In order to understand the sedimentary features of the Ordos Basin in EarlyMiddle Jurassic, the principles and methodologies of baselevel cycle analysis are used to study in detail the EarlyMiddle Jurassic baselevel cycles of different orders in this basin. A high resolution sequence stratigraphic framework is established for the Fuxian FormationYan'an Formation in the Ordos Basin, and 4 longterm and 10 mediumterm baselevel cycles are identified. In view of the characteristics of sedimentary facies in this basin, this paper discusses the sequence filling dynamic processes of fluvial and delta depositional systems, presents the distribution pattern of baselevel cycle superimposition styles in different facies belts, and studies the evolutionary history of sedimentary filling in combination with high resolution sequence division.

为了研究鄂尔多斯盆地侏罗纪早中期的沉积特征，运用基准面旋回分析原理和方法，剖析了该盆地早中侏罗世不同级次基准面旋回划分，建立了鄂尔多斯盆地富县组—延安组高分辨率层序地层格架，共识别出了4个长期和10个中期基准面旋回。针对盆地沉积相发育特点，讨论了河流体系和三角洲体系的层序充填动力学作用过程，进一步指出了基准面旋回叠加式样在盆地内不同相带的分布规律；同时，结合高分辨率层序划分，揭示了该盆地的沉积充填演化史。

The author initiated and adopted the single factor analysis and multifactor comprehensive mapping method as a new methodology of quantitative lithofacies palaeogeography in order to reconstruct quantitative lithofacies palaeogeography By meaning， single factors are the factors which can independently reflect some characteristics of sedimentary environments of a stratigraphic interval of a section in an area Presence or absence as well as high or low percentage of single factors can all independently and quantitatively reflect some characteristics of sedimentary environments of the interval of the section in the area, such as water depth, water energy, nature of the sedimentary environments, etc The thickness of the interval and its specific rock types, texture constituents, mineral composition, chemical composition, fossils and their ecological assemblages, etc, can all be taken as single factorsThe single factor analysis and multifactor comprehensive mapping method include three steps First, an indepth petrological and lithofacies study of each section, especially fundamental section, should be made in order to obtain various reliable firsthand qualitative and quantitative data, especially quantitative data, and to understand the characteristics of sedimentary environments of each interval of each section Second, according to the mapping units, from the quantitative data of each section, select those factors which can independently reflect the characteristics of sedimentary environments, ie the single factors Then the statistics of the percent contents of various single factors of each mapping unit of each section in the area are made Based on these percentage data, the various quantitative single factor maps, mainly isoline maps， are composed These single factor maps can quantitatively reflect the characteristics of sedimentary environments of the mapping unit of the area from different aspects This is the single factor analysis Third, through superimposition and synthesis of these quantitative single factor maps, combined with other quantitative and qualitative data of this mapping unit of the area, with the dross discarded and the essential selected, with the false eliminated and the true retained, the quantitative lithofacies palaeogeography map of the mapping unit of the area can be composed This is the multifactor comprehensive mappingThe core of this methodology is quantification That is, based on the quantitative single factor data of each section, starting from analysis of various quantitative single factor maps, through superimposition and comprehensive analysis and judgement, finally the quantitative lithofacies palaeogeography map can be composed In such palaeogeography map, the definition of each palaeogeographic unit is based on quantitative data and quantitative single factor maps Therefore, such lithofacies palaeogeography maps are no longer sketchy and qualitative, but quantitative instead Quantification is the most important character of the author's lithofacies palaeogeography maps This makes lithofacies palaeogeography map and lithofacies palaeogeogaphy develop into the quantitative stage This is an important development in palaeogeography

笔者倡导并持续采用单因素分析多因素综合作图法这一定量的岩相古地理学方法论。单因素是能独立地反映某地区、某地质时期、某沉积层段沉积环境某些特征的因素,它的有无或含量的多少均可独立地反映该地区、该层段沉积环境的某些特征,如沉积环境水体的深浅、能量大小、性质等。某沉积层段的厚度、岩石类型、结构组分、矿物成分、化学成分、化石及其生态组合等，均可作为单因素。单因素分析多因素综合作图可分三个步骤：第一，是对各剖面尤其是各基干剖面进行认真的地层学和定量岩石学研究，取得各种第一手的定性和定量资料，尤其是定量资料，了解各剖面各沉积层段的沉积环境特征。第二，在已取得的各剖面的定量资料中，按要求的作图单位，选择出那些能独立地反映其沉积环境特征的因素，即单因素；并把全区各剖面各作图单位的各种单因素的百分含量都统计出来，作出各种相应的单因素图，主要是等值线图。这些单因素图可以从不同的侧面定量地反映该地区该沉积层段的沉积环境。这就是单因素分析。第三，把这些定量的单因素图叠加起来，并结合该地区该沉积层段的其他定量和定性资料，去粗取精，去伪存真，全面分析，综合判断，即可编制出该地区该沉积层段的定量岩相古地理图。这就是多因素综合作图。这一方法论的核心是定量，即以各剖面的定量单因素资料为基础，从各单因素图的分析入手，再通过各单因素图的叠加和综合分析判断，最后作出定量的岩相古地理图。在这种岩相古地理图中，各古地理单元的确定都有确切的定量资料和单因素图为依据。定量是笔者等用单因素分析多因素综合作图法编制出的岩相古地理图的最大特色。这就使岩相古地理图和岩相古地理学发展到了定量的阶段。这在古地理学中是个重大的进展。

On the basis of high-resolution sequence stratigraphy,the detailed study on the subdivision of different orders of the base-level cycles in middle Jurassic Yanan Formation has been performed in Yanshui river cross section,and a corresponding high-resolution sequence framework has been established in the middle part of Ordos Basin.There can be recognized 34 short,8 middle and 3 long base-level cycles.Simultaneously,the paper has also discussed the relationship between the stacking patterns of different cycles and sedimentary facies,deposition and tectonics,and furthermore,investigated the basinal filling history by the base-level cycle sequences.

利用高分辨率层序地层学方法,以延水河剖面研究为重点,详细剖析了中侏罗统延安组不同级次基准面旋回划分,建立了鄂尔多斯盆地延安地区延安组高分辨率层序地层格架。共识别出了36个短期、8个中期和3个长期基准面旋回。讨论了不同级次基准面旋回叠加式样与沉积相、沉积作用和构造作用等的响应关系,进一步通过基准面旋回层序研究了盆地的充填演化史。

Comprehensive research on the structure attributions, the primary basin features, the combination of lithology and lithofacies, provenance analysis, and the distinction of thickness distribution of the Ordos Basin in the Mesozoic, suggests that the depocenters of the basin transferred contraclockwise from southeast to north, then to southwest from middle Late Triassic to Early Cretaceous. There was no a unified or lager scale accumulation center present at the west of the basin before Early Cretaceous, but only small, isolated accumulated centers occurred. The reason why thicker strata appear to the west of the basin in multi stages is that these areas were much close to the west boundary of the primary basin, where abundant water source offered huge power. Therefore it stands for the local accumulation centers. Till Early Cretaceous, the depocenters, the accumulation and subsidence centers were superposed as an entity in the southwest of the basin. It was not until the Middle Jurassic that the extant residual basin in the west of the Yellow River took a paleogeographic structural pattern of high in the west and low in the east. The depocenters of the Ordos Basin remained and were superposed consistently from middle Late Triassic to middle Jurassic. The higher thermal maturation of Mesozoic and Paleozoic strata in the depocenters and its neighborhood indicate an active effect at depth in these areas. Comprehensive research suggests that superposition of depocenters in several periods and its consistence with higher thermal maturation centers, reflect that the basin is controlled generally by subsidence centers. Therefore, the depocenters may represent the centers of subsidence. Most of the subsidence or depocenter centers within the large scale Ordos craton during Mesozoic were distributed in the south of the Ordos Basin, and are closely associated with flexing and subsiding of the foreland, resulted from strong converged orogenic activity, which took place at the same time as the Qinling Orogenic belt.

通过对鄂尔多斯盆地中生代构造属性、原盆面貌、岩性岩相组合、物源分析和厚度分布特征等的综合研究表明，从中晚三叠世至早白垩世，盆地沉积中心由东南向北、再向西南发生逆时针迁移；在盆地西部，早白垩世沉积前没有统一或规模较大的堆积中心，仅存在孤零分布或彼此分割、规模不大的局部堆积中心。盆地西部多个时期出现的地层较厚分布区带，是该区距盆地西界较近，物源供给充足、水动力作用强所致，故代表局部堆积中心。早白垩世，沉积、堆积和沉降中心才在盆地西南部“三位一体” 叠合分布。直到中侏罗世末，在黄河之西的今盆地残留区，总体仍呈西高东低的古地理―构造格局。盆地中晚三叠世―中侏罗世各期的沉积中心在位置上大体一致，上下大部重叠；该沉积中心及近邻，古生界和中生界的热演化程度为盆地最高，显示该区深部作用较为活跃。综合分析认为，中生代各期沉积中心的叠置及其与高热演化地区的重合，反映为总体受沉降中心控制所致，可作为盆地沉降中心的代表。大型鄂尔多斯克拉通内盆地中生代各期沉积(沉降)中心在位置上偏于盆地南部，与秦岭造山带同期强烈的会聚造山活动产生的前陆挠曲沉降相关。