Integrated Paleontological, Geochemical, and Paleoceanographic Studies on the Taconic Foreland Basin

对纽约Taconic前陆盆地大约500万年的中奥陶世序列的研究解决了以下问题：从大陆碳酸盐台地到俯冲沟外斜坡的过程中，水温和氧含量是如何随深度变化的？海洋深层环流是由来自低纬度平台的温暖咸水下沉驱动的吗，就像这次和其他最高海位时期所提出的那样？12年的地层学和古生物学背景研究，包括一项正在进行的为期两年的可行性研究，为回答这些问题和相关问题提供了一个独特的机会，这些问题来自广泛的底栖无脊椎动物壳的碳和氧同位素研究，以及沉积物的碳和硫分析。相对水深是根据沿着单个火山灰层的下坡横断面上的位置来测量的，随着时间的推移，通过对化石组合的梯度分析来测量。相对水温将由一个关节腕足动物（低镁方解石）、两个非关节腕足动物（磷酸钙）和其他分类群的氧同位素组成来确定。显然，结构和化学性质保存较好的钙质腕足动物的同位素变化不大，来自同一采样站的标本的180值与保存最完好的中奥陶世和晚奥陶世的样品相似。腕足动物壳上的斑点密度（与现代形式的温度成正比）与相对深度成正比，可以作为温度测量的80O的检查。研究将有助于古海洋学重建和确定可能进行资源勘探的地区。

Studies on a roughly five million year long Middle Ordovician sequence in the Taconic Foreland Basin, New York are addressed to these questions: How did water temperature and oxygen content vary with depth in going from a continental carbonate platform down the outer slope of a subduction trench? Was oceanic deep circulation driven by sinking of warm, saline water from low-latitude platforms, as has been suggested for this and other times of highest sea stand? Twelve years' background work on the stratigraphy and paleontology of the sequence, including an ongoing two-year feasibility study, has made a unique opportunity for answering these and related questions from carbon and oxygen isotopic studies on shells of bathymetrically wide-ranging benthic invertebrates, and from carbon and sulfur analyses of sediments. Relative water depth is measured in terms of position on downslope transects along individual volcanic ash layers and, over time, through gradient analysis of fossil assemblages. Relative water temperature will be determined from oxygen isotopic composition in one articulate brachiopod (low-Mg calcite), two inarticulate brachiopods (calcium phosphate), and other taxa selected for comparison. Evidently, texturally and chemically well-preserved calcareous brachiopods are isotopically little-altered: specimens from the same sampling station yield tightly clustered 180 values similar to those of the best-preserved Middle and Late Ordovician material. The density of puncta on the articulate brachiopod's shell (proportional to temperature in modern forms) is proportional to relative depth, and may provide a check on 80O as a temperature measure. Research will aid in paleoceanographic reconstruction and in identification of possible areas for resource exploration.