Upper Pennsylvanian Shoreline Deposits from Iowa and Nebraska: Their Recognition, Variation, and Significance

Abstract

Research Article| February 01, 1972 Upper Pennsylvanian Shoreline Deposits from Iowa and Nebraska: Their Recognition, Variation, and Significance J. A FAGERSTROM; J. A FAGERSTROM Department of Geology, University of Nebraska, Lincoln, Nebraska 68508 Search for other works by this author on: GSW Google Scholar RAYMOND R BURCHETT RAYMOND R BURCHETT Nebraska Geological Survey, University of Nebraska, Lincoln, Nebraska 68508 Search for other works by this author on: GSW Google Scholar Author and Article Information J. A FAGERSTROM Department of Geology, University of Nebraska, Lincoln, Nebraska 68508 RAYMOND R BURCHETT Nebraska Geological Survey, University of Nebraska, Lincoln, Nebraska 68508 Publisher: Geological Society of America Received: 27 May 1971 Revision Received: 20 Aug 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 (2): 367–388. https://doi.org/10.1130/0016-7606(1972)83[367:UPSDFI]2.0.CO;2 Article history Received: 27 May 1971 Revision Received: 20 Aug 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. A FAGERSTROM, RAYMOND R BURCHETT; Upper Pennsylvanian Shoreline Deposits from Iowa and Nebraska: Their Recognition, Variation, and Significance. GSA Bulletin 1972;; 83 (2): 367–388. doi: https://doi.org/10.1130/0016-7606(1972)83[367:UPSDFI]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 Evidence from stratigraphy, carbonate mineralogy, and primary sedimentary structures indicates that the Rakes Creek Shale, Ozawkie Limestone, and Oskaloosa Shale Members in eastern Nebraska and western Iowa were deposited along the shore of a fluctuating sea Adjacent positive land areas were located to the west (Nehawka Arch) and locally to the south (Redfield Anticline); the subsiding Forest City basin was located to the southeast.Stratigraphic evidence supporting these conclusions includes the progressively decreased thickness, increased insoluble content, and increased amount of red shale in these members toward the west. There is also a general increase in the dolomite content of these rocks from the ancient intertidal to the supratidal zone. Primary sedimentary structures suggestive of supratidal and intertidal origin such as birdseyes, desiccation structures, “worm” trails, and thin, wavy laminations are also more abundant toward the west. However, the most diagnostic shoreline features are the well-developed and varied cryptalgal structures of the lower Ozawkie Member which are arranged in subparallel belts analogous to those in the modern intertidal and supratidal zones of Shark Bay, Western Australia. The cryptalgal structures further indicate that the tidal range was at least 8 in., and the paleoslope of the intertidal-supratidal zone was only about 2 in./mi.The interval from the Rakes Creek to the Oskaloosa Shale is part of a typical midcontinent Pennsylvanian megacyclic sequence, the Deer Creek Megacyclothem (Moore, 1936). The sequence began with the subaerial accumulation of clastic sediments of the Rakes Creek Shale Member followed by marine invasion and deposition of the Ozawkie Limestone Member. The overlying Oskaloosa Shale Member represents a minor regressive phase which ended with a second marine transgression during deposition of the Rock Bluff Limestone Member. Another minor regression with restricted circulation is represented by the lower Larsh Shale Member, which in turn was succeeded by a third transgression during deposition of the upper Larsh and lower Ervine Creek Members. The megacyclic sequence ended with a final major regression at the end of Ervine Creek time. 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.