陕北永宁山丹霞地貌造景地层地质特征

永宁山作为陕北地区丹霞地貌典型代表,其造景地层下白垩统洛河组(K₁l)在岩性、岩石特征、物源、沉积环境等方面的研究较少。通过剖面测量,抗压强度、薄片鉴定、X衍射分析、常量元素与稀土微量元素测试,对洛河组岩性岩相、地球化学特征进行了分析、总结。洛河组岩性主要为沙漠相风力作用沉积的一套紫红、灰红色细—中粗粒长石砂岩、石英砂岩、岩屑长石石英砂岩,岩石呈颗粒支撑,胶结类型为孔隙式、连生胶结,岩石次生变化较强,分选性好,抗压强度较大；岩层发育产状较统一的中大型板状、楔状斜层理,指示沉积作用主要受单向西北风控制。洛河组风成砂岩地球化学岩石类型为亚长石砂岩、长石砂岩和砂屑砂岩；物源区位于被动大陆边缘,砂岩的成分成熟度高,遭受风化程度很低；古气候条件表现为干燥、炎热。通过本次研究探讨永宁山一带洛河组砂岩地质特征、古气候、古环境变迁与变化,对陕北地区丹霞地貌成因机理研究,科学保护、合理利用具有重要意义。

The landscaping strata of the Danxia landform in Yongning Mountain, northern Shaanxi Province

As a typical Danxia landform in northern Shaanxi, there are few studies on lithology, rock characteristics, provenance and sedimentary environment of the early Cretaceous Luohe formation (K₁l) in Yongning Mountain. The lithologic lithofacies and geochemical characteristics of Luohe formation were analyzed and summarized by profile measurement, compressive strength, thin section identification, X-ray diffraction analysis, and test of major elements and rare earth trace elements. The lithology of Luohe formation is mainly a set of purple red, grey red fine to medium coarse arkose sandstone, quartz sandstone, lithic arkose quartz sandstone deposited by desert phase wind action. The rocks have the characteristics of grain support, pore type of cementation, continuous cementation, strong secondary changes of the rocks, good wind separation and great compressive strength. The medium-and large-sized plate-shaped and wedge-shaped oblique bedding with uniform occurrence was developed, indicating deposition was mainly controlled by one-way northwest risk. The geochemical rocks of the aeolian sandstone of Luohe formation are subarkose, arkose and arenaceous sandstone. The source area is located at the passive continental margin. The composition of the sandstone is mature and the degree of weathering is very low. Paleoclimate conditions are dry and hot. Through this study, the geological characteristics, paleoclimate, and paleoenvironmental changes and changes of the Luohe formation sandstone in the Yongning Mountains area are discussed, which is of great significance to the genetic mechanism research, scientific protection and rational utilization of the Danxia landform in northern Shaanxi.