Thermoluminescence dating of Dimlington Stadial deposits in eastern England   总被引：2，自引：0，他引：2  

ANN G. WINTLE  JOHN A. CATT 《Boreas: An International Journal of Quaternary Research》1985,14(3):231-234

The loess component of a solifluction deposit of the Dimlington Stadial exposed at the inland site of Eppleworth in eastern England gave a thermoluminescence date of 17.5 ± 1.6 × 10³ years. The solifluction deposit is overlain by a slightly weathered till correlated with the Skipsea Till of coastal exposures. which lies between organic horizons with radiocarbon dates of 18,500–18,240 B.P. and 13,045 B.P. Although the till must have been deposited during the Dimlington Stadial (after 18,240 B.P. at Dimlington and after 17,500 B.P. at Epplcworth), it gave apparent TL dates of 42.1 ± 3.6 × 10³ years at Eppleworth and 102 ± 9 × 10³ years at Dimlington, indicating that the components of the till were not exposed to light immediately before deposition.  相似文献   

A Biotite Isograd in South-Central Maine, U.S.A.: Mineral Reactions, Fluid Transfer, and Heat Transfer     

FERRY  JOHN M. 《Journal of Petrology》1984,25(4):871-893

The biotite isograd in pelitic schists of the Waterville Formationinvolved reaction of muscovite + ankerite + rutile + pyrite+graphite + siderite or calcite to form biotite + plagioclase+ ilmenite. There was no single reaction in all pelites; eachrock experienced a unique reaction depending on the mineralogyand proportions of minerals in the chlorite-zone equivalentfrom which it evolved. Quartz, chlorite, and pyrrhotite werereactants in some rocks and products in others. All inferredbiotite-forming reactions involved decarbonation and desulfidation;some were dehydration reactions and others were hydration reactions.P-T conditions at the biotite isograd were near 3500 bars and400 °C. C-O-H-S fluids in equilibrium with the pelitic rockswere close to binary CO₂-H₂O mixtures with X_CO2 = 0.02–0.04.During the biotite-forming reaction, pelitic rocks (a) decreasedby 2–5 percent in volume, (b) performed – (4–11)kcal/liter P-V work on their surroundings, (c) absorbed 38–85kcal/liter heat from their surroundings, and (d) were infiltratedby at least 0.9–2.2 rock volumes H₂O fluid. The biotite isograd sharply marks the limit of a decarbonationfront that passed through the terrane during regional metamorphism.Decarbonation converted meta-shales with 6–10 per centcarbonate to carbonate-free pelitic schists. One essential causeof the decarbonation event was pervasive infiltration of theterrane by at least 1–2 rock volumes H₂O fluid early inthe metamorphic event under P-T conditions of the biotite isograd.Average shale contains 4–13 per cent siderite, ankerite,and/or calcite, but average pelitic schist is devoid of carbonateminerals. If the Waterville Formation serves as a general modelfor the metamorphism of pelitic rocks, it is likely that worldwidemany pelitic schists developed by decarbonation of shale caused,in part, by pervasive infiltration of metamorphic terranes byseveral rock volumes of aqueous fluid during an early stageof the metamorphic event.  相似文献   

Large-scale glacial thrusting and related processes in North Dakota   总被引：1，自引：0，他引：1  

JOHN P. BLUEMLE  LEE CLAYTON 《Boreas: An International Journal of Quaternary Research》1984,13(3):279-299

Large-scale thrusting by the glacial ice occurred in many parts of the Interior Plains of North Dakota, Alberta, and Saskatchewan in late Wisconsinan time. Thrust features are especially prominent in parts of North Dakota. Many of the topographic features of the glaciated landscape of North Dakota formed, either entirely or in part, by the thrusting mechanism, and many individual ice-thrust features have been recognized. The ice-thrusting process was also related to fluting by the glacier, and, as a result, drumlins and other types of fluted features are commonly closely associated with ice-thrust topography. Thrusting by the glacier was dependent primarily on groundwater conditions beneath the ice; thrusting occurred only where hydrologic conditions were appropriate. Most of the individual ice-thrust features that have been recognized are located over discrete aquifers, and the sizes and shapes of the thrust features are dependent upon the sizes and shapes of the aquifers.  相似文献   

Age and Geochemical Characteristics of a Mafic Dyke Swarm in the Archaean Vestfold Block, Antarctica: Inferences about Proterozoic Dyke Emplacement in Gondwana   总被引：1，自引：0，他引：1  

COLLERSON  KENNETH D.; SHERATON  JOHN W. 《Journal of Petrology》1986,27(4):853-886

Archaean gneisses in the Vestfold Block, Antarctica are cutby abundant tholeiite and rare alkaline dykes. At least fivegenerations of dykes have been recognized on the basis of intrusiverelationships, petrography and geochemistry. Rb-Sr isotopicdata indicate that intrusion of the tholeiites occurred overa period of c. 1000 Ma, during three clearly defined events(viz. c. 2400, 1800, and 1400 Ma). Dykes in the southwesternpart of the Vestfold Block were recrystallized during a lateProterozoic (c. 1000-1100 Ma) high-grade event. Mineral-wholerock Rb-Sr isotopic data show that the terrain was also variablyaffected by an even younger thermal event c. 500 Ma ago whichis correlated with the Pan-African Orogeny. Isotopic, major element and trace element data suggest thatthe tholeiite dyke suites were derived by varying degrees ofpartial melting of compositionally distinct, in some cases ratherheterogeneous subcontinental mantle source regions, combinedwith variations in the extent and nature of crystal fractionation.Extensive crustal contamination does not appear to have playeda significant role in determining compositional trends withinthe different suites, although minor contamination cannot bediscounted. The oldest dykes, a diverse group of high-Mg tholeiites,and the youngest, c. 1400 Ma tholeiites, appear to have beenderived from isotopically similar source regions, which werenevertheless characterized by quite different abundances ofhighly incompatible elements (Pb, Rb, Ba, Th, K, La, and Ce).1800 Ma tholeiites were derived from a more radiogenic mantlesource region, characterized by long-term enrichment in incompatibleelements. Such enrichment is interpreted to be a consequenceof metasomatism of their mantle source region. 2400 Ma high-Mg dykes in Enderby Land have virtually identicalchemical and isotopic compositions to those in the VestfoldBlock, indicating generation from a similar source region; however,1200 Ma tholeiites were apparently derived from a more radiogenicsource region like that of the c. 1800 Ma Vestfold Block dykes.Hence, both Sr isotopic and geochemical data indicate that theancient subcontinental lithospheric mantle beneath Gondwanawas extremely heterogeneous.  相似文献   

Petrogenesis of the Kinsman Intrusive Suite: Peraluminous Granitoids of Western New Hampshire   总被引：1，自引：0，他引：1  

CLARK  RUSSEL G.  JR.; LYONS  JOHN B. 《Journal of Petrology》1986,27(6):1365-1393

The Kinsman Intrusive Suite occurs in six major plutons of westernNew Hampshire, covering a total area of 2240 km². It is an Acadian-agesyntectonic gneissic S-type peraluminous granitoid, rangingin composition from quartz diorite to granite. Much of the Kinsmanis characterized by very large (up to 120 mm in maximum dimension)megacrysts of alkali feldspar, but the bulk chemistry of therocks indicates that these cannot be phenocrysts crystallizedfrom initially homogeneous melts. Locally, there is abundant(20 per cent) almandine-rich garnet, and graphite is a commonaccessory.In contrast to the unannealed orthoclase in surroundingmetapelites, the alkali feldspar of the Kinsman has, for themost part, inverted to maximum microcline. The garnets havecore temperatures in the range of 800 to 900 ?C, and are pseudomorphedby, or show reaction rims to, biotite. Plagioclase commonlyshows zoning, some of it oscillatory. These features are magmaticin nature, and argue against the conclusions of previous investigatorsthat the mineralogy and textures of the rock are due to regionalmetamorphism of a previously-crystallized two-mica granitoidwhich has undergone prograde reactions such as:muse + bio +3 qtz 2 Kfs + gar + 2H₂O.The intrusives have also producedrecognizable contact-metamorphic features in the wallrocks andare probably coeval with the dominant M2 Acadian metamorphism.Majorelement analytical data for the Kinsman suite has been examinedby least squares mixing-model and extended Q-mode factor analysis.These calculations, supported by consideration of REE data,suggest that the most likely origin for the Kinsman magmas isby deep-crustal anatexis of slightly calcareous metapelites,and involves a reaction such as:bio + Al₂SiO₅ + qtz + feldspars gar + cord + Kfs + plag + melt.In non-calcareous pelites thisreaction produces a water-undersaturated peraluminous melt attemperatures above 700 ?C, and allows for the early crystallizationor recrystallization of K-feldspar, plagioclase, and garnetin a crystal-liquid mush or migma. Geochemically, garnet + plagioclaseare treated as restite, and a minimum-melt granite as the magmain the Q-mode and mixing-model calculations. The variabilityin chemistry of the Kinsman Intrusive Suite is best explainedon the basis of mixing of leucogranitic anatectic melts withgarnet-plagioclase restitic material and a quartz-feldspar-sillimanite-biotiterock, but only very slightly affected by crystal settling.  相似文献   

An early Holocene caribou antler from northern Ellesmere Island, Canadian Arctic Archipelago   总被引：1，自引：0，他引：1  

THOMAS G. STEWART  JOHN ENGLAND 《Boreas: An International Journal of Quaternary Research》1986,15(1):25-31

During the last glaciation of northern Ellesmere Island many areas remained ice-free. A caribou antler from deglacial-marine sediments in Clements Markham Inlet dates 8,415 ± 135 B.P. (S-2501). If locally derived it places caribou at the northern limit of their contemporary range at the onset of deglaciation in this area. Immediately to the south, on the Hazen Plateau, ice remained at its limit until c . 8,000 B.P. Therefore, this antler may indicate the presence of caribou during full glacial time.  相似文献   

Lake shoreline development, frost weathering and rock platform erosion in an alpine periglacial environment, Jotunheimen, southern Norway   总被引：2，自引：0，他引：2  

JOHN A. MATTHEWS  ALASTAIR G. DAWSON  RICHARD A. SHAKESBY 《Boreas: An International Journal of Quaternary Research》1986,15(1):33-50

Ice-dammed lake Boverbrevatnet existed for 75–125 years in the 'Little Ice Age'. After about A.D. 1826, glacier retreat led to a fall in lake level and to exposure of the former shoreline, which includes well-developed platforms cut in metamorphic bedrock. The rock platforms, up to 5.3 m wide and backed by cliffs up to 1.55 m high, are partially covered by large angular boulders which form pavements. Accurate levelling has permitted correlation of platform fragments, overflow cols and related features of the shoreline, such as benches eroded in moraines, ice-push ridges, a perched delta, vegetation trim-lines, lichen limits and a 'lichen-kill' zone. The evolution of the lake, the chronology of deglaciation and the period of formation of the rock platforms have been dated by lichenometry, supported by ¹⁴C dating, Schmidt hammer 'R'-values and historical data. The morphology of the rock platforms, together with estimates of their rate of erosion ranging from 1.4 to 7.1 cm/year, indicate the importance of frost shattering (frost riving, frost wedging or macrogelivation) at the lake margin under a periglacial climate, while the permanence of such platforms as landscape features suggests their use in the reconstruction of former periglacial environments. A semi-quantitative model is outlined for the development of rock platforms which emphasises deep penetration of the annual freeze-thaw cycle, the movement of unfrozen lake water towards the freezing plane, and the growth of segregation ice in fissures and cracks at the interface between lake ice and bedrock. Ice-push and ice-pull processes are involved primarily as transporting agents in the formation of boulder pavements and in the removal of debris from the platforms. Analogous processes may occur on polar coasts producing coastal rock platforms.  相似文献   

Monitoring of Saharan dust fallout on Crete and its contribution to soil formation   总被引：3，自引：0，他引：3  

TOMAS NIHLÉN  JAN O. MATTSSON  ERS RAPP  CHRISOULA GAGAOUDAKI  GEORGES KORNAROS  JOHN PAPAGEORGIOU 《Tellus. Series B, Chemical and physical meteorology》1995,47(3):365-374

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Glacial sedimentary processes and environmental reconstruction based on lithofacies     

JOHN SHAW 《Sedimentology》1987,34(1):103-116

Glacigenic sediments exposed in pits around Villeneuve, near Edmonton, Alberta, are subdivided into facies based on grain size, sedimentary structure, glacially-induced deformation and faulting, and groove marks. Two diamicton facies are recognised, one of which is interpreted as a primary till, deposited directly from glacier ice, and the other as a product of mass-movement. The diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits. The stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities. At any one place the glacier appears to have alternated between being attached to the bed, causing thrusting and sole marking, and being separated from the bed by a cavity in which fluvial and mass-movement sediments accumulated. The net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance. The correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history. In addition, the interpretations presented here have implications regarding the formation of soft zones in ‘till’. They indicate that the soft zones are beds of sorted sediment redeposited by mass-movement.  相似文献   

Report of the Editors     

JOHN BRIDGE  PAUL BRIDGES  MAURICE TUCKER 《Sedimentology》1987,34(1):190-191

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