汾渭盆地古近系—新近系沉积特征

汾渭盆地位于鄂尔多斯地块与秦岭造山带的衔接部位，地理位置十分特殊。作为一个新生代断陷盆地，在周缘及内部一系列断裂带控制下，具有边断、边陷、边沉积的特征，新生代地层厚度逾几千米。本文根据大量野外露头及相关钻井资料，综合岩石学、沉积构造、古生物化石、测井及区域地质资料，系统研究了汾渭盆地古近系—新近系各时期的沉积相特征。结果表明，新生代汾渭盆地发育冲积扇、河流、三角洲、湖泊及风成沉积5种沉积类型。盆地边缘及山前主要发育冲积扇沉积，向盆地中心逐渐过渡为河流、三角洲及湖泊沉积，风成堆积集中分布于盆地边缘。各次级盆地沉积演化具有差异性，除三门峡地区外，汾渭盆地主体自晚始新世开始沉积并持续至渐新世早期；渐新世晚期在经历隆升剥蚀作用后，中新世再次沉降，沉积范围逐渐扩大；至晚中新世，渭河盆地的西安凹陷、固市凹陷两大沉积区以及三门峡—芮城、运城—永济一线均为湖相分布区。上新世湖盆沉积范围达到最大，湖泊广泛分布，盆地边部则大量发育风成沉积。

Sedimentary characteristics of Paleogene-Neogene in Fenwei Basin

Fenwei Basin has a special geographical location for it is situated at the conjunction of Ordos block and Qinling orogenic belt. As a Cenozoic faulted basin which is controlled by a series of fault zones distributed in the peripheral and internal areas, the rifting and sedimentation occurred almost simultaneously in the basin, forming the Cenozoic strata with a thickness of several thousand meters. Based on a large number of field outcrops and some drilling data, especially signal features such as lithology, palaeontology, sedimentary structures, paleontological fossils, as well as logging data and regional geological backgrounds, we study the sedimentary facies of different geological periods of Paleogene-Neogene in Fenwei Basin, and five sedimentary types can be distinguished, i.e., alluvial fan, fluvial, delta, lacustrine and aeolian deposit. More specifically, alluvial fan deposits are mainly developed in the basin margin and front areas of mountains, then gradually change into fluvial, delta, and lacustrine facies toward the lake centre while almost all aeolian deposits are observed at the edge of the basin. Except Sanmenxia area, the main part of Fenwei Basin began to deposit from the Late Eocene to the Early Oligocene. During the Late Oligocene, Fenwei Basin experienced regional uplift and the sedimentation was interrupted. Since then, the basin subsided again and the sedimentary range gradually expanded. Xi'an depression and Gushi depression of Weihe Basin, as well as the Sanmenxia-Ruicheng area and Yuncheng-Yongji area all develop lacustrine facies by the Late Miocene. During the Pliocene, the largest the sedimentary range of the Fenwei Basin was formed, and lake was widely distributed in the centre of the area, and aeolian deposits began to be sedimented at the edge of the basin.