西秦岭关家沟组的沉积环境及其物源

西秦岭关家沟组地层中碎屑颗粒的总体粒度呈现向上变粗的韵律性旋回:下段为以泥质岩、砂岩互层为主的典型浊流沉积组合；中段的碎屑颗粒有向上变粗、砾岩层加厚的趋势；上段以厚层砾岩为主，夹薄层块状砂岩，砾岩中砾石含量、粒度大小分别表现出向上增加、增大的趋势。化石组合表明关家沟组为海相地层，进一步推断关家沟组可能为海底扇浊流沉积体系。对关家沟组杂砂岩组分进行了碎屑颗粒百分含量统计及粉砂岩、板岩的地球化学分析，结果表明稀土元素w(La)、w(Ce)、w(ΣREE)和δ（Eu）等特征值与大陆岛弧构造环境的相似。以本区地层斜层理产状及砾石优选方位为依据，结合砾石颗粒大小在横向上的变化，对关家沟组岩层古水流方向综合分析，推测其古水流方向为230°～356°，以北西向为主；砾石的优选方位在228°～338°之间，以北北西向为主。砾石的统计资料表明，由南向北关家沟组砾石具有颗粒由大逐渐变小、磨圆度由差→较好、优选方位由杂乱→较好的变化趋势。结合前人成果，关家沟组处于碧口弧前盆地系统内，推测关家沟组沉积物主要来自南东向的岛弧。

Sedimentary Environment and Provenance of the Guanjiagou Formation of the Western Qinling Mountains

Sediment association of the Guanjiagou Formation is characterized by increasingly coarsening upwards sequence. The lower of the Guanjiagou Formation is typical turbidity current deposit, which consists mainly of mudstone and sandstone. Its grain-size changes coarse upwards and the conglomerate stratum becomes thick in the middle part. The upper part is thicker conglomerate with lamella massive sandstone. The content of gravel in conglomerate and granularity increases and augments respectively. By study, the Guanjiagou Formation is marine sediments which were showed by the fossil. Therefore, it is deduced that the Guanjiagou Formation is submarine fan. The geochemistry characteristics of siltstone and slate show that the values of La,Ce,ΣREE, (δ(Eu)) of the Guanjiagou Formation are similar to those of island arc. By the tilted lay of stratum, the excellent trend of gravel and the change of gravel in orientation ,the current of the Guanjiagou Formation is analyzed synthetically and it is deduced that the direction of paleo-current is about 230° to 356°, and most is west-north; while the gravel excellent trend is 228° to 338°, most north-northwest. From south to north, the size of gravel becomes small gradually, gravel round increasing, and gravel excellent trend is from disorder to order by field statistic. With previous results, the Guanjiagou Formation is in Bikou forearc basin and it is presumed that the sediments were from east-southern island arc.