Reconsideration of the Morrison formation in the type area, Jefferson County, Colorado

Abstract

Research Article| September 01, 1944 Reconsideration of the Morrison formation in the type area, Jefferson County, Colorado W. A. WALDSCHMIDT; W. A. WALDSCHMIDT Search for other works by this author on: GSW Google Scholar L. W. LeROY L. W. LeROY Search for other works by this author on: GSW Google Scholar GSA Bulletin (1944) 55 (9): 1097–1114. https://doi.org/10.1130/GSAB-55-1097 Article history received: 29 Oct 1943 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation W. A. WALDSCHMIDT, L. W. LeROY; Reconsideration of the Morrison formation in the type area, Jefferson County, Colorado. GSA Bulletin 1944;; 55 (9): 1097–1114. doi: https://doi.org/10.1130/GSAB-55-1097 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The section of the Morrison formation recommended as the “type” has been selected because the entire Morrison is exposed along the West Alameda Parkway road cut, 2 miles north from Morrison, Colorado, and because the locality is readily accessible.The Morrison formation at the recommended type section is a distinct cartographic unit which can be subdivided into six parts primarily on the basis of lithologic characteristics of the sedimentary rocks.Fossils in this section of the Morrison formation are confined to three horizons. Dinosaur remains occur in limited number in basal sandstones of the gray shale and sandstone unit. Probable fresh-water sponge spicules are plentiful throughout an interval of 25 feet in the central part of the gray clay and limestone unit. A few spicules, however, are also present from 2 to 6 feet above the dinosaur-bearing sandstone. Aclistochara, the occurrence of which has not been mentioned previously in literature on the Morrison formation in Colorado, is relatively abundant in the upper 30 feet of the gray and red shale unit. This would place the highest occurrence of Aclistochara 63 feet above the base of the Morrison formation.The results of copper nitrate staining of samples from the calcareous rocks of the Morrison formation indicate that the greatest amount of calcite is present in the gray clay and limestone unit. In all probability the distribution and intensity of copper nitrate stains could be used effectively in connection with petrographic studies to identify several strata within the formation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.