Time and Tectonism in the Late Jurassic and Early Cretaceous: Evidence from the Morrison and Cedar Mountain Formations

晚侏罗世和早白垩世的时间和构造作用：来自莫里森山和雪松山地层的证据

• 批准号: 8720651
• 负责人: Bart Kowallis
• 金额: $ 6.2万
• 依托单位: Brigham Young University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-04-01 至 1991-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8720651&HistoricalAwards=false
• 关键词: Time; Tectonism; Late; Jurassic; Early

The Morrison and Cedar Mountain Formations in the Colorado Plateau are key units in understanding Late Jurassic and Early Cretaceous tectonism in western North America. In addition, these units contain a rich fossil record of Mesozoic dinosaurs from numerous quarry sites in several states. The ages and time- correlation of these formations are, however, still poorly understood. This creates problems in understanding regional tectonics and in determining the evolutionary trends of the dinosaurs. A threefold approach is proposed to resolve these problems: 1) develop better techniques for regional correlation using volcanic ashes (which are quite common in many stratigraphic sections worldwide); 2) obtain new isotopic ages to resolve the problems of time and correlation of the dinosaur-bearing strata; and 3) use the correlated ashes and ages to determine the relationships between sedimentation, subsidence, and tectonics for this period of time in the western United States. Samples will be collected of ash beds for dating from sections both along and across the basin in which these sediments were deposited. Fission track 40/39 Ar laser probe techniques on single grains will be employed to avoid detrital contamination and obtain realistic ages. Attempts will be made to correlate ash layers from one section to another by examining zircon morphologies, inclusions, and uranium distributions within the zircons, as well as by examining the trace element chemistry of the ashes, mineralogy of the ashes, and any other distinguishing feature we can find for each ash layer. Three of the sections to be studied are located near dinosaur quarries so that the ages obtained can be used to resolve long-standing controversies about the age of the fossils and the relationships with other sections in western North America.

科罗拉多高原的莫里森和雪松山组是了解北美西部晚侏罗世和早白垩世构造作用的关键单元。此外，这些单元还包含了从几个州的众多采石场中发现的丰富的中生代恐龙化石记录。然而，人们对这些地层的年龄和时间相关性仍然知之甚少。这给理解区域构造和确定恐龙的进化趋势带来了问题。为了解决这些问题，提出了一种三重方法：1)利用火山灰（在世界各地的许多地层剖面中都很常见）开发更好的区域对比技术；2)获得新的同位素年龄，解决了含恐龙地层的时间和对比问题；3)利用相关的火山灰和年龄来确定美国西部这一时期的沉积、沉降和构造之间的关系。将从沿盆地和横跨盆地的部分收集火山灰床样本，以确定这些沉积物沉积的年代。采用单粒裂变径迹40/39氩激光探测技术，避免碎屑污染，获得真实年龄。将尝试通过检查锆石的形态、内含物和锆石中的铀分布，以及检查灰烬的微量元素化学、灰烬的矿物学和我们能找到的每个灰烬层的任何其他区别特征，来将一个部分的灰烬层与另一个部分的灰烬层联系起来。其中三个被研究的部分位于恐龙采石场附近，因此所获得的年龄可以用来解决长期以来关于化石年龄以及与北美西部其他部分关系的争议。