贺兰山下古生界陆源碎屑-碳酸盐岩混合沉积特征

陆源碎屑和碳酸盐岩的混合沉积现象分布广泛,但由于混合沉积的研究起步较晚,且受不同沉积条件的制约,研究相对薄弱。贺兰山地区早古生代发育了陆源碎屑岩和海相碳酸盐岩的混合沉积建造,目前国内外学者对贺兰山地区的混合沉积现象的研究至今没有涉及。研究区早古生代混合沉积狭义上表现为混积岩,主要类型包括:泥质灰岩、含泥灰岩、灰质砾岩、灰质粉砂岩;广义上表现为混积层系,主要类型包括:陆源碎屑岩-碳酸盐岩、混积岩-陆源碎屑岩、混积岩-碳酸盐岩。本文从沉积相变关系、区域地层间接触关系、残余地层展布、物源分析等方面对研究区下古生界混合沉积特征进行了较为深入的探讨,研究区寒武纪和奥陶纪表现出了截然不同的混合沉积样式:寒武纪为"拼贴式"混合沉积,而奥陶纪为渐变式混合沉积。板块运动、全球海平面变化、陆源碎屑物质的供给等因素共同控制了研究区早古生代混合沉积的形成。从研究区早古生代不同时期特有的沉积样式人手,分析了研究区早古生代盆地类型及演化。研究区早古生代经历了寒武纪大洋和克拉通盆地共存-早奥陶世的局限克拉通盆地-中、晚奥陶世的前陆盆地雏形这样一个演化过程。

Early Paleozoic mixed clastic rock-carbonate sedimentary characteristics of Helan Mountain

Clastic rock-carbonate mixed sediment is widespread in various depositional environment, however, because of the restriction of the different deposition conditions and a rather later start research, the degree of the clastic rock-carbonate mixed deposits study is relatively weak. Clastic rock-carbonate mixed deposits are very developed in Lower Paleozoic in Helan Mountain and lack of systematic investigation so far. Narrowly speaking, mixed deposition of the Early Paleozoic in study area is peperite which contains argillaceous limestone, marl, calcirudyte and limy siltstone. Broadly speaking, mixed deposits of the Early Paleozoic in study area are mainly mixed product series which include inter-bedded clastic beds and carbonate beds, diamictite beds and clastic beds, mixed sedimentary beds and carbonate beds. The paper discusses the mixed deposition characteristic from 4 aspects as follows: Sedimentary phase transformation, regional stratigraphic contact relationship, residual strata distribution and detrital material source. The Cambrian and Ordovician showed different mixed depositional character: The Cambrian shows the "collage" mixed sediment pattern, while the Ordovician shows the gradual mixed sediment pattern. Plate movements, changes of sea level and the supply of terrigenous materials together controlled the mixed sedimentation of Early Paleozoic of study area. The basin type of the Early Paleozoic of study area experienced such an evolutionary process: The coexistence of oceanic and cratonic basin in the Cambrian, confined cratonic basin in the Early Ordovician and foreland basin in the Late Ordovician.