Lithofacies and Sequence Framework of the Sauk Ii-Iii Transition Interval in the Illinois Basin

Lasemi, Yaghoob; Askari, Zohreh

doi:10.1130/abs/2016nc-275686

Cited by 1 publication

(5 citation statements)

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“…South of 40˚ N latitude, the succession including the capping lower Middle Ordovician interval is classified as the Knox Group (Fig. 1A), which includes Bonneterre, Davis, Derby-Doerun, Potosi, Eminence, Oneota, Shakopee, and Everton stratigraphic units (Kolata, 2005) consisting chiefly of fine to coarsely crystalline dolomite (Lasemi & Askari, 2014).…”

Section: Geologic Setting and Stratigraphymentioning

confidence: 99%

“…1A and 2G). The Potosi thickness ranges from 100 feet (30 m) in northern Illinois to over 600 feet (183 m) in southern Illinois (Lasemi & Askari, 2014). In southwestern Indiana, rocks equivalent to Davis, Derby-Doerun, Potosi, and Eminence stratigraphic units of Illinois are included in the Potosi Dolomite because they are hardly distinguishable (Shaver et al, 1986;T.…”

Section: Geologic Setting and Stratigraphymentioning

confidence: 99%

“…Drusy quartz is a distinctive feature of the Potosi in Missouri (Palmer, 1989;T. L. Thompson et al, 2013) and Illinois (Buschbach, 1975;Lasemi & Askari, 2014, 2021. The Potosi commonly has very low porosity and, based on crystal size classification of Folk (1959), is composed of medium (0.062-0.25 mm) to coarse (0.25-1 mm) crystalline dolomite; its primary depositional fabric is destroyed but ghosts of carbonate grains (Fig.…”

Section: Lithofacies and Reservoir Propertiesmentioning

confidence: 99%

“…1A) and is a relatively uniformly dolomitized unit with low siliciclastic content. Studies to date of the Potosi in the Illinois Basin have been mainly of general stratigraphic nature (e.g., Buschbach, 1975;Lasemi & Askari, 2014). The Potosi is characterized by very low intercrystalline porosity but encompasses vug and fracture/cavern porosity intervals (terminology after Chocquette & Pray, 1970) in which several hundred barrels of fluid may be lost during drilling (Lasemi & Askari, 2014, 2021Leetaru et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Studies to date of the Potosi in the Illinois Basin have been mainly of general stratigraphic nature (e.g., Buschbach, 1975;Lasemi & Askari, 2014). The Potosi is characterized by very low intercrystalline porosity but encompasses vug and fracture/cavern porosity intervals (terminology after Chocquette & Pray, 1970) in which several hundred barrels of fluid may be lost during drilling (Lasemi & Askari, 2014, 2021Leetaru et al, 2014). Cavernous intervals could serve as reservoirs for oil and gas, groundwater, and ore mineralization (e.g., Loucks, 1999), or serve as repositories for CO 2 and hazardous waste material.…”

Section: Introductionmentioning

confidence: 99%

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Multiple Paleokarst Events in the Cambrian Potosi Dolomite, Illinois Basin

Lasemi,

Askari

2024

The Sedimentary Record

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The Cambrian (Furongian) Potosi Dolomite (100-183 m) in Illinois is part of the Cambro-Ordovician Knox Group. It is a uniformly dolomitized unit with very low intercrystalline porosity but contains very permeable vug, fracture/cavern porosity intervals. Here, we interpret the characteristics of the widespread porous zones in the Potosi as paleokarst features formed by rising hypogenic basinal/hydrothermal fluids. The conformity bounded Potosi Dolomite is characterized by massive dolomitization, overdolomitization and occlusion of previously generated intercrystalline porosity, void filling mineralization, and extensive dissolution and formation of cavity-conduit systems. The pore spaces are typically lined with drusy quartz or are characterized by partial to complete infilling with chalcedonic silica and/or dolomite cements. Clay minerals may partially fill pore spaces; physical properties and thorium-potassium crossplot suggest chlorite as the main clay mineral present. Dolomite crystals typically are planar-s or nonplanar with open-space filling, inclusion rich saddle dolomite displaying curved and zigzag crystal faces. Void filling cement does not exhibit sign of pressure solution and in places vug porosity is developed along bedding parallel stylolite indicating post burial origin of these features. Cavern reservoirs in the Potosi are laterally extensive and often stacked with intervening very low porosity dolomite; very low bulk density, excursion of caliper log signature from the baseline, and loss of fluid circulation during drilling in these intervals signify anomalously high porosity and permeability interpreted as being the result of cavern forming multiple paleokarst events. Post burial origin of cavities and void filling cements, association of saddle dolomite and chlorite, and occurrence of Mississippi Valley-type (MVT) ore deposits in Missouri suggest karstification by hypogenic warm basinal/hydrothermal fluids. Dissolution and mineralization likely occurred by flow of deep basinal formation waters and hydrothermal fluids (sourced from the crystalline basement underlying the Reelfoot Rift and the Illinois Basin) along numerous basement-rooted normal, reverse, and strike-slip faults, and the associated fold and fractures. Expansion and contraction because of fault-related seismicity likely developed fracture porosity in brittle host dolomite and possibly ruptured any underling impermeable units to enable large-scale upward and outward fluid movement. The Potosi fracture/cavern porosity intervals are confined by thick very low porosity dolomite intervals that could serve as effective seal. There is no report of any show of oil in the Potosi Dolomite, but the unit has an excellent potential to serve as a combined reservoir and seal for storing anthropogenic CO2 and waste material.

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Section: Geologic Setting and Stratigraphymentioning

confidence: 99%

Section: Geologic Setting and Stratigraphymentioning

confidence: 99%