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Depositional System and Source Rock Potential of the Sharon Springs Formation in Colorado

机译：科罗拉多Sharon Springs组的沉积体系和烃源岩潜力

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摘要

The Sharon Springs Member of the Pierre Shale has recently been divided and reclassified as the Gammon Ferruginous Formation and Sharon Springs Formation, with the Pierre Shale being upgraded to group status. Deposition took place between 82 and 77 Ma in a conformable succession of facies following the Niobrara Highstand, and an overall progradation of siliciclastics into the Western Interior Seaway. These units gradually decrease over time in calcite content associated with chalk filled fecal pellets, to clay and quartz dominated deposits with a large constituent of pyrite. This interval has the potential to be a significant source rock where thermally mature, within the Denver and Piceance basins. Biomarker analyses on oil collected form the Florence-Canon City Field suggest that the Sharon Springs has contributed to production from fractured members of the Pierre Shale up section. Thermal maturity indicators in biomarkers indicate that the oil produced from the Pierre is slightly more mature than source rock extracts taken from core in the field, suggesting that oil has a mixed source and likely migrated from further down dip.;As a potential source rock, it is important to understand how these units were deposited and where they are most organic-rich. The previous model for Sharon Springs deposition and preservation of organic carbon was pelagic sedimentation in an anoxic, stratified and stagnant water column. Observations made in core and outcrop suggest that the Sharon Springs and Gammon Ferruginous formations were deposited by offshore sediment gravity flows. Storms likely assisted in reworking shelf muds and transporting them offshore where they are hydrodynamically sorted and often contain normally-graded beds, ripples and bioturbation. During the process of offshore transport, fine-grained sediment and organic matter which is commonly adsorbed onto clay grains or amalgamated into clay floccules, are concentrated, resulting in elevated accumulations of organic carbon. Organic carbon was then preserved through euxinic conditions below the sediment water interface due to low oxygen diffusion rates in the fine-grained material. Biogenic fecal pellets are abundant in the lower Gammon Ferruginous Formation, representing pelagic sedimentation in the most distal reaches of the basin. This interval, however, is not exceptionally organic-rich. This suggests that the prograding siliciclastic clinothems not only concentrated fine-grained sediment and organic matter at the distal portion of the deposits, but may be the primary mode of transport for organic matter to offshore regions. As the siliciclastics stepped basinward, the carbonate factory shut down and was replaced by organic-rich clay having a TOC of ∼5% in the more proximal regions and reaching ∼14% in the more distal areas where there is less detrital dilution.;Bioturbation in the offshore deposits suggests that the water column was not euxinic or stagnant, but often oxygenated and active. Active water column mixing then resulted in high rates of primary productivity, and increased likelihood of organic matter preservation. The Western Interior Seaway was likely shallow enough (∼200 m) to be frequently churned by storms, bringing nutrients into the photic zone, and resulting in algal blooms. The frequency of these storms then allowed enough organic matter to be deposited on the basin floor that preservation was likely, despite the oxygenated bottom-water conditions. This method of organic matter preservation is contrary to the pelagic sedimentation model, but explains the heterogeneity and presence of detrital feeding organisms within the organic rich units.;Regional stacking patterns in the Wattenberg Field area of Weld County, Colorado show a progradation of facies to the northeast. Biostratigraphic correlation connects the progradation of these clinoforms, to prograding sandstones on the western margin of the basin associated with the Blackhawk and Castlegate Sandstone. Similar turbidite deposits and normally-graded siliciclastics have also been described within the Prairie Canyon Member of the Mancos, between the more proximal sandstones and basinal shales. This biostratigraphic and lithostratigraphic succession of facies presents a strong argument for a connection of the depositional system in eastern Colorado to the prograding units in western Colorado. Through the Wattenberg field area, however, local tectonics complicate the deposition of these siliciclastics, resulting in variability in unit thickness. This structural high is associated with faulting along the Colorado mineral belt, and has been shown to migrate to the south over time. Faulting also results in thermal conduits and a heat anomaly, resulting in the Sharon Springs and Gammon Ferruginous formations being thermally mature in this area and a potential source rock for exploration.
机译：Pierre页岩的Sharon Springs成员最近被划分并重新分类为Gammon铁质岩层和Sharon Springs岩层，Pierre Shale升格为集团地位。沉积发生在82至77 Ma之间，依次是Niobrara Highstand后相一致的相相，以及硅质碎屑整体进入了西部内部海道。这些单位随着时间的推移，与白垩粉填充的粪便颗粒相关的方解石含量逐渐降低，成为具有大量黄铁矿成分的粘土和石英为主的沉积物。在丹佛和Piceance盆地内，该层段可能是热成熟的重要烃源岩。对从佛罗伦萨-佳能城市油田收集的石油进行的生物标志物分析表明，沙龙温泉为皮埃尔页岩上段断裂成员的开采做出了贡献。生物标记物中的热成熟度指标表明，皮埃尔（Pierre）生产的石油比采自田间岩心的烃源岩提取物更为成熟，这表明该油具有多种来源，并有可能从下倾角进一步迁移。重要的是要了解这些单元是如何沉积的以及它们最富含有机物的位置。 Sharon Springs沉积和保存有机碳的先前模型是在缺氧，分层且停滞的水柱中进行的浮游沉积。在岩心和露头进行的观测表明，Sharon Springs和Gammon铁质地层是由近海沉积物重力流沉积的。暴风雨可能会帮助重新处理架子上的泥浆，并将其运送到近海，在那里对它们进行流体动力分选，并且通常包含正常分级的床，波纹和生物扰动。在海上运输过程中，通常被吸附到粘土颗粒上或被混凝成粘土絮状物的细颗粒沉积物和有机物被浓缩，导致有机碳积累增加。然后，由于细粒材料中的氧扩散速率低，有机碳通过沉积物水界面以下的共溶条件得以保存。较低的Gammon铁质地层中存在大量生物粪便颗粒，代表该盆地最远端的浮游沉积。但是，该间隔并不是富含有机物。这表明，渐进的硅质碎屑岩不仅在沉积物的远端集中了细颗粒的沉积物和有机质，而且可能是有机质向近海地区运输的主要方式。随着硅质碎屑向盆地迈进，碳酸盐工厂关闭，取而代之的是富含有机物的粘土，在较近端区域的TOC约为5％，而在较远端区域的碎屑稀释率较低，TOC约为14％。离岸沉积物中的水表明，水柱不是富余的或停滞的，而是经常被充氧而活跃的。然后，主动水柱混合导致较高的初级生产率，并增加了有机物保存的可能性。西部内陆海道可能足够浅（约200 m），经常被暴风雨搅动，将营养物质带入光合带，并导致藻华。然后，这些暴风雨的频率使足够多的有机物沉积在盆地底部，尽管存在底部含氧条件，但仍有可能进行保存。这种保存有机物的方法与浮游沉积模型相反，但是解释了有机富集单元内碎屑性补给生物的异质性和存在。科罗拉多州威尔德县沃滕伯格田地地区的区域堆积模式显示了向东北。生物地层学相关性将这些斜状岩体的发育联系到与黑鹰和Castlegate砂岩有关的盆地西部边缘的砂岩的发育。在更近的砂岩和盆地页岩之间的Mancos的Prairie Canyon成员内，也描述了类似的浊浊沉积物和正常梯度的硅质碎屑岩。相的这种生物地层学和岩相地层学相继提出了一个强有力的论据，认为科罗拉多州东部的沉积系统与科罗拉多州西部的沉积单元有关。然而，在瓦滕堡（Wattenberg）野外，局部构造使这些硅质碎屑的沉积复杂化，导致单位厚度的变化。这种结构上的高度与科罗拉多州矿带的断裂有关，并且已经显示出随着时间的推移会向南迁移。断层还会导致热导管和热量异常，从而导致该地区的莎朗斯普林斯（Sharon Springs）和加蒙（Gammon）铁质地层热成熟，并有可能勘探。

著录项

  • 作者

    Allred, Evan S.;

  • 作者单位

    Colorado School of Mines.;

  • 授予单位 Colorado School of Mines.;
  • 学科 Geology.;Petroleum geology.;Sedimentary geology.
  • 学位 M.S.
  • 年度 2017
  • 页码 173 p.
  • 总页数 173
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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