skip to main content

Title: Genesis of clay mineral assemblages and micropaleoclimatic implications in the Tertiary Powder River Basin, Wyoming

An x-ray diffraction (XRD) study was undertaken on the clay mineralogy of the early Tertiary coal-bearing sequences of the Powder River basin. The vertical and lateral distribution of alternating fluvial conglomerates, sandstones, mudstones, shales, coals, and paleosols reveals a transition from alluvial fans along the basin margin to an alluvial plain and peat bogs basinward. Samples included unweathered shales and mudstones from a borehole and a variety of corresponding surface outcrop samples of Cambrian to Eocene age. Samples older than Tertiary were collected along the basin margin specifically to determine the potential source of parent material during Tertiary sedimentation. XRD analyses were performed on the <2-{mu}m fraction prepared as oriented aggregates. To investigate the materials in their natural state, no chemical pre-treatments the authors applied before the analysis. A series of specific post-treatments, consisting of catonic saturation (Li+, K+), a solution with polyalcohols, heating, acid attack and hydrazine saturation was selectively applied. These post-treatments permit a good discrimination between the mimetic clay minerals such as smectite and illite-smectite mixed layers that constitute the bulk of the clay fraction in the Tertiary rocks. When analyzed only using routine XRD, these swelling minerals are apparently uniformly distributed in the fluvial sedimentary rocksmore » and are better interpreted as a single smectitic population. However, the post-treatments clearly differentiate both qualitatively and quantitatively this smectitic stock. Other clays include illite and kaolinite, which have different degrees of crystallinity, and minor interstratified clays (i.e., illite-chlorite, chlorite-smectite). The clay minerals in pre-Tertiary (and pedogenic) materials are different from those in the Tertiary rocks.« less
Authors:
;  [1] ; ;  [2]
  1. (Geological Survey, Denver, CO (USA))
  2. (Liege State Univ. (Belgium))
Publication Date:
OSTI Identifier:
7092518
Report Number(s):
CONF-900605--
Journal ID: ISSN 0149-1423; CODEN: AABUD
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA); Journal Volume: 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; 58 GEOSCIENCES; CLAYS; MINERALOGY; COAL DEPOSITS; WYOMING; PALEOCLIMATOLOGY; ALLUVIAL DEPOSITS; CHLORITE MINERALS; CONGLOMERATES; ILLITE; KAOLINITE; POWDER RIVER BASIN; SHALES; SMECTITE; TERTIARY PERIOD; X-RAY DIFFRACTION; ALUMINIUM COMPOUNDS; ALUMINIUM SILICATES; CENOZOIC ERA; COHERENT SCATTERING; DIFFRACTION; FEDERAL REGION VIII; GEOLOGIC AGES; GEOLOGIC DEPOSITS; MINERAL RESOURCES; MINERALS; MONTANA; NORTH AMERICA; OXYGEN COMPOUNDS; PALEONTOLOGY; RESOURCES; ROCKS; SCATTERING; SEDIMENTARY ROCKS; SILICATE MINERALS; SILICATES; SILICON COMPOUNDS; USA 011000* -- Coal, Lignite, & Peat-- Reserves, Geology, & Exploration; 580000 -- Geosciences