Geologic framework of the ground-water system in Jurassic and Cretaceous rocks in the Northern Great Plains, in parts of Montana, North Dakota, South Dakota, and Wyoming

Mineral resources of the Seven Blackfoot Wilderness Study Area, Garfield County, Montana

“…Fold axes and faults ( fig. 5) trending to the northeast may be related to regional lineaments similar to those mapped and described by Anna (1986) and Thomas (1974).…”

“…Stoner and Lewis (1980). Approximate locations of lineaments from Anna (1986). Axis of Coburg syncline queried where uncertain (based on gravity data).…”

“…6) suggest that the Coburg syncline may extend into and terminate in the vicinity of the study area. Anna (1986) mapped a prominent lineament ( fig. 4) based on the geometry of subsurface sedimentary rocks.…”

“…Thomas (1974) suggested that such lineaments are the result of a Laramide lateral adjustment of basement blocks along Precambrian shear zones, and that the resulting block framework has affected the regional migration and accumulation of mineralizing solutions, oil, and gas. Anna (1986) cites evidence that Precambrian structural movement along the Precambrian shear zones probably continued into Jurassic and Cretaceous time, was enhanced by the Laramide orogeny, and that the resulting structural systems have influenced the depositional systems and geometry of sediment accumulation during Jurassic and Cretaceous time. Frahme (1979) suggested that Tertiary intrusive and extrusive activity has occurred along similar lineaments located south and west of the Charles M. Russell National Wildlife Refuge.…”

“…Gravity and magnetic data are described by Zietz and others (1968) and the Bendix Field Engineering Corporation (1983). Regional lineaments related to Precambrian shear zones are mapped and described by Thomas (1974) and Anna (1986).…”