Charles T. Helfrich

Disrupted coal and carbonate facies within two Pennsylvanian cyclothems, southern Illinois basin, United States

Two cyclothems contain an unusual suite of disrupted fabrics. This study9s interdisciplinary integration of coal maceral and sedimentological information offers significant new interpretations of coal-limestone interchange, both depositionally and diagenetically. Disrupted fabrics within the Herrin Coal and Providence Limestone are interpreted as representing previously undocumented interactive processes between coals and limestones. The Herrin Coal contains brecciated beds that are the result of marine transgression over a coastal-plain mire, representing high-energy conditions at the swamp-beach interface. This interface has rarely been documented in detail. Peat is inherently unstable prior to its conversion to coal, and we document this by interpreting conglomeratic beds in overlying strata. Differential compaction of Herrin peats generated subaqueous debris flows in the overlying Providence Limestone. This mechanism for syndiagenetic and early diagenetic sediment deformation has not been previously recognized. In addition, near-surface and surface processes produced other disrupted fabrics in the Providence Limestone, such as in situ mosaic breccias, nodular fabrics, and calcrete horizons. This study also documents that stratigraphically adjacent, alkaline carbonate sediments were further altered by undersaturated acidic pore waters, derived from compacting peats during early diagenesis. Our interdisciplinary approach to distinguishing and interpreting all of these disrupted fabrics led to a new appraisal of the importance of depositional and postdepositional interactions between coal and limestone. The presence of mire deposits can have a significant influence on the thickness, distribution, and fabrics in overlying strata. In cyclothems, climatic and eustatic changes may control overall depositional patterns, but peat compaction may determine certain facies.

Palynologic and petrographic variation in the Pond Creek coal bed, Pike County, Kentucky

Abstract Recent studies of the petrology and ash geochemistry of the Pond Creek coal bed (Middle Pennsylvanian Breathitt Formation) in Pike and Martin Countries, Kentucky, have defined vertical and lateral trends that are related to the development of the northeast-trending Belfry anticline contemporaneous with the deposition of the Pond Creek peat. To the northwest of the anticline the coal bed has a high-CaCO3 middle zone and a high Fe2O3-high sulfur upper zone. To the east of the anticline, particularly in the Lick Creek and Jamboree 7 1 2 ′ quadrangles, the coal bed exhibits a distinctive petrographic zonation. In the latter area, the usual megascopic sequence is a basal durain followed by a bright clarain-durain/dull The palynology of the Pond Creek coal bed was investigated in six sets of bench/lithotype samples from the Lick Creek and Jamboree 7 1 2 ′ quadrangles. The low-vitrinite basal durain (zone 1) has a palynomorph assemblage which reflects the importance of tree ferns and herbaceous lycopods. The easternmost site has a bright clarain below the durain. The latter lithotype has a fair diversity of palynormph groups and also has the highest percentage of arborescent lycopod forms of any bench below the bone (zone 5). The bright zone 2 above the durain has the greatest maceral group range and the greatest floral diversity of any of the lithotypes. The zone 3 dull lithotype has increased amounts of herbaceous lycopods and decreased amounts of arborescent lycopods, sphenopsids and tree ferns. The zone 4 bright lithotypes are generally over 80% vitrinite and, in general, exhibit a dominance of arborescent lycopods although sphenopsid, tree fern and small fern forms exhibit varying importance. The high-ash bone (zone 5) has 71.6–77.0% vitrinite. This lithotype is marked by a dominance of herbaceous lycopods at the expense of arborescent lycopods and sphenopsids. The zone 6 bright clarian is marked by an increase in arborescent lycopods and a large decrease in herbaceous lycopods. The low-vitrinite terminal durain has an assemblage with high percentages of herbaceous lycopods and low percentages of arborescent lycopods as well as increase in tree fern spores over zone 6. In general, the petrology and palynology trends are predictable. Dull lithotypes have abundant herbaceous lycopod representation and bright lithotypes have abundant arborescent lycopod representation. The greatest deviation from this simple pattern is within the zone 4 bright lithotypes, where diverse palynomorph assemblages occur among the high-vitrinite benches. Overall, the greatest floral diversity appears to have occurred near the base of the coal bed.

Petrography and palynology of the Blue Gem coal bed (Middle Pennsylvanian), southeastern Kentucky, USA

Petrographic and palynological trends in the Blue Gem coal bed (Middle Pennsylvanian Westphalian B, Breathitt Formation), a thin, low-sulfur, low-ash coal in southeastern Kentucky, were studied in order to establish a depositional model for the seam. Within the study area, the coal bed averages 67 cm and has two distinct zones. The lower and middle parts of the seam (the lower 45–55 cm) are enriched in well-preserved vitrinite and are dominated by arborescent lycopods, sphenopsids, and tree ferns. Fusinite-rich layers, dominated by arborescent lycopods, but also containing herbaceous lycopods and sphenopsids, occur within the lower and middle parts of the seam. The upper part of the seam (the upper 15–25 cm) is recognizable in the field and is distinct in that it contains a greater amount of degraded macerals, and is characterized by high palynomorph diversity, primarily by miospores that are associated with sphenopsids, herbaceous lycopods and arborescent lycopods. These data, in conjunction with geochemical data available for the seam, suggest that initially the peat swamp was fairly diverse and well-nourished (the base of the seam being characterized by a relatively diverse miospore assemblage and a slightly higher ash content). Following this initial planar stage, the Blue Gem peat swamp was probably planar to slightly domed during accumulation of most of the lower and middle parts of the seam, as suggested by the very low ash and sulfur contents, the high telovitrinite content, and the preponderance of arborescent lycopod spores. In its final stages, the peat swamp was domed and is characterized by a more diverse flora and greater levels of degradation of the peat constituents. Sulfur content of this seam is generally low (<1%) but can increase locally to 3–4%. Factors influencing sulfur content include the thickness and nature of the overburden (shale versus sandstone) and petrographic composition.

Coal metamorphism in the upper portion of the Pennsylvanian Sturgis Formation in western Kentucky

Coals from the Pennsylvanian upper Sturgis Formation (Missourian and Virgilian) were sampled from a borehole in Union County, western Kentucky. The coals exhibited two discrete levels of metamorphism. The lower-rank coals with vitrinite reflectances indicative of high volatile C bituminous were assumed to represent the normal level of metamorphism. A second set of coals with vitrinite reflectances indicative of high volatile A bituminous was found to be associated with sphalerite, chlorite, and twinned calcite. The latter mineral assemblages indicate that hydrothermal metamorphism was responsible for the anomalous high rank. Consideration of the sphalerite fluid-inclusion temperatures from nearby ores and coals and the time-temperature aspects of the coal metamorphism suggests that the hydrothermal metamorphic event was in the 150 to 200 °C range for a brief time (10 5 –10 6 yr), as opposed to the longer term (25–50 m.y.) 60 to 75 °C ambient metamorphism.

Lithologic succession in the Path Fork coal bed (Breathitt Formation, Middle Pennsylvanian), southeastern Kentucky

Abstract The Path Fork coal bed (Breathitt Formation, Middle Pennsylvanian/Westphalian B) on the Pine Mountain thrust sheet in southeastern Kentucky and adjacent portions of Virginia exhibits a lithologic succession which is traceable for about 25 km. Lateral continuity of lithotypes within the bed can be demonstrated using organic petrography, palynology, and ash geochemistry. The lithologic continuity is a consequence of the initial levelling of the pre-peat topography and the interaction of the peat with growing anticlines and synclines.

Palynologic and petrographic variation in the Otter Creek coal beds (Stephanian, Upper Carboniferous), Western Kentucky

Abstract The palynology and petrology of the Lisman (Lower Otter Creek) and Upper Otter Creek coals of the Stephanian portion of the Sturgis Formation of the Western Kentucky coal field was investigated in samples from mine and roadcut exposures. The Lisman coal bed exhibits an upward decrease in palynologic diversity and an upward increase in inertinite macerals. These factors suggest a change in swamp paleoecology in response to a climate which was gradually becoming drier. The Upper Otter Creek coal bed exhibits less lateral continuity in palynomorph assemblages than does the Lisman. The Upper Otter Creek palynomorph assemblages are less diverse than the Lisman assemblages. Overall, the variation in the Upper Otter Creek coal bed cannot be attributed with certainty to any factor other than the local relief within the swamp.

The Upper Hance coal bed in southeastern Kentucky: palynologic, geochemical, and petrographic evidence for environmental succession

The Upper Hance coal bed in Bell County, eastern Kentucky exhibits considerable variation in depositional setting on a mine scale. Palynology and geochemistry of the coal are examined in order to supplement previous petrographic examinations. The various depositional settings of the Upper Hance mire progress from the pioneer, possibly partially allochthonous, settings at the mire margins and base; to the well-developed, planar to domed main body of the mire; and finally to the terminal events of flooding, clastic influx, and temporary reestablishment of mires now seen as the thin rider coals. Palynologic diversity generally decreases upwards from the basal lithotype through the main body of the coal bed. The cannel and rider lithologies represent distinct depositional events.

Palynologic and petrographic intervals in the upper Pennsylvanian McLeansboro Group, Western Kentucky

Abstract The McLeansboro Group (formerly the Sturgis Formation) in the Western Kentucky coal field spans the upper Desmoinesian (Westphalian D) and the Missourian and Virgilian series (Stephanian). Extensive drilling has demonstrated the lateral continuity of major and minor beds in the group, making it possible to study vertical and lateral changes in palynology and petrology. Significant features of the McLeansboro Group are the marine zones over most of the coals and paleochannels, which are the only disruptions to the continuity of other lithologies. The Desmoinesian Baker (No. 13) and Wheatcroft (No. 13a) coal beds were included in the study but the primary emphasis is on the Missourian and Virgilian coals. Patoka Formation (lower Missourian) coals are dominated by tree fern spores with lesser amounts of sphenopsids, ferns and cordaites spores. This is in marked contrast to the arborescent lycopod-dominated Desmoinesian coals. Only the No. 15 coal bed exceeds 80% vitrinite: the vitrinite content of the No. 16 coal bed is less than 72%, the lowest of any Western Kentucky humic coal. The Bond Formation (upper Missourian) represents a distinct floristic interval, with a greater diversity of plant groups than in the Patoka Formation. Herbaceous lycopod spores, which are relatively minor contributors to the Patoka coals, are common in the Bond Formation. The coals generally exceed 80% vitrinite. The Mattoon Formation (Virgillian) coals have a variety of palynomorph assemblages. The low-sulfur Geiger Lake coal bed is dominated by tree fern spores, with important contributions from other ferns and sphenopsids. Similar to the underlying tree fern interval, vitrinite contents are less than 80%. The uppermost Mattoon coals are dominated by tree ferns and are notable in being the only coals more than 1 m thick in the Stephanian portion of the section, with the top coal being 4.3 m thick. The uppermost coals generally contain more than 80% vitrinite. The Permian Mauzy Formation overlies the McLeansboro Group. The palynologic/petrographic intervals appear to represent fluctuating dry (low vitrinite) and wet intervals within the Stephanian, which was itself drier than the Westphalian D.