Pb and Sr systematics of ultrapotassic and basaltic rocks from the central Sierra Nevada,California

This study presents Sr and Pb isotopic ratios and Rb, Sr, U, Th, and Pb concentrations of an ultrapotassic basaltic suite and related rocks from the central Sierra Nevada, California. The ultrapotassic suite yields a narrow range of Sr and Pb isotopic compositions (⁸⁷Sr/⁸⁶Sr=0.70597–0.70653; ²⁰⁶Pb/ ²⁰⁴Pb=18.862–19.018; ²⁰⁷Pb/²⁰⁴Pb=15.640–15.686; ²⁰⁸Pb/ ²⁰⁴Pb=38.833–38.950). Associated basalts containing ultramafic nodules have less radiogenic Sr (⁸⁷Sr/⁸⁶=0.70430–0.70521) and generally higher Rb/Sr ratios than the ultrapotassic suite. Leucitites from Deep Springs Valley, California, contain high ⁸⁷Sr/⁸⁶Sr (71141–0.71240) and low ²⁰⁶Pb/²⁰⁴Pb (17.169–17.234) ratios, reflecting contamination by crustal granulite.The isotopic relationships support an origin of the ultrapotassic basaltic suite by partial melting of an enriched upper mantle source. Dehydration of a gently inclined oceanic slab beneath the Sierra Nevada may have provided Ba, K, Rb, Sr, and H₂O, which migrated into the overlying upper mantle lithosphere. The end of subduction 10 m.y. ago allowed increased asthenospheric heat flow into the upper mantle lithosphere. The increased heat flow enhanced fluid movement in the upper mantle and contributed towards isotopic homogenization of the upper mantle source areas. Continued heating of the enriched upper mantle caused partial melting and subsequent eruption of the ultrapotassic lavas.     

The effects of a photosynthesis inhibitor atrazine,on salt marsh edaphic algae,in culture,microecosystems, and in the field

A 10^?5 M (2.2 ppm) concentration of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) reduced the rate of photosynthesis, chlorophyll content, and cell numbers in unialgal cultures of Nitzschia sigma Grun. and Thalassiosira fluviatilis Hustedt isolated from a salt marsh habitat. Results with lower atrazine concentrations indicated an ability to maintain chlorophyll production and cell division with reduced photosynthesis. The effects of a 10^?5 M concentration of atrazine in unialgal cultures were also evident in microecosystems and in the field at the same concentration, although atrazine effects were less severe in the field than in microecosystems or cultures. Cell number and productivity of the diatoms from microecosystems not treated with atrazine agreed well with field data and previously published data. Diatom species diversity was not affected by 10^?5 M atrazine in microecosystems or in the field but the number of Cymatosira belgica Grun. was increased. Diatom assemblages in atrazine-treated vs non-treated microecosystems were very similar (SIMI>0.838). Results were less conclusive in the field but the trend was toward a lower level of similarity. Based on the least effect level of atrazine to diatoms, the maximum safe level for atrazine in the salt marsh is 10 ppb.     

Alpha emitters in a coral from Bikini lagoon: A testimony to nuclear blasts in the Western Pacific

In the years between 1946 and 1958, Bikini Atoll was the site of a series of nuclear device tests which led to the contamination of the calcium-carbonate tests of organisms, including those of corals. Alpha emitters and other radio-nuclides concentrated in these tests. The purpose of our study was to determine where in these test-alpha-emitters concentrated.Petrography of ultra thin sections, in conjunction with solid state alpha-track detectors, shows that it is possible to assign the alpha activity to different parts of the fabric within a coral. The application of this technique to a coral,Favites virens, from the lagoon of Bikini Atoll showed that the theca, septa and dissepiments of the coral skeleton contain very low concentrations of alpha emitters. By contrast, high concentration of alpha emitters occur in damaged parts of the coral. Some of these damaged areas contain cryptocrystalline calcium carbonate, different organisms (algae and/or bryozoan-like tests) and skeletal debris. High concentrations of alpha emitters are associated with the cryptocrystalline calcium carbonate (up to 3000 pCi/g), the skeletal debris (up to 550 pCi/g), bryozoan-like material, and algae (up to 700 pCi/g).

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Lichenometry on calcareous substrates in the Canadian Rockies

Lichen distribution and growth were examined at several sites in the Canadian Rockies between Mt. Robson and Banff townsite to determine the feasibility of lichenometry on calcareous deposits. The only lichen common enough to be of use is Xanthoria elegans, a bright orange lichen with round or elliptical thalli. It is not an ideal species for lichenometry because (a) it grows fairly quickly and has a range of only a few centuries, (b) growth is influenced by the presence of animal dung, (c) parts of some thalli weather away before maximum size is attained, (d) thalli may thicken as well as grow laterally with age, (e) the species is succeeded by other species relatively quickly in heavily forested environments, and (f) the species is not abundant on some deposits due to sometimes-unexplained environmental influences. However, when used with caution the species is still useful for dating purposes.A growth curve for Xanthoria elegans was developed using moraines dated dendro-chronologically and man-made structures. After an ecesis interval of one or two decades the lichen grows at a rate of 0.68 mm/yr for several decades, then slows down to a rate of 0.22 mm/yr.     

Development and use of the Gill UVW anemometer

A three-component anemometer, developed and refined during the past ten years, measures the three orthogonal wind-speed components directly along the instrument's three axes,X, Y, Z. The basic sensor for each of the three components is a light-weight helicoid propeller driving a tiny precision tachometer generator, which develops a D.C. voltage linearly proportional to the rate of turning of the propeller and reversing in polarity when the direction of rotation reverses. Each propeller turns at a rate almost linearly proportional to the instantaneous wind speed and the cosine of the angle subtended by the wind with the axis of the propeller. Propeller sensors have a starting speed of about 0.2 m s^?1; a distance constant of about 1 m; and may be used in winds up to 30 m s^?1. Over 500 of these instruments are now in use at research stations throughout the world.     

Appraisal of the future climate of the Holocene in the Rocky Mountains

Consideration of the history of Holocene climate in the Rocky Mountains indicates that the over-all trend during the past 2500 yr has been toward increasing warmth, interrupted by cooler times of minor advances of cirque glaciers. Comparison of Holocene climatic history with the record of past interglacials in the region suggests that the present interglacial is not complete and that the climate may become first warmer and subsequently wetter before it is completed. Correlation of the timing of the regional glacial-interglacial record for the past 140,000 yr with the record of major sea level changes and with the calculated changes in the earth's insolation suggest that the present interglacial may be completed within a few millenia and that it may be followed by a significant cooling of the climate.     

Hydrothermal convection in carbonaceous chondrite parent bodies

Numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur. The present study considers variations of permeability, radiogenic heating, and body radius. The model accounts for the radial variation of gravity within the body, melting of ice, freezing of liquid water, and variable water properties and incorporates a realistic equation of state for water. Some regions of a parent body experience no pore water flow while other regions experience hundreds of pore volumes of liquid water flow. The spatial heterogeneity in pore water flow reflects the convective pattern in the body. Hydrothermal alteration of minerals inside the parent body will accordingly vary greatly with location in the body, and one parent body could be the source of chemically diverse meteorites.