandstone skeleton clasts analysis and Dickinson triangle diagrams, the tectonic background of the source area belongs to the re-cyclic orogenic belt. Based on the previous studies on source-sink system and continental deposits, the palaeogeomorphology of Yan 10 and Yan 9 in Yan'an Formation was restored, the types of sedimentary facies in target strata were analyzed, and the plane distribution characteristics of Yan 10 and Yan 9 sand bodies in Yan'an Formation were revealed. The main body of Yan 10 is fluvial deposits with Gan-Shan ancient river as the main channel, while the main body of Yan 9 is shallow lake deposits with different provenance directions, which were controlled by provenance directions and sedimentary facies. On the basis of this study, combined with previous data, this paper develops a complete Source-to-Sink system: Yanwu Highland, Ziwuling High and Low, Jiyuan Slope Zone as provenance zone; Ningshan Ancient River, Mengshan Ancient River, JinShaan Ancient River, Qingxi Ancient River and Ganshan Ancient River as transportation zone; and shallow lakes of Yan 9 in Yan'an-Ganquan area as sedimentary zone. Establishment of this source-to-sink system model provides ideas for search of sand body in hydrocarbon exploration.