PRELIMINARY AGE DETERMINATION OF UNCONSOLIDATED DEPOSITS ON TOP OF TABLE MOUNTAIN, FREMONT CO., WYOMING

The age of sedimentary deposits on top of Table Mountain in Fremont County remains an enigma despite its prominence in the local landscape (2500 feet above), and its location near some of the most studied geology in the country. Many university field camps cross its path each summer and one, the Branson Geological Laboratory of the University of Missouri, sits just below its rim. While not the specific topic of many research or general papers in the immediate area, it is mentioned by several, and its age has been stated as being anywhere from Eocene to Pleistocene. Four samples from the southwest part of the mountain yielded Be-10 ages from 783 ka to 135 ka (Dahms, 2004).

Our Main Question: What is(are) the age(s) of the sedimentary deposit(s) on top of Table Mountain? Questions that need to be answered prior to answering the above question:(1) Is the entire deposit on top of the mountain one layer or more?;(2) If more than one layer, what is the distribution of the different types of sediments?;(3) Are there any other mountains, of similar elevation, in the surrounding area that have a similar veneer of sediment(s)?; (4) What is(are) the best method(s) to date deposits of this type and of such young geologic age?; (5) What is the best way to sample these deposits and prepare them for preliminary age dating?

As an undergraduate research project, supported by Wyoming ESPCoR, we have begun a quantitative inventory of the large boulders on top of the flat surface of the mountain. Other parameters that may be investigated in the future include soil profiles, carbon dating, tree cores and pollen identification. With a plan to use Be-10 isotopic dating on boulder samples, we have chosen only those boulders standing 1 meter or higher on the top surface. The majority of boulders on the southern half of Table Mountain are blocky, split, leucocratic granite with hard surfaces and lichen growth on the eastern faces. They are sitting on top of a matrix of lightly weathered grus and smaller rounded boulders. Based on these preliminary findings, we are confident that the boulders on the southern part of Table Mountain have the proper characteristics for isotopic dating, and that future analysis will lead to a narrower age range.