Abstract

A two-dimensional photoelastic model constructed of Araldite and Hysol plastic is used to study how preferentially oriented microfractures originate in carbonate rocks. The model experiments suggest that orthogonal sets of microfractures should trend parallel to principal tectonic axes and that when diagenetic changes, such as dolomitization, are intense microfractures could be generated during both loading and unloading episodes in the history of a sedimentary basin.Petrographic observation of carbonates in the Turner Valley Formation illustrates the occurrence of microfractures. Laboratory tests demonstrate their preferred alignment in principal tectonic directions. Field measurement of joints in Turner Valley strata along Elbow River in southwest Alberta shows that the pattern of larger fractures can also consist of orthogonal fracture sets.The model experiments indicate therefore that development of preferentially oriented sets of microfractures in carbonates is probably a usual result of diagenetic and tectonic events that most of these rocks undergo during basinal evolution.

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