Correlation and Causes of Fifth Order Cycles Within the Upper Cretaceous Eagle Formation, Bighorn Basin of Wyoming

<p>Cyclic stratification was examined in the Upper Cretaceous (Santonian-Campanian) section (Eagle Formation) within the Bighorn Basin of Wyoming. Of particular concern was the 10³ to 10⁴ year band, which in marine settings has been attributed to orbital forcing (Milankovitch cyclicity). A series of 19 sections were measured through the Virgelle Member of the Eagle Formation. Most were measured on the “J”-shaped escarpment that constitutes the nose and north flank of the Thermopolis anticline. Several others were measured at sites up to 30 km to the northwest along paleo-shoreline. In the study, detailed thickness data of all sections and grain size data of three sections were used to test the hypothesis that fifth-order cycles are of eustatic origin. Spectral analysis of limited grain size data clearly indicated a strong 41,000-year Milankovitch cycle (the obliquity cycle) along with a well-defined 20,000-year Milankovitch cycle (the precession cycle). The Sherman statistic, a statistic which tests whether events are periodic or random, was used on the more extensive thickness data. Results indicated the presence of Milankovitch events at periodicities of 41,000 and 20,000-years, and these events have been correlated along paleo-shoreline as well as into the basin. This data has been interpreted as a result of varying monsoonal strength often ascribed to precessional control. Variation in monsoonal strength may have caused the rate of sediment input to vary, or may have caused sea level to vary, or both.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Ocean & Earth Sciences

Year dc:date.available

2005

Author dc:creator

• Johnson, Kimberly Ann

Contributors dc:contributor

• Donald J. P. Swift
• Dennis Darby
• James Castle
• Chester Grosch

• Bighorn Basin
• Cretaceous
• Eagle Formation
• Fifth-order cycles
• Wyoming
• Geology

Statement dc:rights

• <p>In Copyright. URI: <a href="http://rightsstatements.org/vocab/InC/1.0/">http://rightsstatements.org/vocab/InC/1.0/</a> This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).</p>

Identifier

9780542157462

OAI identifier oai:identifier

oai:digitalcommons.odu.edu:oeas_etds-1050