Initial Deposits in the Cordilleran Geosyncline: Evidence of a Late Precambrian (<850 m.y.) Continental Separation

Abstract

Research Article| May 01, 1972 Initial Deposits in the Cordilleran Geosyncline: Evidence of a Late Precambrian (<850 m.y.) Continental Separation JOHN H STEWART JOHN H STEWART U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN H STEWART U.S. Geological Survey, Menlo Park, California 94025 Publisher: Geological Society of America Received: 17 Jun 1971 Revision Received: 29 Sep 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1972) 83 (5): 1345–1360. https://doi.org/10.1130/0016-7606(1972)83[1345:IDITCG]2.0.CO;2 Article history Received: 17 Jun 1971 Revision Received: 29 Sep 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation JOHN H STEWART; Initial Deposits in the Cordilleran Geosyncline: Evidence of a Late Precambrian (<850 m.y.) Continental Separation. GSA Bulletin 1972;; 83 (5): 1345–1360. doi: https://doi.org/10.1130/0016-7606(1972)83[1345:IDITCG]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Upper Precambrian and Lower Cambrian strata in western North America are exposed in a narrow slightly sinuous belt extending from Alaska and northern Canada to northern Mexico, a distance of 2,500 mi. Within this belt, the strata thicken from 0 ft on the east to 15,000 to 25,000 ft in areas 100 to 300 mi to the west. The basal unit of this sequence is a diamictite (conglomeratic mudstone) which is widely distributed but discontinuous and is generally considered to be of glacial origin. Overlying sedimentary rocks consist predominantly of siltstone, shale, argillite, quartzite, and conglomerate. Tholeiitic basalt forms thick and widespread units near the base of the sequence but is sparse higher in the section.The distribution pattern and lithologic characteristics of the upper Precambrian and Lower Cambrian sequence fit the recently developed concept that thick sedimentary sequences accumulate along stable continental margins subsequent to a time of continental separation. The depositional pattern of the sequence is unlike that of underlying rocks, a relation consistent with the idea of a continental separation cutting across the grain of previous structures. The pattern is, on the other hand, similar to that of overlying lower and middle Paleozoic rocks, suggesting that the diamictite and post-diamictite rocks were the initial deposits in the Cordilleran geosyncline. Thick units of volcanic rock near the bottom of the sedimentary sequence indicate volcanic activity related to the thinning and rifting of the crust during the continental separation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.