THE FEATURES OF THE BARRIER ISLAND SYSTEMS OF THE EPEIRIC SEA AND THEIR EVENT DEPOSITS OF COAL-BEARING FORMATIONS IN CARBONIFEROUS OF NORTH CHINA

The Huabei coal-forming area which is located in North China in Upper Paleozoic Era is one of the biggest coal-forming basins in the world. It is about more than 800,000 km2. The reconstruction of the paleographic settings is the key for further recognition the huge Huabei Basin. It makes' possible to explore new theories and discover new resources. The coal-bearing formations of Carboniferous on North China including Benxi Formation of Middle Carboniferous and Taiyuan Formation of Upper Carboniferous, are a set of, coexisting deposits which spread widely and consist of limestone with subtidal carbonate platform facies and biogenetic bank facies and the terrigenous fragment with barrier island facies, lagoon facies and tidal flat facies. The coal beds are distributed widely and stablely. So the coal-bearing formation deposit belongs to the epeiric sea and their features of paleogeographic settings are a greater number of barrier island systems of epeiric sea with coexisting clear and turbid water. Barrier island and lagoon-tidal flats are repeated many times and existed alternately. The carbonate platforms are located outside the barrier island systems. The main coal-forming conditions are the peat flat environments on tidal flats with different types: carbonate platform-peat flat, lagoon-peat, flat, back barrier-peat flat, tidal delta-peat flat and estuary-peat flat. The important basin events in coal-forming period are the storm deposits and the volcanic deposits. Due to the characters of epeiric sea, the storm deposits are distributed widely in the Huabei coal-forming basin. The main marks of storm deposits in this area are the following: the hummocky under the surface of the erosion, the storm detention bed, the hummocky cross bedding, the sequence association and the trace fossil association. The tempesitite can be divided into carbonates and terrigenous elastics in the Huabei coal-forming basin. The main types are the follows: the proximal and distal carbonate tempesitite of the undertow current type, the carbonate tempesitite of the stirring type, sandstone tempesitite of the proximal type, sandstone tempesitite of the overflow type and gravel fragment mudstoae tempesitite. The distribution of coal seams caa be influenced by the storm deposits. The volcanic event deposits occurred in the middle and the upper parts of the Taiyuan Formation. The main types are as follows; the plastic fragment tuff, tufflava, tuff and tuffite, The volcanic deposits can be divided into the accumulation under water and above water.