冰川型海平面变化控制下的台地碳酸盐岩成岩作用:以陕西镇安西口石炭-二叠系界线剖面为例

以陕西镇安西口石炭-二叠系界线剖面为具体实例, 探讨了冰川型海平面变化控制下的台地碳酸盐岩成岩作用规律.描述了陕西镇安西口石炭-二叠系界线剖面碳酸盐岩的各种成岩作用类型.根据成岩组构将研究区碳酸盐岩的成岩环境分为海水、大气淡水和埋藏环境.综合分析了各种成岩作用及其成岩环境的纵向分布特征.研究表明, 剖面上碳酸盐岩成岩作用和成岩环境的特征与岩石在高频旋回中的相对位置存在明显的对应关系, 受大振幅、高频率的冰川型海平面变化控制.早期海平面相对上升, 形成旋回的下部单元, 岩石首先经历海底成岩作用, 随着上覆沉积物的增加, 逐渐进入浅埋藏环境, 成岩作用表现为以压溶、重结晶作用发育为主要特征.晚期形成旋回的上部单元, 由于海平面相对下降, 沉积物逐渐抬升, 早期海底成岩作用尚未充分发育就脱离海水环境, 进入大气淡水成岩环境, 以强烈的大气淡水成岩作用为特征.      

含煤岩系层序地层学研究进展

层序地层学是分析聚煤规律的一种有效方法。层序地层学应用于含煤地层的分析始于20世纪90年代,Diessel最先在经典层序地层格架中建立了煤层的聚集模式;之后,Bochacs和Stuer通过讨论可容纳空间的变化速率和泥炭聚集速率之间比值的变化,具体分析了不同可容纳空间的煤层厚度、连续性及形态。通过对层序地层中煤层发育和分布的研究,多数煤田地质学家们认为,厚煤层主要发育于低位体系域晚期至海侵体系域早期及海侵体系域晚期至高位体系域早期。由于巨厚煤层往往是许多次级层序及界面的复合体,因此巨厚煤层不能简单地作为成因层序地层的界面,但可以通过煤岩学和地球化学方面的指标对其进行精细划分确定。我国煤田地质学家通过对国内海相煤层的研究,提出了海侵事件聚煤和海相层滞后时段聚煤等观点,从而大大促进了含煤岩系层序地层学的发展。      

The species diversity of fusulinaceans and high-frequency sea-level changes in the Carboniferous-Permian boundary section at Xikou, Zhen’an County, Shaanxi Province, China

The study on the interrelation between sea-level changes and biodiversity with its evolution has great significance for understanding the impact of global changes on organic evolution and exploring the inherent laws of life-environment coevolution in geological history. In this paper, the stratigraphic distribution of fusulinacean fauna in the Carboniferous-Permian boundary section at Xikou, Zhen’an County, Shaanxi Province, is analyzed quantitatively, and the relationship between the species diversity of fusulinaceans and relative sea-level changes is discussed. As a whole, the species numbers of fusulinacean fauna experience a rapid increase and an obvious decline in Xikou, Zhen’an County, from the Late Carboniferous to the Early Permian. There is a significant increase in species diversity around the Carboniferous-Permian boundary, which is one of the biggest bio-events of the fusulinacean fauna, and represents the radiation of Pseudoschwagerininae subfamily in the studied area. Integrated fusulinacean species diversity into sequence stratigraphic framework, detailed study suggests that the species diversity of the fusulinaceans is closely related to its relative stratigraphic location, and is essentially controlled by the sea-level changes, especially by the high-frequency sea-level changes. Generally, the species diversity of fusulinaceans is low, and the number of first and last appearance datum is small in the lower unit of high-frequency depositional cycle formed during the quick rise of the sea level; whereas the species diversity of fusulinaceans is high, and the number of first and last appearance datum is large in the upper unit of high-frequency cycle formed during the slow fall of the sea level. Within the third-order depositional sequence, the species diversity of the fusulinaceans at the first flooding surfaces and the maximum flooding surfaces is low, and it increases upward. The fusulinacean species diversity is low within the transgressive systems track, and it is high within the highstand systems track. The second-order rise and fall in sea level coincide with the bloom and decline of high order taxa of fusulinaceans.     

雪峰山西侧地区中上寒武统——层序地层学特征及层序格架

综合利用沉积学、岩石矿物学、碳同位素地球化学等分析手段,对研究区中-上寒武统层序地层学特征进行了分析。结果表明:中-上寒武统可以划归为1个二级层序和5个三级层序,在二级层序时限范围内,浅水相区经历了由局限台地潮坪→开阔台地→局限台地潮坪的沉积演化,斜坡过渡带则经历了由台地边缘→前缘缓斜坡→台地边缘的演化,研究区东南部的深水相区则由深陆棚→盆地→浅水陆棚组成。三级层序海侵体系域中沉积的颗粒白云岩、叠层石礁以及晚期高水位体系域中形成的溶孔白云岩、岩溶角砾白云岩的层位具有重要的油气勘探潜力,是值得关注和研究的领域。     

朝阳磷矿磷块岩的类型和成因特征

朝阳磷矿的磷块岩有五种类型,即泥晶磷块岩、球粒磷块岩、鲕粒磷块岩、内碎屑磷块岩和细晶磷块岩。其中内碎屑磷块岩占优势。磷酸盐岩沉积在海退旋回中,是处于深水向浅水过渡的层位。磷块岩的沉积环境主要是隆起附近的浅水带。     

古代浅海沉积研究中的数据化方法初探

本文以沉积剖面旋回层为基础,提出了研究古代浅海沉积环境和古沉积的新方法。这一方法可能定量地、较精确地重现古代浅海的某些沉积环境,揭示沉积环境的演变,并对古沉积学、古构造运动以及成矿规律等的研究都具有一定的实际意义.     

Correlation of Upper Devonian and Lower Carboniferous Depositional Sequences in Different Facies Belts on Southern Margin of Upper Yangtze Platform

Ｓｅｑｕｅｎｃｅｓｔｒａｔｉｇｒａｐｈｙｄｅａｌｓｗｉｔｈｔｈｅｃｙｃｌｉｃｉｔｙｉｎｓｅｄｉ－ｍｅｎｔａｒｙｒｏｃｋｓａｎｄｒｅｇａｒｄｓａｔｌｅａｓｔｓｏｍｅｏｆｔｈｅｃｙｃｌｉｃｉｔｙａｓｇｌｏｂａｌｉｎｅｘｔｅｎｔ．Ｉｎｆａｃｔ,ｓｅｄｉｍｅ...     

Genetic Types of Meter-Scale Cyclic Sequences and Fabric Natures of Facies Succession

Ｍｅｔｅｒ ｓｃａｌｅｃｙｃｌｉｃｓｅｑｕｅｎｃｅｓ,ｓｉｍｉｌａｒｔｏｍｅｔｅｒ ｓｃａｌｅｃｙｃｌｅｓｄｅｆｉｎｅｄｂｙＡｎｄｅｒｓｏｎａｎｄＧｏｏｄｗｉｎ (1990 ) ,ｒｅｆｅｒｔｏｆｕｎｄａｍｅｎ ｔａｌｕｎｉｔｓｏｆｓｔｒａｔｉｇｒａｐｈｉｃａｃｃｕｍｕｌａｔｉｏｎｔｈａｔｃｏｕｌｄｂｅｄｉｓｃｅｒｎｅｄｄｉｒｅｃｔｌｙｉｎｏｕｔｃｒｏｐ .Ａｓｔｈｅｆｕｎｄａｍｅｎｔａｌｗｏｒｋｉｎｇｕｎｉｔｓｉｎｓｔｒａｔｉ ｇｒａｐｈｉｃｒｅｃｏｒｄｓ,ｍｅｔｅｒ ｓｃａｌｅｃｙｃｌｉｃｓｅｑｕｅｎｃｅｓｒ…     

Resolving controls on epeiric sedimentation using trend surface analysis

An understanding of patterns of regional sedimentation is crucial to identifying trends of perspective petroleum reservoirs. The Upper Pennsylvanian, Missourian Kansas City Group consists of repetitions of widespread carbonate rock and shale. Each of four cyclothems chosen for subsurface study of western Kansas contains transgressive and regressive lithofacies with evidence of extensive subaerial exposure across the entire paleoshelf. Distribution of carbonate facies on the 350+ km-wide shelf was affected strongly by slight changes in structural configuration of the shelf and variations in sea level. Polynomial trend surface models prepared from selected wireline log information for four successive cyclothems assist in resolving regional and local patterns of sedimentation and help to access the effect of subtle structural deformation on sedimentation. Isopachs of marine portions of four cyclothems were fit by fourth-order trend surfaces, optimizing fit by comparing goodness-of-fit and minimizing skewness of residuals using the smallest order surface. Several cyclothems showed simple patterns of regional, basinward thickening with local, strike-elongated anomalies where goodness-of-fit was maximized with increasing order. One cyclothem did not converge to a good fit at small orders nor did distribution of residuals indicate convergence toward zero. Both anomalies reflected a more complex surface. Rather than thickening regionally, the pattern created by this anomalous cyclothem was more irregular. Mapped patterns resemble those of the present-day structural configuration of these horizons suggesting a general persistence in similar epeirogenic deformation.     

Lacustrine carbonate deposition in Middle Pennsylvanian cyclothems — the Upper Freeport Formation,Appalachian Basin,USA

The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest non-marine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analyses of 25 cores from the Upper Freeport Limestone in western Pennsylvania (Armstrong and Indiana Counties) identified four facies associations containing thirteen separate facies: rudstone-limestone (Association A), rudstone-laminated limestone (Association B), laminated limestone (Association C), and coal — siliciclastics (Association D). We interpreted them, respectively, as shallow, high energy lacustrine margin (A); littoral to sublittoral lacustrine (B); offshore lake (C); and vegetated swamp and marsh (D). The depositional environment is envisaged as an anastomosed channel system surrounded by extensive wetlands containing adjacent densely vegetated swamp and marsh areas and freshwater, carbonate-producing lakes.Lakes developed in the topographic lows of the alluvial plain, protected and filtered from siliciclastic deposition by vegetated swamps. These lakes were small in size (several square km), shallow, and stratified, as indicated by the abundance of laminated facies. They were hydrologically open, and interconnected by surface and ground waters. Carbonate production in this lacustrine system was not triggered by evaporative concentration but by biogenic algal production. Carbonates were continually being recycled, both physicochemically and biologically, within the depositional system. Various early diagenetic processes, including brecciation, pedogenesis and recrystallization, masked original evidence for transport mode. The Upper Freeport Limestone contains numerous features of palustrine carbonates, and provides a case study for one end-member of freshwater carbonate models, characterized by a very short period of subaerial exposure. Small-scale climatic changes or autocyclic processes such as small topographic differences, changes in local drainage patterns, and fluvial dynamics may have controlled Upper Freeport lake level changes.Facies analysis does not support a climate forcing as a control for cyclothem development of non-marine sequences during the Pennsylvanian. Tectonic and autocyclic processes better explain the evolution of these wetland (lacustrine/alluvial) systems with its associated coal formation.This is the seventh paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.