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.