Geology of the Small Horn Canyon, Daly's Spur, Cedar Creek, and Dell areas, southwestern Montana

Abstract

During the summers of 19^6 and 19*4-7 several areas in southwestern Montana were investigated to determine the area! extent and structure of the Phosphoria and adjacent formations as well as the quality and thickness of the phosphate "beds in the Phosphoria formation. This work is part of a study of the phosphate deposits of southwestern Montana which is one phase of a program "by the. Department of the Interior to investigate the natural resources of the Missouri River Basin. The geology of the Small Horn Canyon, Daly*s Spur, and Cedar Creek areas (pi. l), and of the Dell area (pi. 2) was mapped in as much detail as the aerial photographs permitted; the geology of some intervening areas was mapped by reconnaissance. In the area west of Daly's Spur and U. S. Highway No. 91, the geology was mapped "by plane table and aerial photographs, section corners being used as control points. Topography was not mapped. Previous geologic investigations of the Phosphoria formation of this area were undertaken "by C. F. Bowen, I/; D. D. Condit, 2/; and A

Geologic implications of data from the American Quasar 27k-22 Hagenbarth drillhole, Beaverhead County, Montana

“…(Bordenave and others, 1993, p. 251). PI (table 2), the production index, is the 8,7(8,+ S2) ratio, which increases mainly due to cracking of the kerogen (Bordenave and others, 1993, p. 252 (table 1) is estimated to have been originally slightly more than 840 ft thick, close to the 700-800 ft thickness given by Lowell (1949). On the surface, in the Blacktail Mountains to the south, the entire Triassic section is placed in the Dinwoody Formation (Pecora, 1981).…”

“…Dip magnitudes decrease from 7,770 to 7,774 ft from 45°NE to 42°NNE in a tight group of three; next reading is @ 7,790 ft: 23°N, followed by 13°NE @ 7,792 and 18°N @ 7,796 and 7,798 ft. (table 1), are based primarily on my interpretation of the borehole compensated sonic and gamma ray (BHC/GR) log, in conjunction with the compensated neutron-formation density (FDC/CNL) log and log of lithology of returned drill cuttings, commonly known as a mudlog. These data were then compared with those of other drillholes from southwest Montana (Perry and others, 1981;Perry, 1986) as well as descriptions of stratigraphic units by Lowell (1949Lowell ( , 1963, Pecora (1981), and Hildreth (1981). I calculated formation thickness from drilled intervals, picked on the BHC/GR log, on the basis of publicly released dipmeter arrow plots (dip azimuth vs. dip magnitude) for the drill-hole interval 1,002 to 7,918 ft.…”

Geologic and fission-track evidence for Late Cretaceous faulting and mineralization, northeastern flank of Blacktail Mountains, southwestern Montana

“…The mixed-clast conglomerate of the Beaverhead in the northwestern part of the Blacktail Mountains was first mapped by Lowell (1949) and O'Connor (1949) and later by Achuff (1981a, b), Pecora (1981Pecora ( , 1987, and Tysdal (1988a). Both it and the older limestone-clast conglomerate (which lacks Belt clasts) are deformed within the Jake Canyon fault system near the mouth of Small Horn Canyon (locality A, fig.…”