Throughgoing fractures in layered carbonate rocks

Abstract

Fracture surveys were conducted across a broad anticline in southern Israel in order to investigate the development and geometries of throughgoing fractures in layered carbonate rocks. At Halukim anticline, throughgoing fractures form by the linkage and coalescence of preexisting, bed-confined joints. Thus the internal morphology of these structures is highly segmented, often consisting of vertically aligned zones of subparallel fractures and bed partings linked together across the stratigraphy. The large population (n = 132) of throughgoing fractures represents a continuum of structures at various stages of development that can be classified into three main geometric categories corresponding to increasing levels of brittle strain: incipient, linked, and linked with aperture. Despite the wide variety of internal morphologies and geometries, the throughgoing fractures display a consistent east-northeast–west-southwest orientation, parallel to a set of bed- confined cross joints. The spatial distribution of throughgoing fractures varies as a function of structural position, the highest frequency and estimated strain intensity being located at the fold crest. Results suggest that throughgoing fractures develop only after a critical level of strain is achieved, as quantified by the density of bed-confined joints. Throughgoing fractures are multilayer structures that may greatly enhance the connectivity of a fracture network; therefore, understanding their formation, geometry, and distribution may contribute to efforts of flow modeling in fractured carbonate rocks.