David L ClarkEmeritus Paleontology
One advantage of living among Paleozoic-Mesozoic mountains is the opportunity to use conodonts in solving geologic problems. In the central Wasatch Mountains, the Cambrian Maxfield Limestone is unconformably overlain by the Late Devonian Fitchville Dolomite. The missing 150 my interval is said to be the result of tectonic activity that supposedly resulted in the removal of all Late Cambrian to Late Devonian sediment deposited in this area, which during the Paleozoic was close to the western shoreline of North America. I have always been interested in this tectonic event and the erosive power attributed to it. Is it possible that there is no Late Cambrian, Ordovician, Silurian or Early and Middle Devonian sediment remaining in the central Wasatch Mountains?
Because unfossiliferous dolomites are the dominant lithology for the section in question, this summer we used the large sample size technique developed by UW grad Jeff Kuglitsch for his study of the Wisconsin Silurian. With the help of BYU graduate student Drew Derenthal and the BYU lab of UW grad Scott Ritter, two to four kg samples were taken at closely spaced intervals over a three meter span above and below the unconformity. To-date almost one half of the samples have been processed and our first results indicate the presence of Middle Devonian and possibly older Paleozoic rocks that until now have been assigned to the Middle Cambrian Maxfield Limestone. While I am still hoping to find Ordovician, our first results already modify the accepted interpretation of this Wasatch unconformity.January 2010