Maquoketa Shale Research Articles

High-Resolution Pore Space Imaging, Mineralogical Characterization, and Sealing Capacity Estimates of Confining Units at a Geologic Carbon Storage Demonstration: The Illinois Basin–Decatur Project, USA

At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.

Variations of organic matter transformation in response to hydrothermal fluids: Example from the Indiana part of the Illinois Basin

Thermal maturation of organic matter in sedimentary rocks is a complex process controlled by multiple parameters. In this study, we examined the thermal history of one location in the Indiana part of the Illinois Basin. A total of 21 samples spanning the time interval from the Ordovician to the Mississippian were selected for maturity assessment and chemical structure characterization of vitrinite/vitrinite-like particles, solid bitumen, and alginite. The reflectance of vitrinite/vitrinite-like particles (VRo) reveals erratic variations with depth from 0.61% to 1.18%. Solid bitumen reflectance (SBRo), ranging from 0.43 to 0.92%, is slightly lower than VRo across this maturity range in this borehole. In addition to documenting reflectance variations with depth, variations within single organic matter particles were analyzed in the Upper Devonian New Albany Shale and Upper Ordovician Maquoketa Shale samples; these samples were targeted because they contained more organic matter than the samples from other stratigraphic units. SBRo shows significant variations within a single solid bitumen particle with a difference up to 0.81%. Significant maturity-related chemical differences within individual particles of solid bitumen and alginite were also revealed using micro-FTIR technique. An increase in temperature with depth of burial is certainly the key factor in controlling the thermal transformation of organic matter in sedimentary rocks. However, it is apparent that this mechanism alone does not explain the stratigraphic variations of VRo throughout the core and reflectance variations within individual solid bitumen and alginite particles. We suggest that the flow of hydrothermal fluids through the New Albany and Maquoketa Shale caused the observed thermal maturity anomaly. High concentrations of chlorine, vanadium, chromium, and zinc also suggest that organic matter transformation was enhanced by the flow of hydrothermal fluids in the study area.

Hydrogeochemical controls on aquifers of northwestern Illinois’ Driftless Area, USA

Groundwater in the Driftless Area of northwestern Illinois is a very hard Ca–Mg-bicarbonate-type water that reflects the dolomite aquifer material in this karst region. Groundwater in shallow aquifers has a short residence time and is susceptible to surface-borne contaminants. Deeper aquifers have distinct chemistry indicating longer flowpaths, most clearly indicated by low tritium values and elevated potassium and fluoride concentrations. Thirty water samples were collected from springs from across Jo Daviess County in northwestern Illinois between 2015 and 2016. The groundwater samples collected from what were initially identified as springs were found to be of two types: (1) natural springs that are stratigraphically controlled and discharging from crevices and bedding planes, especially where the underlying Galena Dolomite or overlying Silurian dolomite aquifer intersects the Maquoketa Shale; and (2) abandoned flowing-artesian wells, often with no identifiable well casing at the surface, that had been mistaken for springs. Background concentrations of eight water-quality parameters were calculated to determine pre-settlement and present-day background thresholds. The background concentrations, overall chemical compositions, tritium concentrations, and F/Cl and K/Cl ratios were used to characterize and group groundwater within the study area. The results of this investigation combined with recent work by the authors [Panno et al. (IL State Geological Survey Circular 586, 2017)] were used to determine the geologic, hydrogeologic, and geochemical controls on springs in this part of the Driftless Area. The results of this investigation revealed the susceptibility of the Galena Dolomite and Silurian dolomite aquifers to surface-borne contaminants. In addition, this work has developed a means, using ion ratios and spring location relative to bedrock geology to identify discharge from abandoned wells.

Turnover from mollusk-dominated Depauperate Zone (late Ordovician) to brachiopod-dominated (early Silurian) faunas in central North America

The Depauperate Zone from the base of the Ordovician (Katian) Maquoketa shale in Dubuque, Iowa, features a range of diminutive infaunal, epifaunal, nektonic and planktonic members with multiple growth stages. Fossils are preserved as phosphatized internal molds. In rare cases, shell replacement conserves growth lines. Sixteen species were recovered, including three-dimensional graptolites (Rectograptus peosta). The bivalves Palaeoneilo fecunda and Nuculites neglectus are most abundant, but the orthid brachiopod Plaesiomys subquadrata also is common. Bivariate analyses were conducted on the bivalve and brachiopod species, two gastropods (Liospira micula and Cyrtolites carinatus), a reputed sponge (Hindia sphaeroidalis) and the graptolite. All mollusks follow an isometric growth pattern and the same is especially characteristic of the orthid brachiopod. Winnowing by waves or bottom currents was minimal. Pene-contemporaneous replacement of fine details was due to concentrations of P2O5 in seawater intermittently brought from the shelf margin through upwelling. Paedomorphosis was likely, because the brachiopod P. subquadrata shows a record of individuals 150% larger in adult size elsewhere in North America. In contrast, populations of Silurian Pentamerus oblongus preserve a full range of immature to adult individuals with a curvi-linear growth pattern. Clear-water deposition under conditions of good marine circulation prevailed during much of the Silurian, although secondary silicification of original CaCO3 shells was common. The muddy Maquoketa substrate vanished due to sea-level rises that flooded all clastic sediment sources.

Late Ordovician–Early Silurian δ13C chemostratigraphy in the Upper Mississippi Valley: implications for chronostratigraphy and depositional interpretations

ABSTRACTA pioneer study of the previously unknown δ13C chemostratigraphy in the Ordovician/Silurian boundary interval in eastern Iowa and northeastern Illinois resulted in the discovery of the Hirnantian Isotope Carbon Excursion (HICE). The presence of this major isotope excursion in the Mosalem Formation in Iowa and the Wilhelmi Formation in Illinois, which indicates that the excursion interval in these units is of Hirnantian (latest Ordovician) rather than Early Silurian age, necessitates a revised chronostratigraphic classification of these units. Although the precise level of the Ordovician/Silurian boundary remains somewhat uncertain in the absence of the diagnostic graptolites, it is herein placed in the upper part, but well below the top, of the Mosalem Formation and at the top of the Wilhelmi Formation. During a major regression following the deposition of the Maquoketa Shale, the upper part of the latter clastic unit was in some places deeply eroded, resulting in a topographically dissected landscape with upland areas separated by wide incised valleys. During a subsequent late Hirnantian transgression, these palaeovalleys were gradually filled with marine sediments, but the upland areas were not transgressed until earliest Silurian times. The new chemostratigraphical evidence is in good agreement with the available biostratigraphical data, especially from corals, conodonts, and brachiopods. A preliminary chemostratigraphical study of the presumably coeval Edgewood Group successions in Pike County, northeastern Missouri failed to document any heavy δ13C values characteristic of the HICE and some, or all, of the Hirnantian values obtained there may be diagenetically overprinted.

Tempestites in a teapot? Condensation-generated shell beds in the Upper Ordovician, Cincinnati Arch, USA

Skeletal concentrations in mudstones may represent local facies produced by storm winnowing in shallow water, or time-specific deposits related to intervals of diminished sediment supply. Upper Ordovician (Katian) of the Cincinnati region is a mixed siliciclastic-carbonate succession including meter-scale cycles containing a shelly limestone-dominated phase and a mudstone-dominated phase.The “tempestite proximality model” asserts that shell-rich intervals originated by winnowing of mud from undifferentiated fair-weather deposits. Thus shell beds are construed as tempestites, while interbedded mudstones represent either fair-weather or bypassed mud. Meter-scale cycles are attributed to sea-level fluctuation or varying storm intensity.Alternatively, the “episodic starvation model” argues, on the basis of petrographic, taphonomic, and stratigraphic evidence, that, despite widespread evidence for storms or other turbulence events (e.g. tsunamis), winnowing alone could not generate shell beds where none had previously existed. Instead, variations in sediment supply are construed as the principal cause of shelly-mudstone cycles. Shell-rich deposits accrue during periods of siliciclastic sediment starvation and relatively shell-free mud accumulates during periods of sediment influx.Tempestite proximality and episodic starvation models lead to contrasting predictions about proximal-to-distal facies patterns. These are: (i) large versus small volumes of distally-deposited, bypassed mud; (ii) proximal grainstones and distal packstones versus distal grainstones and proximal packstones; and (iii) proximal versus distal amalgamation and condensation of shell beds.In this paper, these predictions are tested by (i) comparing meter-scale cycles from different horizons and depositional environments through the lower Cincinnatian succession (Kope through McMillan Formations representing deep subtidal through intertidal environments), and (ii) correlating intervals and individual meter-scale cycles from the Fairview Formation of the Cincinnati Arch (shallow subtidal) north and west into the Maquoketa Shale (deep subtidal) in subsurface of Ohio and Indiana. Both approaches show patterns consistent with episodic starvation, not winnowing, including: (i) small differences in stratigraphic thickness indicate small volumes of bypassed mud; (ii) discrete distal deep-water grainstones that splay proximally into bundles of thinner shallow-water packstones alternating with shelly muds show that grainstones formed from a lack of, rather than removal of mud; and (iii) distal shell‐bed amalgamation and condensation (and corresponding proximal splaying) of shell beds shows a proximal source of mud.Thus, winnowing by storms or other turbulence events did not generate shell beds or cycles from undifferentiated sediments despite abundant evidence for storm deposition. High-resolution correlations imply that the shell-bed and mud-bed hemicycles reflect simultaneous basin-wide changes in sedimentary style rather than contemporaneous facies belts that track sea level. In this sense, shell-rich and mud-rich hemicycles are “non-Waltherian” facies.

Upper Ordovician microphytoplankton of the Bill's Creek Shale and Stonington Formation, Upper Peninsula of Michigan, U.S.A.: Biostratigraphy and paleogeographic significance

An abundant, diverse, and well-preserved organic-walled microphytoplankton assemblage is described from the Upper Ordovician Bill's Creek Shale and the lower Stonington Formation (Bay de Noc Member) in the Upper Peninsula of Michigan, U.S.A. Based on graptolite and conodont evidence, the Bill's Creek Shale and Stonington Formation are Richmondian (=Ashgill) in age. The assemblage is dominated by acritarchs, which comprise 29 species (including the enigmatic palynomorph Gloeocapsomorpha prisca) assigned to 20 genera. The prasinophyte phycomata are represented by undifferentiated species of Leiosphaeridia and Tasmanites. In addition, chitinozoans are abundant, and scolecodonts and graptolite fragments are common. Paleontologic-palynologic and sedimentologic evidence indicates that the Bill's Creek Shale was deposited in a low-energy, shallow, nearshore marine environment. The overlying Bay de Noc Member of the Stonington Formation also accumulated in a low-energy, normal marine environment, but in a more offshore, somewhat deeper water setting. Both formations experienced minor transgressive and regressive episodes as indicated by fluctuations in the composition of the palynoflora. The combined Bill's Creek/Stonington acritarch assemblage closely resembles those described from the Richmondian-aged Maquoketa Shale (Missouri and Kansas), Sylvan Shale (Oklahoma), and Vauréal Formation (Anticosti Island, Québec, Canada). The overall composition of the acritarch assemblage from these four formations reflects a distinctive, recognizably Laurentian character. Nonetheless, many of the Bill's Creek/Stonington acritarchs have been reported from Upper Ordovician localities elsewhere, providing additional evidence for Late Ordovician cosmopolitanism of the marine microphytoplankton community. Additionally, the restricted stratigraphic range of many of the taxa further enhances their biostratigraphic application, both regionally and globally, and reaffirms the Richmondian (=Ashgill) age of the Bill's Creek Shale and Stonington Formation.

Dolomitization and Dolomite Neomorphism: Trenton and Black River Limestones (Middle Ordovician) Northern Indiana, U.S.A.

ABSTRACT The Trenton and Black River Limestones are dolomitized extensively along the axis of the Kankakee Arch in Indiana, with the proportion of dolomite decreasing to the south and southeast of the arch. Planar and nonplanar dolomite replacement textures and rhombic (type 1) and saddle (type 2) void-filling dolomite cements are present. Three stages of dolomitization, involving different fluids, are inferred on the basis of petrographic and geochemical characteristics of the dolomites. Nonferroan planar dolomite has relatively high 18O values (-1.8 to -6.1o/oo PDB) and has 87Sr/86Sr ratios (0.70833 to 0.70856) that overlap those of Middle Ordovician seawater. Petrography, geochemistry, and the geometry of the dolomitized body suggest that the planar dolomite was formed in Middle and Late Ordovician seawater during the deposition of the overlying Maquoketa Shale. Ferroan planar and nonplanar dolomite occurs in the upper few meters of the Trenton Limestone, confined to areas underlain by planar dolomite. This dolomite contains patches of nonferroan dolomite with cathodoluminescence (CL) characteristics similar to underlying planar dolomite. Ferroan dolomite has relatively low 18O values (-5.1 to -7.3o/oo PDB) and has slightly radiogenic 87Sr/86Sr ratios (0.70915 to 0.70969) similar to those obtained for the overlying Maquoketa Shale. These data indicate that ferroan dolomite formed by neomorphism of nonferroan planar dolomite as fluids were expelled from the overlying Maquoketa Shale during burial. The absence of ferroan dolomite at the Trenton-Maquoketa contact, in areas where the earlier-formed nonferroan planar dolomite also is absent, indicates that the fluid expelled from the overlying shale did not contain enough Mg2+ to dolomitize limestone. Type 1 dolomite cement has isotopic compositions similar to those of the ferroan dolomite, suggesting that it also formed from shale-derived burial fluids. CL growth zoning patterns in these cements suggest that diagenetic fluids moved stratigraphically downward and toward the southeast along the axis of the Kankakee Arch. Type 2 saddle dolomite cements precipitated late; their low 18O values (-6.0 to -7.0o/oo PDB) are similar to those of the type 1 dolomite cement. However, fluid-inclusion data indicate that the saddle dolomite was precipitated from more saline, basinal fluids and at higher temperatures (94° to 143°C) than the type 1 cements (80° to 104°C). A trend of decreasing fluid-inclusion homogenization temperatures and salinities from the Michigan Basin to the axis of Kankakee Arch suggests that these fluids emerged from the Michigan Basin after precipitation of type 1 cement.

Stratigraphic and Paleogeographic Significance of An Upper Ordovician Acritarch Flora from the Maquoketa Shale, Northeastern Missouri, U.S.A.

A well-preserved and moderately diverse acritarch assemblage was recovered from the upper Ordovician Maquoketa Shale of northeastern Missouri. Based on graptolite and conodont evidence, the Maquoketa in northeastern Missouri is considered Richmondian (=Ashgill) in age.The acritarch assemblage comprises 28 species, distributed among 17 genera including two new genera,CaelatosphaeraandStictosoma.There are 11 new species,Baltisphaeridium adiastaltum, Caelatosphaera verminosa(type species),Dorsennidium undosum, Elektoriskos aktinotos, Lophosphaeridium acinatum, L. varum, Micrhystridium hirticulum, M. prolixum, Peteinosphaeridium accinctulum, P. septuosum, andStictosoma gemmata(type species); together with two species similar to previously named species and three species left in open nomenclature. Cosmopolitan and stratigraphically important species identified includeBaltisphaeridium perclarumLoeblich and Tappan, 1978;Cheleutochroasp. cf.C. diaphorosaTurner, 1984;Dorsennidium hamii(Loeblich, 1970) Sarjeant and Stancliffe, 1994;Excultibrachium concinnumLoeblich and Tappan, 1978;Orthosphaeridium insculptumLoeblich, 1970;O. rectangulare(Eisenack, 1963) Eisenack, 1968, andVillosacapsula setosapellicula(Loeblich, 1970) Loeblich and Tappan, 1976.Polygonium gracileVavrdová, 1966 emend. Sarjeant and Stancliffe, 1994 andMicrhystridium hirticulumnew species dominate the assemblage, followed byDorsennidium undosumnew species,Baltisphaeridium oligopsakiumLoeblich and Tappan, 1978,Veryhachiumsp. cf.V. oklahomenseLoeblich, 1970,Peteinosphaeridium accinctulumnew species, andLophosphaeridium acinatumnew species. Additionally, the palynoflora contains chitinozoans, scolecodonts, cryptospores, and the enigmatic palynomorphGloeocapsomorpha priscaZalessky, 1917 emend. Foster, Reed, and Wicander, 1989.Paleontologic-palynologic and sedimentologic evidence indicates that the Maquoketa Shale at the two studied localities accumulated under low energy, somewhat offshore, and unrestricted marine conditions. The present Maquoketa Shale acritarch palynoflora shows greatest similarity to those of the Sylvan Shale (Ashgill; Richmondian) of Oklahoma and the Maquoketa Shale (Caradoc and Ashgill) of Kansas. Whereas there are some cosmopolitan acritarch species present in the Maquoketa Shale, its palynoflora shows no pronounced similarity with age-equivalent acritarch suites from outside of North America.

Glacial recharge and paleohydrologic flow systems in the Illinois basin: Evidence from chemistry of Ordovician carbonate (Galena) formation waters

The Illinois basin provides an opportune setting for elucidating the roles of remnant evaporite brines and meteoric waters in the evolution of formation waters in an intracratonic sedimentary basin. Formation waters from carbonate reservoirs in the Upper Ordovician Galena Group have been analyzed geochemically to study the origin of their salinity, their chemical and isotopic evolution, and their relationship to paleohydrologic flow systems. Chloride/bromide ratios and CI/Br-Na/Br relations indicate that initial brine salinity resulted from subaerial evaporation of seawater rather than from halite dissolution. Subsequent subsurface dilution of the brines by meteoric waters is disclosed by δD-δ 18 O covariance; however, the remnant evaporite brine has not been completely expelled from these Ordovician strata. Galena formation waters have 87 Sr/ 86 Sr ratios that range from 0.708 17 (a value nearly equal to that of coeval seawater) to 0.710 43. This is the greatest range of Sr isotopic ratios found in waters from any stratigraphic unit in the basin. Two fluid mixing events are revealed in plots of 87 Sr/ 86 Sr vs. 1/Sr: introduction of 87 Sr-enriched fluids from a siliciclastic source, probably overlying Maquoketa shale, and a later event that only affected reservoir waters in the western shelf of the basin. General covariance between Sr and H-O isotopes suggests that the later event is related to meteoric water recharge. The point of intersection of the δD-δ 18 O trend with the meteoric water line implies that this mixing event involved Pleistocene glacial meltwater that recharged Galena reservoirs near outcrops along the western margin of the basin. Ordovician Galena formation waters are geochemically distinct from those in both Silurian-Devonian and Mississippian-Pennsylvanian strata, a distinction that has evidently been maintained by the overlying Maquoketa regional aquitard.

Geochemical Indicators of Depositional Environment and Source-Rock Potential for the Upper Ordovician Maquoketa Group, Illinois Basin

Two depositional cycles are recognized within the Upper Ordovician Maquoketa Group of the Illinois basin in a core from the New Jersey Zinc 1 Parrish well of Fulton County, Illinois. Organic carbon (Corg), total sulfur, 13C content of the organic carbon (^dgr13Corg ), hydrogen and oxygen indices (HI and OI) from Rock-Eval pyrolysis, and yields of extractable organic matter (EOM) vary through the cycles. Dark-brown to black, laminated shales are present in the lower portion of each cycle and have high values of Corg (1.0-3.0%), HI (500-1000 mg hydrocarbon [HC]/g total organic carbon[TOC]), and EOM (500-2500 ppm), and more negative ^dgr13Corg values (^dgr13Corg = -30 to -30.5^ mil). Gray to greenish-gray, bioturbated shales are present in the upper portion of each cycle and have low values of Corg (<1.0%), HI (<500 mg HC/g TOC), and EOM (<500 ppm), and more positive ^dgr13Corg values (-28.5 to -29.5^pmil) compared to the laminated shales. Although thermally immature to marginally mature in this core, the laminated shales represent potential source rocks for petroleum because they contain good to excellent quantities of oil-prone organic matter and are more deeply buried in other areas of the basin. Kerogen elemental data and Rock-Eval data suggest that the source of organic matter in the Maquoketa was uniform, with the notable exception of graptolite-rich layers. Distributions of saturated hydrocarbons for Maquoketa samples resemble those derived from amorphous organic matter. The organic-walled microfossil Gloeocapsomorpha prisca was not identified in kerogens of the Maquoketa shale, and its absence is most likely due to an unfavorable depositional environment and/or climate. Variations in bulk geochemical data and carbon isotopic compositions within the Maquoketa Group indicate substantial reworking and degradation of organic matter associated with bioturbation and oxygenated depositional conditions. Organic-rich shale was deposited in an environment where circulation of the water column was sluggish and dissolved-oxygen concentrations were low, resulting in the preservation of organic matter. Organic-poor shale was deposited in an environment where circulation of the water column was strong, dissolved-oxygen concentrations were high, and burrowing organisms thoroughly reworked the sediment, resulting in the degradation of organic matter. A maximum difference in carbon isotopic ratios of 2^pmil between organic-rich and organic-poor units of the Maquoketa roup suggests that heterotrophic reworking of organic matter was important in the depositional environment. The carbon isotopic composition and H/C ratio of kerogen for graptolite-rich shale suggests that organic productivity may have played an intermittent role in the accumulation of organic matter in the Maquoketa shale.

Paniculaferum missouriensis gen. et sp. nov., a new Upper Ordovician acritarch from Missouri, U.S.A.

A new acanthomorphic acritarch, Paniculaferum missouriensis gen. et sp. nov., is formally established. It was recovered from the Upper Ordovician (Ashgill) Maquoketa Shale of Missouri. Complexly branched processes and two wall layers characterize this distinctive acritarch.

Geochemical Evolution in the Cambrian‐Ordovician Sandstone Aquifer, Eastern Wisconsin: 2. Correlation Between Flow Paths and Ground‐Water Chemistry

AbstractA finite‐difference ground‐water flow model linked to a particle‐tracking routine was used to determine ground‐water flow paths and residence times in the Cambrian‐Ordovician sandstone aquifer of eastern Wisconsin. The modeled region was a cross section along an approximate flow line that included the boundary between unconfmed and confined conditions in the aquifer. Modeling results indicate that lower conductivity units within the sandstone aquifer produce vertically stratified flow in the confined region. These simulation results help explain chemical signatures of ground water in different parts of the aquifer. Three distinct regions of the flow system are identified: the unconfmed zone where vertical mixing across the aquifer yields a homogeneous chemistry, the shallow part of the confined zone where sodium and sulfate charged water from the Maquoketa Shale mixes with water that has migrated from the unconfmed area, and the deeper region of the confined aquifer, containing older water that entered the system in the unconfmed area. Radium activities in ground water increase with distance along flow paths predicted by the simulation, consistent with a low concentration source of solid phase uranium and release of decay products to ground water by desorption and dissolution throughout the sandstone aquifer.

Geochemical Evolution in the Cambrian‐Ordovician Sandstone Aquifer, Eastern Wisconsin: 1. Major Ion and Radionuclide Distribution

AbstractGround water from wells in the Cambrian‐Ordovician sandstone aquifer of eastern Wisconsin often contains elevated concentrations of dissolved solids, chloride, and sulfate and locally approaches or exceeds the current drinking‐water standard for combined radium activity. Samples were collected from wells located along an approximate flow line in order to gain an improved understanding of the chemical evolution of ground water in this system. The concentrations of chloride, sulfate, and sodium increase where the aquifer is confined by the Maquoketa Shale, and the highest combined radium activity is also found in this area. Charge balance calculations and geochemical modeling indicate that dissolution of trace evaporite minerals and cation exchange are important mechanisms controlling major ion distribution. Isotopic equilibrium calculations and analysis of well cuttings from one well with alpha‐sensitive film indicate that the dissolved radionuclide activities are consistent with a uranium source occurring in shaly intervals of the sandstone aquifer at maximum local concentrations of 5 ppm.

Lopatin Analysis of Maturation and Petroleum Generation in the Illinois Basin

A modified Lopatin approach was used to evaluate the present-day maturity of Paleozoic source rock units across the Illinois basin, timing of generation, regional porosity trends, and basin paleostructure during major generative events. Ten cases were modeled at 100 locations to test assumed paleogeothermal gradients, post-Pennsylvanian overburden thicknesses, and rates of erosional stripping. Lopatin predicted maturities for the Herrin ({number sign}6) Coal and the New Albany Shale are in good agreement ({plus minus}0.02% R{sub O}) with measured maturities if 500-3,000 ft of post-Middle Pennsylvanian strata and were deposited and subsequently eroded between the Permian and mid-Cretaceous and if paleogeothermal gradients were within a few {degree}C/km of present-day gradients. Predicted mean reflectance levels range from 1.0 to 4.0% R{sub O} at the base of the Potsdam Megagroup, 0.7 to 3.5% at the base of the Know Megagroup, and 0.6 to 1.3% at the base of the Maquoketa Shale, excluding only a small high-maturity area in southeastern Illinois. The Knox and Potsdam section attained oil generation 475-300 Ma, while the Maquoketa and the younger New Albany Shale reached the oil window much later: 300-250 Ma. Because most significant structures in the basin formed after 300 Ma, any pre-Maquoketa source rocks were alreadymore » within the gas zone and may have been largely spent by the time known structures formed. Any Know or deeper traps in the basin will probably contain gas, be restricted to old structures (earlier than 300 Ma) or stratigraphic traps, and will hold pre-300 Ma generated hydrocarbons which subsequently cracked to gas.« less

Petroleum Potential of the Upper Ordovician Maquoketa Group in Illinois: A Coordinated Geological and Geochemical Study: ABSTRACT

The Ordovician Maquoketa Group in Illinois, predominantly composed of shale, calcareous shale, and carbonates, has long been considered a potential source for Illinois basin hydrocarbons. Methods used to better define the petroleum potential of the Maquoketa in the Illinois basin were lithostratigraphic study, Rock-Eval (pyrolysis) analyses, comparison of molecular markers from whole-rock extracts and produced oil, and construction of burial history models. Organic-rich submature Maquoketa potential source rocks are present in western Illinois at shallow depths on the basin flank. Deeper in the basin in southern Illinois, Rock-Eval analyses indicate that the Maquoketa shale is within the oil window. Solvent extracts of the Maquoketa from western Illinois closely resemble the Devonian New Albany Shale, suggesting that past studies may have erroneously attributed Maquoketa-generated petroleum to a New Albany source or failed to identify mixed source oils. Subtle differences between Maquoketa and New Albany solvent extracts include differences in pristane/phytane ratios, proportions of steroids, and distribution of dimethyldibenzothiophene isomers. Maquoketa solvent extracts show little resemblance to Middle Ordovician oils from the Illinois or Michigan basins. Lithostratigraphic studies identified localized thick carbonate facies in the Maquoketa, suggesting depositional response to upper Ordovician paleostructures. Sandstone facies in the Maquoketa in southwestern Illinois offermore » a potential source/trap play, as well as serving as potential carrier beds for hydrocarbon migration. Maquoketa source and carrier beds may feed older Ordovician rocks in faulted areas along and south of the Cottage Grove fault system in southern Illinois.« less

Sulfur isotope evidence for regional recharge of saline water during continental glaciation, north-central United States

Sulfate concentrations in ground water from the Cambrian-Ordovician aquifer of south-eastern Wisconsin and northern Illinois increase up to hundreds of times where the aquifer is confined beneath the Maquoketa Shale. There is no sulfate source in the aquifer or overlying rocks except for minor amounts of finely disseminated pyrite. Coinciding with increasing sulfate concentrations, {delta}{sup 34}S of the dissolved sulfate increases from less than {minus}5{per thousand} in the unconfined part of the aquifer to a nearly constant value of +20{per thousand} where the aquifer is confined and where sulfate reduction is minimal. The most likely source for this isotopically heavy sulfate is ground water associated with Silurian evaporites under Lake Michigan. It is uncertain if the sulfate-rich water was emplaced in pulses or mostly during the last glaciation.

Exploration Model for Shallow Silurian (Kankakee) Carbonate Reservoirs in Western Illinois: ABSTRACT

Reservoirs in shallow (600-650 ft deep) basal Silurian Kankakee carbonates at Buckhorn consolidated, Siloam, and Kellerville oil fields in western Illinois have produced nearly 2 million bbl of oil, but were developed essentially by random drilling. A new exploration model that combines lithologic studies and isopach mapping has been developed at the Illinois State Geological Survey. Isopach mapping of Silurian and Devonian rocks between an organic facies in the Mississippian-Devonian New Albany Shale and the top of the Ordovician Maquoketa Shale reveals thickened sequences that coincide with most of the oil fields. These thickened intervals apparently reflect subtle paleovalleys eroded into the Maquoketa shale during the Ordovician-Silurian hiatus. During the initial Silurian marine transgression, these paleovalleys at the base of the Kankakee were filled with carbonates to form the thickened sequences. Differential erosion at the top of the Kankakee does not satisfactorily explain the locally thickened sequences in the Kankakee. Lithologic studies suggest that subsurface fluid flows concentrated along these paleovalleys contributed to subsequent diagenesis of valleyfill carbonates. Diagenetic alteration of these carbonates resulted in development of basal Kankakee reservoirs within the paleovalleys. This concept of Kankakee reservoirs occurring within paleovalleys at the Ordovician-Silurian unconformity is a new exploration modelmore » that can aid in the search for similar traps in western Illinois.« less

Source Rock Screening Studies of Ordovician Maquoketa Shale in Western Illinois: ABSTRACT

Source Rock Screening Studies of Ordovician Maquoketa Shale in Western Illinois: ABSTRACT

Engineering properties of the Maquoketa shale in northwestern Illinois : Preber, T In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984)P381–389. Publ New York: AIME, 1984

Engineering properties of the Maquoketa shale in northwestern Illinois : Preber, T In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984)P381–389. Publ New York: AIME, 1984