Alluvial architecture of the Horsefly unit (Basal Quartz) in southern Alberta and northern Montana: influence of accommodation changes and comtemporaneous faulting

Abstract

Research Article| March 01, 2002 Alluvial architecture of the Horsefly unit (Basal Quartz) in southern Alberta and northern Montana: influence of accommodation changes and comtemporaneous faulting T.D. Lukie; T.D. Lukie Nexen Canada Limited, 801 - 7 Avenue SW, Calgary, AB T2P 3P7 Search for other works by this author on: GSW Google Scholar G.W. Ardies; G.W. Ardies EnCana Corporation, 150 - 9 Avenue SW, Calgary, AB T2P 2S5 Search for other works by this author on: GSW Google Scholar R. W. Dalrymple; R. W. Dalrymple Department of Geological Science, and Geological Engineering, Queen’s University, Kingston, ON K7L 3N6 Search for other works by this author on: GSW Google Scholar B.A. Zaitlin B.A. Zaitlin EnCana Corporation, 150-9 Avenue SW, Calgary, AB T2P 2S5 Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2002) 50 (1): 73–91. https://doi.org/10.2113/50.1.73 Article history received: 18 May 2001 accepted: 17 Sep 2001 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 T.D. Lukie, G.W. Ardies, R. W. Dalrymple, B.A. Zaitlin; Alluvial architecture of the Horsefly unit (Basal Quartz) in southern Alberta and northern Montana: influence of accommodation changes and comtemporaneous faulting. Bulletin of Canadian Petroleum Geology 2002;; 50 (1): 73–91. doi: https://doi.org/10.2113/50.1.73 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 SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract The Basal Quartz (Early Cretaceous) consists of a nested succession of mineralogically distinct, unconformity-bounded units. The second oldest of these, the Horsefly sandstone, occupies a broad (28–52 km wide), north-south trending, flat-floored valley (the Taber-Cutbank valley) in northern Montana and southern Alberta (south of Township 15) that has a maximum relief of 50 m. The valley-fill deposits are entirely fluvial in origin. Two internal sequences are recognized. Each begins with a regional erosion surface and sheet sandbody consisting of amalgamated channel sandstones. Contemporaneous overbank sediments (now represented by mudstone-pebble conglomerates) were completely eroded. These sandstones are overlain by mudstone-dominated deposits which consist mainly of red vertisols and contain isolated, ribbon channel sandstones and sheet sandstones formed by crevasse splays. Each sequence accumulated under conditions of continuously increasing accommodation space. Tectonic movements, perhaps in response to episodic thrust loading, are thought to be the major control on accommodation; eustatic fluctuations were probably not important because the study area lay far inland at the time of deposition.Syndepositional block faulting partially overprinted the regional changes in accommodation, producing constrictions in the valley at the location of cross-valley uplifts; slightly greater uplift of the northern part of the valley caused an overall down-stream narrowing. Local areas of greater subsidence trapped the northward-moving, extrabasinal gravel, accelerating the proximal distal fining trend. Such areas also tend to display evidence of higher water tables, including the preservation of organic-rich deposits, and to contain a higher number of channel sandstones because the rivers preferentially avoided the subtly uplifted areas. This study shows that the influence of subtle faulting can be significant during times of limited accommodation because it is not masked by rapid sedimentation. This content is PDF only. Please click on the PDF icon to access. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.