Geology topics

S.F. Greb

Publications and source records attributed to S.F. Greb.

22 records · Page 2Linked to original sources

USGS1996

Paleoslumps in coal-bearing strata of the Breathitt Group (Pennsylvanian), Eastern Kentucky Coal Field, U.S.A

The benefits of geologic analysis for roof-control studies and hazard prediction in coal mines are well documented. Numerous case studies have illustrated the importance of recognizing geologic features such as paleochannels, coal riders, and kettlebottoms in mine roofs. Relatively understudied features, in terms of mining, are paleoslumps .Paleoslumps represent ancient movement and rotation of semi-consolidated sediment. Because bedding in paleoslumps is deformed or inclined, these features cause instability in mine roofs, haul roads, surface highwalls, and other excavations. Various types of paleoslumps above coals in the Eastern Kentucky Coal Field were studied in order to aid in their recognition and prediction in mines. The paleoslumps studied all showed characteristic slump-deformation features, although some differences in magnitude of deformation and overall slump size were noted. Coals beneath slumps often exhibited folding, reverse displacements, truncation, clastic dikes, and locally increased thickness. Slumps are inferred to have been triggered by a wide range of mechanisms, such as loading of water-saturated sediment on rigid substrates, synsedimentary faulting, and over-pressurization of channel margin and bar slopes. Analysis of paleoslumps in underground mines, where paleoslumps are viewed from beneath rather than in profile is difficult, since characteristic bed rotation may not be conspicuous. Sudden increases in bed-dip angle inferred from changes in rock type or bedding contacts in the roof; occurrence of bounding, polished rotation surfaces; or roof irregularity and occurrence of loading features may indicate the presence of paleoslumps. Another key to recognition may be the sudden appearance of over-thickened coal, which can occur because of slump-created paleotopography, synsedimentary faults, and slump-generated overthrusting. In addition, steeply inclined, folded, or transported coal marginal to paleoslumps can create apparent increases in coal thickness in cores. Although thick coals are obviously a target of exploration, anomalously thick coals may actually indicate adjacent paleoslumps accompanied by hazardous roof conditions and loss of seam thickness.

International Journal of Coal Geology↗

USGS1996

Lower and lower Middle Pennsylvanian fluvial to estuarine deposition, central Appalachian basin: Effects of eustasy, tectonics, and climate

Interpretations of Pennsylvanian sedimentation and peat accumulation commonly use examples from the Appalachian basin because of the excellent outcrops and large reserve of coal (>100 billion metric tons) in the region. Particularly controversial is the origin of Lower and lower Middle Pennsylvanian quartzose sandstones; beach-barrier, marine-bar, tidal-strait, and fluvial models all have been applied to a series of sand bodies along the western outcrop margin of the basin. Interpretations of these sandstones and their inferred lateral relationships are critical for understanding the relative degree of eustatic, tectonic, and climatic controls on Early Pennsylvanian sedimentation. Cross sections utilizing >1000 subsurface records and detailed sedimentological analysis of the Livingston Conglomerate, Rockcastle Sandstone, Corbin Sandstone, and Pine Creek sandstone (an informal member) of the Breathitt Group were used to show that each of the principal quartzose sandstones on the margin of the central Appalachian basin contains both fluvial and marginal marine facies. The four sandstones are fluvially dominated and are inferred to represent successive bed-load trunk systems of the Appalachian foreland. Base-level rise and an associated decrease in extra-basinal sediment at the end of each fluvial episode led to the development of local estuaries and marine reworking of the tops of the sand belts. Each of the sand belts is capped locally by a coal, regardless of whether the upper surfaces of the sand belts are of fluvial or estuarine origin, suggesting allocyclic controls on deposition. Peats were controlled by a tropical ever-wet climate, which also influenced sandstone composition through weathering of stored sands in slowly aggrading braidplains. Recurrent stacking of thick, coarse-grained, fluvial deposits with extra-basinal quartz pebbles; dominance of bed-load fluvial–lowstand deposits over mixed-load, estuarine-transgressive deposits; thinning of sand belts around tectonic highs and along faults; cratonward shift and amalgamation of successive sand belts on the margin of the basin; and truncation of successive sand belts toward the fault-bound margin of the basin are interpreted as regional responses to Alleghenian tectonism, inferred to have been the dominant control on accommodation space and sediment flux in the Early Pennsylvanian basin.

Geological Society of America Bulletin↗

USGS1992

Transgressive channel filling in the Breathitt Formation (Upper Carboniferous), Eastern Kentucky Coal Field, USA

Carbonaceous shales of brackish or marine origin in the Breathitt Formation may exhibit sharp bases with local channel-form scours. Minor channels at the bases of these shales exhibit three general types of fill: (1) shale, (2) bioturbated, heterolithic strata, and (3) coal overlain by shale or bioturbated, heterolithic strata. Most of the scours at the bases of the channels were formed during a depositional hiatus that preceded transgression. Some may also have been formed by transgressive reworking of underlying estuarine and deltaic siliciclastics. The channel fills are bioturbated and may contain crudely cyclical rhythmites, subordinate and dominant siltstone-laminae couplets, wave ripples, and bimodal current ripple trends. The fills are interpreted to represent estuarine sedimentation during marine transgression. Channels are capped by sideritic, bioturbated sandstones that separate the fills from the overlying dark shales deposited under brackish- to marine-water conditions. Some of these sandstones may represent local transgressive surfaces. The occurrence of these types of channels in different parts of the coal-bearing Breathitt Formation supports the hypothesis of multiple transgressions during the Late Carboniferous in the Central Appalachian Basin.

Eastern Kentucky Coal Field↗

USGS1991

Examination of micrinite concentrates from the Cannel City coal bed of eastern Kentucky: Proposed mechanism of formation

A high volatile B, micrinite-rich bituminous coal from Morgan County, Kentucky, was crushed and screened to −100 mesh, demineralized and subjected to density gradient centrifugation (DGC). In an initial density separation, micrinite concentration was increased from 52 vol% in the demineralized coal to a maximum of 67% in the 1.25–1.26 g/ml density fraction. Micrinite enriched fractions (1.21–1.29 g/ml) were combined to yield a sample containing ∼61% micrinite. This sample was crushed to −200 mesh in an attempt to enhance micrinite liberation then reprocessed by DGC. Reprocessing resulted in a slight increase in purity to 69 vol% in the 1.25–1.28 g/ml density fraction. The original −100 mesh sample was density separated a second time with the material recovered between 1.22 and 1.30 g/ml combined, crushed, screened past 325 mesh and reprocessed by DGC. Micrinite was recovered at a purity ranging up to 73% (1.27–1.28 g/ml) from the −325 mesh sample. A density of 1.26g/ml and H/C atomic ratio of 0.79 was calculated for micrinite in one of the higher purity micrinite fractions. These values are notably different than published fusinite values and are more similar to vitrinite values measured in high volatile-B coals. The results from this study suggest that the partitioning of micrinite to a density near that of vitrinite was governed by the inherent micrinite density and not particle aggregation. Transition of the micrinite precursors through a mobile liquid phase is proposed as an explanation for the discrepancy between chemical properties and reflectance as well as to account for the observed microlithological occurrences of micrinite in this sample.

Kentucky↗