Paleoecological investigation of recent lake acidification in the Adirondack Mountains,N.Y.     

Donald F. Charles  Michael W. Binford  Edward T. Furlong  Ronald A. Hites  Myron J. Mitchell  Stephen A. Norton  Frank Oldfield  Michael J. Paterson  John P. Smol  Allen J. Uutala  Jeffrey R. White  Donald R. Whitehead  Robert J. Wise 《Journal of Paleolimnology》1990,3(3):195-241

Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH < 5.5 and alkalinity < 10 eq l^-1 have acidified recently. The onset of this acidification occurred between 1920 and 1970. Loss of alkalinity, based on quanitative analysis of diatom assemblages, ranged from 2 to 35 eq l^-1. The acidification trends are substantiated by several lines of evidence including stratigraphies of diatom, chrysophyte, chironomid, and cladoceran remains, Ca:Ti and Mn:Ti ratios, sequentially extracted forms of Al, and historical fish data. Acidification trends appear to be continuing in some lakes, despite reductions in atmospheric sulfur loading that began in the early 1970s. The primary cause of the acidification trend is clearly increased atmospheric deposition of strong acids derived from the combustion of fossil fuels. Natural processes and watershed disturbances cannot account for the changes in water chemistry that have occurred, but they may play a role. Sediment core profiles of Pb, Cu, V, Zn, S, polycyclic aromatic hydrocarbons, magnetic particles, and coal and oil soot provide a clear record of increased atmospheric input of materials associated with the combustion of fossil fuels beginning in the late 1800s and early 1900s. The primary evidence for acidification occurs after that period, and the pattern of water chemistry response to increased acid inputs is consistent with current understanding of lake-watershed acidification processes.This is the second of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.  相似文献   

Systematics of zircon crystallisation in the Cretaceous Separation Point Suite, New Zealand, using U/Pb isotopes, REE and Ti geothermometry   总被引：5，自引：3，他引：2  

Robert Bolhar  Steve D. Weaver  J. Michael Palin  Jim W. Cole  Lorraine A. Paterson 《Contributions to Mineralogy and Petrology》2008,156(2):133-160

Plutonic zircons from the Cretaceous Separation Point Suite (SPS) were analysed by LA-ICPMS for U–Pb isotope ratios and trace element concentrations. Pooled ²⁰⁶Pb/²³⁸U ages range from 112 to 124 Ma. Cathodoluminescence imaging reveals minor inheritence and textural evidence of repeated dissolution and re-precipitation of zircon. Core and rim spot analyses, however, document zircon growth during extended periods of time (>2 myr). Protracted crystallisation histories for simple plutonic systems are inconsistent with generalised thermal constraints, which predict cooling below the solidus within <1 myr. Consequently, we conclude that the SPS granitoids sampled in this study were not emplaced rapidly but incrementally over extended time periods. Zircon Th/U and Zr/Hf ratios are positively correlated with crystallisation temperatures, consistent with crystallisation from evolving melts. However, highly variable trace element concentrations, along with temperature reversals are indicative of complex crystallisation histories involving continuous fractional crystallisation repeatedly punctuated by hotter, more mafic magma recharge. Normalised abundances of the redox-sensitive elements Eu and Ce in zircon vary systematically with degrees of whole rock differentiation, pointing to evolutionary trends in magmatic oxidation states coupled with feldspar crystallisation.  相似文献   

北京西山房山岩体西北部强变形带的成因新解   总被引：2，自引：1，他引：1  

燕滨  何斌  徐义刚  Scott Paterson  张焘 《大地构造与成矿学》2008,32(4)

北京西山房山岩体西北缘不对称发育一条弧形塑性强变形带,前人根据岩体东南部组构缓倾和岩体内部强应变分布特征提出岩浆斜向底辟侵位模式(王人镜等,1990;张吉顺和李志中,1990)。本文在前人研究的基础上,对房山岩体的组构进行系统观测,研究了西北缘固态塑性强变形带地质特征,着重探讨了岩体侵位时围岩热结构状态。文章认为岩浆同侵位固态塑性强变形带的形成需要早期岩浆进入准固态-固态和后期岩浆膨胀动力这两个必要条件。房山岩体西北部的强变形带是由于岩体侵位时西部围岩的温度较低,岩浆较早进入准固态-固态,后期岩浆侵位时膨胀动力双重因素造成的,提出了围岩热结构状态是房山岩体不对称的固态塑性强变形带的控制因素,而不是岩浆斜向底辟侵位的结果。这一研究成果不仅较合理地解释了房山岩体强变形带不对称发育特征,而且对研究同类花岗质岩体的定位机制有一定启示意义。  相似文献   

Superplastic flow in finegrained limestone   总被引：1，自引：0，他引：1  

S.M. Schmid  J.N. Boland  M.S. Paterson 《Tectonophysics》1977,43(3-4)

Creep of Solnhofen limestone at temperatures between 600° and 900° C was found to fall into three different flow regimes: regime 1 with an exponential stress-dependence of strain rate, regime 2 with power-law creep and n ~ 4.7 and finally a superplastic regime 3 with n ~ 1.7. Within the superplastic regime the creep behaviour is strongly grain-size dependent, the strain rate increasing markedly with decrease in grain size at a given stress. Microstructural observations indicate that in regimes 1 and 2 intracrystalline plasticity is dominant whereas the superplastic regime is characterized by grain-boundary sliding. The crystallographic preferred orientation within the superplastic regime is weaker and of different geometry when compared with that in flow regimes 1 and 2. In a discussion on the deformation mechanisms it is suggested that flow regimes 1 and 2 are regimes of dis location creep in which the rate controlling step is diffusion assisted; for the superplastic regime existing models of grain-boundary sliding are compared with the observations Finally, the tectonophysical importance of superplasticity is discussed and by extra polating the observed creep behaviour to geological strain rates it is found that super plasticity in rocks is to be expected under a wide range of conditions, particularly at smal grain sizes.  相似文献   

Experiments on preferred orientation of platy minerals     

Dr. W. D. Means  M. S. Paterson 《Contributions to Mineralogy and Petrology》1966,13(2):108-133

Polycrystalline aggregates of phlogopite, talc, and brucite have been grown hydrothermally from their constituent oxides at 300–600° C, 3–5 kb, and compressed 10–30% in short-term experiments (typically 30 minutes). Under hydrostatic conditions, approximately random orientation of crystals results. When the specimen is strained at high temperature, either during or after growth of the minerals, a preferred orientation of basal planes normal to the axis of compression results. Since a similar result is obtained by straining at room temperature after growth of the minerals, the mechanism of orientation is probably mainly mechanical rotation after formation. Microscope examination showed that the preferred orientation is most marked in coarser grains of the aggregates. A second kind of foliation is defined in some specimens by closely spaced, narrow domains within which coarse grains are slightly rotated. These domains occur in conjugate sets symetrically oriented at about 45° to the axis of compression. They are interpreted as shear domains and are geometrically similar to incipient strain-slip cleavage in foliated rocks. The experiments may represent likely behavior in geological situations where the temperature or time scale precludes recrystallization during deformation, but they are probably not directly revelant to cases of axial-plane cleavage where reorientation through an influence of stress or strain during recrystallization is believed to have occurred. No unequivocal indication of the latter process was obtained in the experiments.  相似文献   

A brief overview of the ACEP project: Ecosystem Processes in the KwaZulu-Natal Bight§     

ST Fennessy  MJ Roberts  AW Paterson 《African Journal of Marine Science》2016,38(1):S1-S6

This introductory paper lays the basis for this supplementary issue by briefly presenting the state of knowledge on the KwaZulu-Natal (KZN) Bight at the start of this multi-disciplinary, multi-institutional, ship-based research project that ran from 2009 to 2013. The rationale and aims of the project are also described. The project was a major component of the South African Department of Science and Technology’s African Coelacanth Ecosystem Programme (ACEP), which has been prominent in supporting research on the east coast of South Africa and the wider South-West Indian Ocean. Pivotal to this was the RS Algoa, which was made available for two 30-day surveys (winter and summer) in the KZN Bight by the Department of Environmental Affairs. Although some aspects of the bight ecology are known, much of the research is dated and fragmented, and required refreshing and consolidation in order to produce a platform upon which the understanding of the region’s ecosystem functioning could be established. Much of the oceanographic knowledge is also dated, with no dedicated surveys and significant measurements undertaken since 1989. The overarching theme of the KZN Bight project was to examine the relative importance of sources of nutrients to the central KZN coast and how these are taken up and recycled in the ecosystem, and to describe aspects of the benthic biodiversity, which is poorly described in much of this region. An ambitious project, its accessibility to a ship-based research platform and the diverse scientific skills of the participating scientists allowed considerable success, as reflected in the papers that follow.  相似文献   

Zr–LREE rich minerals in residual peraluminous granulites, another factor in the origin of low Zr–LREE granitic melts?     

C. Villaseca  D. Orejana  B.A. Paterson 《Lithos》2007,96(3-4):375-386

There is a significant enrichment in some trace elements in the major residual minerals of peraluminous granulite xenoliths from the lower crust. Those trace elements are released from the breakdown of accessory phases at high-T granulite-facies conditions (> 850 °C). Around 10–35% of Zr is hosted in granulite rutile and garnet, whereas, the entire LREE–Eu budget is controlled by feldspar. The Zr- and REE-compatible behaviour of the major granulite phases, combined with the scarcity of accessory phases, which are mostly included in major granulite minerals, leads to a disequilibrium in accessory dissolution in the peraluminous partial melts. Thus the melt extracts less Zr and LREE and, consequently, generates the false impression of having lower-T when applying current accessory phase dissolution models.  相似文献   

A high-pressure,high-temperature apparatus for studies of seismic wave dispersion and attenuation     

Ian Jackson  M. S. Paterson 《Pure and Applied Geophysics》1993,141(2-4):445-466

An apparatus is described which provides for the investigation of viscoelasticity/anelasticity in geologic and related materials under conditions of high pressure and temperature. Cylindrical specimens are tested in torsion—a geometry particularly well suited to shear mode observations at the low strain amplitudes of the linear regine. Forced oscillation experiments allow the measurement of disperision and attenuation at the low frequencies of teleseismic wave propagation. The conduct of complementary forced oscillation and creep tests allows recoverble anelastic strains to be distinguished from those of permanent viscous deformation. It has been demonstrated that robust measurements can be made at strain amplitudes below 10^–5 and frequencies of 1 mHz–1 Hz, underP-T conditions to 300 MPa and 1200°C. The prospects for further development of this facility are outlined.  相似文献   

Changes since the onset of acid deposition among calcium-sensitive cladoceran taxa within softwater lakes of Ontario, Canada     

Adam Jeziorski  Andrew M. Paterson  John P. Smol 《Journal of Paleolimnology》2012,48(2):323-337

Aqueous calcium (Ca) concentrations are currently decreasing in many softwater lakes on the Boreal Shield. As the onset of these declines often pre-date direct monitoring programs, indirect techniques are required to examine the impacts of reduced Ca availability on aquatic communities with relatively high Ca demands such as the Cladocera (Class: Branchiopoda). Among the Cladocera, the family Daphniidae has been identified as a taxonomic group potentially useful for inferring past Ca concentrations due to their high Ca demands and preservation in lake sediments. Here, we use a ??top/bottom?? paleolimnological analysis to compare present-day cladoceran communities preserved in the surface sediments of 36 softwater lakes in south-central Ontario, Canada, which are potentially vulnerable to Ca decline (i.e. small headwater systems with present-day lakewater [Ca]?<?3?mg?L^?1), with the communities present in lake sediments deposited prior to the onset of regional acid deposition. To distinguish the potential impacts of lake acidification from those of Ca availability (as Ca and pH trends are strongly correlated in this region), the study lakes were chosen to be evenly distributed about a present-day lakewater pH of 6 and Ca concentration of 1.5?mg?L^?1 (threshold values). Despite the importance of pH as an explanatory variable for the present-day assemblages, a comparison of the sedimentary remains from the two time periods indicate there have been large declines since pre-industrial times in the relative abundances of Ca-rich Daphnia spp. (particularly of the Daphnia longispina species complex), regardless of present-day pH, accompanied by increases in the Ca-poor species Holopedium glacialis. These observations suggest that recent declines in Ca concentration may have already fallen below baseline conditions, with marked implications for ecosystem function due to the differential responses among cladoceran taxa.  相似文献   

The uptake and solubility of water in quartz at elevated pressure and temperature     

J. Gerretsen  M. S. Paterson  A. C. McLaren 《Physics and Chemistry of Minerals》1989,16(4):334-342

The uptake of water in quartz at 1.5 GPa total pressure, 1173 K and high water fugacity, over times up to 24 h, has been investigated using a newly developed assembly to prevent microcracking. It is found that the uptake is small, and below the detectability of the presently used technique of infrared spectroscopy and serial sectioning. This observation reflects either a low value for the diffusivity or the solubility or a combination of both, and is in agreement with the observations of Kronenberg et al. (1986) and Rovetta et al. (1986). It brings into question the interpretation of the early experiments on water weakening by Griggs and Blacic (1964) and the recent estimates of the solubility and diffusivity by Mackwell and Paterson (1985). Rults of a combined T.E.M., light-scattering and infrared-spectroscopy investigation of ‘wet’ synthetic quartz before and after heating at 0.1, 300 and 1500 MPa total pressure and 1173 K, strongly suggest that the water in ‘wet’ quartz is mainly in the form of H₂O in inclusions, consistent with the solubility being low, possibly less than 100 H/10⁶Si. From these observations, water-containing inclusions appear to play a major role in the plasticity of quartz, while any role of water in solid solution remains to be clarified.  相似文献