Evaluating the quality of bed length and area balance in 2D structural restorations

Abstract

The use of structural restorations as a tool to investigate structural evolution, fault and horizon relationships, and validity of interpretation has been widespread for more than four decades. The first efforts relied on hand-drafted bed-length measurements of commonly constant thickness stratigraphic units and were typically applied to fold-and-thrust belt settings. The advent of computer-assisted section construction and restoration software allowed for the assessment of more complicated structural interpretations by applying several new methods for forward and inverse strain transformation. Although quicker and more accurate than hand-drafted, the results of computer-aided structural modeling still need to be interrogated. We have reviewed the different strain transformation (restoration) methods available and their implications for bed length and area conservation: (1) fundamental simple shear and its two basic modes (flexural slip and inclined shear inversions), (2) fault-related folding techniques, and (3) the effects of mechanical stratigraphy and compaction. The assessment of the restoration methods was illustrated by examining two examples: the Mount Crandell Duplex Structure in southern Alberta and the Virgin River Extensional Basin in the southeast of Nevada. For both examples, we developed tables listing and confirming the deformed/restored state line lengths and areas. We believe that such tables should be provided for any strain transformation exercise, along with the restoration results as parameters for quality control, to prevent over- and underestimations that deviate more than 5% from the initial interpretation.

Strain analysis of a seismically imaged mass‐transport complex, offshore Uruguay

“…does the section balance and preserve rock volume, thickness, length, etc.) and to quantify strain distribution within the MTC (Dahlstrom, 1969;Hossack, 1979;Lingrey & Vidal-Royo, 2015). The MTC studied here is defined by packages of chaotic reflections (e.g.…”

“…To help mitigate these effects, we orientated the sections parallel to the dominant MTC transport direction through identification of kinematic indicators such as lateral margins (Figure 3a). Due to the component of ductile strain within MTCs, simple shear and flexural slip methods have also been tested and compared with the line-length approach to quantify model sensitivities (Lingrey & Vidal-Royo, 2015). Before calculating longitudinal strain, the MTC was decompacted to remove the effects of volume decrease driven by burial-related porosity reduction.…”

Workflow: From photo-based 3-D reconstruction of remotely piloted aircraft images to a 3-D geological model

“…Deformation within the 2-D sections is then restored, which includes faulting and folding. The areas of the stratigraphic layers and the line lengths of the layer contacts should remain constant between the final deformed section and the initial, undeformed section to create a balanced 2-D cross-section (Dahlstrom, 1969;Lingrey and Vidal-Royo, 2015). If the section cannot be balanced and there is no known geological reason to explain why (e.g., non-plane strain, erosion, or variation in bed thickness), the subsurface geology needs to be reinterpreted until it is balanced.…”

What is Trishear?

“…These first-order unknowns have important implications for how we structurally restore extensional forced-folds (cf. Lingrey and Vidal-Royo, 2015), and for our understanding of what key geological parameters controls fold geometry through time and, therefore, where such structures may best develop (cf. Allmendinger, 1998;Ford et al, 2007;Conneally et al, 2017).…”