排序方式： 共有23条查询结果，搜索用时 31 毫秒
11.
RAYMOND S. EILERTSEN GEOFFREY D. CORNER ODD AASHEIM LOUISE HANSEN 《Sedimentology》2011,58(7):1784-1809
Lithofacies characteristics and depositional geometry of a sandy, prograding delta deposited as part of the Holocene valley‐fill stratigraphy in the Målselv valley, northern Norway, were examined using morpho‐sedimentary mapping, facies analysis of sediments in exposed sections, auger drilling and ground penetrating radar survey. Various lithofacies types record a broad range of depositional processes within an overall coarsening‐upward succession comprising a lowermost prodelta/bottomset unit, an intermediate delta slope/foreset unit containing steeply dipping clinoforms and an uppermost delta plain/topset unit. Bottomset lithofacies typically comprise sand‐silt couplets (tidal rhythmites), bioturbated sands and silts, and flaser and lenticular bedding. These sediments were deposited from suspension fall‐out, partly controlled by tidal currents and fluvial effluent processes. Delta foreset lithofacies comprise massive, inverse graded and normal graded beds deposited by gravity‐driven processes (mainly cohesionless debris flows and turbidity currents) and suspension fall‐out. In places, delta foreset beds show tidal rhythmicity and individual beds can be followed downslope into bottomset beds. Delta plain facies show an upward‐fining succession with trough cross‐beds at the base, followed by planar, laminated and massive beds indicative of a bedload dominated river/distributary system. This study presents a model of deltaic development that can be described with reference to three styles within a continuum related primarily to water depth within a basin of variable geometry: (i) bypass; (ii) shoal‐water; and (iii) deep‐water deltas. Bypass and deep‐water deltas can be considered as end members, whereas shoal‐water deltas are an intermediate type. The bypass delta is characterized by rapid progradation and an absence of delta slope sediments and low basin floor aggradation due to low accommodation space. The shoal‐water delta is characterized by rapid progradation, a short delta slope dominated by gravity‐flow processes and a prodelta area characterized by rapid sea‐floor aggradation due to intense suspension fallout of sandy material. Using tidal rhythmites as time‐markers, a progradation rate of up to 11 m year?1 has been recorded. The deep‐water delta is characterized by a relatively long delta slope dominated by gravity flows, moderate suspension fall‐out and slow sea‐floor aggradation in the prodelta area. 相似文献
12.
The computer model for near shore wave propagation,SWAN,was used to study wave climates in Liverpool Bay,northwest England with various input parameters,including bottom friction factor,white capping,wind drag formulation and effects of tidal modulations.Results were compared with in-situ measurements and reveal the impacts from these inputs on the predictions of wave height and propagation distributions.In particular,the model results were found very sensitive to different input formulations,and tend to underestimate the wave parameters under storm conditions in comparison with the observations.It is therefore important to further validate the model against detailed field measurements,particularly under large storms that are often of the primary concern. 相似文献
13.
Kevin J. WALSH A. MORBIDELLI S. N. RAYMOND D. P. O’BRIEN A. M. MANDELL 《Meteoritics & planetary science》2012,47(12):1941-1947
Abstract– The asteroid belt is found today in a dramatically different state than that immediately following its formation. It is estimated that it has been depleted in total mass by a factor of at least 1000 since its formation, and that the asteroids’ orbits evolved from having near‐zero eccentricity and inclination to the complex distributions we find today. The asteroid belt also hosts a wide range of compositions, with the inner regions dominated by S‐type and other water‐poor asteroids and the outer regions dominated by C‐type and other primitive asteroids. We discuss a model of early inner solar system evolution whereby the gas‐driven migration of Jupiter and Saturn brings them inwards to 1.5 AU, truncating the disk of planetesimals in the terrestrial planet region, before migrating outwards toward their current locations. This model, informally titled “The Grand Tack,” examines the planetary dynamics of the solar system bodies during the final million years of the gaseous solar nebula lifetime—a few million years (Myr) after the formation of the first solids, but 20–80 Myr before the final accretion of Earth, and approximately 400–600 Myr before the Late Heavy Bombardment of the inner solar system. The Grand Tack attempts to solve some outstanding problems for terrestrial planet formation, by reproducing the size of Mars, but also has important implications for the asteroid population. The migration of Jupiter causes a very early depletion of the asteroid belt region, and this region is then repopulated from two distinct source regions, one inside the formation region of Jupiter and one between and beyond the giant planets. The scattered material reforms the asteroid belt, producing a population the appropriate mass, orbits, and with overlapping distributions of material from each parent source region. 相似文献
14.
PIETER BERTIER RUDY SWENNEN DAVID LAGROU BEN LAENEN RAYMOND KEMPS 《Sedimentology》2008,55(5):1375-1417
The Westphalian C and D fluvial sandstones in the Campine Basin (north‐east Belgium) are potential reservoirs for the sequestration of CO2 and interesting analogues of the hydrocarbon reservoirs in the Southern North Sea. Although these sandstones were deposited in a relatively short period of time, their reservoir properties and mineralogical compositions are very different. A petrographic study complemented with stable isotope analyses, fluid inclusion microthermometry and X‐ray diffraction analyses of the clay fractions of the sandstones, which were sampled from deep boreholes (>1000 m) in the Campine Basin, revealed that these differences are related mainly to the climate at the time of deposition. The most important eogenetic processes affecting the Westphalian sandstones were the generation of a pseudomatrix by physical compaction of Al‐silicates and lithic fragments that were strongly altered by extensive meteoric leaching, kaolinitization of unstable silicates and precipitation of siderite. These processes had a detrimental influence on the reservoir properties of Westphalian C sandstones, but their impact on the Westphalian D sandstones was minimal. The difference is assumed to be related to the climate at the time of deposition, which changed from tropical humid in the Westphalian C to semi‐arid/arid during the Late Westphalian D. Both the Westphalian C and D sandstones were affected by similar mesogenetic processes. Mesogenetic quartz cementation resulted from chemical compaction and illitization of kaolinite, K‐feldspar and smectitic clays. Illitization of kaolinite was controlled by the available quantities of co‐existing kaolinite and K‐feldspar and mainly affected the Westphalian D sandstones. Illitization of K‐feldspar was controlled by the K‐feldspar content. It had a much larger impact on the reservoir properties of the Westphalian D as, in these sandstones, K‐feldspar was less affected by eogenetic alteration. The illitization of smectitic clays resulted in illite, quartz and ankerite cementation in both reservoirs. This process had a more important impact on the Westphalian C reservoir, since cementation here also resulted from smectite to illite conversion in the interbedded and underlying shales. The effect of mesogenetic alterations on the reservoir properties was much less drastic than the impact of eodiagenesis. Mesogenetic alterations do exert a significant control on the properties of the Westphalian D. The vast impact of eodiagenesis on the Westphalian C sandstones made them less susceptible to mesogenetic alteration. The effect of telogenetic processes on the porosity and permeability of the Westphalian sandstones was small and restricted to the top reservoir intervals that directly underlie the Cimmerian Unconformity. No significant telogenetic alterations related to the Variscan Unconformity were observed. 相似文献
15.
RAYMOND M. RICE 《水文科学杂志》2013,58(3):315-321
16.
LYNDA A. DREDGE 《Boreas: An International Journal of Quaternary Research》2000,29(2):144-156
Regional carbonate dispersal trains cross Melville Peninsula in the northeastern Canadian Arctic. These trains are 50-125 km across and 100-300 km long. The northern dispersal train crosses upland and lowland areas, while the Rae Isthmus train follows the lowlands. The distribution of carbonate in boulder, pebble and matrix till fractions indicates long-distance glacial transport of limestone, a low rate of dilution, and comminution from pebble to silt sizes. Dispersal patterns and geotechnical properties of the till suggest deforming bed and basal gliding mechanisms of ice flow associated with ice-streaming. Regional ice streams may have been 'normative' in carbonate terrain during the main Foxe (Wisconsin) Glaciation. Till plumes within regional dispersal trains, showing little dilution of carbonate down-ice from bedrock sources, are oriented towards lowlands. These features, sharp-edged and 300 mwide, mark zones of augmented flow. They are late-glacial features that formed after calving bays developed in Committee Bay. The dimensions of the dispersal trains, and ice-flow styles and mechanisms, are similar to those of modern Antarctic ice streams. The sharp edges of till plumes may delineate flow boundaries marked by lateral crevasse zones in the late-glacial ice sheet. Secondary streams-within-ice streams have not been reported previously in the literature. 相似文献
17.
Stromatactis is a spar network whose elements in cross section have flat to undulose lower surfaces and digitate upper surfaces. The network is composed principally of isopachous crusts of centripetal cement and commonly occurs embedded in finely crystalline limestone. It is the cement filling of interconnected cavities. Stromatactis of Upper Silurian red stromatactis limestone from Gaspé Peninsula, Québec Appalachians, exhibits two types of cements: (1) an isopachous cement that lined the walls of the conduits and is interpreted as early marine; and (2) a later blocky cement that occupies the centres of cavities. The first cement is composed exclusively of non-ferroan calcite, whereas the second cement is mixed non-ferroan and ferroan calcite. The early isopachous cement is white on polished slabs and has a turbid aspect under transmitted light. In a few samples, the relative homogeneity of this early cement is broken by the presence of distinctive grey clear calcite. Under cathodoluminscence, the grey clear calcite is non-luminescent and exhibits well defined bladed crystal shapes, whereas the white turbid cement has a dull orange luminescence and indistinct crystal shapes. The relationships between the two cements indicate that the dull luminescent cement is a secondary form of the non-luminescent cement, and it is concluded that the dull cement is the product of alteration of the non-luminescent cement by burial or meteoric fluids. The later blocky cement has the same dull luminescence as the white turbid cement and is thought to have been precipitated from the same fluids as those responsible for the alteration of the early marine cements. Oxygen isotopic values of the dull cement of the early isopachous crusts (mean δ18O= -6.8%o are intermediate between those of the non-luminescent early marine cement (mean δ18O= -5.3%o) and the dull luminescent blocky cement (mean δ18O= -11.8%o), while carbon isotopic values do not differ significantly (δ13C=+2.9, +2.4 and +2.6%o, respectively). The alteration also has affected the distribution of some trace elements, particularly Mg. Both unaltered and altered cements contain less than 1% microdolomite inclusions, but the Mg content of the background calcite of unaltered cement is three times that of altered cement (14171 vs. 5502 ppm). Precursor early marine cement is thought to have been low-Mg calcite. The mean δ18O value (− 5.3%o) of unaltered early marine cement is higher than values for the oxygen isotopic signature of Silurian oceans provided by brachiopod shells. 相似文献
18.
LYNDA JOHNSTON 《New Zealand geographer》1997,53(2):29-33
In this paper I highlight some spatial and body politics of the HERO parade, Aotearoa/New Zealand's biggest gay pride parade. The proposed site change of the HERO parade, from Queen Street to Ponsonby Road, was debated at length in local newspapers. This debate can be theorised as contingent on western hierarchical dualisms such as mind/body, public/ private, straight/gay. 1 offer an embodied geography through a focus on the constitutive relationship between bodies and places. 相似文献
19.
LYNDA JOHNSTON 《New Zealand geographer》1995,51(1):16-18
I suggest that the training environment and the female built body are both politicised sites of change. The gym provides a material and discursive environment that reworks bodies in the masculine/feminine binary. The specific materiality of women's muscled (built) bodies provides the ground for contestation of Western heirarchical dualisms, thereby opening up new spaces to reconceptualise the sexed body in geography. 相似文献
20.
The effects of source lithology, transport, deposition and sampling scale on the composition of southern California sand 总被引：2，自引：0，他引：2
The Transverse Ranges of southern California represent an uplifted and variably dissected Mesozoic magmatic arc, and Mesozoic to Holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings. Modern sand within part of the Western Transverse Ranges represents: first-order sampling scale of the Santa Monica and the San Gabriel Mountains; second-order sampling scale of the Santa Clara River draining both mountain ranges; and third-order sampling scale of the beach system between the mouth of the Santa Clara River and the eastern Santa Monica Mountains, and turbidite sand of the Hueneme-Mugu submarine fan. Source lithology includes plutonic and metamorphic rocks of the San Gabriel Mountains, and sedimentary and volcanic rocks of the Santa Monica Mountains. First-order sands have large compositional variability. Sand from local coastal drainage of the Santa Monica Mountains ranges from basaltic feldspatholithic to quartzofeldspathic. Sand of the San Gabriel Mountains local drainages has three distinct petrofacies, ranging from metamorphiclastic feldspatholithic to mixed metamorphi/plutoniclastic and plutoniclastic quartzofeldspathic. Second-order sand is represented by the main channel of the Santa Clara River; the sand has an abrupt downstream compositional change, from feldspathic to quartzofeldspathic. Third-order sand (beaches and deep-sea turbidite samples) of the Santa Monica Basin is quartzofeldspathic. Beach sand is more quartz-rich than is Santa Clara river sand, whereas turbidite sand is more feldspar-rich than is beach sand. Deep-sea sand has intermediate composition with respect to second-order samples of the Santa Clara River and third-order samples of the beach system, suggesting that (1) the Santa Clara River is the main source of sediments to the marine environment; and (2) local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions. Petrologic data of modern sand of the study area are highly variable at first- and second-order scale, whereas third-order sand is homogenized. The homogenized composition of deep-marine sand is similar to the composition of most ancient sandstone derived primarily from the Mesozoic dissected magmatic arc of southern California. This study of the Western Transverse Ranges illustrates the effects of source lithology, transport, depositional environment, and sampling scale on sand composition of a complex system, which provides insights regarding actualistic petrofacies models. 相似文献