The edge of a Permian erg: Eolian facies and provenance of the Lyons Sandstone in northern Colorado

Q3 Earth and Planetary Sciences
Oguzhan Kendigelen, Sven Egenhoff, William A. Matthews, Christopher S. Holm-Denoma, Karen R. Whiteley, Virginia Gent, M. Longman, J. Hagadorn
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引用次数: 0

Abstract

Facies of the Permian Lyons Sandstone are described and interpreted based on analyses of 23 cores from Larimer and Weld counties, Colorado. Here, the Lyons Sandstone consists of very fine- to medium-grained sandstone with minor silt and mudstone interbeds. The unit has five recurrent siliciclastic facies that can be grouped into two facies associations (FA). FA1 consists of (1) high-angle, cross-laminated sandstone (Facies 1; interpreted as eolian dune remnants); (2) low-angle, cross-laminated and horizontally laminated sandstone (Facies 2; interdune); and (3) chaotically bedded to folded sandstone (Facies 3; lower dune flanks). FA2, in contrast, is mainly (4) wavy- to irregularly laminated silty sandstone (Facies 4; wet to damp interdune); and (5) massive to wavy-laminated silt-rich mudstone (Facies 5; ponded water areas between dunes) with minor amounts of high-angle, cross-laminated sandstone (Facies 1) and low-angle, cross-laminated and horizontally laminated sandstone (Facies 2). FA1 is hypothesized to have been produced in an eolian system akin to those that might exist in the dune-dominated portion of an erg, whereas FA2 was deposited in the intermittently wet portion of this eolian system, perhaps along erg margins or in flat dune-adjacent settings that were impacted by the water table. Isopach data suggests that the study area is on the fringe of a larger Lyons system that spans > 100,000 km2, and was deposited close to the Ancestral Rockies—a paleogeography consistent with deposition in erg to erg-margin paleoenvironments. Detrital zircon populations from nearby Colorado Front Range outcrops and from 12 correlative eolian units are dominated by small, well-rounded Paleoproterozoic and Mesoproterozoic grain populations that are remarkably similar between units, signaling a well-mixed system that also received an influx of distally sourced sediment from the Appalachian orogen. Detrital zircon-based maximum depositional ages of the Lyons Sandstone and its equivalents are internally consistent with deposition of the unit during the latest Artinskian to Kungurian.
二叠纪糜烂的边缘:科罗拉多州北部里昂砂岩的风化层和产地
根据对科罗拉多州拉里默和韦尔德县 23 个岩心的分析,描述并解释了二叠纪里昂砂岩的岩相。这里的里昂砂岩由细粒至中粒砂岩组成,夹少量粉砂和泥岩。该单元有五个反复出现的硅质岩相,可分为两个岩相组合(FA)。FA1 包括:(1)高角度、交叉层理砂岩(岩相 1;解释为风化沙丘遗迹);(2)低角度、交叉层理和水平层理砂岩(岩相 2;沙丘间);以及(3)混沌层理至褶皱砂岩(岩相 3;下部沙丘侧翼)。相比之下,FA2 主要是(4)波状至不规则层状粉砂质砂岩(岩相 4;潮湿至潮湿的沙丘间);以及(5)块状至波状层状富含粉砂的泥岩(岩相 5;沙丘间的积水区),还有少量高角度交叉层状砂岩(岩相 1)和低角度交叉层状及水平层状砂岩(岩相 2)。据推测,FA1 是在类似于麦地以沙丘为主的部分可能存在的风化系统中产生的,而 FA2 则沉积在这一风化系统的间歇湿润部分,可能是在麦地边缘或受地下水位影响的平坦沙丘邻近地区。Isopach数据表明,研究区域位于面积大于10万平方公里的大型里昂系统的边缘,沉积地点靠近原始落基山脉--这与沉积在erg至erg边缘古环境中的古地理环境相一致。来自附近科罗拉多前沿山脉露头和 12 个相关风化单元的碎屑锆石群以小而圆的古近纪和中新生代晶粒群为主,这些晶粒群在不同单元之间非常相似,表明这是一个混合良好的系统,同时也接受了来自阿巴拉契亚造山带的远源沉积物的涌入。基于碎屑锆石的里昂砂岩及其同类沉积物的最大沉积年龄与该单元沉积于阿尔廷斯基晚期至昆古里亚期的时间在内部是一致的。
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来源期刊
Rocky Mountain Geology
Rocky Mountain Geology Earth and Planetary Sciences-Geology
CiteScore
1.10
自引率
0.00%
发文量
4
期刊介绍: Rocky Mountain Geology (formerly Contributions to Geology) is published twice yearly by the Department of Geology and Geophysics at the University of Wyoming. The focus of the journal is regional geology and paleontology of the Rocky Mountains and adjacent areas of western North America. This high-impact, scholarly journal, is an important resource for professional earth scientists. The high-quality, refereed articles report original research by top specialists in all aspects of geology and paleontology in the greater Rocky Mountain region.
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