Characteristics of detached faults and their control on coal in Longyong coal field

Faulting structures with gentle angle are widely developed at the top and the bottom of Tongziyan Formation of Middle Permian coal measures in Longyong coal field. This geological structure caused absence of stratum and has big influence on the occurrence of coal measures. In Fujian coal geological sector, it is called "detached fault". The fault developed in certain layers, at several horizons along layers in cross section, parallel to each other, superimposed, occurred as group. From the old to the young horizons of the fault development, there are fault F₀ between the limestone of Qixia Formation and underlying Devonian-Carboniferous, F₀ between the limestone of Permian Qixia Formation and the coal measures of Tongziyan Formation, F₀₁ between the first segment and the third segment of Tongziyan coal measures, F₀₂ between Tongziyan coal measures and Upper Permian Cuipingshang Formation, F₀₃ between Cuipingshan Formation and Lower Triassic Xikou Formation. The formation mechanism of the detached faults in Longyong coal field is as follows:in the Late Paleozoic, there were some big anticlines, and during Indosinian Period, the anticlines further uplifted, inducing instability of the gravity of the strata, there was a weak mechanical plan for the detachment of layers from the high place to the low place; the exterior trigging factors such as earthquake and volcano erruption made the rocks slide from the high place to the low place. Different horizons of the fault development had different influence on the coal measures. If developed in the bottom of the coal measures, the faults destroyed the coal measures, are unfavorable to coal searching based on geology, if developed in the top of the coal measures, the faults protected the coal measures,and made the burial depth of coal measures shallower, favorable to deep coal searching.