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首页> 外文期刊>Journal of nannoplankton research: A publication of the International Nannoplankton Association >Preliminary biostratigraphic and morphometric comparisons between a new species of Tribra chia tus and T. orthostylus
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Preliminary biostratigraphic and morphometric comparisons between a new species of Tribra chia tus and T. orthostylus

机译：新物种的Tribra chia tus和T. orthostylus的初步生物地层学和形态计量学比较

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摘要

Detailed biostratigraphic analyses of lower Eocene sediments from the South Dover Bridge (SDB) core, Maryland (USA), and preliminary analyses of outcropping sediments along the Waipara River in New Zealand, have revealed the presence of a new species of Tribrachiatus that has a distinctly different morphology and biostratigraphic range from T. orthostylus. Tribrachiatus orthostylus consists of triangular-shaped specimens that exhibit low birefringence under polarized light, and have three relatively flat arms of equal length, often showing bifurcations at the ends. The first occurrence (FO) of T. orthostylus is in upper Zone NP10, and is commonly used to delineate the base of Zone NP11 in truncated sections. In comparison, Tribrachiatus sp. consists of crescent-shaped specimens that exhibit a higher order of birefringence under polarized light, have two arms of similar length that are strongly curved, and a third, shorter arm that extends upward and is perpendicular to the curved arms. In the SDB core, the first occurrence of T. orthostylus is at the base of Zone NP11 (187.1 m); NP10 is truncated because of erosion at this site. The first occurrence of Tribrachiatus sp. is at 184.8 m, after the FO of Discoaster kuepperi and just before the FO of D. lodoensis at 184.0 m. The last occurrence of both species occurs at the top of Zone NP12, after the FO's of Ericsonia formosa,Helicosphaera seminulum, and Reticulofenestra spp. Comparison of the percent abundances of both T. orthostylus and Tribrachiatus sp. to the bulk δ~(13)C curve of the SDB core suggests that both of these species were sensitive to changing paleoclimate conditions during early Eocene hyperthermal events.
机译：来自美国马里兰州南多佛大桥（SDB）岩心的始新世沉积物的详细生物地层分析，以及新西兰怀帕拉河沿岸露头沉积物的初步分析表明，存在着一种新的Tribrachiatus物种，该物种具有明显不同的特征。 T. orthostylus有不同的形态和生物地层学范围。 Tribrachiatus orthostylus由三角形的标本组成，这些标本在偏振光下显示出低双折射，并具有三个长度相等的相对扁平的臂，通常在末端出现分叉。首次出现（FO）的T. orthostylus在上部区域NP10中，通常用于在截断部分中描绘区域NP11的底部。相比之下，Tribrachiatus sp。由新月形的样本组成，这些样本在偏振光下表现出更高的双折射水平，两个臂的长度相似，但都强烈弯曲，而第三个较短的臂则向上延伸并垂直于弯曲的臂。在SDB核心中，首次出现的T. orthostylus位于NP11区（187.1 m）的底部。 NP10由于该部位的侵蚀而被截断。 Tribrachiatus sp的首次出现。在迪斯科斯特·库佩里（Discoaster kuepperi）的FO之后，紧接D. lodoensis的FO在184.0 m处，位于184.8 m。两种物种的最后一次出现在NP12区的顶部，分别是爱立信菌，半球形Helicosphaera和Reticulofenestra spp的FO。 T. orthostylus和Tribrachiatus sp。的百分比丰度比较。 SDB核的总体δ〜（13）C曲线表明，这两个物种在始新世早期高温事件中都对古气候条件的变化敏感。

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