Studies of the stratigraphic and structural record of large volcanic and impact events.

摘要

The mass extinction at the end of the Cretaceous is one of the five major biological crises in history of life on Earth. Numerous theories have been advanced to explain the mass extinction, but none has generated as much interest and as much controversy at the meteorite impact hypothesis. Chapters of this dissertation deal with aspects of this theory. One chapter deals with completeness of the stratigraphic record and probability that the geologic record will record such a short-term event. This chapter presents data that suggests that pelagic sediments are more complete than previously thought and that synchronous extinctions are likely to represent true simultaneous extinction rather than an artifact caused by hiatus or erosional unconformity. In another chapter the origin of shocked quartz found at the Cretaceous-Tertiary boundary is discussed. Using Cathodoluminescence techniques, shocked quartz at the boundary is shown to have a non-volcanic origin. In an appendix to this dissertation evidence is presented that suggest that the large (70 km diameter) Manicouagan bolide produced impact structure may be related to the end-Triassic extinction event defined by new Jurassic vertebrate discoveries from Nova Scotia, Canada.; An alternate causal-hypothesis for the extinction at the end of the Cretaceous is one in which presumed hotspot generated volcanism of the Deccan Traps, India, accounts for the extinctions and other physical evidence at the Cretaceous/Tertiary boundary thought to be evidence for a large meteorite impact. In a second major division of this dissertation, there are two chapters dealing with the thermomechanical effects of the Yellowstone hotspot. Although explosive volcanism similar to Yellowstone-type explosive volcanism has been suggested as the cause of extinctions at the end of the Cretaceous, the Yellowstone hotspot is Miocene-to-present in age and unrelated to the Cretaceous extinctions. Studies of Neogene displacement rates on faults within the circum-eastern Snake River Plain suggest that there is a parabolic distribution of historical seismicity and latest Quaternary faulting which has migrated in tandem with the hotspot. Presented is a thermomechanical model which is thought to be a reasonable explanation for the migrating patterns of fault displacement rates.