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首页> 外文期刊>Stratigraphy >The significance of dinoflagellates in the Miocene Choptank Formation beneath the Midlothian gravels in the southeastern Virginia Piedmont
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The significance of dinoflagellates in the Miocene Choptank Formation beneath the Midlothian gravels in the southeastern Virginia Piedmont

机译：在弗吉尼亚州山南部的中美胸甲砾石下甲基氯蛋白在中医Choptank形成中的重要性

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摘要

The Fall Line (formally "Tidewater Fall Line") separates the more resistant igneous, metamorphic, and consolidated sedimentary rocks of the Piedmont from the typically unconsolidated deposits of the Coastal Plain of Virginia. Widespread but now discontinuous patches of a deeply weathered sand and gravel are found west of the Fall Line, capping the highest hilltops. Near the community of Midlothian, Virginia, the gravels are underlain by fine-grained marine silts that bear an informative assemblage of fossil dinoflagellate cysts (dinocysts). In situ dinocysts belong to middle Miocene zone DN7, which is calibrated to similar to 12-13 Ma. These deposits are assigned to the upper part of the Choptank Formation, which crops out similar to 25 km(15 mi) to the east at an elevation similar to 60m(200 ft) lower. The dinocyst assemblage suggests that the maximum extent of this Choptank transgression probably covered a significant expanse of the Virginia Piedmont. The Choptank marine silts constrain the age of the unconformably overlying Midlothian gravels to younger than the latter part of the middle Miocene. Previous work has indicated that these gravels also are older than the Pliocene Yorktown Formation. Rare, reworked dinocysts in these Choptank outcrops west of the Fall Line are sourced from older deposits of more than one age. The source could be older updip strata of the lower Eocene Nanjemoy Formation, now erosionally removed. Alternatively, the source could be material referable to the upper Eocene Exmore Formation that resulted from the Chesapeake Bay impact event.
机译：跌倒线（正式“潮水跌落线”）将皮埃蒙特的耐抗性的耐火性，变质和综合沉积岩与弗吉尼亚州沿海平原的典型未夺取的沉积物分开。普遍但现在在秋季线以西发现深层风化的沙子和砾石的不连续斑块，覆盖最高的山顶。弗吉尼亚弗吉尼亚州中美噻舰的社区附近，砾石是由细粒般的海洋淤泥的下层，含有氟硝Dinoflagellate囊肿（DinoCysts）的信息。原位DinoCysts属于中间内肾域区DN7，校准为类似于12-13 mA。这些沉积物被分配到Choptank地层的上部，该剧作与东部相似的庄稼与60米（200英尺）较低的高度相似。 DinoCyst组合表明，这次Choptank违规的最大程度可能涵盖了弗吉尼亚皮埃蒙特的重要扩展。 Choptank Marine Silts限制了非全身覆盖的中间人砾石的年龄，而不是中间内烯的后半部分。以前的工作表明，这些砾石也比Pliocene Yorktown的形成年龄大。稀有，在秋季线以西的这些Choptank露头的替代替代DinoCysts来自超过一个年龄的较旧的矿床。来源可能是较低的yocene纳米月地层的旧功能较大，现在侵蚀。或者，源可以是由切萨皮段湾冲击事件引起的上埃克莫牛肉形成的材料。

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  • 来源
    《Stratigraphy》 |2018年第3期|共17页
  • 作者

    Edwards Lucy E.; Weems Robert E.; Carter Mark W.; Spears David B.; Powars David S.;

  • 作者单位

    US Geol Survey Natl Ctr 926A Reston VA 20192 USA;

    US Geol Survey Natl Ctr 926A Reston VA 20192 USA;

    US Geol Survey Natl Ctr 926A Reston VA 20192 USA;

    Virginia Div Geol &

    Mineral Resources 900 Nat Resources Dr Suite 500 Charlottesville VA 22903 USA;

    US Geol Survey Natl Ctr 926A Reston VA 20192 USA;

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  • 正文语种 eng
  • 中图分类 地质学;
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