摘要
新疆焉耆盆地沉积环境研究表明,该盆地侏罗纪煤系具有两种不同的成因环境:即浅水原地环境和深水异地环境.从煤层的产状,与煤共生的泥岩中的有机质类型,与煤共生的碎屑岩的成分、结构、构造和相序等方面论述了焉耆盆地中生界含煤地层深水成因的证据,并建立了深水煤系沉积模式.
Yanqi basin is one of the widely developed coal-bearing basins in Northwest China with a pre-Mesozoic basement overlain by Triassic, Jurassic, Tertiary and Quaternary rocks. The Jurassic system, a set of petrol-bearing strata, is considered to have main reservoir and source rocks of the basin. Much has been done on the sedimentary environment of coal measured strata and the coal抯 origin. Environments favorable for coal抯 formation from continent to marine are fluvial-alluvial plain, lake bay and shoal swamp, abandoned delta and fan delta, the inter-distributary of an active delta, coastal marsh and backbarrier-estuarine environment. Coal beds or seams in these environments were originated from shallow water reducing swamps. The core analysis shows that the Jurassic of Yanqin basin is a set of coal抯 series of terrestrial strata, but sedimentary facies indicators do not surport the standpoint of coal抯 shallow water origin. Any other facies markers indicative of shallow water environment have not yet been found, while there are lots of deep-water characters contradictory to traditional standpoint on origin of coal measures, so it is necessary to establish a new depositional model for the deep-water coal seams. In this article, the dimension of the coal beds, the types of organic matter, and the components, structures, textures and facies sequences of the clastic rocks which are associated with the coal beds were taken into account as the evidences of the deep-water origin of the Mesozoic coal-bearing beds, further more a depositional model of coal was proposed. The main features of deep water-formed coal measures have been listed below: (1) The deep-water coal beds have a direct contact with overlying and underlying rocks. Plant root and seat stones, marks of in situ growth and anochtnonous deposition, have not been identified. (2) The colors of mudstone range from deep grey to black. Pyrite can be found in the mudstone which is sometimes interbeded with thin thin silt-fine sand beds and has deformed beddings and Bouma sequence characteristic of distal turbidite. (3) Mudstones interbeded with shallow water coals are remarkablely different from the normal distal mudstone in their kerogen type and components. (4) The constituent of the debris is characterized by a moderate feldspar content with maximum value of 30 percentage, average 21, and minimum 15, and relatively high lithic content with maximum value of 48 percentage, average 39 and minimum 20, implying a paleo-environment characteristic of active tectonic movement with mechanical weathering, fast transportation and deposition. (5) The probability diagram shows a gentle slope straight line or a slight upward arc ,suggesting that only a graded suspension subpopulation existed. C-M plot has features of a gravity flow sedimentation. (6) Sedimentary structures common in the core are parallel bedding, slump deformation bedding, massive bedding, graded bedding or multiply graded beddings, flute cast, coal rips-up and typical Bouma seqence. In addition, evidences from the discriminant analysis and sedimentary features show that coal measures in Yanqi basin are different from those in other basins in Northwest China, while they have some similarities with typical deep-water rift-subsidence basin of East China. These coals occur near the maximum flooding surface. The sharp sedimentary slope, deep water, developed vegetations at the basin margin and debris flows make it possible that coals are associated with deep-water clastic rocks and mudstones.
出处
《新疆地质》
CAS
CSCD
2002年第1期53-57,共5页
Xinjiang Geology
