Character, relative age and implications of fractures and other mesoscopic structures associated with detachment folds: an example from the Lisburne Group of the northeastern Brooks Range, Alaska

Abstract

Fractures and other mesoscopic structures formed at different times during the evolution of individual detachment folds in Lisburne Group carbonates of the northeastern Brooks Range. These structures provide clues to the mechanism of folding, the conditions under which folds evolved and the paragenesis of fractures in the fold-and-thrust belt as a whole. The earliest fractures strike NNW and probably represent orogen-normal extension fractures that developed in the foreland basin in advance of the fold-and-thrust belt. These rocks and fractures were later incorporated into the thrust belt, where they were thrust-faulted and folded. Later fractures, strained markers and dissolution cleavage developed during detachment folding as a result of flexural slip and homogeneous flattening. Fracturing associated with flexural slip occurred early in the development of folds. These early fractures were commonly overprinted or destroyed by ductile strain as later homogeneous flattening accommodated additional shortening. This penetrative strain was in turn overprinted by late extension fractures that formed during flexural slip in the waning phases of folding or after folding due to unroofing of the orogenic wedge.Early fracturing, overprinting by ductile structures and subsequent later fracturing in detachment-folded Lisburne Group emphasizes the importance of understanding the unique character and history of each fold-and-thrust belt in a successful hydrocarbon exploration effort. In particular, the mechanical stratigraphy and conditions of deformation play an important role in the type of fold that develops, the fold mechanisms that are active and the subsequent distribution and character of fractures and other mesoscopic structures. RÉSUMÉLes fractures et autres structures mésoscopiques se sont formées à différentes époques au cours de l'évolution de plis de décollements individuels dans le groupe des carbonates de Lisburne du nord-est de Brooks Range. Ces structures fournissent des indices sur le mécanisme de plissement, les conditions dans lesquelles les plis se développent et la

Evaluation of the Controls on Fracturing in Reservoir Rocks

“…Narr and Heffner, 2001;Silliphant et al, 2002). For example, Narr and Heffner (2001) found only a weak correlation between the density (surface area per rock volume) of some fracture sets and curvature, and no correlation between other fracture sets and curvature Distance (m) Cumulative number of joints (also see Engelder et al, 1997;Hanks et al, 2004). The example in Fig.…”

Neural Network Modeling with Sparse Datasets

“…It is also a well-documented fracture-controlled hydrocarbon reservoir in the subsurface north of the thrust front. The distribution and character of fractures in the Lisburne Group are controlled by a variety of factors, including carbonate lithology, bedding thickness, structural setting, and stratigraphic position (Hanks et al, 2004).…”

Understanding the Relationship between Large-Scale Fold Structures and Small-Scale Fracture Patterns: A Case Study from the Oman Mountains

“…Hanks et al [11], working within the detachment folds of the Lisburne Group in the Brooks Range, considered lithology as the primary control for the fracture density. Hanks et al [12] further added that the analysis of fold curvatures in the Lisburne Group is not a reliable method for predicting the density of fold-related fractures, and that fracture density data do not show a marked increase in fold hinges. The distribution of fractures within these folds suggests a strong relationship with flexural slip folding and penetrative strain [12].…”

“…Hanks et al [12] further added that the analysis of fold curvatures in the Lisburne Group is not a reliable method for predicting the density of fold-related fractures, and that fracture density data do not show a marked increase in fold hinges. The distribution of fractures within these folds suggests a strong relationship with flexural slip folding and penetrative strain [12]. In contrast, the authors of [13][14][15] presented a model in which fracture density was predicted based on the fold curvature, regardless of the type of folding.…”

“…Regional fractures are formed during the early stages of layer-parallel shortening. They are oriented orthogonally to beddings and usually trend perpendicularly and less-commonly parallel to the fold axis [10,12,16]. Local fold-related fractures exhibit a more complex relationship.…”