中国海域区古近纪含煤盆地与煤系分布研究

The Paleogene coal-bearing basin and coal-measures distribution of China sea area

新近纪和古近纪是全球重要的聚煤期。中国古近纪聚煤盆地分布在东部沿海省区,是全球性环太平洋聚煤带的组成部分。中国海域区含煤沉积盆地虽然也属于断陷盆地和坳陷盆地类型,且成群出现,但总体构造背景有利于含煤沉积的持续发展,盆地群连续性好,含煤沉积厚度大,如琼东南盆地、东海海域西湖凹陷,含煤沉积厚度达1km以上,这是陆上区古近纪含煤盆地所不能相比的。研究表明,海域区的聚煤盆地内大多由若干凹陷组成,为聚煤凹陷,可分为两大类,即半地堑凹陷和地堑凹陷。根据成煤盆地的水体深浅又可分为深水半地堑凹陷和浅水半地堑凹陷,地堑凹陷均为深水凹陷。盆地内表现为明显的两个聚煤带:缓坡聚煤带和陡坡聚煤带,缓坡聚煤带占绝对优势。在潮坪体系的潮上带和潮间带沼泽,利于聚煤作用的广泛发生。泥炭的堆积可能存在两种形式:原地堆积和异地堆积。由于盆地构造的频繁活动异地堆积可能是海域区聚煤盆地成煤作用的重要形式。海域区巨厚的含煤沉积为海域区煤成气成藏提供了丰厚的物质基础。又由于含煤地层埋深大,煤的变质作用程度相对较高,成为良好的烃源岩。

Paleogene and Neogene are important coal forming periods around the world.The Paleogene coal accumulation basins in the eastern coastal provinces of China are parts of the global Tertiary coal accumulated zone beyond the Pacific Rim.Although the coal-bearing basins of China Sea area are fault basins and depressed basins,and formed in groups,the overall structures are suitable for the development of coal-bearing deposition,the continuity of basin groups is good,and the coal-bearing depositions are thick.For example,in Qiongdongnan Basin,and Xihu Sag of East China Sea the thickness of coal-bearing deposition is more than one kilometer,which is incomparable for the Paleogene continental coal basins.Research shows that the coal accumulation basins in sea areas mainly consist of many sags.There are two types of coal accumulation sags,half-graben sag and graben sag.On the basis of their water depth,coal accumulation sags also can be classified into： the deep water half-graben sag and the shallow water half-graben sag,and the graben sags are mostly deep water sags.There are two distinct coal-accumulated zones in the basin＇ gentle slope and steep slope.And the gentle slope is dominant.The marsh of supratidal zone and intertidal zone in tidal flat system is suitable for the coal accumulation process to take place widely.There could be two types of peat accumulation： in situ accumulation and allochthonous accumulation.Because of the frequent tectonic activities in the basin,allochthonous accumulation is more favorable for coal forming activities in sea area.The very thick coal-bearing deposition in sea area provide with a comparably rich material base for the concentration of the coal-generated gas.Also as a result of the deep burial depth,the degree of coal metamorphism is relatively high,so the coal-bearing strata become good hydrocarbon source rocks.