Precambrian Rocks and their Relationship to Laramide Structure along the East Flank of the Bighorn Mountains near Buffalo, Wyoming

Laramide structures and basement block faulting: Two examples from the Big Horn Mountains, Wyoming

“…Hudson's main purpose was to evaluate the nature and extent of Precambrian control during Laramide deformation in the Piney Creek area (1969, p. 284), but his data on joints in Precambrian and Paleozoic rocks led him to conclude that a conjugate shear joint system and associated maximum principal stress oriented N52°E-S52°W represent early Laramide compressive deformation (p. 287). Other workers have established the existence of thrusting along the east flank of the central Big Horns structural segment (Bucher and others, 1934;Demorest, 1941;Hoppin, 1961), so the explanation of the Piney Creek lobe as a thrust block on July 7, 2015 memoirs.gsapubs.org Downloaded from appears to be consistent with these studies. Strike-slip movement would be one way to explain the lateral separation of the mountain front.…”

“…Even though the basement was described as deforming en bloc, cross sections were drawn (1967, PI. 2) with the basement surface bending smoothly and conformably with the overlying bedding. Hoppin (1970), p. 2410) suggested that the difficulty of finding definitive exposures is the reason for this widespread practice. In any case, revised cross sections that obey the axiom of "do not fold the basement" (Stearns, 1975, p. 150) are given as conjectural representations of the Horn structures-interpretations that are consistent with the field data and with current ideas about the mechanical properties of the basement and its sedimentary veneer.…”

“…Stearns (1975) rotation of basement blocks, particularly for Rattlesnake Mountain where distributive shear can be disproved. Hoppin (1970) demonstrated that pervasive shearing permitted rotation of adjacent basement blocks in the Five Springs Creek area of the Big Horn Mountains. In the Horn, the adjacent blocks are the east flank of the southern Big Horns and the east dipping Horn block.…”

Die Entstehung von Plumose-Kluftflächenmarkierungen und ihre tektonische Interpretation

“…Kliiftung mit Plumose-Strukturen kann einer bereits sehr fri,ih angelegten Gesteinsanisotropie folgen und zu Fehlschliissen bez[iglich der Orientierung der Hauptspannungsrichtungen nach den bekannten Kriterien fiir isotrope Medien ffihren (vergl. auch Pt~IcE (1975, 64ff) HOPPIN (1958), SP~NCEt~ (1959), WISE (1959, GP, IGGS & HANDIN (1960), Bt<ACE (1964 …”

Geology of Black Mountain Quadrangle: Bighorn County, Wyoming

“…Lehman (1975) reports an orthogonal NW-NE near vertical set of Precambrian joints which correlates to those found in the sedimentary strata. A subhorizontal set of joints is also present, which Hoppin (1961) attributed to relict sheeting resulting from unloading. Hoppin and Palmquist (1965) report that the most common joint trend that occurs in the Bighorns is N 10-15 0 E associated with Precambrian shear foliation.…”