Huron Member Research Articles

Organic petrology and micro-spectroscopy of Tasmanites microfossils: Applications to kerogen transformations in the early oil window

The transformation of kerogen to hydrocarbons in the early stages of oil generation is critical for understanding the resource potential of liquid-rich shale plays. Organic petrology commonly is used for visual evaluation of type, quality, and thermal maturity of organic matter, but the relationship of visual petrographic changes to chemical transformations is not well characterized. To improve understanding of these processes, organic-walled microfossils of the unicellular green alga Tasmanites (composed of algaenan) in Upper Devonian Ohio Shale (Huron Member, Appalachian Basin) were analyzed by micro-spectroscopy techniques including micro-Fourier transform infrared (micro-FTIR), X-ray photoelectron (XPS), electron probe microanalysis (EPMA), and fluorescence. Immature to mid-oil window maturation sequences of core and outcrop samples with solid bitumen reflectance (BR) and vitrinite reflectance (VR) values ranging from 0.45 to 0.80%Ro were used. Hydrous pyrolysis was applied to low-maturity (BR: 0.25–0.39%Ro) Huron and time-correlative New Albany shale samples to create similar artificial maturation sequences for comparison. Micro-FTIR spectroscopy revealed a decrease in the CH2/CH3 ratio with increasing maturity, indicating Tasmanites aliphatic chains become shorter and more branched. Oxygenated functional groups decreased relative to aliphatic stretching bands and increased aromaticity was noted at the highest maturities. In samples that were pyrolyzed for 72h at temperatures of 300–320°C (BR: 0.56–0.68%Ro), Tasmanites showed similar trends, whereas at pyrolysis temperatures of 340°C and higher (BR>1.0%Ro), Tasmanites was pseudomorphed by accumulations of solid bitumen, carbonate and sulfide. Replacement of Tasmanites by these phases in hydrous pyrolysis experiments ≥340°C and its absence at higher maturities (peak oil, VR and BR≥0.9%Ro) in naturally matured samples, as documented in a previous study, implies that a large fraction of the algaenan component of original organic carbon is converted to petroleum during thermal maturation. XPS analysis indicated the molar proportion of aliphatic carbon increases with increasing thermal maturity, accompanied by decreases in oxygenated functional groups and olefinic carbon. EPMA of Tasmanites showed highest concentrations of S, with concentrations of redox-sensitive trace elements U, Mo, Ni and V generally at or below detection limits. Decrease in organic S with increasing thermal maturity may be related to cleavage of Tasmanites at CS linkages; however, this relationship was inconsistent and presence of adjacent or entrained nanoscale silicate or sulfide phases may impact measured trace element concentrations. Fluorescence microscopy and spectroscopy showed a red shift in spectral maxima and decreased emission intensities with increasing maturity, interpreted as due to non-radiative energy loss possibly because of increased aromaticity. Collectively, these results provide new insights into the in situ chemical transformations that accompany petrographic changes as oil-prone kerogen converts to petroleum with thermal advance from immature conditions into the mid-oil window.

Petrographic maturity parameters of a Devonian shale maturation series, Appalachian Basin, USA. ICCP Thermal Indices Working Group interlaboratory exercise

This paper presents results of an interlaboratory exercise on organic matter optical maturity parameters using a natural maturation series comprised by three Devonian shale samples (Huron Member, Ohio Shale) from the Appalachian Basin, USA. This work was conducted by the Thermal Indices Working Group of the International Committee for Coal and Organic Petrology (ICCP) Commission II (Geological Applications of Organic Petrology). This study aimed to compare: 1. maturation predicted by different types of petrographic parameters (vitrinite reflectance and spectral fluorescence of telalginite), 2. reproducibility of the results for these maturation parameters obtained by different laboratories, and 3. improvements in the spectral fluorescence measurement obtained using modern detection systems in comparison with the results from historical round robin exercises.Mean random vitrinite reflectance measurements presented the highest level of reproducibility (group standard deviation 0.05) for low maturity and reproducibility diminished with increasing maturation (group standard deviation 0.12).Corrected fluorescence spectra, provided by 14 participants, showed a fair to good correspondence. Standard deviation of the mean values for spectral parameters was lowest for the low maturity sample but was also fairly low for higher maturity samples.A significant improvement in the reproducibility of corrected spectral fluorescence curves was obtained in the current exercise compared to a previous investigation of Toarcian organic matter spectra in a maturation series from the Paris Basin. This improvement is demonstrated by lower values of standard deviation and is interpreted to reflect better performance of newer photo-optical measuring systems.Fluorescence parameters measured here are in good agreement with vitrinite reflectance values for the least mature shale but indicate higher maturity than shown by vitrinite reflectance for the two more mature shales. This red shift in λmax beyond 0.65% vitrinite reflectance was also observed in studies of Devonian shale in other basins, suggesting that the accepted correlation for these two petrographic thermal maturity parameters needs to be re-evaluated.A good linear correlation between λmax and Tmax for this maturation series was observed and λmax 600nm corresponds to Tmax of 440°C. Nevertheless if a larger set of Devonian samples is included, the correlation is polynomial with a jump in λmax ranging from 540 to 570nm. Up to 440°C of Tmax, the λmax, mostly, reaches up to 500nm; beyond a Tmax of 440°C, λmax is in the range of 580–600nm. This relationship places the “red shift” when the onset of the oil window is reached at Tmax of 440°C. Moreover, the correlation between HI and λmax (r2=0.70) shows a striking inflection and decrease in HI above a λmax of 600nm, coincident with the approximate onset of hydrocarbon generation in these rocks.

Tetrentactinia barysphaera Foreman, 1963: skeletal structure and age of a biostratigraphically important Famennian (Upper Devonian) radiolarian from the Ohio Shale, USA

Tetrentactinia barysphaera Foreman, 1963 is a very characteristic Famennian (Upper Devonian) radiolarian species from the Huron Member of the Ohio Shale of North America. Its skeletal structure shows a massive, double-layered shell with main spines constructed from radial beams and concentric bars over a primary ray as the core. The species is common in limestone concretions at the type locality Milan, Ohio, associated with a diverse radiolarian fauna of predominantly spherical spumellarian forms, but has also been recorded from the Russian platform. It may be highly useful as an index species for the mid-Famennian time interval as it is one of the few spumellarians that is easily recognized and differentiated in the fauna.

Geochemical paleoredox indicators in Devonian–Mississippian black shales, Central Appalachian Basin (USA)

The degree of anoxia that existed during accumulation of Devonian–Mississippian black shales in central Kentucky has been debated widely. In this study, geochemical data were used to elucidate paleodepositional environments for these units. Using analyses from ten cores collected from the outcrop belt in central Kentucky, sulfur, carbon, and selected trace-element relationships were compared. The Sunbury Shale (Tournasian, Lower Mississippian) and the Cleveland and Huron members of the Ohio New Albany Shale (Fammenian, Upper Devonian) show different relationships between carbon, sulfur, and trace elements. C–S–Fe relationships for the Sunbury suggest anoxic, possibly even euxinic, conditions prevailed during sediment accumulation. Analysis of C–S–Fe data suggests that the Cleveland may have accumulated under anoxic conditions, with intermittent dysoxia, whereas the Huron Member may have accumulated under a relatively wide range of conditions, from anoxic, to dysoxic, to possibly oxic. These three units exhibit different degrees of trace-element enrichment, with the approximate order of enrichment relative to an average shale being Mo>Pb>Zn>V>Ni>Cu>Cr>Co. The Sunbury shows the highest levels of enrichment, followed by the Cleveland, with the Huron showing only slight enrichment for most of these trace elements. Differing degrees of enrichment may reflect differences in depositional environment during accumulation. High Mo concentrations in the Sunbury (generally 200–550 ppm) may infer euxinic conditions prevailed during sediment accumulation. The Cleveland and the Huron both show considerably lower Mo contents (averaging around 100 ppm). Geochemical ratios, including Ni/Co, V/Cr, and V/(V+Ni), also indicate variable paleoredox conditions for these shales. Based on previously established thresholds, V/Cr and Ni/Co ratios infer at least anoxic conditions during accumulation of the Sunbury, anoxic to dysoxic conditions during Cleveland accumulation, and dysoxic to oxic conditions for the Huron. V/(V+Ni) ratios tend to indicate consistently lower oxygen regimes than do other paleoredox indicators, and this discrepancy is greatest for the Huron Member. It is suggested that thresholds established for paleoredox indicators in previous studies should not be applied strictly, but that relative differences in these indicators collectively can infer variations in the degree of anoxia. In addition, relationships between C org and redox elements may help elucidate the role of anoxia in OM accumulation. It may be concluded from this study that the Devonian–Mississippian black shales of central Kentucky accumulated under variable bottom-water conditions. At least anoxic conditions prevailed during accumulation of much of the Sunbury Shale and the upper part of the Cleveland Member, and possibly euxinic conditions for the Sunbury. Bottom-water conditions may have been intermittently anoxic and dysoxic during deposition of the lower Cleveland. During accumulation of the Huron Member, it is likely that conditions ranged from anoxic to dysoxic to marginally oxic, possibly being close to normal marine conditions at times during accumulation of the lowermost Huron sediments.

Accumulation of Organic Matter in the Rome Trough of the Appalachian Basin and Its Subsequent Thermal History: Discussion

666 This discussion is intended to correct a major error of fact concerning the organic carbon concentration of the lower Huron Member of the Ohio Shale in eastern Kentucky. Figure 2 of Curtis and Faure (1997) showed a map of total organic carbon concentrations in the lower Huron Shale, based on data collected for the Gas Research Institute. This map is essentially identical to those previously published by Curtis (1988, his plate II) and Curtis (1990, his figure

Accumulation of Organic Matter in the Rome Trough  of the Appalachian Basin and Its Subsequent Thermal History

We used geochemical data to examine the origin and preservation of organic matter contained in the lower part of the Huron Member of the Ohio Shale formation and the Rhinestreet Shale Member of the West Falls Formation (Devonian) in Kentucky, Ohio, West Virginia, and Virginia. The thermal history of the organic matter was determined by relating relative temperatures experienced by the organic matter to the geologic setting. The organic matter in these formations is predominantly marine in origin and was most probably derived largely from algal organisms. Although the rate of production of marine organic matter may have been uniform within the basin, its preservation apparently was controlled by the existence of a set of fault-bounded anoxic subbasins associated with the Rome trough, a Cambrian structural complex. These subbasins apparently were anoxic because they limited oxygen recharge by circulating waters. Preservation of organic matter was also enhanced by periodic blooms of the alga Tasmanites and similar organisms in the waters above the subbasins during both early Huron and Rhinestreet deposition. A significant negative correlation was identified between the vitrinite reflectance peak temperature, an integrated measure of the thermal history of a rock, and the hydrogen index, a measure of the remaining hydrocarbon-generation potential of kerogen. Although peak temperatures were controlled by burial depth, excess heating occurred locally, perhaps by hot brines rising from depth through fractures associated with major structures in the study area.

The significance of oil shale fabric in primary hydrocarbon migration

Scanning electron microscopy (SEM) and thin-section analysis of the fabrics (particle orientation) of some well known ‘oil shales’ reveal they all share two common characteristics: (1) even though preferred platy particles dominate, there is present an open network of numerous interconnecting pores; and (2) fine lamination of alternating silt and organic clay-rich zones is common. Shales selected for analysis include the Woodford Shale, Sunbury Shale, torbanite, Rundle Shale and Ohio Shale (Huron Member), West Falls Formation (Rhinestreet Member), New Albany Shale (Clegg Creek Member) and the Exshaw Formation. A model is proposed, based upon fabric information, for the migration of hydrocarbons from source rocks. Hydrocarbons generated in organic-rich zones migrate through the micropores until reaching adjacent silt laminae, which act as ‘pipelines’ to facilitate further migration out of the source rock.

Characterization of Devonian Ohio Shale SDO‐1 as a USGS Geochemical Reference Sample

Recommended concentrations for 38 elements in the U.S. Geological Survey reference sample, Ohio Shale (Devonian) SDO‐1, are presented here. For an additional 25 elements, average concentrations or ranges are reported for information. Also presented are the supporting analytical data and a description of the statistical procedure used in deriving recommended concentrations from that data. The sample is a brownish‐black, fissile, platy shale containing flattened pyrite nodules and a high organic content. It is typical of “eastern gas shale”, in contrast to the USGS reference sample SGR‐1, which typifies oil shale from the Green River Formation. SDO‐1 was collected from the Huron Member of the Late Devonian Ohio Shale in western Rowan County, Kentucky. The sample is available as fine splits for detailed chemical analysis and as coarse splits for hand, microscopic, and microfossil examination.

Porosity and Permeability of Eastern Devonian Gas Shale

Summary High-precision core analysis has been performed on eight Devonian gas shale samples from the Appalachian basin. Seven of the core samples consist of the Upper Devonian Age Huron member of the Ohio shale, six of which came from wells in the Ohio River valley, and the seventh from a well in east-central Kentucky. The eighth core sample consists of Middle Devonian Age Marcellus shale obtained from a well in Morgantown, WV. The core analysis was originally intended to supply accurate input data for Devonian shale numerical reservoir simulation. Unexpectedly, the work has identified a number of geological factors that influence gas production from organic-rich shales. The presence of petroleum as a mobile liquid phase in the pores of all seven Huron shale samples effectively limits the gas porosity of this formation to less than 0.2%, and gas permeability of the rock matrix is commonly less than 0.1 μd at reservoir stress. The Marcellus shale core, on the other hand, was free of a mobile liquid phase and had a measured gas porosity of approximately 10%, and a surprisingly high permeability of 20 μd. Gas permeability of the Marcellus was highly stress-dependent, however; doubling the net confining stress reduced the permeability by nearly 70%. The conclusion reached from this study is that the gas productivity potential of Devonian shale in the Appalachian basin is influenced by a wide range of geologic factors. Organic content, thermal maturity, natural fracture spacing, and stratigraphic relationships between gray and black shales all affect gas content and mobility. Understanding these factors can improve the exploration and development of Devonian shale gas.

Subdivision of Lower Portion of Huron Member of Ohio Shale, Kanawha and Boone Counties, West Virginia, and Applications to Gas Production: ABSTRACT

Current work funded by the Gas Research Institute indicates that, in Kanawha and Boone Counties, West Virginia, most gas wells completed in the Devonian shales produce from the lower part of the Upper Devonian Huron Member of the Ohio Shale. Discrete assemblages of black shale emplacement in this part of the Appalachian basin can be discerned and are mappable using log data from wells that penetrate the lower Huron section. Black shale isolith maps across the two-county area show discrete elongate trends of black shale, thinning predominantly from northeast to southwest. These elongate black shale minima are interpreted herein as sites where newly deposited, black organic mud substrates were scoured by the action of relatively high-velocity turbidite plumes entering this part of the basin from shallower regions toward the east and northeast. Turbidite-transported muds and silts were then laid in the newly scoured areas in close vertical and lateral contact with the surrounding black muds. This interfingering of organic black shales with the gray silty shales and siltstones is significant to gas production from the Devonian shales in that the interbedded nature of these rocks provides a mechanism whereby gas generated and held by absorption in the black shales canmore » migrate into the more porous and permeable gray shales and siltstones, hence from there into a fracture system or a well bore.« less

Structural and Stratigraphic Controls on Natural Gas Production from Devonian Shales of Appalachian Basin of Southeastern Ohio: ABSTRACT

Detailed subsurface mapping and evaluation of production data from 12 Devonian shale units in southeastern Ohio indicate that the lower Huron Member of the Ohio Shale is the primary gas-producing zone. Jointed or fractured structural traps serve as the dominant reservoirs and consist of (1) regional joint or fracture systems, (2) fractures related to anticlinal or domal features, and (3) fractures related to monoclines. Evaluation of production data shows the Devonian shale reservoirs to be a multiple-porosity system. Gas is released from the reservoir in a stepwise manner: first, from the open fracture system; second, from adsorbed gas on the fracture surface; and third, from adsorbed gas within the shale matrix. Rapid decline of production typically occurs during the first year. However, release of adsorbed gas from the shale matrix has resulted in wells producing for 50 years. Stratigraphic variations in the shale units are of secondary importance. Isopach mapping is most useful in defining areas of penecontemporaneous faulting during shale deposition. These areas may serve as untested jointed or fractured reservoirs characteristic of Devonian shale reservoirs in southeastern Ohio.

Organic-Matter Preservation in Chattanooga Shale: Revised Late Devonian Correlations, Kentucky and Tennessee: ABSTRACT

Continued interest in the carbon-rich shale of Devonian and Mississippian age in Kentucky is reflected by intensive leasing and drilling to evaluate the potential reserves of oil shale. Hydrocarbons and heavy metals are associated with layers rich in organic matter (OM). Thicker accumulations of shale suitable for surface extraction lie along the flanks of the Cincinnati arch in both the Illinois and Appalachian basins. Distribution of the OM-rich shale is not uniform, but is controlled by subtly defined lithostratigraphic units. The shale tends to thin across the Cincinnati arch by an order of magnitude (100 versus 10 m, 330 versus 33 ft), and individual units disappear entirely. Key beds have been used with mixed success in tracing these changes. Recognition of these key beds in cores provided by a recently completed 70-core drilling program in and near the outcrop is the basis for revising earlier suggested correlations. One key bed, marked by the occurrence of the alga? Foerstia (Protosalvinia), occurs in the lower part of the lower (Huron) member of the Ohio Shale in the Appalachian basin. The Huron Member is overlain by a lithostratigraphic marker, the Three Lick Bed. The Foerstia Zone has been traced in core and outcrop to the upper part of the uppermost (Clegg Creek) member of the New Albany Shale in the Illinois basin. Discovery in this widespread continuous biostratigraphic marker at the top of the upper (Gassaway) member of the Chattanooga Shale near the designated reference section in Dekalb County, Tennessee, suggests that the Three Lick Bed of the Ohio Shale does not correlate with the middle unit of the Gassaway Member of the Chattanooga Shale as thought. Field relations indicate that the Three Lick Bed is absent by nondeposition, and starved-basin conditions prevailed into Early Mississippian time in this part of Tennessee. These stratigraphic revisions become significant in a regional synthesis of the anoxic-basin depositional model of OM--rich shale and syndepositional tectonics during Late Devonian time in Tennessee and Kentucky. End_of_Article - Last_Page 495------------

Foerstia from the Antrim Shale (Devonian) of Michigan

The inconspicuous fossil Foerstia marks a time zone within the black shale sequences of Late Devonian age of the eastern United States. It is best known from locations in Ohio, but it has been reported from Ontario to Tennessee and provides a basis for stratigraphic correlation between the Illinois and Appalachian Basins. The discovery of Foerstia in Michigan aids correlation of Michigan Basin sequences to those of the Appalachian and Illinois Basins. A cored zone some 1.5 m thick contains several foerstian remains within Unit 2 in a well located in eastern Michigan. Unit 2 correlates with the Middle Huron Member of the Ohio Shale, and Units 1A, 1B, and 1C in the Antrim correlate with the Lower Huron. Units 3, 4, and 5 and 6 correspond, respectively, to the Upper Huron, Chagrin, and Cleveland. Unit 4 may contain a Three Lick Bed equivalent. A new division of Antrim at the stratigraphic position of Foerstia should be considered.

Radon and Hydrocarbons in Soil Gases of Northeast Ohio: ABSTRACT

Radon survey techniques are being used to determine whether significant variations of Rn222 content occur in soil gases of northeastern Ohio and, if so, whether they have hydrocarbon prospecting potential. Radon activities are determined by using electronic detectors for short-term variations and film cups for long-term variations. Preliminary traverses covered more than 300 sites. Three localities were found in which the radon activities are reproducibly higher than regional background by a factor of 5 to 10. One case correlates with proximity to the outcrop belt of the uranium-rich Huron Member of Ohio Shale. The others consist of localized anomalies not directly associated with uranium-rich shales. Laboratory experiments of soil samples showed radon in anomalous regions is not produced in situ within the upper 1 to 2 ft (0.3 to 0.6 m) of soil, suggesting a deeper origin for migration of radon to near-surface soil gas. Occasional localized seeps of natural gas occur in northeastern Ohio. Light hydrocarbons C1 to C3 are usually associated with reducing environments causing precipitation of uranium and its products at shallow depths which could conceivably enhance radon activity at the surface. Also, hydrocarbons migrating upward from deeper sources would carry radon to the surface along more permeable and fractured rocks and create a radon anomaly. Light hydrocarbon analyses of shallow soil gases showed greater total hydrocarbon contents and greater C2/C1 and C2/C3 ratios in areas of higher radon activities. Measurements of hydrocarbons at greater soil depth, coupled with additional radon measurements, are in progress to interpret furt er the significance of radon-survey data. End_of_Article - Last_Page 244------------

Fractured Devonian Shale Reservoir, Appalachian Basin: ABSTRACT

Detailed structural analysis along the west flank of the Appalachian basin in Kentucky and West Virginia demonstrates the importance of detached and basement deformation in developing fracture permeability within Devonian shales. A porous fracture facies of regional extent within the organic-rich lower Huron Member of the Devonian shale partially relates to unique physical properties of the organic sediments, but an important factor for widespread gas production is fractures caused by differential shortening of sediments above a detachment surface in the lower Huron Member. Mineralized, uniquely oriented, and slickensided fractures, and increased fracture intensity within the organic lower Huron shales perpendicular to Alleghanian stress support this interpretation. The p rous fracture facies is most permeable (commercial) beyond the region of major tectonic transport where permeability is only local in extent. Linear trends of abnormally high final open flows in the producing area relate to trends of intensely fractured organic shale. These fracture zones seemingly reflect unique, complex, and perhaps more intense shear stress within organic shale found in flexures above basement faults. Gas migrated updip along open fractures placing the best wells slightly updip along the fracture trend or on the flank of adjacent low-relief flexures. This unique reservoir forms its own source and seal, and the lithologically restricted fracture facies imparts the permeability. Tailoring completion techniques which limit the vertical extent of induced fractures and whi h enhance recovery in the more common orthogonally fractured shale of the mid-continent region will be important for future development of this huge resource. End_of_Article - Last_Page 630------------

Upper Devonian Black Shales Across Appalachian Basin: ABSTRACT

The relatively high positive gamma-ray response and corresponding low-compensated density of black shales facilitated extension of outcropping Upper Devonian black shales (the Rhinestreet Shale Member of the West Falls Formation, the Pipe Creek Shale Member of the Java Formation, and the Dunkirk Shale Member of the Perrysburg Formation) southward in the subsurface beneath the Appalachian Plateau about 500 mi (800 km) to wells in the Greendale syncline in southwestern Virginia. Subsurface mapping clearly outlines an arcuate area from western New York through northwestern Pennsylvania, eastern Ohio, and western West Virginia to southwestern Virginia, in which the black shales are laterally continuous. Presumably, depositional environments were also uniform throughout this area at any given time during the accumulation of these dark rocks. Regionally, the black shales delineate an offshore part of the extensive Upper Devonian delta complex, although their distribution is somewhat restricted by a westward-expanding Middle Devonian unconformity against which the Rhinestreet and Pipe Creek Shale Members feather out. However, the Dunkirk Shale Member equivalent is present in outcrop as the lower part of the Huron Member of the Ohio Shale in Ohio and northern Kentucky, and in the corresponding part of the Gassaway Member of the Chattanooga Shale in central Tennessee and contiguous southern Kentucky. To the east, in the Appalachian basin, the black shales grade laterally into an eastward-thickening sequence of gray shale and siltstone turbidite beds. In the absence of extensive key beds, the thick sequence of coarser grained clastic rocks cannot be divided stratigraphically. End_of_Article - Last_Page 1167------------

Geochemistry of Mississippian and Devonian Oil Shales of Northeastern Kentucky: ABSTRACT

Detailed chemical analyses were conducted on 10 cores drilled in Lewis and Fleming Counties of Kentucky in an oil-shale resource assessment funded by the U.S. Department of Energy. The stratigraphic units studied include the Sunbury Shale and the Ohio Shale, which is divided (from top to bottom) into the Cleveland Member, the Three Lick Bed, and the Huron Member. The chemical analyses include C, H, N, S, major element oxide, and trace-element determinations from 760 samples. Carbon concentration was found to increase from top to bottom in the Sunbury Shale and Huron Member, and decrease in the Cleveland Member of the Ohio Shale. Average carbon concentrations were 11%, 6%, and 9% by weight in these intervals, respectively. Oil yield was determined by Fischer-assay and a good correlation with carbon was found. The Cleveland produced approximately 10% more oil per unit of carbon than the Sunbury. Although C, H, N, and S showed significant stratigraphic variability, the distribution patterns for these elements were found to be highly correlatable. The only systematic geographic variation of note was a 15% increase in hydrogen concentration in the Sunbury and Huron from north to south in the study area. The Sunbury Shale was the least siliceous of the stratigraphic intervals and had the highest concentration of trace elements. Trace elements could be placed into four groups based on major element affinities: (1) those elements that showed strong association with carbon (Cu, Cr); (2) those with a weaker association with carbon (Ni, V, U); (3) those with an affinity for sulfur (Co, Mo, Pb, Zn); and (4) those with an inorganic affinity (Ba, Rb, Sr, Zn). End_of_Article - Last_Page 903------------

Stratigraphy and Resource Assessment of Mississippian and Devonian Oil Shales of Northeastern Kentucky: ABSTRACT

Heightened interest in the organic carbon-rich shale of Mississippian and Devonian age as a source of oil has resulted in intensive leasing along the shale outcrop belt in Kentucky. Twelve cores of shale from Lewis and Fleming Counties were examined and analyzed in an effort to relate details of stratigraphy to the oil-rich horizons and to outline areas of minable potential resources. Formations of interest are the Sunbury Shale (Lower Mississippian) and the Ohio Shale (Upper Devonian). The generalized stratigraphy (Lower Mississippian through Upper Devonian) is, in descending order: Borden Formation, Sunbury Shale, Berea Sandstone, Bedford Shale, and Ohio Shale. Useful key markers in the sequence are the Three Lick Bed and the Foerstia zone, which are both in the Ohio Shale. The Three Lick Bed divides the Ohio Shale into the Cleveland Member, above, and the Huron Member, below. The Ohio Shale is underlain by Silurian Bisher Limestone and Crab Orchard Formation. Organic content is high in the Sunbury Shale and in the upper part of the Cleveland Member of the Ohio Shale. In cores, the total thickness of the Sunbury ranges from 12.0 to 18.4 ft (3.7 to 5.6 m). The combined thickness of Berea Sandstone and Bedford Shale ranges from 28 to 122 ft (8.5 to 37.2 m). The Cleveland shale ranges from 50 to 65 ft (15.2 to 19.8 m). Assuming a stripping ratio of 2.5 to 1, more than 2.9 × 106 acre-ft (3.6 × 103 cu hm) of shale having a Fischer-assay oil yield greater than 11 gal/ST (38 l/MT) is minable by means of existing methods. A conservative estimate of the amount of the potential strippable shale-oil resource in these two counties is more than 2 × 109 bbl. End_of_Article - Last_Page 897------------

Trace Fossils and Stratigraphy of Devonian Black Shale in East-Central Kentucky: ABSTRACT

In recent years trace fossils have been studied in carbonate and siliceous rocks. Shales have largely been ignored. This study describes trace fossils from the anoxic Upper Devonian black shale in east-central End_Page 729------------------------------ Kentucky along the western margin of the Appalachian basin. Trace fossils occur where dolomite overlies black shale in the lower part of the Huron Member (basal New Albany or Ohio Shale). Cruziana, Zoophycos, Planolites, Phycodes, Chondrites (Type A), Trichichnus, Teichichnus, Laevicyclus, and a newly described large burrow form are common. Up section, trace fossils are found where gray shale overlies black shale in the upper lower part of the Huron Member (Teichichnus, Planolites, Chondrites-Type B, Rhizocorallium, and Zoophycos) and the Three Lick Bed (Chondrites-Types C and D, Planolites-like burrows, Zoophycos, and pyritic burrows). A combination of interpretations based on the stratigraphy, lithology sedimentary structures, and trace fossils suggests that the Devonian black shale was deposited in an upward-deepening sequence transgressive over the axis of the present Cincinnati arch in east-central Kentucky. The carbonate environment of the underlying Middle Devonian Boyle dolomite contains trace fossils and features suggestive of shallow water. At the beginning of the Upper Devonian, migration of black muds onto the platform rimming the Cincinnati arch allowed interbedding with the carbonates. Up section, the carbonate-black shale environment was replaced by entirely black shale deposition. Periodic oxygenation allowed brief periods of burrowing. Trace fossil correlation will be helpful in understanding the detailed stratigraphy within the mid-continent Upper Devonian black shale. End_of_Article - Last_Page 730------------

Elemental Analyses of Devonian Shales in Southern West Virginia: ABSTRACT

Elemental compositions were determined on 690 samples of well cuttings from 19 wells in the Devonian shales of southern West Virginia; each well was sampled at roughly 50-ft (15 m) intervals. Sampling included all major stratigraphic intervals with special emphasis on five stratigraphic units: Chagrin Shale, Huron Member of the Ohio Shale, White Slate (correlates with Java Formation and Angola Shale Member of the West Falls Formation), Rhinestreet Shale Member of the West Falls Formation, and the Marcellus Shale. After calculating mean percentages within each unit, hand contouring maps, making trend-surface analyses, and diagramming vertical variations, individual elements showed regional and stratigraphic trends. Silica increases upsection, whereas potassium and MgO decr ase. The Marcellus Shale exhibits very high values for calcium and phosphate. Sulfur, strontium, and zinc appear to reflect the quantities of organic matter, which are higher in the black shale of the Huron Member and the Rhinestreet Member relative to the gray shales of the White Slate and the Chagrin Shale. The amounts of titanium, iron, and phosphate are low in black shales. Regionally, sulfur is higher in the westernmost parts of the study area and appears to be related to the presence of a platform where conditions were conducive to its concentration. Silica is low in the central part of the area. Manganese is highest in the gray shales and areas of black shales interpreted to have been deposited in deeper water; manganese correlates inversely with sulfur, suggesting the influence of redox conditions on manganese deposition. The results confirm the recent work on stratigraphic correlation of the Devonian shales in West Virginia. They also conform to the picture of the Devonian sea in this area as a platform with a deeper area and sediment source in the east, and possibly a second source in the west. End_of_Article - Last_Page 1580------------