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

科罗拉多的莫里森组和雪松山组 高原是认识晚侏罗世和早侏罗世的重要单元 北美洲西部白垩纪构造作用。 另外这些 单位包含丰富的中生代恐龙化石记录， 在几个州有许多采石场。 年龄和时间- 然而，这些地层的相关性仍然很差 明白 这就造成了理解区域性问题的困难。 构造和确定的演化趋势， 恐龙 提出了一种三重方法来解决这些问题 问题：1）发展更好的区域对比技术 使用火山灰（在许多地层中很常见） 2）获取新的同位素年龄，以解决 含油气地层的时间和对比问题; （3）利用相关的灰分和年龄来确定 沉积、沉降和构造之间的关系， 这段时间在美国西部。 将从火山灰层中采集样本， 沿着和穿过盆地的剖面， 都存了下来 裂变径迹40/39 Ar激光探测技术 将采用单一颗粒以避免碎屑污染， 获得现实的年龄。 我们将尝试把火山灰 通过检查锆石， 形态、包裹体和铀分布 锆石，以及通过检查微量元素化学 灰烬，灰烬的矿物学，以及任何其他区别 我们可以找到每一个灰层的特征。 其中三个部分， 被研究的地点都在恐龙采石场附近， 可以用来解决长期存在的争议， 化石的年代以及与其他部分的关系 在北美洲西部。

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.