Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence

Abstract

Research Article| May 01, 1976 Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence JOHN HOWER; JOHN HOWER 1Department of Earth Sciences, Case Western Reserve University, Cleveland, Ohio 44106 Search for other works by this author on: GSW Google Scholar ERIC V. ESLINGER; ERIC V. ESLINGER 2Department of Geology, West Georgia College, Carrollton, Georgia 30117 Search for other works by this author on: GSW Google Scholar MARK E. HOWER; MARK E. HOWER 3Department of Mathematics, Middlebury College, Middlebury, Vermont 05753 Search for other works by this author on: GSW Google Scholar EDWARD A. PERRY EDWARD A. PERRY 4Department of Geology, University of Massachusetts, Amherst, Massachusetts 01002 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN HOWER 1Department of Earth Sciences, Case Western Reserve University, Cleveland, Ohio 44106 ERIC V. ESLINGER 2Department of Geology, West Georgia College, Carrollton, Georgia 30117 MARK E. HOWER 3Department of Mathematics, Middlebury College, Middlebury, Vermont 05753 EDWARD A. PERRY 4Department of Geology, University of Massachusetts, Amherst, Massachusetts 01002 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (5): 725–737. https://doi.org/10.1130/0016-7606(1976)87<725:MOBMOA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN HOWER, ERIC V. ESLINGER, MARK E. HOWER, EDWARD A. PERRY; Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence. GSA Bulletin 1976;; 87 (5): 725–737. doi: https://doi.org/10.1130/0016-7606(1976)87<725:MOBMOA>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 A detailed mineralogical and chemical investigation has been made of shale cuttings from a well (Case Western Reserve University Gulf Coast 6) in Oligocene-Miocene sediment of the Gulf Coast of the United States. The <0.1-, 0.1- to 0.5-, 0.5- to 2-, 2- to 10-, and >10-µm fractions from the 1,250- to 5,500-m stratigraphic interval were analyzed by x-ray diffraction. Major mineralogic changes with depth take place over the interval 2,000 to 3,700 m, after which no significant changes are detectable. The most abundant mineral, illite/smectite, undergoes a conversion from less than 20 percent to about 80 percent illite layers over this interval, after which the proportion of illite layers remains constant. Over the same interval, calcite decreases from about 20 percent of the rock to almost zero, disappearing from progressively larger size fractions with increasing depth; potassium feldspar (but not albite) decreases to zero; and chlorite appears to increase in amount. Variations in the bulk chemical composition of the shale with depth show only minor changes, except for a marked decrease in CaO concomitant with the decrease in calcite. By contrast, the <0.1-µm fraction (virtually pure illite/smectite) shows a large increase in K2O and Al2O3 and a decrease in SiO2 The atomic proportions closely approximate the reaction smectite + Al+3 + K+ = illite + Si+4. The potassium and aluminum appear to be derived from the decomposition of potassium feldspar (and mica?), and the excess silicon probably forms quartz. We interpret all the major mineralogical and chemical changes as the response of the shale to burial metamorphism and conclude that the shale acted as a closed system for all components except H2O, CaO, Na2O, and CO2. Compositional changes in the shale as a function of metamorphic grade closely parallel compositional changes in shale as a function of geologic age. 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.