Book review     

Douglas M. Hawkins 《Mathematical Geology》1986,18(4):433-435

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A reconstruction of Quaternary pluvial environments and human occupations using stratigraphy and geochronology of fossil‐spring tufas,Kharga Oasis,Egypt     

Jennifer R. Smith  Robert Giegengack  Henry P. Schwarcz  Mary M. A. McDonald  Maxine R. Kleindienst  Alicia L. Hawkins  Charles S. Churcher 《Geoarchaeology》2004,19(5):407-439

We carried out a geologic survey and a preliminary archaeological survey of four fossil‐spring tufa localities in Kharga Oasis, Egypt, to constrain the timing of pluvial episodes in the Western Desert, and to document prehistoric occupation contemporaneous with times of increased rainfall. Uranium‐series dating of the tufas confirms that at least five episodes of tufa deposition are represented in Kharga, although not every event is represented at each locality. Across the region studied, tufas were most frequently deposited as part of a fluvial barrage system, characterized by terraced, vegetated pools impounded by arcuate tufa dams and separated by small waterfalls. Available water resources during pluvial phases would have included not only spring‐fed streams but also small freshwater lakes. While Earlier Stone Age (ESA) and Middle Stone Age (MSA) lithic artifacts may be found either as surficial lags on tufas, or, less commonly, encased within tufas, Epipalaeolithic and Neolithic artifacts are generally found in or on silts within surface deflation depressions in the tufas, principally at Wadi Midauwara. © 2004 Wiley Periodicals, Inc.  相似文献   

U-Pb monazite, xenotime and titanite geochronological constraints on the prograde to post-peak metamorphic thermal history of Paleoproterozoic migmatites from the Grand Canyon, Arizona   总被引：2，自引：0，他引：2  

David P. Hawkins  Samuel A. Bowring 《Contributions to Mineralogy and Petrology》1999,134(2-3):150-169

The petrology and U-Pb geochronology of pelitic migmatite and calc-silicate gneiss reveal a detailed prograde to post-peak metamorphic thermal history for a single outcrop of Paleoproterozoic supracrustal rocks in the eastern part of the Grand Canyon. Metamorphic monazite from paleosomal pelitic schist grew on the prograde path beginning at about 1708 Ma and continued to grow until about 1697 Ma. The U-Pb dates for magmatic xenotime and monazite from peraluminous granite and pegmatite leucosomes indicate that partial melting, which involved the breakdown of muscovite to sillimanite, commenced at about 1702 Ma, prior to the metamorphic peak. Partial melting continued until about 1690 Ma, the youngest U-Pb date from magmatic monazite in the leucosomes. Field and petrographic evidence, as well as inheritance patterns in monazites from the leucosomes, suggest that some of the leucosomes appear to represent in situ partial melts that did not escape the source region. Between 1702 and 1690 Ma, the migmatite package heated to peak metamorphic conditions of about 720 °C and 6 kbar, cooled to about 675 °C at a cooling rate >30 °C/million years, and decompressed to about 4 kbar. The U-Pb geochronological data for metamorphic titanite from a calc-silicate gneiss exhibit a clear relationship between grain size and the ²⁰⁷Pb/²⁰⁶Pb date indicating that the titanite crystals record cooling ages. These data, combined with the titanite Pb diffusion data of Cherniak (1993), yield a cooling rate of 5.4_−0.9 ^+1.7 °C/million years, integrated over the interval 1690 to 1676 Ma and suggest that by 1675 Ma, the cooling rate slowed to less than 2 °C/million years. The rapid decompression during the peak of metamorphism and the change in cooling rate immediately following peak metamorphism are interpreted to reflect large-scale tectonic processes associated with the accretion of juvenile crust to the margin of Laurentia. Juvenile arc crust appears to have been assembled, accreted and stabilized into Laurentian lithosphere in less than 30 million years. Received: 21 January 1998 / Accepted: 27 August 1998  相似文献   

Gender and Water in Mongolia     

Roberta Hawkins  Joni Seager 《The Professional geographer》2013,65(1):16-31

Global institutions, academics, and practitioners have long acknowledged the need to consider gender in creating sustainable water management plans. However, for most countries a dearth of context-specific information on gender and water relations hinders gender-sensitive plan development. Mongolia is particularly poorly represented in the gender and water literature. This article presents fieldwork revealing distinctive gendered practices around water use, decision making, and management including an unusually high degree of men's participation in water collection. This research adds new context-specific data to the understanding of actual gender and water relations and underscores the need for further investigation into the Mongolian context.  相似文献   

Palaeoecological,archaeological and historical data and the making of Devon landscapes. I. The Blackdown Hills     

Antony G. Brown  Charlotte Hawkins  Lucy Ryder  Sean Hawken  Frances Griffith  Jackie Hatton 《Boreas: An International Journal of Quaternary Research》2014,43(4):834-855

This paper presents the first systematic study of the vegetation history of a range of low hills in SW England, UK, lying between more researched fenlands and uplands. After the palaeoecological sites were located bespoke archaeological, historical and documentary studies of the surrounding landscape were undertaken specifically to inform palynological interpretation at each site. The region has a distinctive archaeology with late Mesolithic tool scatters, some evidence of early Neolithic agriculture, many Bronze Age funerary monuments and Romano‐British iron‐working. Historical studies have suggested that the present landscape pattern is largely early Medieval. However, the pollen evidence suggests a significantly different Holocene vegetation history in comparison with other areas in lowland England, with evidence of incomplete forest clearance in later‐Prehistory (Bronze?Iron Age). Woodland persistence on steep, but poorly drained, slopes, was probably due to the unsuitability of these areas for mixed farming. Instead they may have been under woodland management (e.g. coppicing) associated with the iron‐working industry. Data from two of the sites also suggest that later Iron Age and Romano‐British impact may have been geographically restricted. The documented Medieval land management that maintained the patchwork of small fields, woods and heathlands had its origins in later Prehistory, but there is also evidence of landscape change in the 6th–9th centuries AD. We conclude that the Blackdown Hills area was one of many ‘distinctive subregions’, which due to a combination of edaphic, topographic and cultural factors could qualify as an eco‐cultural region or ‘pays’. It is argued that the use of such eco‐culturally distinctive regions or pays can provide a spatial and archaeological framework for palaeoecology, which has implications for landscape research, designation and heritage management.  相似文献   

Predicting thermal vulnerability of stream and river ecosystems to climate change     

Ryan A. Hill  Charles P. Hawkins  Jiming Jin 《Climatic change》2014,125(3-4):399-412

We use a predictive model of mean summer stream temperature to assess the vulnerability of USA streams to thermal alteration associated with climate change. The model uses air temperature and watershed features (e.g., watershed area and slope) from 569 US Geological Survey sites in the conterminous USA to predict stream temperatures. We assess the model for predicting climate-related variation in stream temperature by comparing observed and predicted historical stream temperature changes. Analysis of covariance confirms that observed and predicted changes in stream temperatures respond similarly to historical changes in air temperature. When applied to spatially-downscaled future air temperature projections (A2 emission scenario), the model predicts mean warming of 2.2 °C for the conterminous USA by 2100. Stream temperatures are most responsive to climate changes in the Cascade and Appalachian Mountains and least responsive in the southeastern USA. We then use random forests to conduct an empirical sensitivity analysis to identify those stream features most strongly associated with both observed historical and predicted future changes in summer stream temperatures. Larger changes in stream temperature are associated with warmer future air temperatures, greater air temperature changes, and larger watershed areas. Smaller changes in stream temperature are predicted for streams with high initial rates of heat loss associated with longwave radiation and evaporation, and greater base-flow index values. These models provide important insight into the potential extent of stream temperature warming at a near-continental scale and why some streams will likely be more vulnerable to climate change than others.  相似文献   

A high-pressure neutron diffraction study of the ferroelastic phase transition in RbCaF3     

Kevin S. Knight  William G. Marshall  Philip M. Hawkins 《Physics and Chemistry of Minerals》2014,41(6):461-472

The fluoroperovskite phase RbCaF₃ has been investigated using high-pressure neutron powder diffraction in the pressure range ~0–7.9 GPa at room temperature. It has been found to undergo a first-order high-pressure structural phase transition at ~2.8 GPa from the cubic aristotype phase to a hettotype phase in the tetragonal space group I4/mcm. This transition, which also occurs at ~200 K at ambient pressure, is characterised by a linear phase boundary and a Clapeyron slope of 2.96 × 10^?5 GPa K^?1, which is in excellent agreement with earlier, low-pressure EPR investigations. The bulk modulus of the high-pressure phase (49.1 GPa) is very close to that determined for the low-pressure phase (50.0 GPa), and both are comparable with those determined for the aristotype phases of CsCdF₃, TlCdF₃, RbCdF₃, and KCaF₃. The evolution of the order parameter with pressure is consistent with recent modifications to Landau theory and, in conjunction with polynomial approximations to the pressure dependence of the lattice parameters, permits the pressure variation of the bond lengths and angles to be predicted. On entering the high-pressure phase, the Rb–F bond lengths decrease from their extrapolated values based on a third-order Birch–Murnaghan fit to the aristotype equation of state. By contrast, the Ca–F bond lengths behave atypically by exhibiting an increase from their extrapolated magnitudes, resulting in the volume and the effective bulk modulus of the CaF₆ octahedron being larger than the cubic phase. The bulk moduli for the two component polyhedra in the tetragonal phase are comparable with those determined for the constituent binary fluorides, RbF and CaF₂.  相似文献   

The 2dF Galaxy Redshift Survey: correlation functions, peculiar velocities and the matter density of the Universe   总被引：1，自引：0，他引：1  

Ed Hawkins  Steve Maddox  Shaun Cole  Ofer Lahav  Darren S. Madgwick  Peder Norberg  John A. Peacock  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Bryn Jones  Ian Lewis  Stuart Lumsden  Will Percival  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,346(1):78-96

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An event-based approach to understanding decadal fluctuations in the Atlantic meridional overturning circulation     

Lesley Allison  Ed Hawkins  Tim Woollings 《Climate Dynamics》2015,44(1-2):163-190

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Winter PRIMER Ocean-Acoustic Solitary Wave Modeling Studies     

Warn-Varnas  A.C. Chin-Bing  S.A. King  D.B. Hawkins  J.A. Lamb  K.G. Lynch  J.F. 《Oceanic Engineering, IEEE Journal of》2007,32(2):436-452

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