Abstract
Stratigraphic sequence contrast and sequence stratigraphic framework are of great significance for the sedimentary phase and sedimentary systems of coal-accumulating basin. In the coal-bearing basin, the variation of the flooding surface controls the migration law of the coal-concentrating centres within the range. Therefore, the sequence comparison work is crucial to find favorable coal-collecting areas. In addition, studying the position of the coal seam in the sequence stratigraphic framework and carrying out the sequence comparison work in the lateral direction can effectively track the change of the position of the coal seam in the sequence stratum and summarize the law of coal seam accumulation and occurrence, which can be better to plan and guide the exploration and development of coal resources in Longdong coalfield.
Highlights
Research area sequence and system domain interface identification principleThe sequence is a set of relatively integrated, connected stratigraphic units, bounded by unconformity and laterally comparable integration surfaces
The Longdong area of Gansu Province, including the areas under the jurisdiction of Pingliang City and Qingyang City, east of Liupan Mountain, is located in the southwestern part of the Ordos Basin
Starting from the study of sequence stratigraphy, Fuxian Formation and Yanan Formation are stratigraphic sequences separated by parallel unconformity(regional unconformity); the top boundary of the Yanan Formation was originally determined to be a parallel unconformity, which has recently been confirmed as a regional unconformity[6]
Summary
The sequence is a set of relatively integrated, connected stratigraphic units, bounded by unconformity and laterally comparable integration surfaces. The stratigraphic unit between sequence bottom boundary and the first flooding surface in the sequence is the initial filling system domain. The initial marine-flooding surface and the maximum flood surface is the basin expanding systems tract. The maximum flood surface and the sequence top boundary is the basin reducing systems tract. The first section of the Fuxian Formation and the Yanan Formation is the filling stage of the basin, and the coarse clastic rocks develop.The stratum changes greatly. The lacustrine mudstone layer developed in a large area of the basin is the roof of the coal 4 layer, which represents the sedimentation of the largest lake intrusion and can be used as the largest lake surface[4]
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