Oronto Group Research Articles

Geochemical assessment of mineral sequestration of carbon dioxide in the midcontinent rift

AbstractThis study examines the potential of Midcontinent Rift rocks to facilitate long‐term CO2 sequestration by providing the necessary Ca and Mg for carbonate mineralization. Surface samples were collected from the Oronto and Bayfield‐Jacobsville Groups around Lake Superior and used for petrography and X‐ray diffraction to determine their mineral composition. Also, X‐ray fluorescence was also used to assess their bulk chemical composition. The samples were then exposed to CO2 and deionized water in Teflon‐lined vessels at 90°C, and the resulting leachate fluids were analyzed for the cation released during the testing. SEM microscopy was used to examine the samples for potential mineralization of carbonate minerals. The Oronto Group sediments consist primarily of feldspathic to feldspathic lithic arenites with a chlorite‐dominated matrix, and the primary porosity is blocked by calcite and hematite cement. The Bayfield–Jacobsville sequences are porous quartz arenites to feldspathic quartz arenites that do not contain significant accumulation of Ca‐, Mg‐, and Fe‐bearing minerals. The leachate fluids obtained from Oronto Group samples exhibit a maximum Ca release rate (5.2 × 10−4 mole/cm2.day), indicating rapid calcite cement dissolution and increased porosity and permeability. SEM/EDS microanalysis revealed areas where pore‐filling calcite was preferentially dissolved. Longer‐term rock‐water reactions resulted in induced carbonate mineralization, as evidenced by calcite crystals observed in a sample reacted for 102 days. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

End-Mesoproterozoic (ca. 1.08 Ga) epeiric seaway of the Nonesuch Formation, Wisconsin and Michigan, USA

Abstract The Nonesuch Formation and related sedimentary units of the Oronto Group, southern Lake Superior region, midwestern United States, are commonly held to have been deposited in a lacustrine rift basin within interior continental Laurentia. Here, we present new sedimentologic and stratigraphic evidence that shows a marine influence on deposition. Tidally influenced shallow-marine sandstone and evaporitic, sandy and muddy tidal flat facies pass upward into fine-grained estuarine and sandy turbidite deposits, which are sharply overlain by mixed sandy and muddy tidal flat and floodplain deposits. These observations are evidence that the lower Oronto Group was deposited in an epeiric seaway, one of several such seaways that developed during the final amalgamation of Rodinia at a time of globally high sea level. Retrogradational-aggradational-progradational-degradational stratal architecture records changes in the relative balance between generation of accommodation space and sedimentation rates, which we interpret to reflect the combined influence of Grenvillian Ottawan phase tectonic subsidence and thermal subsidence from earlier Midcontinent Rift magmatism. We use this revised stratigraphic framework to show that the geochemical proxies of the Nonesuch Formation are tied closely to sedimentary facies and reflect intrabasinal redox heterogeneity rather than global anoxia at the end-Mesoproterozoic. Further, our sedimentology shows that the microfossils recovered from the Nonesuch rocks are primarily associated with tidal flat facies. The combined influence of marine and local nonmarine conditions must be considered when invoking the Nonesuch Formation, or similar marine-influenced interior basin deposits, as global analogues.

The Nonesuch Formation Lagerstätte: a rare window into freshwater life one billion years ago

The Nonesuch Formation in the clastic sedimentary Oronto Group on the Keweenaw Peninsula of the Upper Peninsula, Michigan, USA most likely represents an ancient lake that formed between 1083 and 1070 Ma. Exceptional preservation, seen in palynological preparations, provides a snapshot of cell morphology, biological complexity and ecology at an early stage in the evolution of the eukaryotes. A wide range of unicellular organization is documented in both vegetative and encysted cell morphologies, but the extent to which multicellularity is developed seems very limited at this time. Overall, the Nonesuch microbiota, when viewed as a Lagerstätte, opens up a window onto the early evolution of unicellular eukaryotes, presenting an essential baseline of both eukaryotic diversity and cell structure well in advance of eukaryotic diversification documented in marine deposits from the later Neoproterozoic. Supplementary material: Materials and methods with a detailed specimen list are available at: https://doi.org/10.6084/m9.figshare.c.5183652

Paleomagnetism of the native copper mineralization, Keweenaw Peninsula, Michigan

The age and genesis of Michigan’s world-class native copper deposits are poorly constrained. The copper is hosted by basaltic flow tops and conglomeratic interbeds of the 1095 ± 2 Ma Keweenawan Portage Lake Formation. Progressive thermal demagnetization isolates stable hematite remanent magnetization components at 28 paleomagnetic sites. Paleomagnetic tilt tests show that magnetite in massive flow interiors is primary (1095 ± 2 Ma) and that hematite throughout the formation is syntectonic. The altered cupriferous deposits contain primary ∼1095 Ma and secondary ∼1053 Ma hematite in various proportions. The Caledonia Mine’s basaltic mineralization carries the ∼1053 Ma hematite dominantly whereas the Delaware Mine’s conglomeratic interbed mineralization carries the ∼1095 Ma hematite dominantly. The ∼1095 Ma hematite is attributed mostly to magnetite exsolution during flow extrusion and to weathering oxidation between extrusion events. An infusion of epigenetic hydrothermal fluids emplaced the native copper with additional hematite and polarity self-reversing titanohematite at 1053 ± 7 Ma. Importantly, paleomagnetic evidence supports a 1053 ± 7 Ma age also for the White Pine stratiform sedimentary copper mineralization, for the oxidation of the Oronto Group clastic rocks to red beds, and for the time limits of major tectonic uplift and deformation on the Keweenaw Peninsula.

Lithostratigraphic subdivisions of the Mesoproterozoic Copper Harbor Formation (Oronto Group) in Michigan and Wisconsin, USA

Lithostratigraphic subdivisions of the Mesoproterozoic Copper Harbor Formation (Oronto Group) in Michigan and Wisconsin, USA

New Structural and Stratigraphic Interpretation of Lake Superior Basin from Hydrocarbon Exploration Geophysics and Geology: ABSTRACT

Between October 1987 and April 1992, two deep boreholes were drilled along the south shore of Lake Superior in a test of the hydrocarbon potential of the conglomerate, sandstone and shale composing the Middle Proterozoic Oronto Group ({approximately}1 billion years). These drilling ventures, preceded by geophysical programs, and combined with wireline and core information, support new interpretations of the structural and stratigraphic geology associated with the Midcontinent Rift System in the Lake Superior district. No.7-22 Terra-Patrick: A stratigraphic, but not structural fit. This borehole in Bayfield County, Wisconsin, drilled an expected sequence of Oronto Group clastic redbeds. No viable hydrocarbon shows were encountered. Six second reflection seismology profiles collected in northwestern Wisconsin indicate the Douglas Fault decreases in throw in an easterly direction, changing to a fold northeast of the borehole. This termination is associated with the south flank of White`s Ridge, a pre-rift residual high identified through modeling studies and seismic interpretations by local absence of Midcontinent Rift volcanics and overlying strata. To the southwest of Isle Royale, the pre-rift Grand Marias Ridge exhibits similar characteristics. No.1-29 St. Amour: A structural, but not stratigraphic, fit. Drilled in Alger County, Michigan, the St. Amour well appears to bottom in pre-riftmore » metamorphic basement rocks. This hole was 100% cored. No hydrocarbon shows were reported. Reflection seismology profile analyses verify a change in strike, from northeast to southeast, of the Keweenaw Fault in the eastern Lake Superior Basin. The drilled section included 6,000 feet of pre-Paleozoic red-beds containing cross-bedding, ripple marks, and multiple fining-upward strata.« less

Illite/Smectite Geothermometry of the Proterozoic Oronto Group, Midcontinent Rift System

AbstractCharacterization of the Nonesuch Formation, middle unit of the Proterozoic Oronto Group, as a potential hydrocarbon source for the Lake Superior basin portion of the Midcontinent Rift system requires an understanding of the thermal maturity of the region and its relationship to the thermal history. Illite/smectite (I/S) expandability data were collected from the Nonesuch Formation and the overlying Freda Sandstone and compared with organic thermal maturity data; both data sets coupled with a thermal and burial history for the White Pine area of Michigan allow regional interpretation of maximum formation temperatures of the Nonesuch Formation and the Freda Sandstone with respect to time. Samples collected from drill holes in northeastern Wisconsin display nearly pure smectite within the lower Freda Sandstone trending abruptly to ordered I/S within the Nonesuch Formation. Regular trends of decreasing expandability with depth occur in four other drill holes to the northeast. Comparison of I/S expandability between similar stratigraphic intervals reveals a significant trend of increasing thermal maturity to the northeast, with the lowest thermal maturities observed in the Iron River Syncline area just west of White Pine, Michigan.I/S geothermometry suggests maximum temperatures in the Nonesuch Formation of 140°C in Wisconsin, 115°C in the Iron River Syncline area, 160°C at White Pine, and 190°C near the southern portions of the Keweenaw Copper District. The geographic pattern of temperatures determined from I/S geothermometry is identical to that determined from organic thermal maturity indicators in the Nonesuch Formation (Imbus et al., 1988, 1990; Hieshima and Pratt, 1991; Pratt et al, 1991; Mauk and Hieshima, 1992).Regular variations in I/S expandability with depth occur in the Freda Sandstone and the Nonesuch Formation near the southern limits of the Keweenaw Copper District. These variations suggest a fossil geothermal gradient of 55°C/km and limit the thickness of sediment above the Nonesuch Formation to approximately 3 km. In comparison, 3.6 km of Freda Sandstone are presently exposed near the Wisconsin border, and numerical modeling suggests a range of 4–6 km of sediment overlying the Nonesuch Formation. None of the data indicate the presence of the Bayfield Group sediments above the Nonesuch Formation at the time of clay diagenesis. Samples from White Pine suggest a two-stage burial history: 1) clay reaction, possible hydrocarbon maturation, and copper-sulfide mineralization at maximum temperatures above 100°C during the main rifting and burial event, followed by 2) fracturing, reverse faulting, and fluid circulation during a rift-terminating compressional event that may have allowed petroleum migration and native copper mineralization at temperatures below 100°C. Abrupt changes in I/S expandability with depth and the presence of poorly crystalline I/S (greater than 80% expandable) and kaolinite in the Freda Sandstone in Wisconsin appear to represent later overprinting of the diagenetic assemblage by fluids that were probably cooler and of differing composition than earlier diagenetic fluids. However, the authigenic assemblage from the vicinity of White Pine, Michigan, which includes up to 25% expandable I/S, appears to represent a diagenetic profile formed during the main rifting and burial event. Therefore, these expandable I/S-type clays are essentially 1.0 billion years old.

The Lake Superior Oronto Group, a Middle Proterozoic Exploration Model for the Late Proterozoic Chuar Group of the Grand Canyon

The Lake Superior Oronto Group and the Grand Canyon Chuar Group are the most significant Precambrian hydrocarbon targets within the conterminous United States. These frontier terrains share common Proterozoic age, comparable total organic carbon source rock values, association with Indian-interest properties, plus similarities in reservoir, trap, and maturation characteristics. Extensively studied since 1980, the exploration philosophy applied to the Oronto Group is presented as a model for Chuar Group hydrocarbon evaluation. Hydrocarbon shows have been reported since 1852 from middle Proterozoic rocks of the Lake Superior basin. Occurrences include stains within stromatolitic facies of the Copper Harbor Conglomerate, live subsurface seeps within Nonesuch units in the White Pine copper mine of Michigan, and impsonite-like inclusions within calcite veins of the Freda Formation. These formations compose the Oronto Group, a synrift package infilling the Lake Superior basin of the mid-continent rift system. Seep analyses identify a low sulfur (0.02%), paraffinic (67%), 34 API crude indirectly dated (Rb/Sr) at a minimum of 1047{plus minus}35 Ma. Nonesuch Formation source shales are present within both central horst structures and flank half-grabens. Reservoir-quality criteria are associated with adjacent Copper Harbor and overlying Freda Formation units. Seismically identified traps range from anticlinal and drag folding tomore » onlap, stratigraphic, and unconformity closures. The Lake Superior segment of the mid-continent rift system is subdivided into four structural units (I-IV). Association of oil seeps with stratiform copper deposits (unit III) suggests evidence of geochemical symbiosis. This crude entered oil-window status circa 1.0 Ga due to migrating cupriferous thermal systems.« less

Calcium carbonate cement (caliche) in Keweenawan sedimentary rocks (∼ 1.1 Ga), upper Peninsula of Michigan

Abstract A complex caliche profile, and numerous widespread zones of carbonate cement occur in a thick sequence of fluvial siliciclastic sandstones and conglomerates that were deposited in the Lake Superior basin during and after continental basaltic volcanism, as interflow conglomerates of the Portage Lake Volcanics and as the Oronto Group. In conglomerates the carbonate cement forms discontinuous zones, up to 60 cm thick and several meters in length, consisting of up to 25 vol.% carbonate. Whereas the caliche horizon at the Centennial Mine shows typical upward-grading features characteristic of pedogenic caliche, the widespread sparry carbonate cement is less diagnostic. It is interpreted also as caliche for the following reasons: (1) it predates regional epidote metamorphism; (2) a caliche profile has been described from the same strata; (3) textures characteristic of caliche such as carbonate-rimmed pebbles, pendulose calcite on pebbles, sand grains floating in a carbonate matrix, and exfoliated chlorite; (4) possible vadoids; (5) the carbonate-rich zones are widespread stratigraphically and geographically in basinward-inclined alluvial fans, and (6) the distribution of these zones, and the total quantity of contained carbonate requires other than a point source for the origin of the carbonate. Several lines of evidence suggest that the prevailing climate may have been arid, with a fluctuating, perhaps seasonal rainfall pattern required for caliche: (1) a paleolatitude about 30° north; (2) carbonate-filled shrinkage cracks denoting high evaporation; (3) intermittent, flashy, or ephemeral streams recorded locally in fluvial beds by numerous superimposed horizons of mud-chip conglomerate, enormous, previously cemented mudstone rip-ups; and desiccation-cracked mud drapes. Interpretation of the cement as vadose caliche is compatible with a sedimentation model for the region as a semi-arid intermontane basin, flanked by alluvial fans and with a central saline lake.

Comparative Precambrian Stratigraphy and Structure Along the Mid-Continent Rift

The Mid-Continent rift is a geophysically identified tectonic structure that has been traced from Kansas northeastward into the Lake Superior district. A related arm has been identified by gravity as extending from eastern Lake Superior southeastward into the lower peninsula of Michigan. This rift is of Precambrian (Keweenawan) age and began developing approximately 1.1 b.y.B.P. For most of its extent, this continental-class rift system is buried below Phanerozoic strata. Outcrops are found only in east-central Minnesota, northwestern Wisconsin, and the upper peninsula of Michigan. The most accepted tectonic model of the Mid-Continent rift is that of a central horst partly covered by clastic rocks, bounded by high-angle faulting, and flanked by basins filled with clastic rocks. This model was developed in conjunction with field studies in the southwestern Lake Superior area, and generally has been adopted for Minnesota, Iowa, Nebraska, and Kansas. A comparable model has yet to be presented for the related arm extending into southern Michigan. In the Lake Superior outcrop belt, the oldest recognized rifted rocks are layered basalts of middle Keweenawan age. Overlying these basalts is an upper Keweenawan thick sedimentary sequence composed of the Oronto (older) and Bayfield (younger) Groups. These sedimentary rocks are almost entirely clastic with texture ranging from conglomerate to shale (mudstone). Rock colors are principally reds and browns, with secondary shades of green and white. The Oronto Group is more immature mineralogically and texturally, and more complex structurally, than the Bayfield Group. The Oronto Group also is differentiated by one of its units--the Nonesuch Formation--which contains organic shales that bleed liquid hydrocarbons from subsurface fractures and vugs in a Michigan copper mine. Conditions of eposition for both groups are closely allied with an aquatic, continental environment. Specific paleogeography ranged from alluvial fan and plain, to deltaic, flood plain, fluvial, and lacustrine. Southwest and southeast of the Lake Superior outcrop belt, stratigraphic relationships are known principally from fewer than a dozen significant wells drilled into the Precambrian within the Mid-Continent rift trend. Analysis of the proposed upper Keweenawan red clastic sedimentary rock column within these wells suggests that the Lake Superior stratigraphy can be provisionally correlated throughout the Mid-Continent rift trend.

Refraction seismic investigations of the northern midcontinent gravity high

Eighty-seven seismic refraction profiles have been obtained to define the geologic structure in the upper crust associated with the midcontinent gravity high in Minnesota and Wisconsin. The seismic measurements were taken across a fixed spread of seven geophones from distances up to 13 km. A structural section was prepared for each profile by interpretation of the travel-time graph, and the individual sections were compiled onto regional cross sections. Measured seismic velocities in bedrock fall in the 2.5–7.1 km/sec range. Observed velocities can be assigned to seven categories corresponding to Paleozoic, upper, middle, and lower Upper Keweenawan strata, Middle Keweenawan volcanics, pre-Keweenawan felsic-to-intermediate intrusive rocks, and pre-Keweenawan mafic intrusive rocks. These groups display good continuity through the area and suggest the lithologic equivalence of rock bodies between geologic provinces. The St. Croix horst and its flanking basins underlie the midcontinent gravity high and its parallel gravity lows north of Minneapolis. Minimum throw along the western and eastern boundary fault zones reaches about 3.0 and 2.0 km. Sedimentary rocks in the eastern basin reach a thickness of at least 2.6 km. A complex horst-like structure also underlies the midcontinent gravity high in southern Minnesota; an uplifted basaltic body is bordered by sedimentary basins having strata about 3.0 km thick. Middle Keweenawan basalts are present locally in the eastern and western basins underlying the Upper Keweenawan strata. Rocks probably lithologically equivalent to the Oronto group are rare in the western basin, common in small basins on the St. Croix horst, and abundant in the eastern basin. Rocks probably lithologically equivalent to the Bayfield group are extensive in the western and eastern basins, but they have not been found on the St. Croix horst. The Bayfield group seems to be several kilometers thick across Douglas County north of the Douglas fault, and it does not appear to increase in thickness under the Bayfield peninsula.