Clive Maitland Rice

Bio: Clive Maitland Rice is an academic researcher from University of Aberdeen. The author has contributed to research in topics: Rhynie chert & Devonian. The author has an hindex of 19, co-authored 40 publications receiving 1169 citations. Previous affiliations of Clive Maitland Rice include University of St Andrews & King's College, Aberdeen.

Geological setting of the Early Devonian Rhynie cherts, Aberdeenshire, Scotland: an early terrestrial hot spring system

Abstract: The drilling of nine cored boreholes, including a deep hole (233 m) to a gabbroic basement, in the vicinity of the Rhynie chert locality has resulted in a major revision of the structure and stratigraphy of the area. The main new structural element recognized is a low angle extensional fault system which defines the western edge of a half graben containing the Early Devonian succession. The fault system was the main conduit for the fluids that fed the hot springs, and a heat source to the southeast of Rhynie is indicated. Rapid and unexpected lateral and vertical variations in lithology, together with new lithological units, have been identified. The latter include a thick unit of intensely altered lapilli tuffs which are unique to the Rhynie basin and to other Devonian basins in NE Scotland. Analysis of these lithologies in conjunction with the new structural model allows the succession at Rhynie to be correlated with the succession in the rest of the basin and a model of basin evolution and hot spring development to be constructed. Siliceous sinters were deposited by multiple episodes of hot spring activity and are variably interbedded with shales, sandstones and minor tuffs in a unit about 35 m thick. Sinter deposition was ultimately controlled by repeated subsidence along the basin margin. Geothermal activity was probably widespread in Northern Britain in the Early Devonian but the surface deposits are unlikely to be preserved. The Rhynie deposit has survived due to a fortuitous combination of circumstances.

A Devonian auriferous hot spring system, Rhynie, Scotland

Abstract: The Early Devonian Rhynie hot spring system is the oldest known and is of the low sulphidation type. It extends for at least 1.5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments, plant-bearing sinters and andesitic lavas. The age of sedimentation and hydrothermal activity has been determined by palynological (Pragian) and radio-metric (396 ± 12 Ma) techniques. The outlier is a half graben with a complex stepped western margin. The Devonian rocks show intense hydrothermal alteration along the fault zone. The main alteration minerals are quartz, K-feldspar, calcite, hematite and illitic and chloritic clays. Multiple chert veining and brecciation are widely developed, and geyserite and vent material are also present. Pyrite occurs in veins and all alteration facies. Sinters and altered rocks contain high concentrations of Au, As, Sb, Hg, W and Mo. Gold occurs in arsenian pyrite and as sub-micron particles in oxidized rocks. The fluid(s) responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water. However, incursions of high temperature (300–440°C) magmatic fluids occurred with δD–65‰ and δ 18 O around +8.5‰. δ 34 S (pyrite) and initial 87 Sr/ 86 Sr ratios (vein calcite) lie mainly within the ranges +3.4‰ to +8.5‰ and 0.71138 to 0.71402 respectively. These data indicate that late Proterozoic Dalradian metasediments are a likely source for S and Sr but other sources are possible. δ 13 C values for caliche and vein calcite imply derivation of carbon from non-organic sources. The Rhynie cherts were deposited from a low salinity fluid of probable meteoric origin (δ 18 O chert + 13.1‰ to +16.5‰) which had interacted with the basement rocks and sediments (high Xe/Ar, Br/Cl and I/Cl ratios). Plant-bearing chert yielded an 40 Ar/ 39 Ar ratio (292.1± 0.6) significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere.

Multiphase development of the Atacama Planation Surface recorded by cosmogenic 3He exposure ages: Implications for uplift and Cenozoic climate change in Western South America

Abstract: The Atacama Planation Surface is an extensive west-dipping surface developed between 16°S and 27°S along the Pacific margin of South America. It is considered to have formed between 16 and 7.5 Ma and to have important chronostratigraphic significance. Here we present new cosmogenic 3He exposure dates of boulders on the planation surface using pyroxene and amphibole. Exposure ages display good within- and between-site consistency and range from 22 to 1.2 Ma, with ages of ca. 14.6, 7, and 3 Ma recurring at more than one site on the planation surface. The 14.6 Ma peak records the cessation of the main period of planation surface development, but, contrary to popular opinion, the younger ages reflect subsequent modification of the planation surface by alluvial activity. Comparison with other climate proxies for western South America suggests that since 14.6 Ma, a predominantly hyperarid climate, interspersed with short-lived phases of more intense runoff driven by global climate change, has prevailed. The longevity and composite nature of the Atacama Planation Surface suggest that regionally extensive planation surfaces may have a multiphase history, are unlikely to have any chronostratigraphic significance, and cannot be used to reconstruct uplift histories.

On the mechanism of exfoliation of ‘Vermiculite’

Abstract: Six samples of 'Vermiculite' have been studied to investigate the mechanism of its well known but poorly understood property to exfoliate. The samples were analysed quantitatively by XRD to determine their precise mineralogical composition. Electron microprobe methods, including elemental mapping of native potassium and of caesium (introduced by cation exchange) were used to examine variation in the chemical composition of the particles. Most of the samples examined show heterogeneous mineralogical compositions which occur as distinct zones within the volume of individual particles, presenting a mosaic texture. Exfoliation is related to this mosaic distribution of the different mineral phases within the particles. Lateral phase boundaries between vermiculite and mica layers, or vermiculite and chlorite layers are postulated to prevent or impede the escape of gas from a particle, resulting in exfoliation when the pressure exceeds the interlayer bonding forces that hold the layers together. This mechanism provides a common explanation for the exfoliation of 'Vermiculite' by thermal methods or by treatment with H2O2. Paradoxically, one sample which consists of pure vermiculite, in the mineralogical sense of the term, demonstrates that pure vermiculite does not and should not exhibit the property of exfoliation. Our explanation of the mechanism of exfoliation explains the commonly observed particle size dependence of exfoliation and the tendency for obviously poly-phase 'Vermiculite' samples to show the largest coefficients of expansion.

Arsenic uptake and metabolism in arsenic resistant and nonresistant plant species

Abstract: Summary Elevation of arsenic levels in soils causes considerable concern with respect to plant uptake and subsequent entry into wildlife and human food chains. Arsenic speciation in the environment is complex, existing in both inorganic and organic forms, with interconversion between species regulated by biotic and abiotic processes. To understand and manage the risks posed by soil arsenic it is essential to know how arsenic is taken up by the roots and metabolized within plants. Some plant species exhibit phenotypic variation in response to arsenic species, which helps us to understand the toxicity of arsenic and the way in which plants have evolved arsenic resistances. This knowledge, for example, could be used produce plant cultivars that are more arsenic resistant or that have reduced arsenic uptake. This review synthesizes current knowledge on arsenic uptake, metabolism and toxicity for arsenic resistant and nonresistant plants, including the recently discovered phenomenon of arsenic hyperaccumulation in certain fern species. The reasons why plants accumulate and metabolize arsenic are considered in an evolutionary context.

The Role of Decay and Mineralization in the Preservation of Soft-Bodied Fossils

Abstract: ▪ Abstract Fossil deposits that preserve soft-bodied organisms provide critical evidence of the history of life. Usually, only more decay resistant materials, e.g., cuticles, survive as organic remains as a result of selective preservation and subsequent diagenesis to more resistant biopolymers. Permineralization, the permeation of tissues by mineralizing fluids, may preserve remarkable detail, particularly of plants. However, evidence of more labile tissues, e.g., muscle, normally requires the replication of their morphology by rapid in situ growth of minerals, i.e., authigenic mineralization. This process relies on the steep geochemical gradients generated by decay microbes. The minerals involved, and the level of detail preserved (which may be subcellular), depend on a number of factors, including the nature of microbial activity and amount of decay, availability of ions, and the type of organism that is fossilized. Understanding these controls is essential to determining the conditions that favor exce...