The Glance Conglomerate, a Lower Cretaceous syntectonic deposit in southeastern Arizona
William L. Bilodeau
The middle Mesozoic tectonic environment of southeastern Arizona is poorly understood. Although recent regional syntheses by Drewes (1978) and Titley (1976) have added to our knowledge of the Mesozoic tectonic evolution of this region, much is still unclear. Titley (1976) recognized the presence of a major pre-Laramide, northwest-trending tectonic grain in southeastern Arizona and compiled evidence, primarily of an indirect nature, for vertical tectonic movements during the middle Mesozoic. The geologic structures that define this tectonic pattern are extremely discontinuous and obscure and require further investigation and documentation. Study of clastic sedimentary rocks deposited during this episode of crustal instability greatly clarifies the nature of these structural features and of the accompanying deformation. The most instructive clastic sedimentary deposit of middle Mesozoic age in the region is the Glance Conglomerate.
The Glance Conglomerate is a Lower Cretaceous alluvial fan deposit which provides a direct sedimentary record of extensive erosion associated with pronounced vertical displacements along various exposed and inferred normal faults. These relationships are especially well displayed in the southern Mule Mountains and in the Empire Mountains. In the Santa Rita Mountains, Drewes (1971, 1972) has also related the deposition of coarse conglomerate to Early Cretaceous normal faulting. The syntectonic nature of the Glance Conglomerate makes it a valuable key to understanding the mid Mesozoic tectonic environment of southeastern Arizona.
- Bilodeau, William L., 1978, The Glance Conglomerate, a Lower Cretaceous syntectonic deposit in southeastern Arizona, in: Land of Cochise, Callender, J. F.; Wilt, Jan C.; Clemons, R. E.; James, H. L., New Mexico Geological Society, Guidebook, 29th Field Conference, pp. 209-214.