华南地区晚三叠世含煤岩系层序—古地理

在对露头及钻孔剖面沉积特征研究的基础上,建立了华南地区晚三叠世含煤岩系层序地层格架,恢复了基于三级层序的岩相古地理,并分析了聚煤规律。根据岩相特征及岩相组合类型,在区内晚三叠世含煤地层中识别出陆相和海陆过渡相两大沉积类型,并可进一步识别出冲积扇、河流(包括辫状河和曲流河)、三角洲、湖泊、潮坪—潟湖、滨海平原和滨浅海等7种沉积类型。陆相沉积主要发育在上扬子地区的四川盆地;海陆过渡相沉积主要发育在东南部湘赣粤滨浅海。在晚三叠世含煤岩系中识别出区域性不整合面和构造应力转换面、砂砾岩体底部冲刷面和岩性突变面等类型的层序界面,将含煤岩系划分为5个三级层序。以三级层序为古地理作图单元,恢复了研究区的古地理格局。由煤层厚度与岩相古地理平面展布规律可知,最有利的成煤环境为三角洲沉积体系,其次为河流、潮坪—潟湖沉积体系,聚煤中心主要分部在四川盆地的乐威煤田以及华蓥山煤田、湘赣粤滨浅海地区的湘东南至赣西萍乡一带。

Sequence stratigraphy and lithofacies palaeogeography of the Late Triassic coal measures in South China

The depositional characteristics and environments,and the sequence stratigraphy of the Late Triassic coal measures in South China were studied based on data from outcrops and borehole sections. The third-order sequence-based lithofacies palaeogeography of the coal measures was reconstructed,and the coal accumulation pattern of the Late Triassic in the South China was summerized. Two major facies types,i.e., continental and transitional,were identified within the coal measures based on characteristics of lithofacies and lithofacies associations. The continental facies types include alluvial fan,braided fluvial and meandering fluvial facies,and the transitional facies types include deltaic,lacustrine(mainly shallow lake),tidal-lagoon,coastal plain and neritic facies. The continental facies were mainly distributed in the Upper Yangtze Block,typically in the Sichuan Basin,whereas the transitional facies mainly distributed in the eastern South China,typically in the Hunan-Jiangxi-Guangdong littoral and shallow marine area. Sequence boundaries,including regional unconformities and tectonic stress switching surfaces,fluvial incision surfaces,and abrupt change surfaces of lithology were identified. According to these sequence boundaries,the Late Triassic coal measures were subdivided into five third-order sequences. The lithofacies palaeogeography map of each third-order sequence was reconstructed based on the distribution of facies. The favorable coal accumulating palaeogeographic units were recognized based on the coal thickness and lithofacies palaeogeography maps,and the most favorable coal accumulating palaeogeographic unit was the delta plain unit,followed by fluvial unit,and tidal flat-lagoon unit. It was predicted that the coal-accumulating centers were located in the Leshan-Weiyuan Coalfield and the Huayingshan Coalfield in the Sichuan Basin,and the southeastern Hunan and western Central Jiangxi in the Hunan-Jiangxi-Guangdong littoral and shallow marine area.