Stratigraphy,sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end‐moraine zone     

MARK D. JOHNSON  YLVA STÅHL 《Boreas: An International Journal of Quaternary Research》2010,39(2):199-214

Johnson, M. D. & Ståhl, Y. 2009: Stratigraphy, sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end‐moraine zone. Boreas, 10.1111/j.1502‐3885.2009.00124.x. ISSN 0300‐9483 Deglaciation of the Middle Swedish end‐moraine zone and age of the sediment in and between the moraines have been discussed for about a hundred years. The goal of this project was to determine the stratigraphy and age of the sediment in and between the moraines. Inter‐moraine flats are underlain by clay, 10–25 m thick, overlying thin sand and gravel or till on bedrock. The clay is overlain by a few metres of sand and gravel. Much of the clay beneath the flats consists of rhythmites that grade from grey to red and are 2–74 cm thick. Our interpretation of these rhythmites as being varves is supported by grain size and mineralogical and elemental variations. Foraminifera and ostracods show that the clay was deposited in an arctic marine environment, while radiocarbon dating of the microfossils indicates that the clay was deposited 12 150 cal. ¹⁴C years ago, during the Younger Dryas chronozone (YD). Most of the optical stimulated luminescence dates on the clay are much older, containing quartz sand that was insufficiently bleached. The stratigraphy indicates that the moraines are composed of YD clay pushed into ridge forms during ice‐front oscillations. It is not possible to determine how far north the Scandinavian Ice Sheet retreated prior to the YD advance. We neither support nor reject the suggestion that the ice margin retreated to the northern edge of Mt. Billingen during the Allerød, causing the Baltic Ice Lake to drain.  相似文献   

Evidence of Saharan dust in upper Pleistocene reworked palaeosols of North‐west Sardinia,Italy: palaeoenvironmental implications     

STEFANO ANDREUCCI  MARK D. BATEMAN  CLAUDIO ZUCCA  SELIM KAPUR  İHSAN AKŞIT  ADAM DUNAJKO  VINCENZO PASCUCCI 《Sedimentology》2012,59(3):917-938

A multi‐disciplinary approach was followed to investigate two thick palaeosol strata that alternate with wind‐blown dominated deposits developed along the Alghero coast (North‐west Sardinia, Italy). Optically stimulated luminescence ages reveal that both palaeosols were developed during cooler drier periods: the first one at around 70 ka Marine Isotope Stage 4 and the latter around 50 ka (Marine Isotope Stage 3). In contrast, the pedological features indicate that the palaeosols underwent heavy weathering processes under warm humid to sub‐humid conditions, characteristic of the Sardinian climate during the last interglacial stage (Marine Isotope Stage 5e). To reconcile this apparent data discrepancy, a range of sedimentological and pedological analyses were conducted. These analyses reveal that the palaeosols possess a complex history, with accumulation and weathering occurring during Marine Isotope Stage 5e, and erosion, colluviation and final deposition taking place during the following cold stages. Thus, even if these reddish palaeosols were last formed during the glacial period, the sediments building up these strata probably record the climate of the last interglacial stage (Marine Isotope Stage 5e). Trace element and X‐ray diffraction analyses, together with scanning electron microscope images, reveal the presence of Saharan dust in the parent material of the palaeosols. However, no evidence of any far‐travelled African dust has been observed in the Marine Isotope Stage 4–3 aeolian deposits. It is possible to conclude that in the West Mediterranean islands, Saharan dust input, even if of modest magnitude, is preserved preferentially in soils accumulated and weathered during interglacial stages.  相似文献   

Video support in teaching about geographic information systems: a review of six videotapes     

G. BRENT HALL  MARK H. MACLENNAN 《International journal of geographical information science》2013,27(1):87-95

Abstract

Abstract. The growing interest in teaching about geographic information systems (GIS) raises a number of issues concerning the effectiveness of conventional instructional methods. To convey basic GIS concepts and applications better requires much more emphasis upon visual media. One such medium is that of VHS (or Beta) videotapes. Six currently-available GIS-oriented videotapes are reviewed for this purpose. Their contents are summarized and an evaluation is made of the usefulness of each in classroom-based GIS instruction.  相似文献   

LAND–USE CHANGES AND CONSERVATION OF THE HAWAI‘I ‘AMAKIHI     

MICHAEL K. STEINBERG  JUNICHI SUGISHITA  KEALOHANUIOPUNA MARK KINNEY 《Geographical review》2010,100(2):204-215

Hawai‘ian honeycreepers have undergone widespread extinction and population declines due to human disturbances, including habitat fragmentation, introduced predatory mammals, alien competitors, and introduced avian diseases. The Hawai‘i ‘amakihi (Hemignathus virens) is one of seven extant Hawai‘ian honeycreepers that, like all other native honey‐creepers, vanished from the low‐elevation native forests on the island of Hawai‘i due to these disturbances. But recent observations indicate that ‘amakihi have begun to recolonize low‐elevation forests in eastern Hawai‘i. In this article we discuss the current abundance of Hawai‘ian ‘amakihi in a suburban habitat on the island of Hawai‘i. We also examine the ‘amakihi's relative preference for native or exotic vegetation. Recolonization in low‐elevation habitats underscores the importance of the remaining native forests. However, concurrent with this recolonization, eastern Hawai‘i is undergoing a residential building boom that has resulted in increased deforestation and forest fragmentation. Thus the future of honeycreepers is uncertain, given the widespread environmental changes taking place in eastern Hawai‘i.  相似文献   

Fibrous calcite from the Ordovician of Tennessee: preservation of marine oxygen isotopic composition and its implications   总被引：1，自引：0，他引：1  

KENNETH J. TOBIN  KENNETH R. WALKER  D. MARK STEINHAUFF†  CLAUDIA I. MORA 《Sedimentology》1996,43(2):235-251

Three categories of fibrous calcite from early to middle Caradoc platform-marginal buildups in east Tennessee can be delineated using cathodoluminescent microscopy, minor element chemistry and stable C-O isotopic composition. Bright luminescent fibrous cement has elevated Mn (>1000 p.p.m.), negative δ¹³C and intermediate δ¹⁸O values relative to other types of fibrous calcite. This cement reflects fibrous calcite that interacted with reducing Mn-rich fluids. Dully luminescent fibrous cement has elevated Fe (>400 p.p.m.), positive δ¹³C and negative δ¹⁸O values relative to other fibrous cements. This cement was stabilized by burial fluids. Nonluminescent fibrous cement has low Mn and Fe (generally below 400 p.p.m.) and positive δ¹³C and δ¹⁸O values relative to other types of fibrous calcite. The latter cement is interpreted to be the best material for determining the isotopic composition of calcite precipitated in equilibrium with early to middle Caradoc seawater, which is δ¹³C=1% PDB and δ¹⁸O=?4 to ?5‰ PDB. Results from this study and Ashgillian brachiopods indicate that the average δ¹⁸O composition of the Ordovician ocean, during nonglacial periods, was probably never more negative than ?3‰ SMOW. Assuming an Ordovician seawater δ¹⁸O value of ?1‰ SMOW, Holston Formation fibrous cements would have precipitated at temperatures between 27 and 36 °C, which is near the upper temperature limit for metazoans. A seawater δ¹⁸O value of ?2‰ SMOW yields temperatures ranging from 23 to 31 °C, while a ?3‰ SMOW value yields temperatures of 18–26 °C.  相似文献   

The carbonate factory of Middle Triassic buildups in the Dolomites, Italy: a quantitative analysis     

MARK T. HARRIS 《Sedimentology》1996,43(2):401-402

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Can New Zealand's Covenanting Agencies Meet the Challenge of the Biodiversity Strategy?     

MARK BELLINGHAM 《New Zealand geographer》2002,58(1):43-49

In February 2000 the New Zealand Government released its national Biodiversity Strategy with significant emphasis on the role of central and local government, communities and private landowners in achieving biodiversity conservation on public and private land. New Zealand has had provisions in legislation for the protection of biodiversity on private land for more than 70 years. There are now a wide range of of purposes and management flexibility within the nine types of covenants administered by the Department of Conservation (DoC) and the Queen Elizabeth National Trust's (QE II National Trust) Open Space covenants. In addition a small number of territorial local authorities (TLAs) manage private covenanting schemes, the most notable being the Auckland Region by Rodney and Franklin District Councils. Funding appears to be the critical issue for covenanting agencies being able to meet the objectives of the NZ Biodiversity Strategy affecting the ability of agencies to fund survey, administration, fencing, pest management and landowner advice. Unless funding is addressed landowners will be left shouldering most of the burden of conservation management, planning and funding for these areas and the tide may not have turned for biodiversity protection and enhancement on private land.  相似文献   

Pressure, Temperature, and Structural Evolution of West-Central New Hampshire: Hot Thrusts over Cold Basement   总被引：2，自引：0，他引：2  

KOHN  MATTHEW J.; ORANGE  DANIEL L.; SPEAR  FRANK S.; RUMBLE  DOUGLAS  III; HARRISON  T. MARK 《Journal of Petrology》1992,33(3):521-556

Pressure-temperature (P-T) paths have been calculated from pelitesand amphibolites of several major Acadian structures in west-centralNew Hampshire by using both inclusion thermobarometry and differentialthermodynamics (the Gibbs method). P-T paths calculated forrocks exposed in the Orfordville and Bronson Hill anticlinoriaare ‘clockwise’ and show 1–2.5 kb of exhumationwith 30–100 C of heating. Because this type of path ischaracteristic of the lower plate of overthrust terranes, theserocks are interpreted to be (para)autochthonous. P-T paths forrocks exposed in an intervening synclinorium (the Hardscrabblesynclinorium) show isothermal loading of 1–3 kb followedby possible isobaric cooling. This behavior is characteristicof rocks occupying a middle-plate structural position withina multiple thrust package, and so these rocks are interpretedto be allochthonous. The interpretation that the Hardscrabblerocks are allochthonous differs from previous models, but betterexplains the petrologic data and is consistent with the stratigraphicand structural data on which other models have been based. Correlation of the P-T paths with deformational events throughkinematic and textural analysis indicates that during nappestage deformation, the synclinorial rocks were transported westward,and that the anticlinorial and synclinorial rocks were buriedto depths of 25–30 and 20–25 km respectively. Theexhumation with heating recorded by the anticlinorial samplesoccurred during the dome stage of deformation, and differentiallyuplifted the anticlinorial rocks relative to the synclinorialrocks; this differential uplift may have been accommodated throughreactivation of early thrust faults with normal movement sense.P-T paths of the Hardscrabble synclinorium rocks are suggestiveof a relatively elevated initial geothermal gradient for theirpre-nappe source terrane, which is interpreted to have beenbetween the Kearsarge-Central Maine basin and the Bronson Hillparautochthon.  相似文献   

REPLY     

MARK WILKINSON 《Sedimentology》1992,39(3):518-520

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Dacite Genesis via both Slab Melting and Differentiation: Petrogenesis of La Yeguada Volcanic Complex, Panama   总被引：20，自引：2，他引：20  

DEFANT  MARC J.; RICHERSON  PHIL M.; DE BOER  JELLE Z.; STEWART  ROBERT H.; MAURY  REN? C.; BELLON  HERV?; DRUMMOND  MARK S.; FEIGENSON  MARK D.; JACKSON  THOMAS E. 《Journal of Petrology》1991,32(6):1101-1142

La Yeguada volcanioc complex (LYVC) is one of many major volcanoesthat represent the extension of the Central American arc inwestern Panama and that have resulted from current oblique subductionsouth of Panama. There are two major phases of calc-alkalinevolcanic activity at LYVC based on mapping and K-Ar radiometricdates. The first phase began at {small tilde} 13 Ma and ceasedat {small tilde} 7?5 Ma. This sequence, termed the old group,consists of basalts to rhyolites with typical arc mineralogies(OL, CPX, PL, MGT, and OPX). The samples have similar radiogenicSr and Nd values and appear to be related by fractional crystallizationwith assimilation and/or magma mixing involved in the differentiation.The parental basalts were probably derived from the metasomatizedmantle wedge via melting induced by fluids released from thesubducted lithosphere. There was an apparent period of minor volcanic activity from7–5 to 2–5 Ma (only one documented sample from thisperiod). The second phase (<2?5 Ma), termed the young group,consists only of dacites but with very different mineralogies(PL, MGT, AM, BI, with no PX) and geochemistries (e.g., highSr and low Y and HREE) compared with the old-group dacites (andandesites and rhyolites). The dacites cannot be related to theold group by various petrogenetic modeling techniques. Thesehigh-Al dacites have the characteristics of magmas derived fromthe partial melting of the subducted oceanic lithosphere witha hornblende eclogite residuum. This has been substantiatedby geochemical modeling. Samples similar to the young-group dacites in other arcs havebeen termed adakites and arc associated with the subductionof young hot crust which may explain why the slab melts. ThePanama basin has extremely high heat flow values, comparablewith those of the Galapagos ridge system. The change from normalarc volcanism to adakites suggests that the subducted oceaniccrust became hotter as time progressed. The subduction of anoceanic ridge or new ridge development along the Sandra Riftin the Panama basin can explain the change in volcanism withtime but more geophysical data are needed.  相似文献