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

Abstract

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
Alternate Identifier(s):
OSTI ID: 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

Citation Formats

Flores, R.M., Weaver, J.N., Bossiroy, D., and Thorez, J. Genesis of clay mineral assemblages and micropaleoclimatic implications in the Tertiary Powder River Basin, Wyoming. United States: N. p., 1990. Web.
Flores, R.M., Weaver, J.N., Bossiroy, D., & Thorez, J. Genesis of clay mineral assemblages and micropaleoclimatic implications in the Tertiary Powder River Basin, Wyoming. United States.
Flores, R.M., Weaver, J.N., Bossiroy, D., and Thorez, J. Tue . "Genesis of clay mineral assemblages and micropaleoclimatic implications in the Tertiary Powder River Basin, Wyoming". United States. doi:.
@article{osti_7092518,
title = {Genesis of clay mineral assemblages and micropaleoclimatic implications in the Tertiary Powder River Basin, Wyoming},
author = {Flores, R.M. and Weaver, J.N. and Bossiroy, D. and Thorez, J.},
abstractNote = {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 rocks 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.},
doi = {},
journal = {AAPG Bulletin (American Association of Petroleum Geologists); (USA)},
number = ,
volume = 74:5,
place = {United States},
year = {Tue May 01 00:00:00 EDT 1990},
month = {Tue May 01 00:00:00 EDT 1990}
}

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  • Differences in original conditions of peat formation of Tertiary coals from the Powder River basin can be determined by petrographic analysis. Samples were obtained from intervals associated with environments that we interpreted as anastomosed fluvial Arvada and Smith coals and as meandering fluvial settings, Anderson and Anderson-Dietz coals. The Smith coal is characterized by relatively low amounts of liptinites (1 to 5%), cryptoeugelinite (EG) (8 to 32%), and high amounts of cryptohumotelinite (HT) (44 to 66%). EG is degraded woody material, and HT is preserved woody material. HT is generally enriched at the base of the Smith coal, perhaps becausemore » nutrient-rich waters allowed more luxuriant plant growth there. Data for the Arvada, Anderson, and Anderson-Dietz coals showed lower amounts of preserved woody material (HT = 30-50%) and higher amounts of degraded woody material (EG = 30-60%) and liptinites (4-10%). Variations in the liptinites are the result of differences in the amounts of bituminate, fluorinite, exsudatinite, and noncellular resinite. HT is usually highest at the top and bottom of the bed or near a parting. As in the Smith coal, increases in HT probably reflect more luxuriant plant growth. Preliminary data do not show a clear petrographic distinction between coals accumulated in anastomosed and meandering fluvial systems. However, ratios of HT/EG are greater in the Smith coal than in the other beds. Sampling density is rarely sufficient to assess changes in peat chemistry caused by flooding or channel migration. At the sample locality of the Anderson-Dietz coal, however, sample control was adequate enough in three dimensions so that maceral variations could be directly associated with channel migration and backswamp flooding.« less
  • Coal beds, as much as 250 ft thick, and adjacent sandstones in the Paleocene Tongue River Member of the Fort Union Formation are reservoirs for coal-derived natural gas in the Powder River basin. The discontinuous coal beds were deposited in raised, ombrotrophic peat bogs about 3 mi{sup 2} in size, adjoining networks of fluvial channels infilled by sand. Coal-bed thickness was controlled by basin subsidence and depositional environments. The average maceral composition of the coals is 88% huminite (vitrinite), 5% liptinite, and 7% inertinite. The coals vary in rank from subbituminous C to A (R{sub o} values of 0.4 tomore » 0.5%). Although the coals are relatively low rank, they display fracture systems. Natural gas desorbed and produced from the coal beds and adjacent sandstones is composed mainly of methane with lesser amount of Co{sub 2} ({lt}10%). The methane is isotopically light and enriched in deuterium. The gases are interpreted to be generated by bacterial processes and the fermentation pathway, prior to the main phase of thermogenic methane generation by devolatilization. Large amounts of bicarbonate water generated during early stages of coalification will have to be removed from the fracture porosity in the coal beds before desorption and commercial gas production can take place. Desorbed amounts of methane-rich, bacterial gas in the Powder River basin are relatively low ({lt}60 Scf/ton) compared to amounts of thermogenic coal-bed gases (hundreds of Scf/ton) from other Rocky Mountain basins. However, the total coal-bed gas resource in both the coal beds and the adjacent sandstones is considered to be large (as much as 40 Tcf) because of the vast coal resources (as much as 1.3 trillion tons).« less
  • Eolian dune sandstones are the principal reservoir rocks in the Permian upper part of the Minnelusa Formation, Powder River basin, Wyoming. These sandstones formed as shorelines retreated and dunes migrated across siliciclastic sabkhas. Sandstones are mainly quartzarenites; on average, clay minerals constitute about 5 wt.% the whole rock. Although present in minor amounts, clay minerals play an important role in the diagenetic evolution of these sandstones. Allogenic clay minerals are present in shaly rock fragments and laminae. Early infiltration of clays into porous sabkha sands commonly form characteristic menisei or bridges between framework grains or, when more extensive, form coatingsmore » or rims on grain surfaces. Authigenic clays include nearly pure smectite, mixed-layer illite/smectite (I/S), and late diagenetic illite and corrensite; these clay minerals are present as pore-lining cements. In addition to the deposition and neoformation of clay minerals throughout sandstone paragenesis, the conversion of smectite to illite occurred as temperatures increased with progressive burial. A temperature of 103C is calculated at a present depth of 3,200 m using a geothermal gradient of 30C/km and a mean annual surface temperature of 7C. After correction for uplift and erosion (250 m), the maximum calculated temperature for the conversion of all random I/S to ordered I/S is 100C. This calculated temperature is in excellent agreement with temperatures of 100-110C implied from I/S geothermometry.« less
  • Isopach maps of chronostratigraphic and lithostratigraphic units from the Late Cretaceous (early Campanian-late Maestrichtian) Montana Group of the Powder River basin, Wyoming, reveal a complex interplay between eustatic sea level fluctuations, sedimentation rates, and intraforeland basin subsidence rates. The Montana Group is characterized by numerous asymmetrical, coarsening- and thickening-upward, progradational deltaic, strand-plain, and/or shallow-marine deposits that thin eastward and merge into thick offshore-marine and pelagic deposits on the Pierre Shale. From oldest to youngest these are the Gammon, Shannon, and Sussex Members of the Steele Shale, the Parkman and Teapot Sandstone Members of the Mesaverde Formation, the Teckla Sandstone Membermore » of the Lewis Shale, and the Fox Hills Sandstone. Formation tops and bentonite beds from approximately 30,000 well logs were correlated throughout the Powder River basin and adjacent areas.« less