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1.
JÜRGEN TITSCHACK CAMPBELL S. NELSON TIM BECK ANDRÉ FREIWALD ULRICH RADTKE 《Sedimentology》2008,55(6):1747-1776
Autochthonous red algal structures known as coralligène de plateau occur in the modern warm‐temperate Mediterranean Sea at water depths from 20 to 120 m, but fossil counterparts are not so well‐known. This study describes, from an uplifted coastal section at Plimiri on the island of Rhodes, a 450 m long by 10 m thick Late Pleistocene red algal reef (Coralligène Facies), interpreted as being a coralligène de plateau, and its associated deposits. The Coralligène Facies, constructed mainly by Lithophyllum and Titanoderma, sits unconformably upon the Plio‐Pleistocene Rhodes Formation and is overlain by a Maerl Facies (2 m), a Mixed Siliciclastic‐Carbonate Facies (0·2 m) and an Aeolian Sand Facies (2·5 m). The three calcareous facies, of Heterozoan character, are correlated with established members in the Lindos Acropolis Formation in the north of the island, while the aeolian facies is assigned to the new Plimiri Aeolianite Formation. The palaeoenvironmental and genetic‐stratigraphic interpretations of these mixed siliciclastic‐carbonate temperate water deposits involved consideration of certain characteristics associated with siliciclastic shelf and tropical carbonate shelf models, such as vertical grain‐size trends and the stratigraphic position of zooxanthellate coral growths. Integration of these results with electron spin resonance dates of bivalve shells indicates that the Coralligène Facies was deposited during Marine Isotope Stage 6 to 5e transgressive event (ca 135 to 120 ka), in water depths of 20 to 50 m, and the overlying Maerl Facies was deposited during regression from Marine Isotope Stage 5e to 5d (ca 120 to 110 ka), at water depths of 25 to 40 m. The capping Aeolian Sand Facies, involving dual terrestrial subunits, is interpreted as having formed during each of the glacial intervals Marine Isotope Stages 4 (71 to 59 ka) and 2 (24 to 12 ka), with soil formation during the subsequent interglacial periods of Marine Isotope Stages 3 and 1, respectively. Accumulation rates of about 0·7 mm year?1 are estimated for the Coralligène Facies and minimum accumulation rates of 0·2 mm year?1 are estimated for the Maerl Facies. The existence of older red algal reefs in the Plimiri region during at least Marine Isotope Stages 7 (245 to 186 ka) and 9 (339 to 303 ka) is inferred from the occurrence of reworked coralligène‐type lithoclasts in the basal part of the section and from the electron spin resonance ages of transported bivalve shells. 相似文献
2.
Models of continental crustal magmagenesis commonly invoke theinteraction of mafic mantle-derived magma and continental crustto explain geochemical and petrologic characteristics of crustalvolcanic and plutonic rocks. This interaction and the specificmechanisms of crustal contamination associated with it are poorlyunderstood. An excellent opportunity to study the progressiveeffects of crustal contamination is offered by the compositeplutons of the Alaska Range, a series of nine early Tertiary,multiply intruded, compositionally zoned (Peridotite to granite)plutons. Large initial Sr and Nd isotopic contrasts betweenthe crustal country rock and likely parental magmas allow evaluationof the mechanisms and extents of crustal contamination thataccompanied the crystallization of these ultra-mafic throughgranitic rocks. Three contamination processes are distinguishedin these plutons. The most obvious of these is assimilationof crustal country rock concurrent with magmatic fractionalcrystallization (AFC), as indicated by a general trend towardcrustal-like isotopic signatures with increasing differentiation.Second, many ultramafic and mafic rocks have late-stage phenocrystreaction and orthocumulate textures that suggest interactionwith felsic melt. These rocks also have variable and enrichedisotopic compositions that suggest that this felsic melt wasisotopically enriched and probably derived from crustal countryrock. Partial melt from the flysch country rock may have reactedwith and contaminated these partly crystalline magmas followingthe precipitation and accumulation of the cumulus phenocrystsbut before complete solidification of the magma. This suggeststhat in magmatic mush (especially of ultramafic composition)crystallizing in continental crust, a second distinct processof crustal contamination may be super imposed on AFC or magmamixing involving the main magma body. Finally, nearly all rocks,including mafic and ultramafic rocks, have (87Sr/86Sr)i thatare too high, and (T) Nd that are too low, to represent theexpected isotopic composition of typical depleted mantle. However,gabbro xenoliths with typical depicted-mantle isotopic compositionsare found in the plutons. This situation requires either anadditional enriched mantle component to provide the parentalmagma for these plutons, or some mechanism of crustal contaminationof the parent magma that did not cause significant crystallizationand differentiation of the magma to more felsic compositions.Thermodynamic modeling indicates that assimilation of alkali-andwater-rich partial melt of the metapelite country rock by fractionating,near-liquidus basaltic magma could cause significant contaminationwhile suppressing significant crystallization and differentiation. KEY WORDS: crustal contamination; Alaska Range; isotope geochemistry; zoned plutons; assimilation
*Corresponding author. e-mail: preiners{at}u.washington.edu; fax: (206) 543-3836. 相似文献
3.
Ice wastage and landscape evolution along the southern margin of the Laurentide Ice Sheet, north-central Wisconsin 总被引：1，自引：0，他引：1
NELSON R. HAM JOHN W. ATTIG 《Boreas: An International Journal of Quaternary Research》1996,25(3):171-186
The Chippewa and Wisconsin Valley Lobes of the Laurentide Ice Sheet reached their maximum extent in north-central Wisconsin about 20 000 years ago. Their terminal positions are marked by a broad area of hummocky topography, containing many ice-walled-lake plains, which is bounded on the up-ice and down-ice sides by ice-contact ridges and outwash fans. The distribution of these ice-disintegration landforms shows that a wide zone of stagnant, debris-covered, debris-rich ice separated from the active margins of both lobes as they wasted northward during deglaciation. Accumulation of thick, uncollapsed sediment in ice-walled lakes high in the ice-cored landscape indicates a period of stability. In contrast, hummocky disintegration topography indicates unstable conditions. Thus, we interpret two phases of late-glacial landscape evolution. During the first phase, ice buried beneath thick supraglacial sediment was stable. Supraglacial lakes formed on the ice surface and some melted their way to solid ground and formed ice-walled lakes. During the second phase, buried ice began to melt rapidly, hummocky topography formed by topographic inversion, and supraglacial and ice-walled lakes drained. We suggest that ice wastage was controlled primarily by climatic conditions and supraglacial-debris thickness. Late-glacial permafrost in northern Wisconsin likely delayed wastage of buried ice until after about 13 000 years ago, when climate warmed and permafrost thawed. 相似文献
4.
The Monteregian Hills petrographic province of southwesternQuebec, Canada, consists of a series of alkaline intrusionsemplaced along faults associated with the St. Lawrence graben.The intrusions are crudely cylindrical in shape, show verticalcontacts, and apparently extend to great depths. Where observed,igneous foliation is generally steeply dipping. The western intrusions consist of two petrographically distinctgroups. One group is composed of slightly undersaturated tocritically saturated pyroxenites and gabbros, largely of cumulateorigin, and associated slightly quartz-saturated syenites. Thesecond group is composed of strongly to moderately undersaturateddiorites, monzonites, and syenites which contain significantamounts of feldspathoidal minerals. The Oka carbonatite complexbelongs to the latter group. Available age data indicate that these two petrographic groupsrepresent separate periods of igneous activity. The slightlyundersaturated to critically saturated series has a mean ageof 136 Ma, while the strongly to moderately undersaturated serieshas a mean age of 118 Ma. Mounts Royal and St. Bruno are largely composed of gabbros andpyroxenites which belong to the slightly undersaturated to criticallysaturated series. These units consist of variable amounts ofcumulus pyroxene and olivine and intercumulus minerals. Someof the finer-grained gabbros approximate liquid compositions.Major and trace element rock and mineral chemistry demonstratethat the evolution of these magmas was largely controlled bypyroxene and olivine fractionation, with plagioclase appearingon the liquidus late in the crystallization history. The quartz-bearingsyenites at Mt. St. Bruno represent a late stage differentiatewhich was contaminated by siliceous crustal material. The strongly to moderately undersaturated series is representedby the essexites and pulaskites at Mount Johnson and the nepheline-bearingdiorites and feldspathoidal monzonites and syenites at MountRoyal. The petrogenetic relationships between these rocks arecomplex and apparently involve a number of processes includingliquid immiscibility, contamination, and alkali transport. Low initial Sr isotope ratios (0.7032 to 0.7035) for both ofthese rock series indicate a mantle origin. Calculated initialmelts are alkali picrites for the slightly undersaturated tocritically saturated series and basanites for the strongly tomoderately undersaturated series. The alkali picrites can beproduced by an 8 per cent melt of a light rare-earth enrichedgarnet lherzolite source. The basanites require a much morelimited degree of melting (1–2 per cent) of a spinel lherzolitesource. In the case of the basanites, CO2 may have played animportant role in determining the nepheline-normative characterof the magmas. 相似文献
5.
NELSON R. HAM JOHN W. ATTIG 《Boreas: An International Journal of Quaternary Research》2001,30(1):31-41
Approximately 35 parallel, discontinuous glacial ridges occur in an area of about 100 km2 in north‐central Wisconsin. The ridges are located between about 6 and 15 km north (formerly up‐ice) of the maximum extent of the Wisconsin Valley Lobe of the Laurentide Ice Sheet. The ridges are between 1 and 4 m high, up to 1 km long, and spaced between 30 and 80 m apart. They are typically asymmetrical with a steep proximal (ice‐contact) slope and gentle distal slope. The ridges are composed primarily of subglacial till on their proximal sides and glacial debris‐flow sediment on the distal sides. In some ridges the till and debris‐flow sediment are underlain by sorted sediment that was deformed in the former direction of ice flow. We interpret the ridges to be recessional moraines that formed as the Wisconsin Valley Lobe wasted back from its maximum extent, with each ridge having formed by a sequence of (1) pushing of sorted ice‐marginal sediment, (2) partial overriding by the glacier and deposition of subglacial till on the proximal side of the ridge, and (3) deposition of debris‐flow sediment on the distal side of the ridge after the frozen till at the crest of the ridge melted. The moraines are similar to annual recessional moraines described at several modern glaciers, especially the northern margin of Myrdalsjokull, Iceland. Thus, we believe the ridges probably formed as a result of minor winter advances of the ice margin during deglaciation. Based on this assumption, we calculate the net rate of ice‐surface lowering of the Wisconsin Valley Lobe during the period when the moraines formed. Various estimates of ice‐surface slope and rates of ice‐margin retreat yield a wide range of values for ice‐surface lowering (1.7–14.5 m/yr). Given that ablation rates must exceed those of ice‐surface lowering, this range of values suggests relatively high summer temperatures along the margin of the Wisconsin Valley Lobe when it began retreating from its maximum extent. In addition, the formation of annual moraines indicates that the glacier toe was thin, the ice surface was clean, and the ice margin experienced relatively cold winters. 相似文献
6.
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
7.
The first significant government sponsored community‐based forest management project in Australia was initiated in Central Victoria in 2002. This paper analyses the initial stage of the Wombat Community Forest Management Pilot Project. The paper develops a functional concept of ‘effective community’ for structuring community engagement in these kinds of natural resource management projects. The effective community has characteristics in common with a community of interest, adopts a bioregional perspective, embodies the values of environmental stewardship and interacts in a fully informed way as a ‘discursive community’ (Meppam 2000). The paper offers general advice for organising effective community engagement in such projects and 12 recommendations for governments developing similar initiatives elsewhere. 相似文献
8.
A glove box for the fine-scale subsampling of sediment box cores 总被引：1，自引：0，他引：1
HARRY M. EDENBORN ALFONSO MUCCI NELSON BELZILE JEAN LEBEL NORMAN SILVERBERG BJØRN SUNDBY† 《Sedimentology》1986,33(1):147-150
The construction and operation of a glove box which allows the fine-scale vertical subsampling of sediment box cores under a low oxygen atmosphere is described. 相似文献
9.
PATRICIA NELSON LIMERICK 《Geographical review》1998,88(4):483-491
ABSTRACT. Adopting the persona of the nonacademic, J. B. Jackson was, nonetheless, a major influence on academic scholarship. Expertly and deftly, he played on his understanding of scholarly convention, pushing the boundaries of “legitimate” generalization and assertion. Careful observation of his style reveals eight strategies for testing, mocking, and challenging habits of mind that can unnecessarily constrict scholarly inquiry. From daring in the drawing of conclusions to the wily use of the pronoun “we,” from a refusal to defer to middle-class values to the baiting of environmentalists, Jackson at once had a good time and called much of academic propriety into question. An examination of his “game plan” gives scholars a chance to examine their own habitual practices. 相似文献
10.
K. H. BAINES P. DROSSART T. W. MOMARY V. FORMISANO C. GRIFFITH G. BELLUCCI J. P. BIBRING R. H. BROWN B. J. BURATTI F. CAPACCIONI P. CERRONI R. N. CLARK A. CORADINI M. COMBES D. P. CRUIKSHANK R. JAUMANN Y. LANGEVIN D. L. MATSON T. B. MCCORD V. MENNELLA R. M. NELSON P. D. NICHOLSON B. SICARDY C. SOTIN 《Earth, Moon, and Planets》2005,96(3-4):119-147
The wide spectral coverage and extensive spatial, temporal, and phase-angle mapping capabilities of the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini-Huygens Orbiter are producing fundamental new insights into the nature of the atmospheres of Saturn and Titan. For both bodies, VIMS maps over time and solar phase angles provide information for a multitude of atmospheric constituents and aerosol layers, providing new insights into atmospheric structure and dynamical and chemical processes. For Saturn, salient early results include evidence for phosphine depletion in relatively dark and less cloudy belts at temperate and mid-latitudes compared to the relatively bright and cloudier Equatorial Region, consistent with traditional theories of belts being regions of relative downwelling. Additional Saturn results include (1) the mapping of enhanced trace gas absorptions at the south pole, and (2) the first high phase-angle, high-spatial-resolution imagery of CH4 fluorescence. An additional fundamental new result is the first nighttime near-infrared mapping of Saturn, clearly showing discrete meteorological features relatively deep in the atmosphere beneath the planet’s sunlit haze and cloud layers, thus revealing a new dynamical regime at depth where vertical dynamics is relatively more important than zonal dynamics in determining cloud morphology. Zonal wind measurements at deeper levels than previously available are achieved by tracking these features over multiple days, thereby providing measurements of zonal wind shears within Saturn’s troposphere when compared to cloudtop movements measured in reflected sunlight. For Titan, initial results include (1) the first detection and mapping of thermal emission spectra of CO, CO2, and CH3D on Titan’s nightside limb, (2) the mapping of CH4 fluorescence over the dayside bright limb, extending to ∼
∼750 km altitude, (3) wind measurements of ∼
∼0.5 ms−1, favoring prograde, from the movement of a persistent (multiple months) south polar cloud near 88° S latitude, and (4) the imaging of two transient mid-southern-latitude cloud features. 相似文献