Dakota outcrop geology and sequence stratigraphy, Chama Basin, New Mexico

Abstract

—The Dakota Formation of the Chama Basin records the initial incursion of the Western Interior Seaway into the study area. Dakota outcrops on US Highway 84, northwest of the Ghost Ranch, and at Heron Dam, south of Chama, New Mexico correlate with each other and with well logs located 19 and 44 miles (30.4 and 70.4 km) to the west based on comparison with outcrop gamma-ray logs. The outcrops contain three Dakota depositional sequences defined by unconformities. One of the sequence-bounding surfaces within the formation, S3, truncates and replaces the K2 unconformity between Lower and Upper Cretaceous units and, thus, has regional importance. Sequence stratigraphic variations in the Dakota have economic significance because they may control fluid distribution in the subsurface. FIGURE 1. Index map showing the two outcrop locations discussed in this paper and their relationship to Chama, Abiquiu Lake and the Ghost