Collaborative Research: Radiocarbon Dating of North American Terrestrial Gastropod Shells

合作研究：北美陆生腹足动物壳的放射性碳测年

• 批准号: 0614647
• 负责人: Jason Rech
• 金额: $ 9.34万
• 依托单位: Miami University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-08-15 至 2009-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0614647&HistoricalAwards=false
• 关键词: Collaborative; Research; Radiocarbon; Dating; North

Collaborative Research: Radiocarbon Dating of North American Terrestrial Gastropods ShellsJeffrey S. Pigata, University of Arizona (EAR-0614840)Jason A. Rech, Miami University (EAR-0614647)Jeffrey C. Nekola, University of New Mexico (EAR-0614903) ABSTRACTTerrestrial gastropods are one of the most successful animal groups on Earth. They occupy and thrive in incredibly diverse habitats, ranging from marshes and grasslands to upland forests and arctic tundra. Their distribution in the fossil record is equally diverse. Gastropod shells are commonly found in lake, wetland, alluvial, loess, and glacial deposits, as well as in sediments at archeological sites worldwide. Yet despite their widespread occurrence in the fossil record and the fact that they contain ~12% by weight carbon, gastropod shells are usually avoided for 14C dating because many taxa incorporate 14C-deficient (or "dead") carbon from limestone when building their shells. Geochronologists refer to this as the "Limestone Problem" because the amount of dead carbon incorporated in gastropod shells is variable at all taxonomic levels and can cause 14C ages to be up to 3,000 years too old. However, PIs preliminary results from the American Southwest suggest that some small (maximum body dimension 10 mm) gastropods avoid limestone even when it is readily available. Moreover, these same taxa appear to remain closed systems with respect to carbon over geologic timescales in arid environments. Thus, at least in dry conditions, some small terrestrial gastropod shells may in fact provide reliable 14C ages. The primary research objective of this study is to clearly identify gastropod taxa that are capable of consistently yielding reliable 14C ages, regardless of local lithology, environmental conditions, climate, or ecological habitat. To this end, PIs will conduct a systematic analysis of the 14C content of a suite of modern and fossil terrestrial gastropods that are endemic to North America. They have targeted more than 30 extant species that will be used to answer the following research questions: (1) do individuals of a specific taxon always avoid limestone when building their shells, and (2) if so, do their shells remain closed systems over time regardless of local environmental conditions? The wide taxonomic, ecological, and taphonomic scope of this study will allow PIs to determine what types of gastropod shells can be used to reliably date Quaternary sediments. Moreover, this approach will help other investigators identify additional target species, including those outside North America, by providing a priori guidelines for the identification of taxa that use only metabolically-generated carbon in shell construction and that will hence provide accurate 14C ages.

合作研究：北美陆生腹足类贝壳的放射性碳年代测定。皮加塔，亚利桑那大学（邮编：0614840）杰森A。雷奇，迈阿密大学（邮编：0614647）杰弗里C。Nekola，新墨西哥州大学（邮编：0614903）摘要陆生腹足类是地球上最成功的动物类群之一。 他们占据和繁荣在令人难以置信的多样化的栖息地，从沼泽和草原到高地森林和北极苔原。 它们在化石记录中的分布也同样多样。 腹足类贝壳通常存在于湖泊、湿地、冲积物、黄土和冰川沉积物中，以及世界各地考古遗址的沉积物中。 然而，尽管它们在化石记录中广泛存在，并且它们含有约12%重量的碳，但腹足类贝壳通常不会被14 C测年，因为许多分类群在建造它们的贝壳时含有来自石灰石的14 C缺乏（或“死”）碳。 地质年代学家称之为“石灰石问题”，因为腹足类贝壳中的死碳含量在所有分类学水平上都是可变的，可能导致14 C年龄超过3,000年。 然而，来自美国西南部的PI初步结果表明，一些小的（最大身体尺寸10毫米）腹足动物避免石灰石，即使它是现成的。 此外，这些相同的类群似乎仍然是封闭的系统，在干旱环境中的地质时间尺度的碳。 因此，至少在干燥的条件下，一些小型陆生腹足类贝壳实际上可以提供可靠的14 C年龄。 本研究的主要研究目标是明确确定腹足类类群，能够始终如一地产生可靠的14 C年龄，无论当地岩性，环境条件，气候或生态栖息地。 为此，研究所将对北美特有的一套现代和化石陆生腹足类的14 C含量进行系统分析。 他们已经锁定了30多个现存物种，这些物种将被用来回答以下研究问题：（1）特定分类群的个体在建造贝壳时是否总是避开石灰石，（2）如果是这样，它们的贝壳是否会随着时间的推移而保持封闭系统，而不管当地的环境条件如何？ 广泛的分类学，生态学和埋藏学的范围内，这项研究将允许PI确定什么类型的腹足类贝壳可以用来可靠地定年第四纪沉积物。 此外，这种方法将有助于其他研究人员确定其他目标物种，包括北美以外的物种，通过提供先验的指导方针，用于识别在壳结构中仅使用代谢产生的碳的类群，从而提供准确的14 C年龄。