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121.
Paul F. Green Rob Westaway D.A.C. Manning Paul L. Younger 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(3):450-463
The Cenozoic landscape development of Britain remains relatively poorly understood. On the one hand, ‘plumists’ have tried to explain the present-day topography as a consequence of effects of the Iceland mantle plume during the Palaeocene-Eocene British Tertiary Igneous Province (BTIP) magmatism, with little or no subsequent modification. On the other hand, abundant evidence exists from fluvial and marine terraces and superimposed karstic levels for significant vertical crustal motions during the Quaternary, which clearly has nothing to do with any mantle plume. To shed light on this issue, we present the first publication of data that constrain the Cenozoic thermal history of the North Pennine uplands of northern England, from apatite fission-track analysis of drill cuttings from the Eastgate Borehole in Weardale, in the western part of County Durham. Our results indicate ~650 m of regional denudation since the latest Oligocene/Early Miocene, plus the ~400 m of localized entrenchment that has created the modern Weardale valley. Before the latest Oligocene/Early Miocene, but following the BTIP magmatism, the crust in this region experienced significant cooling, mainly due to a decrease in the geothermal gradient from ~55 to 61 °C km?1 to the present 38 °C km?1, along with ~300 ± 200 m of denudation. Although significant BTIP magmatism occurred in northern England, it thus had only a limited net effect; the crust experienced dramatic heating, but cooled back to its original thermal state within, at most, a few tens of millions of years. We suggest that this rapid cooling effect resulted from westward flow of relatively cold material within the mobile lower-crustal layer, driven by the lateral pressure gradient induced by earlier heating effects and effects of surface processes. Whatever topography developed during the Palaeogene, as a direct result of these heating effects, underplating at the base of the crust, and the associated modest denudation, was presumably also short-lived; significant changes to the crustal thickness, and thus to the topography, can be envisaged as a consequence of subsequent lower-crustal flow. 相似文献
122.
Gayle Hough Jennifer Green Paul Fish Andy Mills Roger Moore 《Marine Geophysical Researches》2011,32(1-2):151-162
Exploration and development of offshore hydrocarbon resources has advanced into remote deepwater regions over the last decade and poses significant technical challenges for the design and installation of wells and facilities at extreme water depths. Seafloor and shallow subsurface processes and conditions in these areas are complex and generally poorly understood, and the geohazards to development are larger scale and fundamentally different to those encountered onshore; consequently the geohazard risk to deepwater development projects is potentially significant and requires careful evaluation and mitigation during the front-end planning and engineering design stages of projects. There are no established industry standards or methods for the assessment of geohazards and engineering-quality geophysical data at the scale of development. The paper describes an integrated and systematic map-based approach for the assessment and mitigation of seabed geohazards and risk to proposed deepwater development. The approach employs a multi-disciplinary team working with engineering-quality field calibrated data to accurately map and assess seafloor ground conditions and ensure that development proposals are not exposed to intolerable geohazard risk. The approach taken is very similar to the practice of establishing geological models for land-based engineering projects, in which the complete geological history of the site is used to characterise and predict the performance of the ground. Such an approach is routine for major projects on land but so far does not seem to be common practice in the offshore industry. The paper illustrates the seafloor geomophological mapping approach developed. The products are being used to optimise development layouts to avoid geohazards where possible and to support site-specific engineering design of facilities based on a detailed understanding of the potential geohazard loadings and associated risk. 相似文献
123.
George G. Waldbusser Erin P. Voigt Heather Bergschneider Mark A. Green Roger I. E. Newell 《Estuaries and Coasts》2011,34(2):221-231
Anthropogenic carbon dioxide (CO2) emissions reduce pH of marine waters due to the absorption of atmospheric CO2 and formation of carbonic acid. Estuarine waters are more susceptible to acidification because they are subject to multiple
acid sources and are less buffered than marine waters. Consequently, estuarine shell forming species may experience acidification
sooner than marine species although the tolerance of estuarine calcifiers to pH changes is poorly understood. We analyzed
23 years of Chesapeake Bay water quality monitoring data and found that daytime average pH significantly decreased across
polyhaline waters although pH has not significantly changed across mesohaline waters. In some tributaries that once supported
large oyster populations, pH is increasing. Current average conditions within some tributaries however correspond to values
that we found in laboratory studies to reduce oyster biocalcification rates or resulted in net shell dissolution. Calcification
rates of juvenile eastern oysters, Crassostrea virginica, were measured in laboratory studies in a three-way factorial design with 3 pH levels, two salinities, and two temperatures.
Biocalcification declined significantly with a reduction of ∼0.5 pH units and higher temperature and salinity mitigated the
decrease in biocalcification. 相似文献
124.
David L. Naftz Frank J. Millero Blair F. Jones W. Reed Green 《Aquatic Geochemistry》2011,17(6):809-820
Great Salt Lake (GSL) is one of the largest and most saline lakes in the world. In order to accurately model limnological
processes in GSL, hydrodynamic calculations require the precise estimation of water density (ρ) under a variety of environmental conditions. An equation of state was developed with water samples collected from GSL to
estimate density as a function of salinity and water temperature. The ρ of water samples from the south arm of GSL was measured as a function of temperature ranging from 278 to 323 degrees Kelvin
(oK) and conductivity salinities ranging from 23 to 182 g L−1 using an Anton Paar density meter. These results have been used to develop the following equation of state for GSL (σ = ± 0.32 kg m−3):
r- r0 = 184.0 10 6 2 + 1.0 4 70 8*\textS - 1. 2 10 6 1*\textT + 3. 1 4 7 2 1 \textE - 4*\textS 2 + 0.00 1 9 9 \textT 2 - 0.00 1 1 2*\textS*\textT, \rho - \rho^{0} = { 184}.0 10 6 2 { } + { 1}.0 4 70 8*{\text{S}} - 1. 2 10 6 1*{\text{T }} + { 3}. 1 4 7 2 1 {\text{E}} - 4*{\text{S}}^{ 2} + \, 0.00 1 9 9 {\text{T}}^{ 2} - 0.00 1 1 2*{\text{S}}*{\text{T}}, 相似文献
125.
126.
The structure of the Tasmanian dolerite at Great Lake 总被引:1,自引:1,他引:0
A gravity survey over Great Lake on the central plateau of Tasmania shows that the structure of the dolerite that intrudes gently dipping Permian and Triassic sediments has appreciable thickening under the northern end of Great Lake and by means of alternate dykes and sills the dolerite moves up and out from the central feeder. This structure facilitates the formation of grano‐phyre over the dykes. The Great Lake intrusion is not unique but a typical form for the Tasmanian dolerite. 相似文献
127.
T. H. Green 《Australian Journal of Earth Sciences》2013,60(2):405-418
A Devonian granite complex intrudes Precambrian and Silurian siltstones and sandstones as well as (?) Cambrian volcanics and dunite. Metamorphism of the Precambrian sediments is slight, and an andalusite‐bearing, pelitic hornfels is the only characteristic assemblage. The (?) Cambrian volcanics give rise to a variety of assemblages; (1) lime‐ and ferromagnesia‐rich (hypersthene — cummingtonite — labradorite; diopside — hornblende — labradorite); (2) magnesia‐rich (cordierite — hypersthene; cordierite — anthophyllite); (3) ultrabasic (olivine and/or pleonaste). Biotite (or phlogopite) is an almost invariable component, and garnet may also be present in these groups. No significant metamorphism of the dunite is evident; minor development of veins and segregrations of aragonite, magnetite, phlogopite, brucite, chalcedony and antigorite may result from low‐grade hydrothermal activity Metamorphic assemblages in calcareous Silurian siltstones contain garnet, diopside, calcite and epidote. A characteristic feature of the contact metamorphic aureole is the occurrence of diopside‐rich bodies in granite, volcanic hornfels, quartzite and dunite host rocks. 相似文献
128.
129.
Thirty K‐Ar dates on Cainozoic volcanic rocks lying at the north end of the Bowen Basin suggest that several episodes of volcanism took place at major structural weaknesses. The oldest volcanism (ca 54 m.y.) was located outside the basin structure. The main volcanism (Nebo and East Clermont Provinces) extended from early Oligocene (34–35 m.y.) to mid‐Cainozoic time (21–22 m.y.?). Isolated Pliocene activity is tentatively suggested by dates on Mt St Martin (ca 3 m.y.). Dating of the Nebo central volcano (31–33 m.y.) supports the model of Wellman &; McDougall, with volcanic activity related to migration of Australia northwards over a mantle magma source. Consideration of the Nebo dates with those of other central volcanoes in north Queensland, suggests that central felsic activity was surrounded by broad zones of peripheral eruptives, petrologically zoned from outer undersaturated basalts to inner saturated basalts. These zones (super provinces) delineate the size and profile of underlying magma sources and appear to trend back in time and space to sea‐floor spreading episodes in the Coral Sea—southeastern Papua region (55 m.y.). The basalt dates also assist in fixing periods of lateritization (mid‐Oligocene) and in determining approximate minimum erosion rates in the northern Bowen Basin since the Eocene (3–5m/m.y.). 相似文献
130.
D.C. Green 《Australian Journal of Earth Sciences》2013,60(2):153-160
Abstract Conventional K-Ar geochronology and the 40Ar/39Ar method in which the ratio of radiogenic argon to postassium is determined by measurement of 39Ar produced by neutron irradiation are used to document the occurrence of the Upper Carboniferous Kanimblan Orogeny in the D'Aguilar Block and Beenleigh Block of southeastern Queensland. Incremental evolution of argon by the heating of an irradiated sample of Neranleigh-Fernvale argillite and 40Ar/39Ar measurements on two hornblendes from alaskite clasts in the Neranleigh-Fernvale Group suggest that part of this unit may be as young as Lower Carboniferous. 相似文献
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