Devonian and Mississippian Sappington Formation in Southwest Montana

Devonian and Mississippian Sappington Formation in Southwest Montana
Author: Aaron P. Rodriguez
Publisher:
Total Pages: 270
Release: 2014
Genre: Geology
ISBN:

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Hydrocarbon production success from the Bakken Formation of the Williston Basin has led to interest in time-equivalent Devonian-Mississippian strata. One of these Bakken-equivalent formations is the Sappington Formation of western Montana. This regionally 30 ft. to 120 ft. thick mixed carbonate and fine-grained siliciclastic unit occurs between thick Devonian and Mississippian carbonates and was deposited in the low-accommodation intracratonic Sappington Basin of the Central Montana Trough (CMT). Differential foreland subsidence and uplift of the CMT resulted in changing depocenter geometries. Despite the tectonic and paleogeographic differences between the Sappington Basin and the Williston Basin, the Sappington and Bakken share similar intracratonic depositional elements. This study focused on outcrop Sappington sections in the Three Forks, Montana area. Regionally, the Sappington pinches out to the south and northeast onto the paleogeographic highs of the Beartooth Shelf and Central Montana Uplift. To the west, correlation of Sappington and Antler Foreland Basin units have been complicated by Sevier and Laramide deformation. Within the Sappington Basin thinning and lateral facies relationships suggest significant early western accommodation of facies with potential for local proximal variations. Similar to the coeval Bakken Formation, the Sappington's three members (Lower, Middle, Upper) are separated by abrupt facies shifts and unconformities. The Lower and Upper Members both display black organic preservation during periods of quiescent anoxic bottom water conditions. Such conditions were driven by early Gondwanan glaciation producing widespread equatorial Late Devonian eustatic effects. The Middle Member is a well oxygenated mix of wave and tidal dominant energies located within the shoreface regime. The low-accommodation intracratonic character of the Sappington Basin complicates establishment of a sequence stratigraphic framework. Episodic flooding and draining of the Sappington Basin is represented by four prominent unconformities within a succession of rocks averaging 75 ft. in thickness and with a depositional timeline of ~8 million years. Subsequently, lowstand system tracts deposits are not observed in the study area and are represented by stacked sequence boundaries and transgressive surfaces.

Upper Devonian-Mississippian Stratigraphic Sequences in the Distal Antler Foreland of Western Utah and Adjoining Nevada

Upper Devonian-Mississippian Stratigraphic Sequences in the Distal Antler Foreland of Western Utah and Adjoining Nevada
Author: Norman John Silberling
Publisher:
Total Pages: 44
Release: 1995
Genre: Geology
ISBN:

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A multidisciplinary approach to research studies of sedimentary rocks and their constituents and the evolution of sedimentary basins, both ancient and modern.

Chemostratigraphy and Geochemical Constraints on the Depostion of the Bakken Formation, Williston Basin, Eastern Montana and Western North Dakota

Chemostratigraphy and Geochemical Constraints on the Depostion of the Bakken Formation, Williston Basin, Eastern Montana and Western North Dakota
Author: David Nyrup Maldonado
Publisher:
Total Pages:
Release: 2012
Genre:
ISBN:

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The late Devonian-early Mississippian Bakken Formation was deposited in a structural-sedimentary intracratonic basin that extends across a large part of modern day North Dakota, eastern Montana, and the southern portion of Canada's Saskatchewan Province. The deposition of the Bakken Formation occurred during a fascinating period of geologic time that is linked to one of the five major mass extinctions. The occurrences of these mass extinctions are recorded worldwide as organic rich mud rocks similar to the ones found in the Bakken Formation. Collectively, the Bakken Formation consists of a middle dolomitic siltstone that is representative of a transgressive deposit and is bound by regressive organic rich mud rocks deposits that were influenced by rapid flooding events induced by the late Devonian-early Mississippian seaway. Geochemical proxies, total organic carbon and stable isotopic results that were recovered from four cores provide insight into the paleoenvironmental conditions during the deposition of the Bakken Formation. Geochemical analysis and interpretation of sample suites exhibit aggregate mineralogical composition from related shifts in elemental concentrations in weight percent (wt. %) consisting of magnesium (Mg), calcium (Ca), silicon (Si), aluminum (Al) and iron (Fe). The occurrence of chemostratigraphic shifts from concentrations of the Bakken Formation's bulk rock mineralogical composition represent facies changes of sedimentary packages within the middle Bakken and are linked to dolomite, calcite, quartz, pyrite, and clay (mainly illite) content. Furthermore, geochemical proxies of redox sensitive elements expressed as enrichment factors (EF) brought insight into the redox conditions during deposition of the upper and lower Bakken shales across the Williston Basin (e.g., Mo, U, V, Zn, Ni, and Cu). Molybdenum-total organic carbon (Mo -TOC) relationships, established two separate anoxic episodes that are represented by the Bakken shales and also provided insight into the degree of basin restriction the Williston Basin experienced during late-Devonian-early Mississippian time. Observed geochemical Mo -TOC relationships from the Bakken shales display similar trends of basin restriction comparable to modern silled basin analogues, specifically the Cariaco Basin (Algeo et al. 2006). The elemental shifts from Mo -TOC vs. depth profiles, demonstrate that the Bakken shales were deposited under semi-restricted conditions. Furthermore, Mo -TOC relationships also inferred water mass residence times and variable hydrographic mixing from deep basin waters from the Williston Basin. TOC and stable isotopic composition of TOC ([delta]13C) from the Bakken shales were utilized as geochemical proxies to examine the change and distribution of organic matter across the Williston Basin. Lastly, stable isotopic composition of TOC results potentially demonstrate a blend of kerogen source formed from marine organic matter (plankton) and land-plant lipids based on previous studies.