https://cyberleninka.org/article/n/651108.pdf

Application of organic petrography in North American shale petroleum systems: A review

Methane is an important greenhouse gas and energy resource generated dominantly by methanogens at low temperatures and through the breakdown of organic molecules at high temperatures. However, methane-formation temperatures in nature are often poorly constrained. We measured formation temperatures of thermogenic and biogenic methane using a “clumped isotope” technique. Thermogenic gases yield formation temperatures between 157° and 221°C, within the nominal gas window, and biogenic gases yield formation temperatures consistent with their comparatively lower-temperature formational environments (<50°C). In systems where gases have migrated and other proxies for gas-generation temperature yield ambiguous results, methane clumped-isotope temperatures distinguish among and allow for independent tests of possible gas-formation models.

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Formation temperatures of thermogenic and biogenic methane

A computer model is used to estimate patterns of lithospheric deformation caused by obduction and removal of loads within orogenic belts. Regions of lithospheric downwarp become sedimentary depocenters and regions of lithospheric upwarp suffer erosion. By following the deposition and erosion of sedimentary packages through a number of model time steps it is possible to calculate a synthetic stratigraphy for a given study area. This model is applied to the post-Early Ordovician stratigraphy of the Eastern Interior region of North America. The loading that drives lithospheric deformation is associated with the development of the Appalachian and Ouachita orogens and the independent development of the Michigan and Illinois intracratonic basins. Model results are shown to be consistent with presently observed stratigraphy, lithology, and cumulative erosion and are then used to estimate the configuration of given sediment packages at discrete intervals following their deposition. These estimates are presented in the form of isopach maps, stratigraphic cross sections, and time-stratigraphic diagrams as a function of time over the last 470 Ma. By tracking the burial and erosion history of sedimentary units we are able to establish a cause and effect relationship between particular tectonic events and the extent of preservation of sedimentary units. In particular, we suggest that the Pennsylvanian–Permian Alleghanian orogeny produced major sediment cover over much of the study area.

Orogeny and stratigraphy: Numerical models of the Paleozoic in the eastern interior of North America

The spots and stains of plate tectonics

The Late Permian climate. What can be inferred from climate modelling concerning Pangea scenarios and Hercynian range altitude

The anisotropic “reflectance fabric” of coal is used as a finite strain marker in the structural analysis of deformed strata in the Broad Top Coal Field of central Pennsylvania. Oriented blocks of coal were collected at various field locations. The reflectances of three orthogonal surfaces were used to estimate the magnitudes and orientations of the three principal reflectance axes. Broad Top coals are shown to have three principal reflectance values, in contrast with most bituminous coals, which have only two. Reflectance values can be represented by a biaxial indicatrix that may be either prolate or oblate. The oblate indicatrices, showing flattening in the bedding plane, are associated with gently deformed strata. The prolate indicatrices, elongated parallel to the fold axes (N32°E), are associated with more intensely folded strata and show the influence of strong lateral compression superimposed upon gravitational loading. The reflectance indicatrices maintain a constant spatial orientation, regardless of the inclination of the enveloping bedding. The minimum principal reflectance axis plunges steeply toward the west, indicating that during deformation the direction of maximum compression was plunging toward the northwest. These results suggest that in the Broad Top field maximum coalification and, therefore, maximum burial were penecontemporaneous with the later stages of deformation, postdating most of the folding.

Optical anisotropy of coals as an indicator of tectonic deformation, Broad Top Coal Field, Pennsylvania

Recent studies of vitrinite reflectance, sedimentary compaction, and fluid inclusions indicate that coal-bearing strata of the Pennsylvania Anthacite region were once buried at depths ranging from 6 to as much as 9 km. Vitrinite reflectance anisotropy suggests that anthracite rank was attained by normal geothermal heating largely prior to and during Alleghanian folding. Paleomagnetic ages for the folding and paleobotanical ages of the youngest extant sediments delimit the maximum burial and deformation to a relatively short interval (285 to 270 Ma). In comparison with typical molasse sequences, the implied thicknesses and rates of deposition are excessive, suggesting that much of the former overburden was emplaced tectonically or by extremely rapid sedimentation. The total implied thickness (about 20 km) of Paleozoic strata in the region is abnormally large for an epicontinental basin. An inferred body of mafic rock embedded in the Precambrian basement, evidenced by the Scranton gravity high (SGH), may have influenced crustal subsidence, especially during the Allegheny orogeny, and produced a large downwarp accounting for the high coal rank. The fact that isorank contours, Paleozoic sediment isopach contours, and a large structural sag all lie roughly parallel to the boundaries of the SGH, oblique to the principal Alleghanian fold trend, lends support to this idea.

Deep burial of coal-bearing strata, Anthracite region, Pennsylvania: Sedimentation or tectonics?

Comment and Reply on ‘Time-temperature-burial significance of Devonian anthracite implies former great (−6.5 km) depth of burial of Catskill Mountains, New York’

Jeffrey Ross Levine

Papers

Optical anisotropy of coals as an indicator of tectonic deformation, Broad Top Coal Field, Pennsylvania

Deep burial of coal-bearing strata, Anthracite region, Pennsylvania: Sedimentation or tectonics?

Comment and Reply on ‘Time-temperature-burial significance of Devonian anthracite implies former great (−6.5 km) depth of burial of Catskill Mountains, New York’

ABSTRACT: Appalachian Anthracites