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Age and structural significance of ophiolite and adjoining rocks in the upper Chulitna District, south-central Alaska
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Early Triassic (Smithian) ammonites of paleoequatorial affinity from the Chulitna terrane, south-central Alaska
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Thermal modeling of flow in the San Diego Aqueduct, California, and its relation to evaporation
The thermal balance of the 26-kilometer long concrete-lined San Diego Aqueduct, a canal in southern California, was studied to determine the coefficients in a Dalton type evaporation formula. Meteorologic and hydraulic variables, as well as water temperature, were monitored continuously for a 1-year period. A thermal model was calibrated by use of data obtained during a 28-day period to determine the coefficients which best described the thermal balance of the canal. The coefficients applicable to the San Diego Aqueduct are similar to those commonly obtained from lake evaporation studies except that a greater evaporation at low windspeeds is indicated. The model was verified by use of data obtained during 113 days which did not include the calibration data. These data verified that the derived wind function realistically represents the canal evaporation. An annual evaporation of 2.08 meters was computed which is about 91 percent of the amount of water evaporated annually from nearby class A evaporation pans. (Kosco-USGS)
The Vermilion Granitic Complex — A new name for old rocks in northern Minnesota
The name Vermilion Granitic Complex is introduced for the heterogeneous granitic and migmatitic rocks of Archean (formerly called Precambrian W) age that occur north of the Vermilion district and south of the Kabetogama peninsula in northern Minnesota. The complex consists of the following subdivisions: Lac La Croix Granite, granite-rich migmatite, schist-rich migmatite, quartz-feldspar gneiss, hornblende quartz diorite and diorite, granodiorite and trondhjemite, amphibolite and amphibolite migmatite, older migmatite, biotite schist, Burntside Gneiss, and pegmatite. Because the name Vermilion Granitic Complex is proposed as a more inclusive group term, the more restricted name Vermilion Granite (Grout, 1923) is hereby abandoned. The new name Lac La Croix Granite is proposed for the uniform, light-pink biotite granite that occurs widely in the eastern and central parts of the complex. It is denned as having less than 5 percent of schistose or gneissic inclusions and is therefore more restricted than the Vermilion Granite of Grout (1926), which included substantial amounts of migmatitic rocks. The name Burntside Gneiss is adopted as a replacement for the older term Burntside Granite Gneiss, originally named by Grout (1926). This change is required by the conclusion that the rock is a metamorphosed dacite and not a metamorphosed granite, as formerly interpreted.
Potassium-argon ages from the Mount Taylor Volcanic Field, New Mexico
Fourteen new K-Ar dates for volcanic rocks of the Mount Taylor field, New Mexico, indicate that most activity occurred between 4.3 and 1.5 m.y. (million years) ago. Peak activity was at about 3.0-2.5 m.y., both on the central andesite-rhyolite shield volcano and on the surrounding alkali basalt-trachyte volcanic plateau, and occurred concurrently with an episode of NNE-trending basin-range faulting. The K-Ar dates also indicate that the regional Ortiz pediment surface, graded to the ancestral Rio Grande, existed in the Mount Taylor area as recently as 3 m.y. ago and that 250-400 m of erosional downcutting has occurred in subsequent time. Growth of the Mount Taylor field was also concurrent with peak volcanic activity along the northeast-trending Springerville-Raton zone, a major late Cenozoic volcanic belt that is considered to reflect the presence of a regional structural discontinuity of Precambrian age in the North American craton.
Crystals of coexisting alunite and jarosite, Goldfield, Nevada
Alunite (KAl 3 (SO 4 ) 2 (OH) 6 ) and jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ) coexist in optically continuous crystals in a sample from the Goldfield mining district, Esmeralda County, Nev. Beam scans with an electron microprobe indicate that no intermediate minerals of the solid-solution series alunite-jarosite occur in these crystals. An Eh-pH diagram demonstrating the equilibrium relations between alunite, jarosite, and geothite suggests the crystals most likely developed by a rise in Eh, which oxidized ferrous to ferric iron, thus allowing jarosite to precipitate.
Zeolitization of Tertiary tuffs in lacustrine and alluvial deposits in the Ray-San Manuel area, Final and Gila Counties, Arizona
Specimens of tuff in the Ray-San Manuel area, southeastern Arizona, have been X-rayed to determine the present approximate mineralogic composition and the type and degree of alteration of the tuffs. Some of the tuffs consist largely of glass or have been partly or completely altered to calcium montmorillonite; many of them have been almost completely zeolitized or contain a zeolite and some clay. Only three zeolitized specimens contain a little glass. With four exceptions, the zeolitie is clinoptilolite; the exceptions are one altered to chabazite, one to mordenite, one to erionite, and one to erionite, clinoptilolite, and chabazite. The tuffs are mostly of airfall origin and of rhyolitic or probable rhyolitic composition and generally contain negligible percentages of crystal and lithic fragments. Two specimens are tuffaceous sedimentary rocks, and two are ash-flow tuffs. The tuffs range in age from early Pliocene or late Miocene to Oligocene. Some were deposited in lacustrine or playa environments; others were deposited in freshwater alluvial environments. All the beds examined in the lower Miocene and older formations have been zeolitized. Zeolitization of beds in younger formations depends on the environment of deposition. Zeolitized tuffs that contain at least 80 percent zeolite and are in beds more than one-third meter thick are considered potentially minable.
Drake Peak — A structurally complex rhyolite center in southeastern Oregon
The Drake Peak volcanic center of middle Miocene age, located about 25 km northeast of Lakeview, Oreg., is a structurally complex eruptive center that resulted from several episodes of intrusion and extrusion of rhyolite. Two thousand meters of andesite and basalt flows, lahars, and volcaniclastic rocks of late Eocene age, and of basaltic andesite, tuff, and flood basalts of Eocene to middle Miocene age were structurally domed by the piston-like intrusion of a large body of rhyolite. The eruption of rhyolite flows at 14.3±2 million years followed the structural doming, and upper Miocene tuffs and basalt flows lapped against the dome and the rhyolite. A felsitic rhyolite ring intrusion 3 km in diameter, emplaced during the doming, is now exposed in the deeply eroded core of the dome. The rhyolites range in Si02 content from 69 to 76 percent and are peraluminous. The nonporphyritic ring intrusion is more silicic than the flows erupted later, which contain up to 23 percent phenocrysts of plagioclase, hypersthene, biotite, clinopyroxene, and quartz. The progressive depletion of Mg, Ca, Sr, Fe, Ti, and Al and the enrichment in silicon and rubidium are compatible with the generation of the observed rhyolite types by tapping a compositionally zoned magma chamber.
Palladium, platinum, and rhodium concentrations in mafic and ultramafic rocks from the Zhob Valley and Dargai complexes, Pakistan
The Zhob Valley and Dargai complexes, Pakistan, consist of harzburgite and dunite tectonites containing chromite deposits, pyroxenite, wehrlite, and gabbro. Both are ophiolite complexes. Palladium, platinum, and rhodium were found in concentrations of up to 170, 200, and 22 parts per billion, respectively. Average concentrations for both complexes and all rock types collected are 28 ppb palladium, 33 ppb platinum, and 9 ppb rhodium. The Pt:Pt+Pd ranges from 0.41 to 0.67 and averages 0.57. The concentration levels and ratios of these metals are similar to other alpine ultramafic bodies that have been analyzed by modern techniques.
Shorter contributions to stratigraphy and structural geology, 1979
PART A: A system of anticlines lies along the trend of the sinuous course of the Colorado River for a distance of 97 km in the central Grand Canyon. Similar anticlines occur in some perennially wet side canyons. The anticlines are most abundant and well developed along northeast-trending reaches of the main canyon where it is floored by the Cambrian Muav Limestone. Dips of the folded strata are as great as 60?, and the folding locally extends more than 250 m from the river. Low-angle thrust faults in the limbs of the anticlines parallel the river and have formed in response to folding of the comparatively brittle carbonate strata. High-angle reverse kink bands, along which rocks are displaced up toward the river, also parallel the anticlines and have develop2d in response to the upward bulging of the canyon floor. The river anticlines are an unloading phenomenon. They result from lateral squeezing toward the river of saturated shaly parts of the Muav Limestone and underlying Bright Angel Shale. The driving mechanism for the deformation is a stress gradient that results from a difference in lithostatic load between the heavily loaded rocks under the 650-m-high canyon walls and the unloaded canyon floor. Saturation appears to weaken the shaly rocks sufficiently to allow deformation to take place. River anticlines are not present in the eastern Grand Canyon, where the Cambrian rocks also occur at river level. Their absence is explained by a lack of shaly rocks that could flow when saturated. PART B: The current interest in contemporary tectonic processes in the Eastern United States is turning up abundant evidence of crustal movements in late geologic time. Topographic analysis of the highland areas from the southern Blue Ridge to the Adirondack Mountains indicates that most of the landforms owe their origin to erosion of rocks of different resistance rather than to tectonic processes. Most areas of high relief and high altitude have been formed on resistant rocks. The Cambrian and Ordovician belt, containing mostly shale and carbonate rock, on the other hand, forms an extensive lowland from Alabama to the Canadian border and girdles the Adirondack Mountains. Differences in altitude can be explained by the presence of resistant rocks outside the belt; these resistant rocks form local base levels on the streams that drain the belt. A few areas may have undergone local uplift at a higher rate than areas nearby--for example, the Piedmont region northwest of Chesapeake Bay. Most estimates of erosion rates, based on the load transported by streams and of uplift rates, based on removal during a known period of time, are of the same order of magnitude, averaging almost 4x 10^-2 millimeters per year. Rates of uplift, based on study of tilted Pleistocene beaches and repeated geodetic traverses, are at least an order of magnitude higher for comparable areas. Tectonic uplift of the highlands has been slow and involves mostly warping or tilting on a large scale. Erosion rates keep up with or exceed the rate of uplift and have been sufficient to mask evidence of faulting or other differential movements. The high rates of uplift that are inferred on tilted water planes in the glaciated regions or that are measured by differences in repeated geodetic traverses cannot have been sustained for long periods of time. PART C: The Hanson Creek Formation southwest of Eureka, Nev., in the Bellevue Peak Quadrangle is composed of three lithostratigraphic members: (1) a basal dark-gray dolomite, (2) a middle silty thin- to thick-bedded, locally nodular, dark-gray, light-yellow-mottled limestone topped by light-gray dolomite, and (3) an upper dark-gray dolomite, which is herein named the Combs Canyon Dolomite Member. Detailed geologic mapping and accompanying fossil collecting prove that the same lithostratigraphic and biostratigraphic sequence is present in the Mountain Boy Range and 11 km to the south near Wood Cone Peak. Minor differences in
Late Cenozoic deposits, landforms, stratigraphy, and tectonism in Kittitas Valley, Washington
Kittitas Valley, a structurally determined wide segment of the Yakima River valley, is partly filled with the Pliocene Thorp Gravel and with Pleistocene till, outwash, and related sediment that accumulated during three glaciations. The Thorp Gravel, whose age according to fission-track dating is about 3.7 m.y., forms a conspicuous fill terrace locally as high as 130 m. Bodies of drift, all younger than the Thorp Gravel, form nested fill terraces along the Yakima River. The massive moraines, intermediate morphostratigraphic position, and well-developed soil of the Kittitas Drift suggest its correlation with the penultimate northern-hemisphere glaciation of about 0.13 m.y. ago. The Lakedale Drift, which composes a single outwash terrace in Kittitas Valley, evidently correlates with the classical late Wisconsin Glaciation. The newly named Lookout Mountain Ranch Drift, which forms moraines at higher altitudes than and is older than the Kittitas Drift, lacks an attendant valley train. Three faults disrupt the Thorp Gravel but apparently not the Kittitas Drift, and therefore probably are between 0.13 and 3.7 m.y. old. The eastward trend and up-to-the-basin throw of the faults probably reflect reverse faulting due to a regional north-south compression that uparched several east-trending anticlines in central Washington. The southeast trend of the dextrally echelon arrangement of the faults apparently is due to a right-lateral couple across a zone parallel to the Olympic-Wallowa lineament.
A systematic revision of the ostracode species described by Ulrich and Bassler and by Malkin from the Chesapeake Group in Maryland and Virginia
Those ostracode species described by Ulrich and Bassler (1904) and Malkin (1953) from the Chesapeake Group of early Miocene to early Pleistocene age are treated systematically. Lectotypes are designated for all species which have syntypic suites and the lectotypes, holotypes, or hypotypes for all but two species are illustrated. A new genus Otikocythere is proposed, with Cythere punctistriata Ulrich and Bassler 1904 as the type species. A new species, Hulingsina calvertensis, is also proposed. All of the species are placed in an updated biostratigraphic framework.
Iron-depositing bacteria and their geologic relations
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