Bow Area Research Articles

Upper Mannville Glauconitic"Channels, Little Bow Area, Alberta: Geologic Models for Seismic Exploration: ABSTRACT"

Upper Mannville Glauconitic"Channels, Little Bow Area, Alberta: Geologic Models for Seismic Exploration: ABSTRACT"

Morphology of hereditary mouse cataract

Histological changes of hereditary cataractous mice lens were studied by light and electron microscope. Until the sixth postnatal day the lens of the defective mouse appeared to develop normally. However, immediately after this period, the denucleation process of the lens cells appeared impaired. Another abnormality observed at this period is the swelling at the distal portion of the lens fibers in the deep posterior suture area of the perinuclear zones. In the bow area, the lens of 12–13-day-old mice the abnormal persistence of the nuclei becomes most apparent. In addition, the lens cells which had failed to show normal denucleation appear to become hydropic. Electron microscopic study revealed that the cytoplasm of the affected lens fibers contained coarse granular substance and many micro-organelles, which are absent in the normal lens fibers.

Precambrian Geochronology of the Medicine Bow Mountains, Southeastern Wyoming

The Medicine Bow Mountains of Wyoming are located in a transitional zone between the 2.5 b.y. old Superior Geochronologic Province to the north and the 1.3 to 1.7 b.y. old Central U.S. Geochronologic Province to the south. The mountains are crossed by a major northeast-trending shear zone, northwest of which is a quartzofeldspathic-gneiss complex that is intruded by the Baggot Rocks granite, by metagabbro, and by pegmatite. The complex is overlain nonconformably by more than 35,000 feet of miogeosynclinal metasedimentary rocks. Rb-Sr whole-rock isochrons indicate that the quartzofelds-pathic gneiss is 2410 ± 50 m.y. old, and the Baggot Rocks granite is 2340 ± 50 m.y. old. The metasedimentary rocks are at least 1550 ± 50 m.y. old, as indicated by a biotite Rb-Sr date, and are younger than 2410 ± 50 m.y. Whole-rock isochrons of 1550 ± 425 m.y. and 1650 ± 60 m.y. for two formations in the metasedimentary sequence may represent times of metamorphism but define at least minimum dates for sedimentation. Pegmatite intruding the gneiss complex is at least 1600 m.y. old; an anomalous initial Sr 87 /Sr 86 (0.745) permits the interpretation that the primary age is closer to 2400 m.y. Gneiss southeast of the shear zone is more calcic and mafic than that to the northwest, and it is intruded by metagabbro, pegmatite, foliated granite, and massive granite thought to be related to the Sherman Granite. The gneiss is unsuitable for direct dating because of low Rb/Sr ratios. Pegmatite yields mineral isochrons ranging from 1455 ± 40 to 1570 ± 40 m.y., and the Sherman-type granite yields a whole-rock isochron of 1335 ± 30 m.y. Analyzed whole-rock samples of foliated granite do not form a single isochron but show no evidence of being older than about 1715 m.y. No evidence has been found to indicate an age of 2.5 b.y. for rocks southeast of the major shear zone in the Medicine Bow Mountains, nor has any been found in nearby areas southeast of the projections of the shear zone. Rubidium-strontium mineral isochrons and individual mineral dates indicate one or more episodes of metamorphism in the Medicine Bow area between 1600 and 1455 ± 40 m.y. ago. We suggest that miogeosynclinal sedimentary rocks in the northern Medicine Bow Mountains, roughly correlative with Animikie and Huronian strata of Minnesota, Michigan, and Ontario, were deposited on the southern edge of a craton consisting of rocks mainly ≥ 2400 m.y. Gneiss of the southern Medicine Bow Mountains and gneiss and graywacke of the Front Range may be the more metamorphosed, eugeosynclinal counterparts of these sedimentary rocks which have been metamorphosed and transformed during the 1600 to 1455 m.y. old, or older, orogeny.

Development of Laramide Structure in Laramie Basin, Wyoming: ABSTRACT

The triangular Laramie basin lies between the Medicine Bow Mountains and the Laramie Range, and south of the Como Bluff fold. The stratigraphic column ranges in age from Pennsylvanian to Recent and is more than 15,000 feet thick. Hydrocarbons are produced commercially from fourteen fields and from six stratigraphic zones. The basin is asymmetric with a gently dipping east and southeast flank, a steeply folded and faulted west margin, and an indefinite northern boundary. Faulted northwest-trending folds interrupt the southern margin of the basin. Fault blocks in which Precambrian is exposed delimit the southwest margin of the basin south of Centennial. Faults bounding the blocks dip both east and west; individual blocks are elevated as much as 8,000 feet; and are bounded by fault complexes which might be anticipated in drilling. North of Centennial the basin is delimited by the Arlington thrust fault. The Centennial Valley syncline extends north-northwest parallel with the Rock River line of folding. Asymmetry of the anticline changes along strike from southwest at Seven Mile to northeast at Rock River. The Centennial syncline is in part overridden by the west-dipping Arlington thrust fault which dips 15° near Centennial and steepens to more than 45° near Arlington. The hanging wall plate is segmented by northeast-trending tear faults. Cooper Hill appears to be a gravity-emplaced klippe detached from the front of the thrust plate. The Laramie basin is segmented by the basinward extension of the Mullen Creek-Nash Fork shear zone in Precambrian rocks of the Medicine Bow Mountains. North of this zone the dominant feature is the Rock River line of folding and the Cooper Lake depression. Cross sections of the anticlines reveal a systematic pattern of internal deformation of the anticline, involving Triassic Chugwater and Cretaceous Niobrara and Frontier formations. The position of the major anticline was probably controlled by basement fracturing. Interference of three structural trends--Como Bluff (N. 30° E.), Seminoe fault zone (N. 65° W.), and Rock River (N. 20° W.) results in the complex of folds characterized by recurved fold axes near Medicine Bow. The mutual relationships between existent structural trends suggest that the first stage of development was broad crustal up-arching aligned north and south and probably extending to the base of the crust. The second stage developed along northeast-trending basement features and resulted in segmentation of the basement and in limits for the overthrusting. The third stage deformed the west margin of the basin either by faulting and folding (north half) or by development of fault blocks (south half). In this stage east-dipping faults appear to antedate west-dipping faults. The fourth stage involved complex reaction to compression in the Medicine Bow area, resulting in folds with variable orientation. Rocks correlated with the Hanna formation (Earliest Eocene) but not definitely dated rest with marked angular unconformity on the Cretaceous Medicine Bow formation. The Arlington thrust may be in part overlapped by the Hanna. Rocks of definite Wind River age are slightly folded. Rocks of Oligocene age are offset by normal faults. Younger Cenozoic deposits exist but have not been definitely dated. End_of_Article - Last_Page 115------------

Horne Bros. Unit Discovery, Medicine Bow Area, Carbon County, Wyoming: ABSTRACT

The Horne Brothers discovery well is located 3½ miles northeast of the Big Medicine Bow field, and 45 miles northwest of the town of Laramie. Surface reconnaissance originally led British-American to acquire acreage on this prospect in 1944. A seismic survey was conducted during the summers of 1948 and 1950. A unit area consisting of 2,280 acres was approved October 11, 1951, by the Department of Interior with British-American holding 78% as operator and Union Pacific Railroad holding 22% in all formations through the Sundance. Structurally, on the surface this is a southwest plunging nose with some indication of cross-faulting. The subsurface structure is little different, the nosing and faulting being confirmed. The fault is believed to be a comparatively low angle thrust, upthrown on the southwest. The discovery, located in the NW, SW, NW, Sec. 16, T. 21 N., 78 W., commenced drilling September 11 in the Mesaverde formation, and completed November 10, 1951, at the total depth of 6,656 in Chugwater. The producing formation is the basal sands of the Morrison, encountered at 5,179 feet. Two sand bodies, 6,179-6,199 and 6,225-6,230, indicate approximately twenty-two feet of effective sand. The well was put on production December 15, 1951, flowing initially 50 barrels of 35 gravity oil per hour through open casing. End_of_Article - Last_Page 967------------