ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING

Research Article| February 01, 1959 ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING: II. OVERTHRUST BELT IN GEOSYNCLINAL AREA OF WESTERN WYOMING IN LIGHT OF FLUID-PRESSURE HYPOTHESIS WILLIAM W RUBEY; WILLIAM W RUBEY U.S. GEOLOGICAL SURVEY, WASHINGTON, D.C.; SHELL DEVELOPMENT CO., HOUSTON, TEXAS Search for other works by this author on: GSW Google Scholar M KING HUBBERT M KING HUBBERT U.S. GEOLOGICAL SURVEY, WASHINGTON, D.C.; SHELL DEVELOPMENT CO., HOUSTON, TEXAS Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIAM W RUBEY U.S. GEOLOGICAL SURVEY, WASHINGTON, D.C.; SHELL DEVELOPMENT CO., HOUSTON, TEXAS M KING HUBBERT U.S. GEOLOGICAL SURVEY, WASHINGTON, D.C.; SHELL DEVELOPMENT CO., HOUSTON, TEXAS Publisher: Geological Society of America Received: 10 Nov 1958 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1959, 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 (1959) 70 (2): 167–206. https://doi.org/10.1130/0016-7606(1959)70[167:ROFPIM]2.0.CO;2 Article history Received: 10 Nov 1958 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation WILLIAM W RUBEY, M KING HUBBERT; ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING: II. OVERTHRUST BELT IN GEOSYNCLINAL AREA OF WESTERN WYOMING IN LIGHT OF FLUID-PRESSURE HYPOTHESIS. GSA Bulletin 1959;; 70 (2): 167–206. doi: https://doi.org/10.1130/0016-7606(1959)70[167:ROFPIM]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 Pressures of interstitial fluids significantly greater than the normal hydrostatic pressure are known in many parts of the world. Many occurrences are in thick sections of relatively young sediments; some are in areas that have been intensely deformed. Abnormal fluid pressures in the Gulf Coast region are associated with thick bodies of shale or mudstone, and with high hydraulic gradients across bedding. The rocks there have been buried rather rapidly and are evidently not yet fully compacted. The mechanism by which clay consolidates under pressure affords a quantitative relationship among the variables—depth, strength of clay, and fluid pressure—and this relationship indicates that the Gulf Coast examples agree fairly well with observations on depth and porosity in Paleozoic shales of Oklahoma and Tertiary shales of Venezuela. Critical data are lacking, but permeability clearly decreases tremendously as clay rocks are compacted. This decrease in permeability provides a self-sealing mechanism that greatly retards the escape of pore water from deeply buried clay rocks. The relationship between rate of compaction and the development of abnormal fluid pressures probably applies not only to clay rocks but also to carbonates and possibly to micaceous and chloritic metamorphic rocks. Conditions of geosynclinal deposition are, in general, those most favorable to the development of abnormal fluid pressures.The hypothesis that large-scale overthrusting is facilitated by abnormal fluid pressures which, in turn, are associated with geosynclinal deposition is applied to the overthrust belt of western Wyoming and adjacent States. This is a long curving belt of several bedding-plane faults which have an aggregate horizontal displacement across the belt of 50 miles or more. The sedimentary rocks that make up the belt were evidently deposited in a major geosyncline bordered by uplands not far to the west. At any given locality, the rate of deposition of the sediments increased continuously until the beginning of intense deformation and overthrusting. The geosynclinal axis and the bordering uplands probably migrated slowly eastward across the belt. Several lines of indirect evidence suggest that abnormal fluid pressures developed in this region during final stages of rapid geosynclinal sinking and that thick plates of Paleozoic and Mesozoic sedimentary rocks sheared off from the underlying rocks and moved slowly eastward. Rate of movement probably was controlled by erosion of upfolds that arose at the front of each moving plate. The fundamental cause of the lateral stresses that propelled the overthrusts is not known, but it may be examined instructively in the light of the fluid-pressure hypothesis. The thrust sheets might, for example, have slid by simple gravitation down the western limb of the geosyncline on reasonable slopes and not improbable fluid pressure-overburden ratios. Such large-scale slumping of thrust sheets, however, seems to require gaps at the rear of the thrust sheets. The long intermontane valleys of Idaho and Utah may possibly have originated as such gaps or rifts, but no proof has yet been recognized that they were formed in this manner. An alternative possibility, regional compression, requires concentration of the lateral stresses within the upper few miles of the earth's crust; in this general region emplacement of the Idaho batholith seems the most likely source of such superficially concentrated stresses. However, this batholith is so far from the front edge of the overthrust belt that it would require extremely high fluid pressure-overburden ratios over a wide area. Perhaps some combination of the two forces—pushing wide thrust plates down a gentle slope—is the most likely explanation. 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.