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NOEL P. JAMES BRIAN JONES CAMPBELL S. NELSON HAMISH J. CAMPBELL JEREMY TITJEN 《Sedimentology》2011,58(4):1007-1029
The Chatham Islands, at the eastern end of the Chatham Rise in the South‐west Pacific, are the emergent part of a Late Cretaceous to Cenozoic stratovolcano complex that is variably covered with limestones and fossiliferous tuffs. Most of these deposits accumulated in relatively shallow, high‐energy, tide‐influenced palaeoenvironments with deposition punctuated by periods of deeper‐water pelagic accumulation. Carbonate components in these neritic deposits are biogenic and dominated by molluscs and bryozoans – a heterozoan assemblage. The widespread Middle to Late Eocene Matanginui Limestone contains local photozoan elements such as large benthonic foraminifera (especially Asterocyclina) and calcareous green algae, reflecting the general Palaeogene sub‐tropical oceanographic setting. More localized Late Eocene to Oligocene deposits (Te One Limestone) as well as Pliocene carbonates (Onoua Limestone) are, however, wholly heterozoan and confirm a generally cooler‐water oceanographic setting, similar to today. Early sea floor diagenesis is interpreted to have removed most aragonite components (infaunal bivalves and epifaunal gastropods). Lack of aragonite resulted in the absence of intergranular calcite cementation during subaerial exposure, such that most carbonates are friable or unlithified. Cementation is, however, present at nodular hardground–firmground caps to metre‐scale cycles. Such cements are microcrystalline or micrometre‐thick isopachous circumgranular rinds with insufficient definitive attributes to pinpoint their environment of formation. The overall palaeoenvironment of deposition is interpreted as mesotrophic, resulting in part from upwelling about the Chatham volcanic massif and in part from nutrient element delivery from the adjacent volcanic terrane and coeval volcanism. Biotic diversity in tuffs is two to three times that in limestones, supporting the notion of especially high nutrient availability during periods of volcanism. These mid‐latitude deposits are strikingly different from their low‐latitude, tropical, photozoan counterparts in the volcanic island–coral reef ecosystem. Ground water seepage and fluvial runoff attenuate coral growth and promote microbial carbonate precipitation in these warm‐water settings. In contrast, nutrients from the same sources feed the system in the Chatham Islands cool‐water setting, promoting active heterozoan carbonate sedimentation. 相似文献
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JEREMY K. LEGGETT 《Sedimentology》1980,27(4):401-417
Thick turbidites accumulated along the northern margin of the Iapetus Ocean in Britain from mid-Ordovician to late Silurian times. Recent plate tectonic reconstructions hold that, during subduction, packets of these sediments, together with the underlying pelagic facies and thin portions of the uppermost ocean crust, were stripped from the descending plate and accreted to the inner trench wall on the Laurentian (North American) continental margin. The resulting accretionary prism is represented today by the Ordovician and Silurian rocks of the Southern Uplands of Scotland and the Longford-Down massif of Ireland. In these areas major reverse faults separate tracts of steeply dipping greywackes and mudstones with minor amounts of cherts and basalts. These tracts are up to several kilometres wide; their constituent beds face predominantly to the northwest, away from the site of the ancient ocean, while becoming progressively younger in each major fault slice towards the Iapetus suture in the southeast. From the stratigraphic sequences in these fault slices the sedimentary history of a portion of the Iapetus Ocean, and the British sector of its northern margin, can be reconstructed. In the Southern Uplands the earliest turbidites (mid- and late-Ordovician) are preserved in the northernmost fault slices. Regional facies trends, and vertical facies analysis, suggest that they accumulated in a trench dominated by a series of relatively small lower trench slope-derived fans. Pelagic sediments of the same age are found in the fault slices to the south, suggesting that the Ordovician turbidites were confined to the trench. During the lower and middle Llandovery, volcaniclastic trench turbidites were separated from quartz-rich ocean-floor turbidites (represented in the southern fault slices) by an elongate rise, on which pelagic deposits accumulated. This is interpreted as the outer trench high. In late Llandovery times the rise was overwhelmed, and thick laterally derived quartzose turbidites blanketed both the trench and the ocean floor. Sedimentation was strongly influenced by the evolution of the accretionary prism. By Llandovery times a trench slope break had emerged, supplying sediment both south to the trench and north to an upper slope basin in the Midland Valley of Scotland. In this basin early Silurian turbidites were followed by shallow-water and terrestrial sediments. Most of the sediment was derived from the emergent trench slope break: the volcanic arc and the Grampian orogenic belt to the north provided little or no detritus. Throughout the Ordovician and Silurian, sediment in the trench and on the ocean floor was derived from the volcanic arc, from the lower trench slope/trench slope break, from a degrading plutonic/metamorphic terrain (the Grampian Orogen), and locally by a minor amount of submarine sliding from carbonate-capped volcanic seamounts. Progressive elevation of the trench slope break in Silurian (and perhaps late Ordovician) times indicates that sediment from the arc-orogen hinterland must have bypassed the upper slope in the unexposed section of the margin to the northeast of the Southern Uplands, and travelled into the area axially along the trench floor. 相似文献
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JEREMY W. CRAMPTON 《Geographical review》2007,97(3):389-403
ABSTRACT. Biopolitical use of geosurveillance can create and sustain a politics of fear. Although the majority of surveillance literature focuses on individuals, in this article I focus on groups and populations, drawing on Michel Foucault's analysis of biopolitics. After discussing the forms and history of geosurveillance I argue that three particularly important factors contribute to these politics: divisions, geospatial technologies, and the risk‐based society. In order to combat the negative unintended consequences of these factors I suggest that more attention be paid to the mutual relationships between geospatial technology and politics, rather than on assessments of the value of individual surveillant technologies. (09–11–06) 12:01 PDT SAN FRANCISCO—A United Airlines flight that was diverted to Dallas this morning after an unclaimed electronic device was discovered onboard has landed at San Francisco International Airport, an airport spokesman said. The flight crew on United flight 351 from Atlanta to San Francisco elected to stop in Dallas around 7 a.m., said SFO spokesman Mike McCarron, after finding a backpack on board that no one claimed. The unattended backpack contained a PDA device, McCarron said, “like a Blackberry.” Authorities searched the plane in Dallas and found nothing unusual, he said.—Marisa Lagos, 2006. 相似文献
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BY NICHOLAS R. GOLLEDGE JEREMY D. EVEREST TOM BRADWELL JOANNE S. JOHNSON 《Geografiska Annaler: Series A, Physical Geography》2010,92(1):111-124
This paper presents new lichenometric population data from the Antarctic Peninsula (67°S), and describes a new approach to lichen growth-rate calibration in locations where dated surfaces are extremely rare. We use historical aerial photography and field surveys to identify sites of former perennial snowpatches where lichen populations now exist. As an independent check on lichen mortality by snowkill, and the timing of snow patch disappearance, we use a positive-degree day (PDD) approach based on monthly climate data from Rothera Research Station. We find that maximum growth rates for lichens <40 mm in diameter on Adelaide Island are around 0.8 mm/yr. Furthermore, we propose that our combined methodology may be more widely applicable to the Polar Regions where the construction of lichenometric dating (age-size) curves remains a problem. 相似文献
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The Geochemical Evolution of Anorthosite Residual Magmas in the Laramie Anorthosite Complex, Wyoming 总被引：6，自引：4，他引：2
MITCHELL JEREMY N.; SCOATES JAMES S.; FROST CAROL D.; KOLKER ALLAN 《Journal of Petrology》1996,37(3):637-660
Olivine- and pyroxene-bearing Fe-enriched dioritic rocks inthe 1434 Ma Laramie anorthosite complex are interpreted to representvariably fractionated and contaminated magmas residual afterthe crystallization of anorthosite. Geochemical characteristicsof this suite include the following: high contents of TiO2,, and P2O5; high incompatibletrace element contents; rare earth element patterns with a largerange of Eu anomalies; and isotopic compositions that reflectthe geographic location of individual samples, with ISr increasingand Nd decreasing from south to north. After extraction fromanorthosite, fractionation of ferrodioritic residual magmasresulted in secondary residual monzodioritic melts and complementaryoxide-rich ferrodiorite cumulates. Geographic trends in isotopiccomposition reflect an increasing Archean crustal componentfrom south to north. Dioritic dikes and cumulates with isotopiccompositions similar to associated anorthosites were derivedlocally. Large isotopic discrepancies between some dioritesand their hosting anorthosites reflect preferential contaminationof residual magma during ascent and emplacement of mantle-derivedplagioclase-rich diapirs, followed by subsequent extractionand isolation of Fe-enriched interstitial melt. Strong isotopiccontrasts between anorthosite and associated Fe-enriched rocksin anorthosite complexes do not preclude a direct relationshipbetween them and reflect the diversity and complexity of processesduring their petrogenesis. KEY WORDS: anorthosite; ferrodiorite; geochemistry; Laramie anorthosite complex; residual magma
*Corresponding author: Present address: Ceramic Science and Technology, Mail Stop K762, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. Phone: (505) 665-3934. Fax: (505) 665-3935. E-mail: jeremy{at}lanl.gov. 相似文献
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NEIL F. GLASSER JAMES L. ETIENNE MICHAEL J. HAMBREY JEREMY R. DAVIES RICHARD A. WATERS PHILIP R. WILBY 《Boreas: An International Journal of Quaternary Research》2004,33(3):224-237
This article presents the results of a geomorphological and sedimentological investigation of former glacial meltwater drainage in the region of the lower Afon Teifi, one of the major rivers of southwest Wales. Former drainage characteristics in the region are reconstructed concentrating on palaeo-drainage routes associated with successive Pleistocene glaciations and their role in the Quaternary evolution of the lower Teifi. Mapping of these features throughout a c. 100 km 2 area reveals a complex evolution in the establishment of the present-day drainage system, with evidence for the following surface channel types: (i) type 1 channels of primary subglacial origin cut during the late Devensian (late Wisconsinan/late Weichselian) glaciation; (ii) type 2 channels representing either pre-late Devensian subaerial fluvial run-off, unconnected to the course of the preglacial Afon Teifi, or originating as subglacial chute channels; (iii) type 3 channels developed as subglacially modified pre-late Devensian tributaries of the Afon Teifi. Two further features are also described: (iv) type 4 channels are drift-plugged abandoned preglacial courses of the Afon Teifi, and (v) type 5 channels formed as lateglacial and post-late Devensian gorges which bypass type 4 channels. A relative chronostratigraphy based on channel geomorphology and sedimentology reveals an evolutionary sequence considerably more complicated than identified in previous studies, with extensive modification of the lower Afon Teifi region by glacial meltwater during at least two periods of Pleistocene glaciation. 相似文献
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The sulfur content in basaltic melts coexisting with eithersulfide or sulfate melts was determined experimentally. Theexperimental conditions were in the range of 1300–1355°Cand 1·0–1·6 GPa, conditions appropriatefor the melting of the upper mantle above subduction zones.Under these conditions, both sulfide and sulfate were presentas immiscible liquids, as inferred from the round geometriesof the quenched sulfide and sulfate phases. The measured S contentin basaltic melts saturated with sulfate liquids ([S] = 1·5± 0·2 wt %) was 10 times higher than the S contentin basaltic melts saturated with sulfide liquids ([S] = 0·14± 0·02 wt %). In our experiments, sulfate liquidswere stable at fO2 as low as FMQ = +1·85 [FMQ = log (fO2)sample– log (fO2)FMQ, where FMQ is the fayalite–magnetite–quartzoxygen buffer], and evidence from other sources indicates thatsulfates will be stable at lower fO2 in melts with lower activitiesof silica. Because chalcophile and highly siderophile elements,such as Cu, Ni, Au, and Pd, are partitioned preferentially intosulfide phases, melting of sufficiently oxidized sources, inwhich sulfides are not stable, would favor incorporation ofthese elements into the silicate melt produced. Such melts wouldhave a higher potential to generate ore deposits. This studyshows that the high sulfur contents of such oxidized basaltsalso means that relatively small amounts of such magmas canprovide significant amounts of sulfur to exsolving volatilephases and account for the bulk of the sulfur expelled in somevolcanic eruptions, such the 1991 eruption of Mount Pinatubo. KEY WORDS: basalt; mantle; oxidation state; sulfate; sulfur 相似文献
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Spatial planning, water and the Water Framework Directive: insights from theory and practice 总被引：1，自引：0，他引：1
JEREMY G CARTER 《The Geographical journal》2007,173(4):330-342
Water is fundamental to the health of the biosphere, strong economic growth and human social well-being. Despite its relative scarcity and absolute importance to life on earth, fresh water resources are often used inefficiently or polluted unnecessarily. Policymakers must work towards developing approaches to balance human demands for water with the water requirements of ecosystems. The European Water Framework Directive, which aims to encourage the sustainable management and protection of freshwater resources, brings this agenda into sharp focus in Europe. Land use change and environmental quality are closely related, and the nature and location of development can significantly influence both the generation and resolution of environmental problems. This places spatial planning, which provides a framework for regulating the development and use of land, in a strong position to affect water quantity and quality issues and thus to aid the achievement of the Directive's goals. In particular, spatial planning has an important function in integrating the use and management of land and water more closely than is presently the case. This paper explores the potential and actual role of spatial planning in addressing challenges associated with the water environment. This enables an assessment to be made of the extent to which spatial planning can help to meet the goals of the Water Framework Directive. 相似文献
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On the transition between 2D and 3D dunes 总被引：3，自引：0，他引：3
Sediment transport in sand-bedded alluvial channels is strongly conditioned by bedforms, the planimetric morphology of which can be either two- or three-dimensional. Experiments were undertaken to examine the processes that transform the bed configuration from two-dimensional (2D) dunes to three-dimensional (3D) dunes. A narrowly graded, 500 μm size sand was subjected to a 0·15 m deep, non-varying mean flow ranging from 0·30 to 0·55 m sec−1 in a 1 m wide flume. Changes in the planimetric configuration of the bed were monitored using a high-resolution video camera that produced a series of 10 sec time-lapsed digital images. Image analysis was used to define a critical value of the non-dimensional span (sinuosity) of the bedform crestlines that divides 2D forms from 3D forms. Significant variation in the non-dimensional span is observed that cannot be linked to properties of the flow or bedforms and thus appears random. Images also reveal that, once 2D bedforms are established, minor, transient excesses or deficiencies of sand are passed from one bedform to another. The bedform field appears capable of absorbing a small number of such defects but, as the number grows with time, the resulting morphological perturbations produce a transition in bed state to 3D forms that continue to evolve, but are pattern-stable. The 3D pattern is maintained by the constant rearrangement of crestlines through lobe extension and starving downstream bedforms of sediment, which leads to bifurcation. The experiments demonstrate that 2D bedforms are not stable in this calibre sand and call into question the reliability of bedform phase diagrams that use crestline shape as a discriminator. 相似文献