Michigan Basin Research Articles

Major ion pore-water chemistry evolution in Lake Michigan benthic sediments: Evidence for direct input from Michigan Basin saline groundwater

The Michigan Basin is composed of geological formations that contain brines and evaporites, and solutes from these geological sources have affected benthic sediment pore-water chemistry in Saginaw Bay (Lake Huron). We hypothesize that there exists similar potential for upward solute transport directly from the Michigan Basin into other Great Lakes areas. To test our hypothesis, we present here previously unpublished pore-water chemistry analyses from sediment cores collected during multiple Lake Michigan sampling events (spanning 1991−1999) and a new evaluation of previously published data. In several box cores, pore-water chloride concentrations increase with depth, and Cl:Br ratios are consistent with a geological formation brine source. In all gravity cores we collected from southern Lake Michigan, pore-water sodium concentrations increase with sediment depth. At one sample station, pore-water sodium concentrations exceed 2000 mg L−1 within 2 m of the sediment-water interface. Given the pore-water chemistry changes reported here, combined with information from previous studies of Lake Michigan bedrock geology, a Devonian formation brine is a plausible solute source. The presence of saline pore water within glaciolacustrine sediments underlying Lake Michigan indicates that this solute flux has been active during the past 10 k.y. However, the origins of this solute flux, including timing (onset) and contributions from advective and/or diffusive transport, are unknown. The specific geological source and solute transport process are important to resolve in order to evaluate potential effects of these Michigan Basin solute sources on the Great Lakes’ sediment biogeochemistry and water quality.

Diagenetic evolution of secondary evaporites and associated host-rock dolostones in the Huron Domain (Michigan Basin): insights from petrography, geochemistry, and C-O-S-Sr isotopes

ABSTRACT In this study, we present a detailed investigation of C-O-S-Sr isotope systematics and elemental analysis of secondary sulfates and associated host-rock carbonates of Cambrian to Devonian sedimentary successions along the eastern flank of the Michigan Basin, Ontario. This study evaluates the diagenetic evolution of pore fluids and their sources in fracture-fill and replacement sulfate minerals in low-permeability carbonate units in the Michigan Basin. Secondary sulfates, represented by gypsum and anhydrite, contain various petrographic types, represented by vug- and fracture-filling fibrous anhydrite in the Cambrian (δ18O vary between 16.8 to 17.6‰ VPDB and δ34S 28.3 to 29.0‰ CDT, 87Sr/86Sr ratios vary from 0.70834 to 0.70991, respectively) and Ordovician fibrous anhydrite (δ18O 16.8‰, δ34S 28.2‰, 87Sr/86Sr ratios 0.70829). These phases display mainly uniform REE patterns with Y/Ho and Zr/Hf ratios, flat La*, Gd*, and Y*, and enriched LREEs. In the Silurian strata, idiotopic satin-spar δ18O values vary between 4.0 and 8.3‰, δ34S 23.4 and 31.4‰ with 87Sr/86Sr ratios 0.70816–0.70866, xenotopic porphyroblast gypsum δ18O values vary between 4.5 and 13.3‰, δ34S 22.6 to 33.1‰, with 87Sr/86Sr ratios of 0.70850–0.70880, alabastrine gypsum δ18O values vary between 4.2 and 11.7‰, δ34S 23.1 to 26.9‰, with 87Sr/86Sr ratios of 0.70816–0.70876 and felted anhydrite δ18O values of 11.1‰, δ34S 27.4‰, with a 87Sr/86Sr ratio of 0.70849. These geochemical proxies suggest a comparable sulfate-rich source for both age groups under similar geochemical conditions. Gypsum in the Silurian Salina Group displays a wide range of REE values with Y/Ho, and Zr/Hf ratios, Nd/YbN and Pr/YbN, flat to strong Ce/Ce*, and a flat to strong Eu/Eu* anomaly, Gd/LaN, Tb/LaN, and Sm/LaN. These sulfates formed at burial from fluids of variable isotope compositions, chemical compositions, and temperatures. The sources of these fluids range from brines migrating from a deeper part of the basin forming anhydrite in the Cambrian and Ordovician sequences which were also affected by dolomitization and later hydrothermal fluid influx, to rehydration of gypsum at shallower burial depths and affected by salt dissolution and incursion of meteoric water during and following the Alleghenian orogeny.

Chemically Enabled CO2-Enhanced Oil Recovery in Multi-Porosity, Hydrothermally Altered Carbonates in the Southern Michigan Basin

Chemically Enabled CO2-Enhanced Oil Recovery in Multi-Porosity, Hydrothermally Altered Carbonates in the Southern Michigan Basin

Uranium isotopes in non-euxinic shale and carbonate reveal dynamic Katian marine redox conditions accompanying a decrease in biodiversity prior to the Late Ordovician Mass Extinction

The Late Ordovician mass extinction (LOME) is the first major mass extinction event in the Phanerozoic. However, global biodiversity started to decline during the Katian (prior to the LOME) and coeval global ocean redox conditions are not well understood. The deposition of Katian organic-rich sedimentary rocks, namely the calcareous Collingwood Member and overlying siliciclastic Rouge River Member, was triggered by the concurrent Taconic Orogeny in southern Ontario (Canada) near the interface between the epicratonic Appalachian and Michigan basins. In this study, we used geochemical elemental proxies and uranium isotope compositions (δ238U) to reconstruct local and global ocean redox states during deposition of both units at seven drill core localities throughout southern Ontario. Local redox conditions are revealed by several proxies (redox sensitive trace metals, Fe speciation, and Corg:P ratios). Collectively, these proxies suggest spatiotemporal redox variations for the Collingwood Member: O2-deficient conditions (non-euxinic) for the deep waters of the Appalachian and Michigan basins and mostly oxic-suboxic conditions for the shallow waters. In contrast, predominantly oxic-suboxic conditions are suggested for the Rouge River Member.Global ocean redox conditions are inferred from the δ238U of both units. The coeval seawater δ238U value during Collingwood Member deposition is estimated to be from ∼−0.87‰ to ∼−0.64‰, based on both carbonate δ238U (samples leached with 1 N HCl) and δ238Ubulk-non-detrital data (corrected from the bulk δ238U). Particularly, the δ238Ubulk-non-detrital data of the Collingwood Member from multiple cores (both shallow and deep waters) are positively correlated with elemental redox proxies, suggesting a local redox control on δ238U offsets between sediments and water columns. In contrast, the δ238Ubulk-non-detrital of the suboxic Rouge River Member (average = −0.32 ± 0.12‰) from several cores do not correlate with local redox proxies. The coeval seawater δ238U during Rouge River Member deposition is estimated between −0.62 ± 0.12‰ and −0.42 ± 0.12‰ assuming a δ238U offset of 0.1–0.3‰ as observed between modern suboxic sediments and seawater. For this range of seawater δ238U, a three-sink U isotope mass balance model suggests a contraction of global euxinic seafloor area from deposition of the Collingwood Member (0.5–31.6%; median = 1.0–14.2%) to the Rouge River Member (0.2–2.0%; median = 0.3–1.0%), which could have been associated with the concurrent Taconic Orogeny. Collectively, global marine redox proxy data (i.e., δ98Mo, δ238U) from this and previous studies imply dynamic Katian ocean redox conditions during the decrease of metazoan biodiversity prior to the LOME. As a similar extent of global ocean euxinia during the LOME2 also occurred episodically during the Katian but did not result in LOME2-like mass extinctions, it is suggested that other factors (e.g., climate), besides expanded ocean euxinia, could have contributed to the second phase of the LOME.

Reactive Transport Modelling of Elevated Dissolved Sulphide Concentrations in Sedimentary Basin Rocks

Groundwater with total dissolved sulphide concentrations in excess of 1.0 × 10 − 4 mol L − 1 3 mg L − 1 is relatively common at intermediate depths in sedimentary basins. However, the mechanisms responsible for the formation and spatial distribution of these sulphidic waters in sedimentary basins, which have been affected by periods of glaciation and deglaciation, are not fully understood. Sulphate reduction rates depend on many factors including redox conditions, salinity, temperature, and the presence and abundance of sulphate, organic matter, and sulphate-reducing bacteria. Two-dimensional reactive transport modelling was undertaken to provide potential explanations for the presence and distribution of sulphidic waters in sedimentary basins, partially constrained by field data from the Michigan Basin underlying Southern Ontario, Canada. Simulations were able to generally reproduce the observed depth-dependent distribution of sulphide. Sulphate reduction was most significant at intermediate depths due to anoxic conditions and elevated sulphate concentrations in the presence of organic matter in waters with relatively low salinity. The simulations indicate that glaciation-deglaciation periods increase mixing of waters at this interfacial zone, thereby enhancing rates of sulphate reduction and the formation of sulphide. In addition, the simulations indicate that glaciation-deglaciation cycles do not significantly affect sulphide concentrations in low permeability units, even at shallow depths (e.g., 25 m), while concentrations in permeable units remain stable below depths of 500 m.

Cross-basin chronostratigraphic correlation of carbonate succession (Llandovery, Michigan Basin, USA) using global carbon δ13Ccarb isotope excursions

Correlating shallow shelf carbonates and their deep basin equivalents is a perennial challenge in the geosciences, with wide-ranging implications. This hurdle is well illustrated in the Llandovery succession of the Michigan Basin, USA, a 40- to 265-m-thick carbonate interval represented by three lithostratigraphic units: the Cataract, the Burnt Bluff, and the Manistique groups. Although extensively studied at various localities within the basin and across the region, the chronostratigraphic relationships between these units remain unknown. The current study presents a cross-basin chronostratigraphic framework for the Llandovery succession utilizing globally documented carbon (δ13Ccarb) isotope excursions (CIEs). From 10 drill cores and three quarry sites throughout the Michigan Basin, five CIEs were identified and chronostratigraphically constrained using conodont biostratigraphy and conodont 87Sr/86Sr data. The five excursions are interpreted to be the global CIEs: the (1) Hirnantian Isotope Carbon Excursion (HICE; Hirnantian Stage), (2) Early Aeronian, (3) Late Aeronian (Aeronian Stage), (4) Valgu (Telychian Stage), and (5) Ireviken (Sheinwoodian Stage). Most importantly, the HICE and the Ireviken CIEs bracket the Llandovery strata preserved in the basin. The new high-resolution δ13Ccarb data suggest that CIEs can be effectively used to correlate among shallow marine shelf carbonates and their deeper water equivalents. The new chronostratigraphic framework shows that CIE-based time horizons across the Michigan Basin cut across lithostratigraphic unit boundaries, which indicates that these lithostratigraphic units are diachronous in the Michigan Basin. In addition to refining the stratigraphy of the Llandovery succession of the Michigan Basin, particularly the timing of various key sedimentary deposits, the new chronostratigraphic framework can be used to: (1) constrain the timing of various regional tectonic phenomena, (2) identify multiple tectonically driven siliciclastic sediment pulses in the basin, and (3) predict various stratal relationships that may result in previously unknown stratigraphic traps and, therefore, new hydrocarbon plays within the basin. The results of the current study also show that δ13Ccarb trends across the shelf-to-basin transect are spatially and temporally variable and do not match those reported in Modern carbonate settings, which possibly suggests that such δ13Ccarb trends, to some extent, reflect variations in water circulation and water mass heterogeneity during deposition.

Cratonic basins as effective sediment barriers in continent-scale sediment routing systems of Paleozoic North America

Provenance studies demonstrate the important control of plate boundary mountain building on continental sediment routing systems. Less well understood is if subsidence and uplift in cratons also has the potential to affect the organization of sediment routing systems on continental scales. New detrital zircon provenance data from the Michigan Basin in the Midcontinent of North America preserve evidence of intrabasin provenance heterogeneity in Cambrian, Ordovician, and middle Devonian strata. These results suggest that cratonic basins serve as effective sediment barriers that prevent mixing within and across basins from 10 to 100 s of millions of years. Internal sediment mixing, sorting, and dispersal may be achieved by a combination of sedimentary processes and inherited low relief topography. These observations are consistent with provenance data sets from eastern Laurentian Midcontinent basins that show locally and regionally variable provenance signatures during the early Paleozoic. By the late Devonian, provenance signatures throughout the basins homogenized, consistent with the emergence of transcontinental sediment transport systems associated with Appalachian orogenesis at the plate margin. These results demonstrate the importance of cratonic basins on local and regional sediment routing systems suggesting that these features may impede the integration of continental-scale sediment routings systems, particularly during periods of plate margin quiescence.

Porosity distribution in the Devonian Antrim Shale: Controlling factors and implications for gas sorption

Unconventional reservoirs, such as oil and gas shales, are characterized by diverse and heterogeneous pore systems, and their detailed knowledge is critical for understanding fluid storage and transport mechanisms. The Devonian Antrim Shale in the Michigan Basin is an unconventional, primarily biogenic gas accumulation with a technical recoverable resource of 19.9 Tcf. While its general formation properties are known, the details of porosity distribution and pore morphology are lacking. This study provides a comprehensive description of the total porosity, pore size distribution, pore morphology and mineral associations for various members of the Antrim Shale sampled at three locations across the basin, and then investigates the factors controlling porosity distribution and the implications for gas sorption. Results indicate that the black-shale members, the Lachine and Norwood, are characterized by a lower porosity (0.1–2%) compared to the organic-lean members, the Paxton and Upper Antrim (2–7% porosity). Total porosity tends to decrease with the increase in organic content in the Antrim Shale as organic matter, in particular solid bitumen, occludes available pore space between mineral grains in the organic-rich black shale members. Organic matter displays little to no porosity of its own at the SEM resolution, but gas adsorption measurements indicate the presence of micropores (<2 nm), whose amount correlates positively to the total organic content. The Norwood member (TOC values up to 25%) is characterized by the largest share of micropores (up to 37% of the total porosity volume), while the organic-lean Paxton Member (TOC < 6%) has the least amount of microporosity (1–6%). Only the Lachine Member and select Upper Member samples showed larger organic matter pores, visible in the SEM images (∼50–100 nm). Mesopores (2–50 nm) are the dominant pore size group in the Antrim Shale, forming 45% to 76% of the pore space, and most of the pores are interparticle and intraparticle pores in and around clays, quartz, feldspar and pyrite grains. No single mineral component influences the total porosity distribution, but clay content exhibits a weak positive correlation to the meso-macro porosity. As microporosity is known to contribute the most to gas adsorption capacity of unconventional reservoirs, TOC appears to be most important factor controlling both CH4 and CO2 storage potential of the Antrim Shale. The Norwood Member, characterized by the highest TOC and microporosity volume as well as surface area of the micropores, is predicted to have the highest gas adsorption capacity but direct sorption measurements will be needed to confirm that. This study highlights some important differences with previous observations about porosity relationship to organic and mineral components of shale reservoirs, and expands the understanding of shale pore systems in the low-maturity range of organic-rich shales.

Prospects for Eocene potash deposition in the East Tethyan domain: New evidence from fluid inclusions and chlorine isotope of halite crystals in the Kuqa Basin, NW China

The level of the Tethys Sea increased several times during the deposition of Mesozoic to Cenozoic sediments in the Kuqa Basin in the Tarim Block. The basin contains Paleogene to Neogene units containing evaporite-rich layers, which are favourable sources for economic concentration of potash (K-rich salt). However, the basin’s geology is poorly understood, lacking knowledge of the source of the brine, paleo-water temperatures, and the degree of evaporation. As a result, the exploration for potash mineralisation has been limited. This study documents the geochemistry, fluid inclusions, and Cl-isotope of Early Eocene halite crystals from the Kuqa Basin. The results show that the homogenisation temperatures of primary fluid inclusions in halite range between 20° and 57 °C, which is close to the temperature range of the seawater in the Tethyan sea during the same period. The average value of ∼ 32 °C is taken as the average temperature of the salt-forming brine in the Early Eocene. The homogenisation temperatures of the inclusions are generally high, with a maximum temperature of ∼ 57 °C, which is consistent with the global Paleocene–Eocene thermal maximum (PETM) climatic event, indicating that the salt-forming brine has experienced long-term and sustained high temperatures and short-term extremely high temperatures. This is consistent with the high temperatures recorded during the deposition of potash in other parts of the earth, such as ∼ 59 °C for the Silurian Michigan Basin in the USA and ∼ 58 °C for the Quaternary Lop Nur region in Mongolia. In addition, the Br content of the halite samples is between 58 and 125 ppm, and the Br × 103/Cl value is between 0.11 and 0.21, which is consistent with the evaporation curve of seawater, indicating that there is a marine environment favourable for potash deposition. The value of δ37Cl is between −0.7 and −0.14 ‰ showing that the salinity of the brine evolved to a higher concentration, especially during the later stage of potash deposition. This indicates that the potential for the presence of potash deposits in the Early Eocene Kuqa Basin is high.

Provenance of middle to late Pleistocene tills in Illinois, U.S.A.: evidence for long-distance (∼ 2000 km) ice transport during two successive glaciations

ABSTRACTZircons extracted from 567 granitic cobbles, in middle to late Pleistocene tills of the Lake Michigan Lobe in Illinois, provide a remarkably consistent Archean age of ∼ 2.7 Ga, with 87% dating between 2.6 and 2.8 Ga. This finding suggests a persistent glacial flow path of the southern Laurentide ice sheet from the Superior Province into the Lake Michigan basin during Marine Isotope Stage 6 (Illinois Episode) and Marine Isotope Stage 2 (Wisconsin Episode). Based on published crystalline bedrock ages in the Canadian Shield, these cobbles are interpreted to have been transported as much as ∼ 2000 km southwestward from the Quebec–Labrador ice dome, east of Hudson Bay, to the ice-sheet terminus in central to southern Illinois, USA. Some of the glacial flow likely skirted eastern Hudson Bay (source of Omar erratics) and southern James Bay, and traversed outcrops of Huronian jasper conglomerate and diamictite along the north shore of Lake Huron. Transport across the Paleozoic strata may have been enhanced, in part, by an ice stream that advanced across relatively soft and water-saturated sediments that underlie the Lake Michigan basin. The Lake Michigan basin, although present earlier in some form, was likely significantly eroded and overdeepened by accelerated glacial flow and erosion during MIS-6, further constraining the southern Laurentide Ice Sheet (LIS) flow path and influencing its subsequent flow during the last glaciation. As the Lake Michigan Lobe thinned and radiated out from the Lake Michigan basin, topographic effects led to separation of sublobes during the LIS advance to its southernmost extent.

Earltonella fredricksi n. gen n. sp. and Thalassocystis striata (Chlorophyta, Bryopsidales) from the Silurian (Llandoverian) of the Timiskaming outlier, Ontario, Canada

AbstractSpecimens of macroalgae are reported and described herein from newly discovered algal-Lagerstätten within the Llandoverian Earlton Formation at two localities separated by a distance of 45 km in the Timiskaming outlier of Ontario, Canada. Both localities are characterized by abundant specimens of the Codium-like bryopsidalean green alga Thalassocystis striata, the details of which, including within-assemblage morphological variation, compare closely to material from the type locality. Previously, this noncalcified taxon was known only from the Llandoverian Schoolcraft Formation in northern Michigan, ~500 km to the west. These new occurrences provide additional evidence that the alga-bearing intervals within the Earlton Formation at both Timiskaming localities correlate with the Schoolcraft Formation in the Michigan Basin. An associated noncalcified form at one of the Timiskaming localities is described as a new genus and species, Earltonella fredricksi LoDuca, n. gen. n. sp., the thallus architecture of which, with a creeping, runner-like stolon and numerous pinnate fronds, broadly resembles that of the living bryopsidalean alga Caulerpa. In broader terms, these new algal-Lagerstätten indicate that for a brief time during the late Llandoverian, as with other times during the Silurian, unusual conditions conducive to both the proliferation and preservation of expansive ‘seaweed meadows’ were established across regional-scale areas of the Laurentian epeiric sea.

Organic-walled tentaculids of Late Devonian (Frasnian) deposits of the Appalachian and Michigan Basins, Laurussia (NY, MI, OH)

This is the first report of organic-walled tentaculid remains from Givetian through Frasnian age deposits of the Michigan and Appalachian Basins in western Laurussia. This adds to the geographic scope of similar finds that have been described from the Frasnian through the Famennian in eastern Laurussia. However, those previous specimens were retrieved through palynological preparations and more closely resemble sheath structures rather than the full forms found herein, which were retrieved through complete maceration with ammonium surfactants.

Unraveling the complex burial history of the Antrim formation in Michigan basin using paleomagnetism, rock magnetism and geochemistry

This paper presents an integrated paleomagnetic, rock magnetic and geochemical study of the Devonian Antrim shale in the Michigan Basin. Specimens were obtained from two unoriented vertical cores (named St. Chester and Krocker) and sampled relative to a master specimen orientation line. Alternating field (AF) demagnetization experiments isolated a lower coercivity component (LC) from 0 to ∼60 mT in the Krocker core and corresponds to a Jurassic (170 Ma ± 25) magnetization. Higher coercivity components (HC) in the Krocker core are unblocked from ∼60 to 120 mT and unlike LC components, occasionally exhibit stable unblocking temperature ranges (e.g., 150–450°C) and higher AF demagnetization ranges (∼60–120 mT). HC components in the Krocker core are unique to certain members within the Antrim shale with a poorly resolved Middle Permian/Late Triassic magnetization in the Paxton member and Late Pennsylvanian (305 Ma ± 10) component in the Norwood. The St. Chester well exhibited a LC component among all specimens with a slightly older (205 Ma ± 10) than the Krocker core. Rock magnetic parameters indicate the magnetization resides in PSD/SD magnetite in both HC and LC components. Overall, the magnetizations are interpreted to be chemical remanent magnetizations (CRMs) with the HC component residing in SD magnetite which formed during hydrothermal activity in both cores. The LC component likely resides in PSD/MD magnetite and is interpreted to have formed in response to fluid flow associated with tectonic uplift and/or hydrocarbon migration. Petrographic observations indicate mineral assemblages consistent with hydrothermal mineralization (e.g., baroque dolomite). Depleted δ18O data from carbonate fractures are consistent with a hydrothermal fluid magnetization mechanism. Consistent anisotropy of magnetic susceptibility (AMS) lineations indicates either a long-lived paleocurrent direction or far-field tectonic shortening originating from the neighboring Acadian orogeny. Inorganic geochemistry indicate that paramagnetic Fe-rich clays carry the AMS signal. Lastly, an evaluation of the origin of chalcopyrite and monazite is performed through provenance analysis. These minerals are attributed to hydrothermal mineralization however, strong evidence suggests that some fraction of these grains were sourced from the Michigan Peninsula.

Possible Effects of Multiphase Methane Evolution During a Glacial Cycle on Underpressure Development in Sedimentary Basins: An Analysis With Application to the Northeast Michigan Basin

In low-permeability systems, groundwater may be accompanied by separate-phase fluids, and measured pore water pressures may deviate from those expected in steady-state, single-phase systems. These same systems may be of interest for storage of nuclear waste in Deep Geologic Repositories. Therefore, it is important to understand the relationship between the presence of a separate phase and anomalous pressure development. At the Bruce site in Southern Ontario, a significant underpressure was observed, and there is evidence for the presence of gas-phase methane in situ. This study used a one-dimensional (vertical) numerical model of the subsurface down to a depth of 844 m beneath the Bruce site to evaluate possible effects of hydromechanical coupling with multiphase flow on pressure evolution during glacial loading and unloading. The simulated pressure conditions were affected strongly by the amount of methane initially present in the system, and the maximum simulated underpressure varied nonmonotonically with increasing initial methane content. When the initial methane content was below the solubility limit, exsolution led to underpressures that briefly exceeded those that formed in the single-phase case. At intermediate initial methane contents (sufficient to produce an immobile gas phase), the gas phase dampened the hydromechanical effects of the glacial cycle. At large initial methane contents (when a mobile gas phase was present), gas migration caused a large decrease in relative liquid permeability, which further contributed to underpressure development in the pore water. Multiple scenarios that spanned a range of initial methane contents yielded underpressures like those observed at the Bruce site.

Depositional setting and organic matter characterization of the Upper Devonian Antrim Shale, Michigan Basin: Implications for hydrocarbon potential

During the Late Devonian, the Michigan Basin in the Eastern Interior Seaway was characterized by phases of well-developed bottom water anoxia, triggering extensive accumulation of organic matter-rich black shales. Palynological analysis for paleoenvironmental reconstruction and biostratigraphy of the Upper Devonian rocks has been previously performed in other basins of eastern North America, but it is lacking in the Michigan Basin. Here, the Upper Devonian Antrim Shale Formation is investigated for biostratigraphic, paleoenvironmental, and sea level reconstructions, organic matter characterization, and source rock potential. 35 core samples from three drill holes across the Michigan Basin spanning the Norwood, Paxton, Lachine, and Upper members. Palynological analysis showed a moderately diverse assemblage of 31 genera represented by 53 species of relatively well-preserved prasinophyte phycomata and acritarchs, with sparse records of plant spores and freshwater algae. Based on marker prasinophytes and acritarchs, an age of late Frasnian was assigned to the Norwood and Paxton members, while an early Famennian age was proposed to the Lachine and Upper members of the Antrim Shale. Two palynofacies assemblages (PFA) were identified from the variation in the particulate organic matter (POM) composition, both of which indicate deposition in a distal inner neritic shelf environment, but the PFA-2 took place in slightly shallower conditions than the PFA-1. Geochemical screening indicated high organic matter content (up to 25 wt%, avg. 8.5 wt%) and excellent hydrocarbon generating potential of kerogen Type II for the Norwood, Lachine, and Upper members. Only the Paxton Member was dominated by poor to fair organic richness (<0.6 wt%) and low hydrocarbon potential with a mixed Type II/III kerogen. Organic petrography indicated that the dominant organic matter assemblage consists mainly of unicellular marine Tasmanites telalginite and Leiosphaeridia, followed by solid bitumen of the initial oil type. Thermal maturity, determined from VRo-eq and Tmax, indicated that all samples are in the oil window, except for some intervals in the Paxton Member.

A composite Llandovery δ13Ccarb record from the Michigan Basin, USA

Abstract A new high-resolution, composite δ13Ccarb curve for the Michigan Basin, USA, was constructed using two stratigraphically overlapping subsurface cores that span the complete Llandovery interval. The Llandovery succession of the Michigan Basin measures between 140 m and 265 m thick and is represented by three lithostratigraphic groups: the Cataract (Manitoulin formation and Cabot Head Shale), the Burnt Bluff (Lime Island, Byron, and Hendricks formations), and the Manistique (Schoolcraft and Cordell formations). The composite δ13Ccarb curve exhibits five positive carbon isotope excursions (CIEs). Conodont and 87Sr/86Sr data suggest that the CIEs correlate with the Hirnantian, Early Aeronian, Late Aeronian, Valgu, and Ireviken global excursions. The new composite δ13Ccarb curve from the Michigan Basin represents the most stratigraphically complete, single-basin Llandovery record worldwide. The composite δ13Ccarb curve permits the ages of three Llandovery lithostratigraphic groups to be chronostratigraphically determined within ca. 1 Ma resolution. The composite δ13Ccarb curve also implies that the Ordovician–Silurian boundary in the Michigan Basin is located at the top of the Manitoulin formation and not at the base of the Manitoulin formation, which is consistent with recent findings from Manitoulin Island, Ontario. From the regional perspective, the high-resolution composite δ13Ccarb curve provides a valuable tool for delineating the depositional history of the Michigan Basin during the Llandovery. From a global perspective, the new composite δ13Ccarb curve sheds light on the dynamics of the global carbon cycle, particularly during the Rhuddanian, which is rarely preserved in other carbonate basins worldwide.

Estimating SHmax azimuth with P sources and vertical geophones: Use P-P reflection amplitudes or use SV-P reflection times?

We compared two methods for extracting the azimuth of maximum horizontal stress (SHmax) from 3D land-based seismic data generated by a P source and recorded with vertical geophones. In the first method, we used the direct-SV mode that is produced by all land-based P sources. P sources generate SV illumination that radiates in all azimuth directions from a source station and creates SV-P reflections that are recorded by vertical geophones. Unless stratigraphy has steep dip, SV-P raypaths recorded by vertical geophones are the reverse of P-SV raypaths recorded by horizontal geophones. Thus, SV-P data provide the same S-wave sensitivity to stress fields as popular P-SV data do. In the second method, we retrieved P-P reflections and then performed an amplitude-variation-with-azimuth (AVA) analysis of the amplitude-gradient behavior of P-P reflection wavelets. We did this analysis in narrow azimuth corridors to determine the gradient of reflection-wavelet amplitudes as a function of azimuth. This P-P AVA amplitude-gradient method has been of great interest in the reflection seismology community since it was introduced in the late 1990s. Each of these methods, AVA analysis of the gradient of P-P reflection amplitudes and azimuth-dependent arrival times of SV-P reflections, can be used to determine the azimuth of SHmax stress. We compare the results of the two methods with ground truth measurements of SHmax azimuth at a CO2 sequestration site in the Michigan Basin. SHmax azimuths were determined from P-P and SV-P data at three major boundaries at depths of approximately 3500 ft (1067 m), 5500 ft (1676 m), and 7500 ft (2286 m). Two estimates of SHmax azimuth (one using SV-P data and one using P-P data) were made at each stacking bin inside a 24 mi2 (62 km2) image space. The result was approximately 98,000 estimates of SHmax azimuth across each of these three boundaries for each of these two prediction strategies. Histogram displays of PP AVA gradient estimates had peaks at correct azimuths of SHmax at all three depths, but the spread of the distributions widened with depth and split into two peaks at the deepest boundary. In contrast, each histogram of SHmax azimuth predicted by azimuth-dependent SV-P traveltimes had a single, definitive peak that was positioned at the correct SHmax azimuth at all three boundary depths.

Chemically Enabled CO2-Enhanced Oil Recovery in Multi-Porosity, Hydrothermally Altered Carbonates in the Southern Michigan Basin

Chemically Enabled CO2-Enhanced Oil Recovery in Multi-Porosity, Hydrothermally Altered Carbonates in the Southern Michigan Basin

Crustal Noble Gas Isotopic Characteristics in Low-Permeability Ordovician Sedimentary Rock, Eastern Flank of the Michigan Basin

Crustal Noble Gas Isotopic Characteristics in Low-Permeability Ordovician Sedimentary Rock, Eastern Flank of the Michigan Basin

Hydrocarbon potential and Organofacies of the Devonian Antrim Shale, Michigan Basin

The Devonian Antrim Shale is an unconventional biogenic gas accumulation with a technical recoverable resource of 19.9 Tcf. However, major knowledge gaps remain regarding understanding of the source rock potential, organic facies assemblages and paleo-depositional conditions of the Antrim Shale members. This work utilized Rock-Eval pyrolysis, reflected light microscopy and solid bitumen reflectance to characterize the source rock quality, organo-facies assemblages, and thermal maturity of the various Antrim Shale members at three different localities in the Michigan Basin. Results showed that the Lachine and Norwood members are richer in organic matter (up to 24 wt%) than the Upper and Paxton members (<8 wt%). Organic matter is mainly dominated by marine Type II kerogen in the black shales of the Lachine and Norwood members, and by Type II and Type II/III in the Paxton Member. Telalginite, which is represented mainly by Tasmanites and Leiosphaeridia cysts, is the dominant organic matter in the black shale members where they account for about two-thirds of the organic matter composition. Solid bitumen, which accounts for less than one-third of the organic matter composition, is second after alginite. Both alginite and solid bitumen populations decline in abundance progressively in the Upper and Paxton members at the expense of inertinite and vitrinite. The dominant organofacies groups in the studied Antrim Shale members can be assigned to the BP type B and type D/E. Organic matter maturity determined from Rock-Eval Tmax and bitumen reflectance varies from immature to marginally mature across the Michigan Basin. The results confirmed that sediment burial depth and lateral position in the basin controlled organic facies assemblages within the Antrim Shale members.