A-level geology in schools: Does a future beckon, or is it merely the shadow of a past?     

P.G. BAKER 《Geology Today》1987,3(3-4):82-83

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Submarine terraces and morphology in the Kieler Bucht, Western Baltic, and their relation to late Quaternary events     

TERRY HEALY 《Boreas: An International Journal of Quaternary Research》1981,10(2):209-217

From analysis of the densest network of echogrammes yet available for the Kieler Bucht, Western Baltic, the submarine erosional terraces have been mapped. In general these correlate well with the features mapped and described by Kolp (1976) for the adjacent Mecklenburger Bucht. The lower terraces are at - 30 m and may reach 2100 m in broadness. Compared to present day conditions, the rates of cliff retreat at the time of formation were evidently much accelerated, due possibly to harsher climatic conditions including a greater intensity of winter lake ice, frosts, wind and rain. Other terraces at - 27, - 24, - 19, and - 14 m were identified, and these are related to syngressions in the various eustatic curves applicable to the Western baltic. A hypsometric curve for the submarine terrain of the Kieler Bucht, when compared to the relative sea level curve shows that 65% of the bay was transgressed in only 700 years. Maximum sedimentation rates in the Kieler Bucht should have occurred at this time, and independent data from dated cores from Vejsnäs Rinne support this prediction.  相似文献   

EXPRESSO flux measurements at upland and lowland Congo tropical forest site   总被引：3，自引：0，他引：3  

D. SERÇA  A. GUENTHER  L. KLINGER  L. VIERLING  P. HARLEY  A. DRUILHET  J. GREENBERG  B. BAKER  W. BAUGH  C. BOUKA&#;BIONA  J. LOEMBA&#;NDEMBI 《Tellus. Series B, Chemical and physical meteorology》2001,53(3):220-234

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Recrystallization of dolomite: evidence from the Monterey Formation (Miocene), California   总被引：2，自引：0，他引：2  

MITCHELL J. MALONE  PAUL A. BAKER  STEPHEN J. BURNS† 《Sedimentology》1994,41(6):1223-1239

Dolomites from the upper calcareous-siliceous member of the Miocene Monterey Formation exposed west of Santa Barbara, California, were analysed for geochemical, isotopic and crystallographic variation. The data clearly document the progressive recrystallization of dolomite during burial diagenesis in marine pore fluids. Recrystallization is recognized by the following compositional and crystallographic variations. Dolomites have decreasing δ¹⁸O and δ¹³C compositions, decreasing Sr contents and increasing Mg contents with increasing burial depths and temperatures from east to west in the study area. δ¹⁸O values vary from 5·3‰ in the east to − 5·5‰ PDB in the west and are interpreted to reflect the greater extent and higher temperature of dolomite recrystallization in the west. δ¹³C values correlate with δ¹⁸O and decrease from 13·6‰ in the east to − 8·7‰ PDB in the west. Sr concentrations correlate positively with δ¹⁸O values and decrease from a mean of 750 ppm in the east to a mean of 250 ppm in the west. Mol% MgCO₃ values inversely correlate with δ¹⁸O values and increase from a minimum of 41·0 in the east to a maximum of 51·4 in the west. Rietveld refinements of powder X-ray diffraction data indicate that the more recrystallized dolomites have more contracted unit cells and increased cation ordering. The fraction of the Ca sites in the dolomites that are occupied by Ca atoms increases slightly with the approach to stoichiometry. The fraction of the Mg sites occupied by Mg atoms strongly correlates with mol% MgCO₃. Even in early diagenetic, non-stoichiometric dolomites, there is little substitution of Mg in Ca sites. During recrystallization, the amount of Mg substituting for Ca in Ca sites decreases even further. Most of the disorder in the least recrystallized, non-stoichiometric dolomites is related to substitution of excess Ca on Mg sites.  相似文献   

THE TRANSIENT ELECTROMAGNETIC RESPONSE OF A POLARIZABLE SPHERE IN A CONDUCTING HALF SPACE1     

TERRY LEE  LINDSAY THOMAS 《Geophysical Prospecting》1992,40(5):541-563

A polarizable sphere embedded in a conducting half-space can give rise to negative voltage transients in a coincident-loop time-domain electromagnetic system. Such transients have been observed in field situations. Our results are obtained from a model in which the contributions of the host rock, the currents in the sphere, and the interaction between the sphere and the host rock are separated and superposed. This model uses approximations to the integral equation solutions rather than finite-element or finite-difference approximations, and so allows very rapid computation. The theoretical demonstration suggests that interpretation of the negative voltage transients as a polarization response is valid, but more detailed interpretation of polarization properties may not be possible, because the superposition of the polarization response on the normal response depends strongly on the position of the target.  相似文献   

Episodic sedimentation on an early Silurian, storm-dominated carbonate ramp, Becscie and Merrimack formations, Anticosti Island, Canada     

TERRY SAMI  RÉ DESROCHERS 《Sedimentology》1992,39(3):355-381

The 150–160 m thick lowermost Silurian (Rhuddanian) Becscie and Merrimack formations of Anticosti Island, Canada, represent continuous deposition on a shallow, open marine carbonate ramp. Several rock types are identified: (a) laminated and homogenous mudstone; (b) laminated and homogenous packstone; (c) argillaceous mudstone and packstone; (d) calcareous shale; (e) laminated calcisiltite; (f) medium- to fine-grained grainstone; and (g) bio/intraclastic rudstone. These rock types are arranged into five distinct lithofacies: (LF1) calcareous mudstone-shale; (LF2) laminated-homogenous mudstone; (LF3) calcareous grainstone-shale; (LF4) laminated mudstone-grainstone; and (LF5) laminated calcisiltite-grainstone. The sequence reflects deposition on a low-energy, muddy, carbonate to argillaceous ramp subject to short-lived, episodic high-energy storms. These events produced fining-upwards storm units 5–80 cm thick, or tempestites, consisting of: a sharp scoured base overlain by intra/bioclastic rudstone grading upwards into medium-grained grainstone, finely laminated calcisiltite and mudstone, or shale. These are interbedded with low-energy, fairweather mudstones and calcareous shales. Deposition progressed from a carbonate mud-dominated ramp in the Becscie Formation to an argillaceous mud-dominated ramp in the Merrimack Formation. Lateral tempestite proximality trends and lithofacies distribution indicate that the Anticosti Basin deepened to the south-east into the Iapetus Ocean and shallowed towards a SW—NE-orientated shoreline to the north-west. Vertical tempestite proximality trends and lithofacies changes identify third-order eustatic sea-level changes. After an initial deepening at the base of the formation, a shallowing-deepening event dominated the sequence. Several higher order fluctuations, defined by lithofacies and tempestite proximality trends, are superimposed on these changes. The fluctuations identified with the aid of tempestite proximality trends are of an order of magnitude higher than those identified by either lithofacies or palaeontological methods.  相似文献   

Development of pollen assemblage zones in soil profiles in southeastern England   总被引：1，自引：0，他引：1  

TERRY H. KEATINGE 《Boreas: An International Journal of Quaternary Research》1983,12(1):1-12

Four soil profiles within c. 4 ha of dry heathland on lping Common, southeastern England were studied. Two were podzols, one was a buried profile from beneath a Bronze-age barrow and one was a profile buried beneath sediment in a small pond. Loss on ignition, particle size analysis, iron concentration and pollen concentration were determined and a pollen diagram prepared for each profile. It is suggested that discrete soil pollen assemblage zones arise from their incorporation by successively shallower-burrowing earthworm populations as the soils and vegetation change from mull to mor types. The implications of this mode of incorporation to the interpretation of soil pollen diagrams are discussed. A sequence of vegetation and soils for this area is suggested as follows:(1) mixed deciduous woodland of Quercus. Tilia and Corylus with a fern-rich understorey growing in a mull soil, (2) scrub woodland of Betula and Corylus with Pteridium and some Callunu, (3) Calluna heathland on podzolised soils. ¹⁴C dates obtained from podzol Bh horizons and the buried soil beneath the pond were inconclusive.  相似文献   

Thermokarst — a mechanism of de-icing ice-cored moraines     

TERRY R. HEALY 《Boreas: An International Journal of Quaternary Research》1975,4(1):19-23

Thermokarst features occur widely in the younger ice-cored moraines and kame terraces in the Dry Valleys region of Victoria Land, Antarctica Common forms are melt dolines, caves, natural bridges, and subsurface. flow. Such features typically develop in stagnant glacial ice with a low material exchange.
The development of a thermokarst cave system near the Taylor Glacier during the southern summer of 1973–74 is described, and the role of the thermokarst process in land-form development in the Dry Valleys area is discussed.  相似文献   

Models for the tectonothermal evolution of the eastern Dalradian of Scotland   总被引：1，自引：0，他引：1  

A. J. BAKER 《Journal of Metamorphic Geology》1987,5(1):101-118

Abstract The preserved array of pressures in the eastern Dalradian indicates that considerable syn- to post-metamorphic differential uplift has occurred. This inferred differential uplift suggests that Buchan sillimanite zone rocks originally lay at higher structural levels than presently adjacent cooler kyanite zone rocks to the west. A number of features are believed to coincide with the western margin of the sillimanite zone. These are a maximum in temperature, sharp thermal features, a high strain zone, and a train of metabasites. These features are explained by invoking syn-metamorphic movement between the Buchan sillimanite zone and the kyanite zone to its west, involving some horizontal component of movement. It is suggested that the lateral, now eroded, equivalents of the Buchan area once provided part of the required tectonic thickening for other parts of the Dalradian. Areas surrounding the Buchan area suffered tectonic burial followed by metamorphism during uplift relative to the Buchan area.  相似文献   

Petrogenesis of the Largest Intraplate Volcanic Field on the Arabian Plate (Jordan): a Mixed Lithosphere-Asthenosphere Source Activated by Lithospheric Extension   总被引：2，自引：0，他引：2  

SHAW  JULIA E.; BAKER  JOEL A.; MENZIES  MARTIN A.; THIRLWALL  MATTHEW F.; IBRAHIM  KHALIL M. 《Journal of Petrology》2003,44(9):1657-1679

Miocene to Recent volcanism in northwestern Arabia producedthe largest intraplate volcanic field on the Arabian plate (HarratAsh Shaam, Jordan). The chemically and isotopically diversevolcanic field comprises mafic alkali basalts and basanites.The magmas underwent limited fractional crystallization of ol± cpx ± plag and rare samples have assimilatedup to 20% of Late Proterozoic crust en route to the surface.However, there are subtle Sr–Nd–Pb isotopic variations(⁸⁷Sr/⁸⁶Sr = 0·70305–0·70377, ¹⁴³Nd/¹⁴⁴Nd= 0·51297–0·51285, ²⁰⁶Pb/²⁰⁴Pb = 18·8–19·2),which exhibit marked correlations with major elements, incompatibletrace element ratios and abundances in relatively primitivebasalts (MgO >8·5 wt %), and cannot be explained byfractional crystallization and crustal contamination alone.Instead, the data require polybaric melting of heterogeneoussources. Semi-quantitative melt modelling suggests that thisheterogeneity is the result of small degree melts (2–5%)from spinel- and garnet-facies mantle, inferred to be shallowArabian lithosphere, that mixed with smaller degree melts (<1%)from a predominantly deep garnet-bearing asthenospheric(?) sourcewith ocean island basalt characteristics. The latter may bea ubiquitous part of the asthenosphere but is preferentiallytapped at small degrees of partial melting. Volcanism in Jordanappears to be the result of melting lithospheric mantle in responseto lithospheric extension. With time, thinning of the lithosphereallowed progressively deeper mantle (asthenosphere?) to be activatedand melts from this to mix with the shallower lithospheric mantlemelts. Although Jordanian intraplate volcanism is isotopicallysimilar to examples of Late Cenozoic volcanism throughout theArabian peninsula (Israel, Saudi Arabia), subtle chemical andisotopic differences between Yemen and Jordan intraplate volcanismsuggest that the Afar plume has not been channelled northwestwardsbeneath the Arabian plate and played no role in producing thenorthern Saudi Arabian and Jordan intraplate volcanic fields. KEY WORDS: asthenosphere; intraplate volcanism; Jordan; lithospheric mantle; Sr–Nd–Pb isotopes  相似文献