Tertiary Coal Beds Research Articles

Differential compaction of interbedded sandstone and coal

Abstract Cretaceous and Tertiary coal beds in the western United States typically contain subvertical opening-mode fractures (cleat). However, closely spaced normal faults abruptly substitute for opening-mode fractures in coal beneath some sandstone lenses having blunt terminations. Differential forced-fold compaction of coal beds around and beneath lens-shaped sandstone bodies accounts for such shifts in fracture style. Finite element modelling of coal deformation shows that shear stress is augmented in coal layers below abruptly tapering edges of sandstones lenses, favouring fault development, whereas under gradually tapering lenses shear stresses are not sufficiently enhanced to cause shifts in fracture style. Upper Cretaceous Mesaverde Group coal beds in southwest Wyoming have significant variations in fracture style over distances of a few to tens of metres. Because these faults have little or no porosity, the coal that contains them is likely to have low permeability compared to coal having typical (generally porous) opening-mode fractures. Thus, shifting fracture style may affect regional and local gas and water flow in coal beds.

Delineation of the distinctive nature of Tertiary coal beds : J. C. Shearer, T. A. Moore & T. D. Demchuk, International Journal of Coal Geology, 28(2–4), 1995, pp 71–98

Delineation of the distinctive nature of Tertiary coal beds : J. C. Shearer, T. A. Moore & T. D. Demchuk, International Journal of Coal Geology, 28(2–4), 1995, pp 71–98

Delineation of the distinctive nature of tertiary coal beds

Floral character in mires has changed progressively through time. In the Carboniferous, pteridophytes, sphenophytes and lycophytes were dominant but by the Permian gymnosperms were an important component of mire flora. During the early Mesozoic gymnosperms remained the characteristic mire vegetation, together with pteridophytes, and conifers became dominant during the Jurassic. Cretaceous and Paleocene vegetation are similar, with taxodiaceous flora being important in mire vegetation. From the Eocene onwards, however, angiosperms were increasingly dominant in mire communities and in the Miocene herbaceous vegetation began to play a significant role. Together with these changes in floral character at least three aspects of coal character also appear to vary sequentially with time and are distinctive in the Tertiary: (1) proportions and thickness of vitrain banding, (2) coal bed thickness and (3) proportions of carbonised material. A compilation has been made of data from the coal literature comparing older coals with those of the Tertiary, in order to give a perspective in which to examine Tertiary coals. It was found that only Tertiary coals contain significant proportions of coal devoid of vitrain bands. In addition, Tertiary coals are the thickest recorded coal beds and generally contain low percentages of carbonised material (many less than 5%) as compared to older coals. It is interesting to note that Paleocene coal beds are similar to Cretaceous coals in that they tend to be thinner and contain higher proportions of carbonised material than do younger Tertiary coals. The absence of vitrain bands in some Tertiary coal beds is thought to result from the floras dominated by angiosperms, which are relatively easily degraded as compared to gymnosperms. The thickness of Tertiary coals may be related to an increase in biomass production from the Carboniferous through to the Tertiary, as plants made less investment in producing lignin, an energy-intensive process. In addition, with less lignin in plants, easier degradation of biomass may have facilitated nutrient recycling which, in turn, led to greater biomass production. Increased biomass production may have also ‘diluted’ the carbonised material present in some Tertiary peats, leading to lower proportions in the coal. Another possible cause of decreased carbonised components in Tertiary coal is that decreasing lignin content resulted in decreased charring during fires, as lignin is particularly prone to charring. A third possibility is that the carbonised component of peat may be concentrated during coalification so that Tertiary coals, generally of lower rank than Mesozoic or Paleozoic coals, contain a smaller fraction of carbonised plant material. It is not at present clear which of these mechanisms may have affected carbonised material in peat and coal but it is clear that lignin type and content has had an important role in determining peat and coal character since the Paleozoic.

Controls on Bacterial Gas Accumulations in Thick Tertiary Coal Beds and Adjacent Channel Sandstones, Powder River Basin, Wyoming and Montana

Controls on Bacterial Gas Accumulations in Thick Tertiary Coal Beds and Adjacent Channel Sandstones, Powder River Basin, Wyoming and Montana

Mineral Assemblages of Volcanic and Detrital Partings in Tertiary Coal Beds, Kenai Peninsula, Alaska

AbstractVolcanic and non-volcanic partings are exposed in coal beds of the Tertiary Beluga and Sterling Formations along the shores of the Kenai lowland, Alaska. About two-thirds of the partings originated as air-fall tephra which fell in coal-forming swamps. The tephra partings in the Pliocene strata are unaltered or slightly altered and have a characteristic mineral assemblage of volcanic glass ± montmoriUonite ± kaolinite ± opal-CT. Miocene strata are slightly altered to totally altered, and a typical mineral assemblage consists of feldspar ± kaolinite ± montmorillonite ± quartz ± crandallite ± altered volcanic glass. Crandallite appears to have formed early in diagenesis by the replacement of volcanic glass prior to the formation of montmorillonite and kaolinite.About one-third of the partings originated primarily as detrital sediments derived from surrounding metamorphic and sedimentary terranes and were deposited by periodic floods. Mixtures of tephra and detrital sediments were also noted and were difficult to distinguish from tephra partings in the field. Detrital partings are characterized by detrital chlorite + illite + smectite + quartz ± feldspar ± siderite ± kaolinite. The chlorite in these strata is allogenic. Smectite is less common in the detrital partings.

Coal-Bed Methane Potential of Tertiary Coal Beds and Adjacent Sandstone Deposits, Powder River Basin, Wyoming and Montana: ABSTRACT

Coal-Bed Methane Potential of Tertiary Coal Beds and Adjacent Sandstone Deposits, Powder River Basin, Wyoming and Montana: ABSTRACT

Nature of Petrographic Variations in Some Tertiary Coal Beds, Powder River Basin, Montana and Wyoming: ABSTRACT

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 because 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 accumulatedmore » 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

Patterns of Thick Coal Deposition Across Powder River Basin in Northeastern Wyoming: ABSTRACT

Tertiary coal beds in the Powder River basin are the nation's largest resource of low-sulfur subbituminous coal. In northeastern Wyoming the north-trending depositional axis of the asymmetric, 100-km-wide basin is within 20 km of the west margin. Interlocking lines of cross sections prepared from geophysical logs of oil and gas wells and coal exploratory holes and set to a sea level datum, outline patterns, locations, and trends of thick coal deposition. Coal beds on the east flank of the basin dip west about 1/2° and tend to merge eastward. Five Paleocene (Fort Union) coals merge along the eastern margin to form a north-trending, 35-m-thick deposit known as the Wyodak coal. Near the depositional axis, five or more Eocene (Wasatch) coals merge to form a north-trendin , 60-m-thick deposit known as the Lake deSmet coal. Across the intervening area two or more succeeding coals merge locally on broad depressed subsurfaces to form north-trending belts of thick coal, and succeeding belts of thick coal are offset westward toward the depositional axis. Lines of cross sections oriented north-south roughly parallel to the depositional strike provide stratigraphic control on the coal. Maximum structural relief (about 400 m) of coal beds on the east flank relates to basin subsidence during deposition of coal-bearing rocks when rates of subsidence progressively increased westward. North-trending patterns of thick coal deposition across paleoslopes are associated with connected areas for which optimum paleoenvironments were stable for extended periods of time and ptimum rates of subsidence were maintained. End_of_Article - Last_Page 732------------

K-Ar and fission-track dating of ash partings in coal beds from the Kenai Peninsula, Alaska: A revised age for the Homerian Stage–Clamgulchian Stage boundary

K-Ar and fission-track mineral ages determined from ash partings in upper Tertiary coal beds from the Kenai Peninsula, Alaska, establish an age of approximately 8 m.y. (late Miocene) for the Homerian Stage–Clamgulchian Stage boundary at the type section for the Homerian Stage and a late Miocene age for the early part of the Clamgulchian Stage. Our data do not support the concept that there is an “Arcto-Tertiary geoflora” which is different in age from similar floras at lower latitudes. This study demonstrates, for the first time, that volcanic ash partings contained wholly within coals are valuable for radiometric dating and stratigraphic correlation.