Abstract: There are much unknown about the Yanghugou Formation in the Qilian sea area in the western Ordos Basin,due to greatly varied strata thickness,diverse lithofacies associations,unclear sedimentary evolution sequences,and complex sedimentary model. Based on the detailed observation of 12 field sections and 28 drilling cores in the Yanghugou Formation in the middle and eastern part of the Qilian sea area,and combined with thin section petrological characteristics,grain size analysis,fossil remains,paleo-flow analysis,geochemistry and well logging data analysis,the lithofacies,lithofacies association characteristics as well as the sedimentary facies and evolution process of the Yanghugou Formation are systematically studied. This research shows that there are 18 lithofacies types and 8 lithofacies associations developed in the Yanghugou Formation in the Qilian sea area,western Ordos Basin,which respectively reflect the delta plain distributary channel,tide dominated delta front subaqueous distributary channel,estuary-tidal flat(tidal channel,tidal sand bar),tidal flat(sand flat,mixed flat and mudflat),barrier coast(barrier island,lagoon),barrier-open shore and shelf sedimentary characteristics. During the Yanghugou Formation depositional period,the central paleo-uplift spread from south to north across the western margin of the basin,dividing the basin into Qilian Sea and the North China Sea,and the western part of the basin is generally located in the Qilian Sea. It was a transitional continental-ocean sedimentary environment,and experienced a cycle of water deepening and then shoaling. During the deposition of the 3^rd member of the Yanghugou Formation,the eastern Ordos basin was still the ancient uplift exposed to denudation,only limited deposition occurred in western basin margin. In the northern part of the study area,the water depth is shallower,and there were tidal delta-tidal flat-barrier island deposits in the Wuda-AlashanZuoqi area,while there are relatively deep water bodies in the central and southern part of the study area,and barrier island-shelf deposits were mainly developed. During the sedimentary period of the 2^nd Member of the Yanghe Formation,due to the barrier of the central paleo-uplift,the east and west sea areas had not communicated,but the sedimentary range and depth of water increased significantly compared with the early period,with strong tidal influences and limited fluvial influences. In the northern Wuda area and the southern Jingyuan area of the study area,estuarine and tidal flat deposits were dominant,and the central area had the deepest water and developed shelf deposits. During the sedimentary period of the 1^st Member of the Yang Formation,due to the transgression of the Qilian Sea to the east and the shrunk of the central paleo-uplift,the east and west seas communicated with each other. Consequently,the depositional area expanded,and the water body became shallower in general. In the western part of the study area,the water body was slightly deep and delta-barrier island deposits were developed,while in the eastern part the water body was shallower and tidal flat deposits were developed.

Key words: lithofacies type, lithofacies association, sedimentary evolution, sedimentary model, Yanghugou Formation, western margin of Ordos Basin

摘要： 鄂尔多斯盆地西缘石炭系羊虎沟组沉积厚度变化大,岩相组合多样,沉积演化序列不明确,沉积模式复杂。在对羊虎沟组12条野外剖面、28口钻井岩心详细观察的基础上,结合岩石薄片、粒度分析、化石遗迹、古流向分析、地球化学特征以及测井资料分析,系统开展了羊虎沟组岩相及岩相组合特征研究,讨论了羊虎沟组沉积相及沉积演化过程。研究表明: 鄂尔多斯盆地西缘羊虎沟组沉积期发育18种岩相类型、8种岩相组合类型,分别反映了三角洲平原分流河道、潮控三角洲前缘水下分流河道、河口湾—潮坪(潮道、潮汐沙坝)、潮坪(沙坪、混合坪—泥坪)、障壁岛—潟湖及陆棚沉积特征。羊虎沟组南北向展布的中央古隆起横亘在鄂尔多斯盆地西部,分割了祁连海和华北海,盆地西部总体处于祁连海域。羊虎沟组沉积期总体为海陆过渡沉积环境,经历了水体变深又变浅的过程: 羊三段沉积期,鄂尔多斯盆地中东部仍为剥蚀古隆起,仅西缘局部地区接受沉积,研究区北部水体较浅,乌达—阿拉善左旗发育潮控三角洲—潮坪—障壁岛沉积,中南部水体相对较深,主要发育障壁岛—陆棚沉积; 羊二段沉积期,受中央古隆起影响,东西海域尚未沟通,但沉积范围及水体深度较早期明显增加,潮汐作用较强,河流作用受限,研究区北部乌达地区及南部靖远地区以河口湾—潮坪沉积为主,中部水体最深,发育陆棚沉积; 羊一段沉积期,祁连海向东超覆,中央古隆起萎缩,东西海域沟通,沉积范围扩大,水体深度总体变小,其中研究区西部水体略深,发育三角洲—障壁岛沉积,东部水体较浅,以潮坪沉积为主。

关键词: 岩相类型, 岩相组合, 沉积演化, 沉积模式, 羊虎沟组, 鄂尔多斯盆地西缘

CLC Number: 

• P534.45