Research on Coal Bed Methane (Gas) Occurrence Controlled by Geological Tectonics in the Southern Margin of North China Plate: A Case Study of the Pingdingshan Coalfield, China

The geological structure is complex in the plate margin zone, and the occurrence of coal bed methane (CBM) is nonuniform with an obvious zoning phenomenon. It plays an important role to reveal the spatial distribution of CBM and its influence factors in plate margin zone for CBM exploitation and gas disaster prevention in coal mines. Based on the data of gas emission during mining, CBM content, and gas pressure in the Pingdingshan Coalfield, lying on the south edge of North China plate, the distribution characteristics of CBM and its influence factors using theories of CBM (gas) geology and statistical analysis method are investigated. The research area is divided into four CBM occurrence belts. There are its own CBM occurrence feature and control structural type in each CBM belt. Likou syncline is the structure that controls the overall distribution of CBM. NW-trending fold-fault belt, Guodishan fault, and Jiaxian fault are the structures that control the CBM occurrence in CBM belt IV, CBM belt II, and CBM belt I, respectively. And the difference in structural types is the main factor of CBM zoning.

Evaluation and formation model of Cambrian high-quality source rocks in the southeast margin of North China Plate

In response to the question of whether effective Cambrian source rocks are developed in the North China Plate, field investigations on the southern margin of North China have been carried out. High-quality marine argillaceous source rocks of continuous thickness of 35 m in the Lower Cambrian were discovered in the south-eastern margin of North China Plate. Phosphorus nodules are common in the source rocks. The TOC is 1.19%∼29.70%, with the average of 7.31%. The organic matter comes from low-level biological algae. Because the carbon isotope of kerogen is relatively more negative, it is judged to be mainly benthic algae. The converted vitrinite reflectance (Ro) from measured bitumen reflectance is 2.24%∼3.45%, which is an over-mature source rock. The Lower Cambrian source rocks in the southern margin of North China occurred under the background of rising sea levels. After the glaciers on the southern margin of the North China Plate melted, the Qinling rift trough developed and the stratum subsidence caused rapid transgression of seawater from southeast to northwest. At this time, algae multiply in large numbers, and after death they accumulate with phosphorus-containing materials to form phosphorus-containing organic matter. Benthic algae mainly live in deep-water shelf not affected by waves and tides. Therefore, the development of source rocks is mainly in the deep water shelf.

LATE PERMIAN PALEOENVIRONMENTAL CHANGES IN THE XINGCHENG AREA, LIAONING PROVINCE, CHINA: SEDIMENTARY SUCCESSION AND ROOT SYSTEMS

ABSTRACT During the late Permian, an alluvial environment prevailed along the northern margin of the North China Plate in the Xingcheng area, Liaoning Province, China. In this region, the middle–late Permian Shihhotse Formation and the late Permian Hamashan Formation record this transition from previous swamp-dominated settings. The two formations are mainly coarse-grained deposits and can be correlated with the Pingdingshan Sandstone, which developed as widespread alluvial facies in the central and southern parts of the North China Plate. Tectonic uplift around the plate due to Variscan orogenic activities probably contributed to the onset of alluvial prevalence, but the sedimentary characteristics in the Xingcheng area indicate that aridification was also an important driver. This is supported by the presence of root systems composed of rhizoliths in the Shihhotse Formation and Stigmaria fossils at the top of the alluvial conglomerate of the Hamashan Formation. Viewed at a larger scale, this basin-wide alluvial episode on the North China Plate was contemporaneous with the Wuchiapingian extreme aridity and followed a short humid interval. The overlying Changhsingian–Induan redbeds mark a paleoclimatic change to semiarid and arid again. The paleoenvironmental changes recorded in the upper Permian and Lower Triassic strata of the North China Plate, therefore, provide essential information for the understanding of late Paleozoic terrestrial evolution.