Testing the influence of topography and material properties on catchment‐scale soil moisture patterns using remotely sensed vegetation patterns in a humid temperate catchment,northern Britain

In order to evaluate the relationship between the apparent complexity of hillslope soil moisture and the emergent patterns of catchment hydrological behaviour and water quality, we need fine‐resolution catchment‐wide data on soil moisture characteristics. This study proposes a methodology whereby vegetation patterns obtained from high‐resolution orthorectified aerial photographs are used as an indicator of soil moisture characteristics. This enables us to examine a set of hypotheses regarding what drives the spatial patterns of soil moisture at the catchment scale (material properties or topography). We find that the pattern of Juncus effusus vegetation is controlled largely by topography and mediated by the catchment's material properties. Characterizing topography using the topographic index adds value to the soil moisture predictions relative to slope or upslope contributing area (UCA). However, these predictions depart from the observed soil moisture patterns at very steep slopes or low UCAs. Copyright © 2012 John Wiley & Sons, Ltd.     

Mesoproboloides excavata n. sp. (Amphipoda: Gammaridea: Stenothoidae) from New Zealand

Mesoproboloid.es excavata n. sp. is described and illustrated from material collected at Kaikoura, New Zealand. It differs most conspicuously from the other three known species of the genus in the posterodistally excavate coxa 4, the stout, blunt lobe distally on article 1 of antenna 1, the crenulate ventral margins of coxae 2–4, and the castellate posterior margin of article 2 of pereopod 5. The structure and distribution of minute organs, probably sensory receptors, densely distributed over much, of the integument was examined by scanning electron microscopy. The genus Mesoproboloides is now seen to be cold temperate‐subantarctic in occurrence.     

Timing of brittle faulting and thermal events,Sydney region: association with the early stages of extension of East Gondwana

Structural studies in the Sydney region have revealed the presence of vertical to near-vertical, north-northeast-striking faults that are manifest as joint swarms and highly brecciated zones in which gouge of varying thickness is developed. Strike-slip movement accompanied by minor dip-slip, normal movement occurred on these faults. Timing of movement on these faults by K–Ar dating of illite and illite–smectite in fractions extracted from fault gouges, was attempted. These dates were compared with dates obtained from the host-rocks. K–Ar ages determined from the 2–10 μm to <0.1 μm fractions produced from the gouge and host-rocks, range from 159.5 ± 3.2 to 106.6 ± 2.1 Ma (n = 26). In <0.5 μm fractions extracted from the gouges that are less contaminated by detrital phases, K–Ar ages vary from 138 ± 4.4 to 106.5 ± 2.1 Ma (mean 121 Ma; n = 6) which are similar to ages obtained from host-rocks in the Sydney region. The similarity in age between the host rocks and gouge suggests that the K–Ar system has been reset. The resetting is attributed to a thermal event at ca 120 Ma related to the underplating of felsic intrusions associated with early stages of breakup of East Gondwana. Subsequent to this event, dykes of Early Eocene age (K–Ar whole-rock: 51.0 ± 1.1 Ma) exploited north-northeast-striking faults and subsequently developed brecciated margins. These observations and the fact that gouge formed before the thermal event suggests that movement took place on north-northeast-striking faults prior to 120 Ma and after 51 Ma.     

Age and composition of dykes emplaced before and during the opening of the Tasman Sea—source implications

Abstract

Dykes are common in the wave-cut platforms along the coast from Newcastle to Sydney. According to some authors, they may be related to the opening of the Tasman Sea that commenced ca 84?Ma ago. However, there are few detailed radiogenic dating and geochemical studies to evaluate this. We attempt to resolve this by K–Ar dating of plagioclase in and geochemical studies of, basaltic dykes intruding Permo-Triassic sequences on the wave-cut platforms and Carboniferous and Permo-Triassic sequences inland. The plagioclase separated from the dykes give K–Ar ages ranging from 266 to 53?Ma with the majority older than 84?Ma indicating that most dykes were emplaced before the Tasman Seafloor formation. The dykes are generally mildly alkaline, high-Ti basalts; fewer are tholeiitic and calc-alkaline, low-Ti basalts. Strongly light rare earth element (LREE)-enriched patterns typify the former and flat, LREE-depleted or slightly to moderately enriched LREE patterns, the latter. High-Ti basalts have ocean-island-basalt-like and low-Ti basalts, calc-alkaline or mid-ocean ridge basalt (MORB)-like patterns. Most high-Ti and some low-Ti basalts show plume-like characteristics, others N-type MORB and arc-like characteristics. Dykes intruding the Carboniferous sequences show a distinct contamination signature that could be crustal or due to subduction-related metasomatism of the subcontinental lithospheric mantle. The sources of the basaltic magmas vary substantially and in places changes with time. All alkali basalts are derived from enriched asthenospheric sources at varying depths (90–147?km) and most tholeiitic, low-Ti basalts have been extracted from asthenospheric and depleted asthenospheric–lithospheric sources indicating substantial compositional heterogeneity of the mantle. Further, Nd model ages varying from Neoproterozoic (940–580?Ma) to Paleozoic (460–370?Ma) suggest variation in the age of mantle sources for the basalts.     

The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling

The oxygen content of the Earth's surface environment is thought to have increased in two broad steps: the Great Oxygenation Event (GOE) around the Archean–Proterozoic boundary and the Neoproterozoic Oxygenation Event (NOE), during which oxygen possibly accumulated to the levels required to support animal life and ventilate the deep oceans. Although the concept of the GOE is widely accepted, the NOE is less well constrained and its timing and extent remain the subjects of debate. We review available evidence for the NOE against the background of major climatic perturbations, tectonic upheaval related to the break-up of the supercontinent Rodinia and reassembly into Gondwana, and, most importantly, major biological innovations exemplified by the Ediacarian Biota and the Cambrian ‘Explosion’.Geochemical lines of evidence for the NOE include perturbations to the biogeochemical cycling of carbon. Generally high δ¹³C values are possibly indicative of increased organic carbon burial and the release of oxidative power to the Earth's surface environment after c. 800 Ma. A demonstrably global and primary record of extremely negative δ¹³C values after about 580 Ma strongly suggests the oxidation of a large dissolved organic carbon pool (DOC), the culmination of which around c. 550 Ma coincided with an abrupt diversification of Ediacaran macrobiota. Increasing ⁸⁷Sr/⁸⁶Sr ratios toward the Neoproterozoic–Cambrian transition indicates enhanced continental weathering which may have fuelled higher organic production and burial during the later Neoproterozoic.Evidence for enhanced oxidative recycling is given by the increase in sulfur isotope fractionation between sulfide and sulfate, exceeding the range usually attained by sulfate reduction alone, reflecting an increasing importance of the oxidative part in the sulfur cycle. S/C ratios attained a maximum during the Precambrian–Cambrian transition, further indicating higher sulfate concentrations in the ocean and a transition from dominantly pyrite burial to sulfate burial after the Neoproterozoic. Strong evidence for the oxygenation of the deep marine environment has emerged through elemental approaches over the past few years which were able to show significant increases in redox-sensitive trace-metal (notably Mo) enrichment in marine sediments not only during the GOE but even more pronounced during the inferred NOE. In addition to past studies involving Mo enrichment, which has been extended and further substantiated in the current review, we present new compilations of V and U concentrations in black shales throughout Earth history that confirm such a rise and further support the NOE. With regard to ocean ventilation, we also review other sedimentary redox indicators, such as iron speciation, molybdenum isotopes and the more ambiguous REE patterns. Although the timing and extent of the NOE remain the subjects of debate and speculation, we consider the record of redox-sensitive trace-metals and C and S contents in black shales to indicate delayed ocean ventilation later in the Cambrian on a global scale with regard to rising oxygen levels in the atmosphere which likely rose during the Late Neoproterozoic.     

Late Devensian and Flandrian palaeoenvironmental changes on the Scottish continental shelf west of the Outer Hebrides

Examination of two radiocarbon-dated vibrocores taken from south of St Kilda at a water depth of about 155 m, a short distance within the maximum position of the Late Devensian (Dimlington Stadial) ice sheet, suggests that the St Kilda Basin became free of glacier ice after 15250 yr BP. Sedimentation in a shallow, low energy, high arctic, muddy environment continued until after 13500 yr BP. There followed a higher energy temperate episode during which water depths were roughly about 40 m: this is correlated with the latter part of the Windermere Interstadial and with the warmer interval known in shallow Scottish seas about or a little before 11 000 yr BP. The Loch Lomond (Younger Dryas) Stadial is marked in the vibrocores by the return of muddy sediments and a cold-water fauna. Relatively shallow water conditions seem to have persisted into the earliest Flandrian, when the water depth was still roughly 60 m, corresponding to a sea-level in the area 90–100 m below present. It is suggested that pack ice was widespread in the northeast Atlantic before the Windermere Interstadial and also during the Loch Lomond Stadial, when it transported shards of Icelandic volcanic ash into the St Kilda basin. Estimates of sea-surface temperature for the last part of the Windermere Interstadial are close to those derived from the deep-sea record for the same period.     

Differences in paleomagnetic interpretations due to the choice of statistical, demagnetization and correction techniques: Kapuskasing Structural Zone, northern Ontario, Canada

The Kapuskasing Structural Zone (KSZ) reveals a section through the Archean lower crustal granoblastic gneisses. Our new paleomagnetic data largely agree with previous work but we show that interpretations vary according to the choices of statistical, demagnetization and field-correction techniques. First, where the orientation distribution of characteristic remanence directions on the sphere is not symmetrically circular, the commonly used statistical model is invalid [Fisher, R.A., Proc. R. Soc. A217 (1953) 295]. Any tendency to form an elliptical distribution indicates that the sample is drawn from a Bingham-type population [Bingham, C., 1964. Distributions on the sphere and on the projective plane. PhD thesis, Yale University]. Fisher and Bingham statistics produce different confidence estimates from the same data and the traditionally defined mean vector may differ from the maximum eigenvector of an orthorhombic Bingham distribution. It seems prudent to apply both models wherever a non-Fisher population is suspected and that may be appropriate in any tectonized rocks. Non-Fisher populations require larger sample sizes so that focussing on individual sites may not be the most effective policy in tectonized rocks. More dispersed sampling across tectonic structures may be more productive. Second, from the same specimens, mean vectors isolated by thermal and alternating field (AF) demagnetization differ. Which treatment gives more meaningful results is difficult to decipher, especially in metamorphic rocks where the history of the magnetic minerals is not easily related to the ages of tectonic and petrological events. In this study, thermal demagnetization gave lower inclinations for paleomagnetic vectors and thus more distant paleopoles. Third, of more parochial significance, tilt corrections may be unnecessary in the KSZ because magnetic fabrics and thrust ramp are constant in orientation to the depth at which they level off, at approximately 15-km depth. With Archean geothermal gradients, primary remanences were blocked after the foliation was tilted to rise on the thrust ramp. Therefore, the rocks were probably magnetized in their present orientation; tilting largely or entirely predates magnetization.