Study Of The Transgressive Event Deposition And Paleogeography Characteristics Of Noepaleozoic In North China Area

In this paper, depositional systems and the characteristic of sequence stratigraphy are studied. Then the sea level characteristics of the Neopaleozoic of North China are analyzed. According to the above, the depositional types and characteristics of transgressive event are studied in detail. Three transgressive events are found, and the paleogeographic maps are drawn. The trangressive event is studied by many subjects, such as sedimentary, paleontology, sequence stratigraphy, lithology, tectonics, and so on. And many methods are applied to the subjects, including logging, physical geography, geochemistry. Main conclusions are in below:Six depositional systems are found by studying the epicontinental basin of the Neopaleozoic in North China, which are carbonate platform depositional systems, tidal flat depositonal system, the barrier-lagoon depositional system, fluvial-controlled shoal water deltaic depositional system, alluvial fan depositional system and river-lake depositional system. On the basis, two tectonic sequences (I and II) and seven third-order sequences are divided by the way of sequence stratigraphy. Then the sequence strata frame of South-North and East-West is constructed. And the distribution of third-order sequences is specially studied.The sea-level was studied based on the sequence stratigraphy. It was divided two long cycles, that is the ones of the tectonic-sea-level change: one is the stage of short larges scale transgression and long time regression in the cycle of tectonic sequence 1^th, the other is regression stage of tectonic sequence 2^th . Different curves of sea-level change were drawn. And the main causes of influencing the change of the sea-level are conclude, which are tectonic subsidence and glacier dissolver. Then the different levels of sea-level change cycles response to the sequences are analyzed.Three differences are concluded between process transgression and spasmodic transgression, which are the background, deposition sequence and the principle of paludification and coalification. Four assembled deposits are founded: the combination of marine limestone-coal bed-exposure deposition; the combination of marine limestone-deeper water mudstone-coal bed-exposure deposition; deeper water mudstone-coal bed-exposure deposition; and the combination of marine limestone or deeper water mudstone-exposure deposition (pelite). The geochemistry characteristics of the transgressive event deposition are analyzed. Many differences are founded in depositional environment between marine sedimentation and coal. The storm deposit model of the epicontinental undulant basin is constructed by studying the characteristics and types of its sedimentation.There are three larger combinations of transgression event deposition, which are Wujiayu Limestone and 11^th coal seam in the transgressive system stand of sequence 1^th, Miaogou-Maoergou Limestone and 8^th coal seam in the transgressive system stand of sequence 2^th, Xiedao Limestone and 7^th coal seam. The transgressive event combination of the trangressive system stand in sequence 2^th is the largest one.By perfecting the coal accumulation theory of transgressive event, four special characteristics can be found. Firstly, coal seam develops in the transgressive system stand; secondly, sulfur content is higher and sulfur isotope ratio is lower in coal seam; Thirdly, coal petrology enrichments are different in the same coal seam. Finally, higher fluorescence intensity and lower reflected intensity become maldistribution in the same coal seam. Four combination of transgressive event coal accumulation between limestone and coal is concluded by the time of transgressive duration and strength of coal accumulation. That is, thicker limestone and thin coal seam, thin limestone and thin coal seam, medium bed limestone and thin coal seam, thicker limestone and thicker coal seam. Each combination characteristic of lime and coal seam is studied. And coal accumulation model figure is drawn by the consideration of the theory of transgressive event and the law of the the storm allochthonous coal accumulation.Transgressive event paleogeography distributions of sequence 1^th and 2^th are studied in detail. The transgression happened from North-East to South-West. The distributions of coal are the same to the marine deposition. So the combination of event deposition lies in the middle-north of China. And it can be traced to the North of North China, Shanxi and Huaibei, etal. The combination of Miaogou-maoergou Limsstone and 8^th coal seam is the most important one, which distributed most of the North China. So it can be founded in the most of North China. Its coal accumulation centre lies in Shanxi and so on, which has negative correlation to the distribution of limestone. The combination of Xiedao Limestion and 7^th coal seam in high system stand of sequence 2^th is event depositon in some areas, such as Shanxi, Henan, etal. Because different sedimentation causes the process transgression in Lianghuai, and event transgression in the north of North China, coal accumulation centre lies in the middle of North China and Lianghuai. And its combination can be founded in limited areas, especially in the middle or north of North China.