Abstract

Opening-mode fractures present in exposures of the Triassic El Alamar Formation in northeastern Mexico show size scaling, spatial arrangement, and fracture-filling cement patterns similar to fractures present in cores retrieved from tight gas sandstone reservoirs. The El Alamar Formation fractures contain abundant quartz cement that was deposited while the fractures were opening. We measured homogenization temperatures from aqueous fluid inclusions in these synkinematic cements. By combining these measurements with quartz cement mapping, crosscutting field relationships, and published regional burial history constraints, we are able to relate fracturing with the previously established regional tectonic framework. Our results indicate that fractures opened during and after maximum burial, and that fractures visible in outcrop and fractures having minute (<0.1 mm) opening displacements opened during the same interval. Comparison of two distinct crosscutting fracture sets indicates fracture intensity and size vary by orientation and opening history, with earlier fractures forming under hotter conditions and reaching larger aperture sizes.