Regional tectonics and fracture patterns in the Fall River Formation (Lower Cretaceous) around the Black Hills foreland uplift, western South Dakota and northeastern Wyoming
Published:January 01, 1999
John L. Wicks, Stuart L. Dean, Byron R. Kulander, 1999. "Regional tectonics and fracture patterns in the Fall River Formation (Lower Cretaceous) around the Black Hills foreland uplift, western South Dakota and northeastern Wyoming", Forced Folds and Fractures, John W. Cosgrove, Mohammed S. Ameen
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The Fall River Formation around the Black Hills uplift is pervasively fractured by layer-perpendicular joints. Systematic joints in the formation maintain consistent orientations over large areas and are commonly abutted by later-formed fractures, resulting in an orthogonal pattern. There are two major systematic sets, trending northeast and northwest, and one minor set trending north-south. The first two sets define two major fracture domains in the study area. The northwest joint set occupies a southern domain where it is the sole systematic fracture set. The northeast joint set is pervasively established throughout the northern domain, where northwest and north-south fracture sets are also developed in well-defined sectors. There is no genetic or spatial relationship between joint sets and local Laramide monoclines or folds of the region. Instead, the stratigraphic record indicates that joint development originated early in the lithification history of Fall River sandstones. Jointing occurred in response to local and regional extensional stresses that pervaded the northern and southern domains as a result of recurrent movement on basement faults that parallel the regional lineament system and surface structural zones throughout the region. Major uplift of the Black Hills and local fold development during Laramide time merely resulted in passive rotation of the early formed systematic and non-systematic joints.
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Forced Folds and Fractures
This volume is concerned with defining the major similarities and difference between forced folds and buckle folds in order that these differences can be used to recognize the type of folding (and therefore the expected fracture pattern) present in regions of poor exposure or where the geologist has to rely on seismic images. An understanding of the differences between the two fold types (their 3D geometry, spatial organization, fracture patterns etc.) provides an invaluable tool for Earth scientists concerned with assessing the possible role of folds and their associated fracture patterns in controlling fluid migration and concentration within the crust.
The papers presented here are grouped into 4 sections. Contributions in the first section describe the use of numerical analyses to investigate the formation of fractures in forced folds, including compaction folds, and the section contains a description of large-scale compaction folding in which the associated fracturing has given rise to the development of large sandstone dykes. The papers in the second section deal with the formation of forced folds as a result of normal faulting in various geological environments including along a classical graben margin and around a resurgent caldera. The third section contains papers relating to forced folding in compressional and strike-slip regimes. The final section considers the temporal and spatial relationships between forced folds and buckle folds, the formation of crustal-scale folds, and a method of determining the distribution of strain on any folded surface, a key parameter controlling the distribution of fractures.