We describe a technique for performing sequential stable-isotope and trace-element analyses on the same aliquot of carbonate usin as little as 30 kg CaC03. The technique producing combined Bj Sr/Ca, Mg/Ca ratios and 6180 and 6 C values is applied to a suite of individual nektic ostracodes from the past 10,000 years from Lake Keilambcte, a crater lake in western Victoria, Australia.Emphasis is placed on those periods of the lake's history where s a y t y and evaporation do not covary. We show that a combination of measurements, particularly 6 '0 values and Sr/Ca ratios, can elucidate the salinity, evaporation and chemical history of this simple lake system but that each technique in isolation fails to adequately describe those changes. The combined technique may be applied to more complex lacustrine basins in order to produce more realistic histories from which paleoclimatic inferences could be drawn.
SUMMARY. A number of minerals and residual glasses from absarokites, shoshonites, and latites have been analysed by electron probe.Clinopyroxenes show very little iron-enrichment and these rocks are thus distinguished from thoteiites and alkali basalts.Glasses from this group are also distinct from tholeiites and alkali basalts and occupy a separate field on a CaO-Na20-K~O diagram.WHEN attention (Joplin, I965) was drawn to the close resemblance between certain lavas on the south coast of New South Wales, the absarokite-shoshonite-banakite series of Wyoming (Iddings, 1895), and the latites of Sierra Nevada (Ransome, I898), it was suggested that these rocks might be related to the alkali basalts or might even represent a distinct magma-type.A review of world occurrences of shoshonitic rocks (Joplin, I968) has shown that compositions may range from ultramafic absarokites to felsic toscanites and liparites and that there is little iron enrichment. Thus, the shoshonitic rocks have some affinities with the calcalkaline andesitic suite and the suggestion that they may be related to the alkali basalts is wrong.The range in composition from absarokites to liparites suggests that they belong to a differentiation series, but the andesite suite also shows a considerable range in composition and many petrologists consider that members of this suite arise by a complex process involving partial melting rather than by fractional crystallization or by contamination of a basaltic magma (Green and Ringwood, I968; Taylor et al., I969). The shoshonitic rocks may have a somewhat similar origin (Jake~ and White, I969). As the word 'series' seems to imply a differentiation series and it is unlikely that the shoshonitic rocks are the differentiates of a single magma, it is preferable to refer to them as members of the shoshonite association.In I965 it was also pointed out that shoshonitic lavas are associated with regions that were incompletely stabilized or only recently stabilized at the time of their extrusion. This is in harmony with their geographical distribution with regard to the andesites in the island arcs.Shoshonites and monzonites have a very similar composition and because many monzonites are associated with nepheline-and melanite-bearing rocks, with or without 9
We have conducted a preliminary survey of analyzed surface sediment samples from approximately twenty lakes in Australia for their Fe, Cu, Pb and Zn concentrations. In addition lake sediments from the gold mining areas of Western Australia (WA) were analyzed for Ag, and samples from NW Victoria were analyzed for Mn, Ni, Co, Cr and V. These lakes are discharge zones for regional and/or local saline groundwaters. The groundwaters entering many of these lakes have very low pH's (pH 3-4) and contain extremely high dissolved Fe concentrations. These low pH waters may also contain high concentrations of trace metals and radionuclides from the 23 8 U decay series.The WA data yield the following information: (1) with the possible exceptions of Ag, these sediments show no trace metal enrichments above average shale/sandstone values; (2) some lakes draining Archean gold mining terrain have high Ag concentrations; (3) the highest Pb concentrations are in a lake where acid groundwater input occurs; and (4) the acid mineral alunite does not appear to be a metal 'sink' in the acid groundwater lakes.In the two NW Victorian lakes, the sulfidic zone below the cyanobacterial mat is enriched above by about 100 x for Cu, 30 x for Zn and 78 x for Pb compared to the sediments outside the discharge zone. The Victorian data set indicates a correlation between Cu and Zn and also between Cr and Ni concentrations. Three generations of 'ironstone-like' sediments were also analyzed. These iron-oxide rich sediments gained Cu but lost Co with age and maturation. The Mn concentration appears to be important in controlling the Zn and Cu in these 'ironstones'. It appears from our data that neither the oxide-rich nor the acid-rich authigenic sediment phases are major sinks for groundwater metal in these systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.