Collaborative Research: Paleobiology, Paleoceanography, and Paleoclimatology of a Time Slice through the Late Cretaceous Western Interior Seaway

摘要本多学科研究提出利用西部内陆海道（WIS）晚坎帕尼亚压缩生物带（74 MA；晚白垩世）圈定的单一区间内发现的原始软体动物的O， C和Sr同位素分析来检验利用PIs和顾问优势的四个总体假设。这些都是:1。地球化学分析了通过单个样本的个体发生——sclerochronology(理智琼斯,1983)——提供年度subdecadal记录环境条件(如季节性的温度波动、水动力学)理解至关重要的动力学晚白垩世陆缘seas.2。晚坎帕尼亚生物的生长速度和其他古生物学方面，如迁移模式，可以使用年代学方法来确定。生物群，特别是软体动物元素，在水柱内和底物上占有不同的生态位，这些不同生境的信号被捕获在它们的同位素特征中。WIS中存在明显的环境梯度，受温度和盐度差异的影响，可以通过保存完好的软体动物壳中的氧和锶同位素来测量和区分。除了解决我们的一般假设之外，同位素数据将使我们能够批判性地分析一系列关于晚白垩纪世界的古海洋学、古生物学和古气候假说。这些包括：WIS内的环流模式，WIS的分层，个别菊石分类群的栖息地范围和深度，白垩纪软体动物的生长速度，以及海洋温度的季节性波动。为了解决上述问题，我们建议在晚白垩世非常化石的皮埃尔页岩中进行一个时间间隔的详细调查，重点是B. compressus生物带。该生物带的沉积在WIS广泛存在，并且通常伴随着早期成岩固结中动物群的精美保存，包括文石元素。为了收集必要的标本，我们将在科罗拉多州中部、南达科他州中部和西部以及蒙大拿州西部到东部的地区取样，这些地区代表了南北和陆上-海上的样带。我们将在所有地点测量详细剖面，收集含有各种软体动物的固结物。在进行任何同位素分析之前，将使用显微镜和地球化学技术对所有标本进行筛选，以寻找成岩作用的证据。那些通过成岩筛选的标本将被分析d13C和d18o，以确定它们的年代。由于壳物质所处的水环境值对于精确估计温度和盐度至关重要，因此我们还建议分析我们的样品子集的Sr同位素比率。最近的研究表明，在河口等淡水输入是系统重要组成部分的地区，87 Sr/86 Sr主要反映盐度而不是地质年龄，我们的初步数据表明该方法可以成功地应用于WIS。这些Sr数据提供了一个独立的盐度代表，可以更好地约束水的同位素组成。总之，这些方法将使我们能够测试我们的三个假设，并大大增加我们对WIS和居住在其中的大型无脊椎动物的理解。这项研究的更广泛的影响包括对温室气候模式的短期生物和环境动力学的见解。预期的结果应该作为“基础事实”对限制温室气候的假设产生重大影响。它还将导致在一个多学科项目中培训几名研究生和本科生，向他们介绍现场和实验室技术之间的协同作用。与过去一样，在那些未被充分代表的群体参与到pi开展的各种项目中，我们将继续努力让这些学生参与到这项努力中来。此外，由于这是一个涉及来自大学、自然历史博物馆和联邦政府的pi的合作项目，它必然涉及到这些机构之间的网络和促进互动。AMNH的参与为向广大公众展示这些研究成果提供了独特的机会。这一点尤其重要，因为更好地了解温室气候对于社会理解预测的人类引起的气候变化以及这些变化可能对未来地球历史产生的更大影响至关重要。

ABSTRACTThis multidisciplinary study proposes using O, C, and Sr isotopic analyses of pristine mollusks found within a single interval delineated by the Late Campanian Baculites compressus biozone (74 MA; Late Cretaceous) from the Western Interior Seaway (WIS) to examine four over-arching hypotheses which exploit the strengths of the PIs and consultant. These are:1. Geochemical analyses taken through the ontogeny of individual specimens - sclerochronology (sensu Jones, 1983) - provides annual to subdecadal records of environmental conditions (e.g., seasonal temperature fluctuations, water-mass dynamics) that are critical to understand the dynamics of Late Cretaceous epicontinental seas.2. Growth rates and other paleobiologic aspects of Late Campanian organisms, such as migration patterns, can be established using the sclerochronologic approach.3. The biota, especially molluscan elements, occupied different niches within the water column and on/in the substrate and the signals of these various habitats are captured in their isotopic signatures.4. Significant environmental gradients existed in the WIS, forced by differences in temperature and salinity, and can be measured and differentiated using oxygen and strontium isotopes from well-preserved molluscan shells. In addition to addressing our general hypotheses, the isotopic data will allow us to critically analyze a range of competing paleoceanographic, paleobiologic, and paleoclimatic hypotheses that have been proposed for the Late Cretaceous world. These include: circulation patterns within the WIS, stratification of the WIS, habitat ranges and depths of individual ammonite taxa, growth rates of Cretaceous molluscs, as well as seasonal fluctuations in marine temperatures. In order to address the questions posited above, we propose to undertake a detailed investigation of a single time interval through the Late Cretaceous in the very fossiliferous PIerre Shale focused on the B. compressus biozone. Deposition during this biozone was widespread in the WIS and was often accompanied by exquisite preservation of the fauna, including aragonitic elements, within early diagenetic concretions. To collect the necessary specimens, we will sample localities in central Colorado, central and western South Dakota, and western to eastern Montana that represent north-south and onshore-offshore transects. We will measure detailed sections at all localities and collect concretions containing diverse molluscan fauna. Before any isotopic analysis is undertaken, all specimens will be screened for any evidence of diagenesis using microscopic as well as geochemical techniques. Those specimens that pass the diagenetic screening will then be analyzed for d13C and d 18O to establish their sclerochronologies. Because the value of the aqueous environment in which the shell material was secreted is critical to deriving accurate estimates of temperature and salinity, we also propose to analyze a subset of our samples for their Sr isotopic ratio. Recent studies have shown that in areas, such as estuaries, where freshwater input is an important component in the system, that 87 Sr/86 Sr dominantly reflects the salinity rather than geologic age and our preliminary data suggest that this approach can be successfully applied to the WIS. These Sr data supply an independent, salinity proxy with which can better constrain the isotopic composition of the water. Together, these approaches will allow us to test our three hypotheses and add significantly to our understanding of the WIS and the macroinvertebrates that inhabited it.The broader impacts of this study include insights into the short-term biologic and environ-mental dynamics of greenhouse climate modes. The anticipated results should have a substantial impact as 'ground truth' for constraining hypotheses generated about greenhouse climates. It will result also in the training of several graduate and undergraduate students in a multidisciplinary project that will introduce them to the synergy between field and laboratory techniques. As in the past, where underrepresented groups have been involved in various projects undertaken by the PIs, we will continue to attempt to involve those students in this endeavor. Furthermore, because this is a collaborative project involving PIs from universities, a natural-history museum, and the Federal government, it will necessarily involve networking and foster interaction among these institutions. The involvement of the AMNH offers unique opportunities to present these research results to a broad, public audience. This is especially significant because a better understanding of greenhouse climate is critical to society's understanding of predicted human-induced climate change as well as to the larger ramifications that these changes may entail for future Earth history.