Distributed normal faults in the Niobrara Chalk and Pierre Shale of the central Great Plains of the United States

Abstract

Normal faults occur in the Niobrara Chalk and Pierre Shale in numerous localities in South Dakota, Nebraska, and Kansas. Lakeshore outcrops provide a window into strata that otherwise outcrop poorly. Various criteria were used to distinguish mass-wasting features from faults that formed at the subsurface. Locally, these faults have variable orientations and throws that vary from centimeters to tens of meters. In the Niobrara Chalk, the fault zones typically display well-developed striae, occasional slickensides, limited to absent damage zones, and dilational jogs with coarse, microvein calcite fill. In places, the faults are associated with gentle monoclines and folds, but elsewhere they occur in horizontal strata. A weathering bias suggests these faults are more common than observed. At any one locality, these faults have been or could be attributed to local tectonism, differential compaction, and/or glacial rebound. If due to tectonism, taken in aggregate, they indicate fairly widespread (albeit low-strain) activity, which is consistent with the idea of a critically stressed continental interior with migrating sites of faulting. An alternate and preferred hypothesis is that these are polygonal faults due to diagenetically driven deformation in fine-grained mud rocks. Subsurface polygonal fault systems have been described from the Niobrara Chalk and Pierre Shale in the Denver-Julesburg Basin area in eastern Colorado. Smectitic clays, associated with polygonal faulting elsewhere, are abundant in these units. The fault kinematics (extension in multiple directions), widespread character, and other traits are consistent with an origin by diagenetically driven deformation.

Siting Deep Boreholes for Disposal of Radioactive Waste: Consequences for Tight Coupling between Natural and Engineered Systems

“…In western Nebraska, groundwater salinity in the Dakota aquifer (TDS ≈ 30 g/L) has been attributed to mixing between modern meteoric water and upwelling ancient seawater, transported from the Pennsylanian carbonate strata through regional faults . These faults, not provided by Condra et al (1940), were identified in more recent cross sections (e.g., Figure b) and are common in fine-grained sedimentary successions here and elsewhere (section ). Hydrogeochemical data for the Carlile formation is sparse, but these faults likely influence fluid flow through the shale and represent a potential path of advective radionuclide transport from a lateral disposal hole to one of the aquifers.…”

“…Cartwright (1997) suggested that polygonal fault systems, characterized by faults with throws ranging from 10 to 100 m spaced 100–1000 m apart, can develop on a basin-wide scale during the compaction process . Pervasive fault and fracture permeability, created through this process, might explain anomalously high hydraulic conductivities in certain argillaceous formations, such as the Pierre Shale (section ), which in South Dakota exhibits a field-scale hydraulic conductivity in excess the matrix permeability by 3 orders of magnitude . More recent studies have identified polygonal fault systems in strata as deep as ∼3 km throughout the Great Plains region of North America and other major sedimentary basins throughout the world …”

Secondary rock structures and the regional hydrogeology of claystone-rich cretaceous strata, Williston Basin, Saskatchewan, Canada

“…The areal extent was estimated by calculating the area found between our three sites and other locations of a known PFS in corresponding units of the Colorado Group (e.g., Niobrara Fm) and the Pierre Fm to the south in the USA. Maher (2014) (Fig. 9).…”

Resolved stress analysis, failure mode, and fault-controlled fluid conduits

“…Permeability behaviorflow pathway versus seal -can be directly related to the deformation modes along a fault, fracture, or fracture network (Carlsson and Olsson, 1979;Sibson, 1996Sibson, , 1998Sibson, , 2000Sibson, , 2003Trippetta et al, 2017;Ferrill et al, 2019a). In any applied stress field, multiple deformation features may form coevally, with failure initiation occurring at varying orientations and in different failure modes (e.g., Hancock, 1985;Lee et al, 1997;Lee and Wiltschko, 2000;Ferrill and Morris, 2003;Schöpfer et al, 2006;Busetti et al, 2014;Maher, 2014;Smart et al, 2014;Douma et al, 2019;Boersma et al, 2020). Deformation behavior, in particular positive or negative dilation versus shear, is closely related to the orientation of the failure plane or zone with respect to the stress field at the time of deformation (e.g., Ramsey and Chester, 2004;Ferrill et al, 2017b).…”