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1.
2.
ACOSTA-VIGIL ANTONIO; LONDON DAVID; DEWERS THOMAS A.; MORGAN GEORGE B. VI 《Journal of Petrology》2002,43(10):1885-1908
The mechanisms and kinetics of equilibration between peraluminousminerals and granitic melt were investigated experimentallyby the dissolution of corundum and andalusite into H2O-saturatedmetaluminous haplogranitic melt at 800°C and 200 MPa. Mineraland haplogranitic glass rods were juxtaposed inside platinumcapsules, and then subjected to experimental conditions fortimes ranging from 12 to 2900 h. Upon melting, the mineral meltinterface retreats with the square root of time. The compositionof the melt at the interface changes with time, but its ASI[aluminum saturation index = molar Al2O3/(CaO + Na2O + K2O)]remains constant at 相似文献
3.
Integrating a GIS has been a common way to combine the functionality of two or more systems for some time. A three-dimensional model of integration is described which shows the range of linkages that can be achieved. Extremely flexible and dynamic linkages between systems can now be created through the recent advances of client/server and object-oriented technology. An expert system shell is coupled with a GIS to create a generic spatial rule-based toolbox called SES (spatial expert shell). An expert system developer using this toolbox can transparently access spatial data and relationships from a GIS by linking application objects to spatial classes. These spatial classes include methods that format and send requests to the GIS server. Thus the linkage is determined at run-time allowing a flexible interwoven interaction between the expert system and the GIS. 相似文献
4.
KEVIN TIMONEY GEORGE PETERSON PAT FARGEY MURRAY PETERSON STEVE McCANNY ROSS WEIN 《Climatic change》1997,35(4):463-483
A historic record of spring ice-jam floods of the Peace-Athabasca Delta was analyzed for the years 1826–1995. The temporal pattern of flooding is non-random. The likelihood of a flood following a flood, or a non-flood following a non-flood, is greater than expected by chance. Probability analysis of flood occurrence reveals that the period 1860–1880 was a time of unusually few floods, and the period 1915–1950 was a time of unusually frequent floods. The long-term flood frequency is 1 flood in 6.25 years. Changes in flood frequency over the record reveal a pattern of oscillation described by a sine-based model that is correlated with the long-term (Gleissberg) cycle of solar activity. Monte Carlo simulation was used to test a Bennett Dam Model and a Cyclic Model. The Bennett Dam Model is unlikely to have generated the observed flood history (p=0.04). The observed flood history shows a better fit to the Cyclic Model (p=0.65). No correlations between floods and ENSO cold or warm events was detected. The most recent wet period began about 1900 and ended in the early 1960's prior to completion of the W. A. C. Bennett Dam in British Columbia. As independent corroboration of climatically-driven changes in flood frequency we present three additional lines of evidence. The pattern of annual muskrat returns (95 year record) reveals both 10 year cycles and long-term patterns that agree well with the observed flood cycle. The annual area burned in Wood Buffalo National Park is inversely related to flood occurrence. Incised channels and dendritic drainage patterns in the bed of Lake Mamawi provide probable evidence of a previous dry period in the delta. Climatic change or oscillation likely underlies the drying trend observed in recent decades in the Peace-Athabasca Delta. 相似文献
5.
Alluvial fans and fan deltas can, in principle, have exactly the same upstream conditions, but fan deltas by definition have ponding water at their downstream boundary. This ponding creates effects on the autogenic behaviour of fan deltas, such as backwater adaptation, mouth bars and backward sedimentation, whereas alluvial fans may lack these effects. Hence the present authors hypothesize that morphodynamics on alluvial fans are determined primarily by upstream boundary conditions, whereas morphodynamics on fan deltas are determined by both the upstream and the downstream boundary condition and changes therein. To isolate the effects of the upstream and downstream boundaries, five new alluvial fan experiments are compared with the details of three fan deltas published earlier that were formed under very similar and simple conditions. Similar to the fan deltas, the alluvial fans build up by sheet flow, whilst quasi‐regular periods of incision cause temporary channelized flow. Incision is followed by channel backfilling, after which the fan returns to sheet flow. The channelization and backfilling in alluvial fans is markedly less pronounced and more prone to autogenic disturbance than in fan deltas. The difference is caused by morphodynamics at the downstream boundary. In a fan delta, the flow expansion of the channel causes deposition of all the sediment, which forms a mouth bar and causes strong backfilling. In an alluvial fan, on the other hand, the slope break at the fan perimeter causes some deposition, but transport is not reduced to zero. Consequently, the backfilling in alluvial fans is less pronounced than in fan deltas. Other published experiments support this trend: removal of the mouth bar by a river leads to permanent channelization, whilst pronounced mouth‐bar formation in highly channelized deltas promotes backward sedimentation. The experimental results for this study predict that, when alluvial fans prograde into lakes or deep rivers, they transition to fan deltas with increasingly deeper channels and thicker backfill deposits. 相似文献
6.
CALVIN J. HEUSSER THOMAS V. LOWELL LINDA E. HEUSSER ARTURO HAUSER BJ
RN G. ANDERSEN GEORGE H. DENTON 《第四纪科学杂志》1996,11(3):173-184
Palaeoecological studies carried out in the Chilean Lake District and Chilotan Archipelago (41°–43°S) record full-glacial and late-glacial pollen assemblages beginning just after 21000 and beetle assemblages after 18000, both sets extending until 10000 14C yr BP. Pollen records indicate that Subantarctic Parkland, the vegetation of the early millennia of record, changed after about 14000 yr BP to become open woodland and later North Patagonian Evergreen Forest. Assemblages of plants and beetles, responding more or less in unison to a strong rise in temperature (≥ 6°C), behaved in accord at around 14000 until 13000–12500 yr BP, the beetle fauna displaying a marked increase in obligate forest types. During full-glacial conditions (17400–16100 and 15300 and 14400 yr BP) and in the late-glacial interval (after about 13000 yr BP), however, climate evidently coerced populations dissimilarly, the pollen sequence showing an increase in plant taxa indicative of colder climate, whereas the beetle fauna underwent little or no variation. Contrasting climate modes implied by plants and beetles may be attributed to differential responses to apparent low-order temperature changes (≤ 2–3°C). 相似文献
7.
Vertical trends in architecture and facies of delta systems are preserved in a clastic wedge of an expanding marine half-graben in which tectonics, eustatic sea-level change and climatic change are roughly known from independent evidence. The studied half-graben is situated on Crete (Greece) and part of a larger, E-W-trending extensional domain situated north of the Hellenic subduction zone. The extension seems to be related to the southward migration of the trench (roll-back) in early Late Miocene times. The infill pattern is discussed in the light of theoretical fault-growth models for expanding half-grabens. The geometry of the half-graben fill is typically wedge shaped, with a thickness of nearly 1000 m near the fault scarp thinning to c. 50 m about 20 km away from the scarp. The lower part of the wedge (Stratified Prina Series) contains coarsening-upward units representing progradational, shallow-marine deltas. At the base of the wedge these units are thin and retrogradationally stacked. Upwards in the succession, the units become composite (coarsening-upward subunits), thicker and finer grained. The composite structure, the thickening and the fining trend is related to progressive increase in accommodation space inherent in fault growth. Rapid deepening of the basin from the photic zone (evidenced by intercalated coral and stromatolite beds) up to a depth of 900 m started at the top of the Stratified Prina Series. The deepening continued over some tens of metres of marly sediments of the base of the Kalamavka Formation and may be related to structural collapse of the fault block. After the structural collapse, basin depth remained more or less constant and basin infilling occurred by progradation of deep-water delta systems. These systems are characterized by a muddy delta slope with channelized conglomerates, and by mainly aggradation of prodelta turbidites deposited in small lobes at the base of slope. 相似文献
8.
The early Holocene S-1 sapropelic sequence in the northwest Hellenic Trench has been studied in six piston cores from the Zakinthos and Strofadhes basins. The S-1 sequence, 0.7-3.5 m thick, consists principally of silt to mud turbidites, with rare, thick, disorganized, sandy turbidites. These lithofacies are described and compared with fine-grained turbidites from the literature. Petrographical data, including the abundance of organic carbon and planktonic microfossils, indicate that the principal source of sediment to the turbidites was from the continental slope. On the basis of composition and texture, five turbidite units can be correlated between the two basins. These basins are fed by separate but adjacent drainage systems. The apparently synchronous occurrence of turbidites in the two drainage systems suggests that the turbidity currents were seismically triggered. Some of the turbidites show poorly organized beds which may reflect the slump origin and the short (30 km) distances of travel. Turbidites were deposited more frequently in the S-1 sapropelic interval than in the over- and underlying sediments. Application of slope stability analysis shows that on the 8° slopes above the basins, a 10-cm-thick sapropel would have a factor of safety of about 2, and would fail with earthquake accelerations in excess of 0.08 g. The frequency of earthquakes likely to produce such accelerations is similar to the observed frequency of turbidites. The low strength of the sapropelic sediment makes it particularly susceptible to such failure. Similar thin-skinned slumping may be an important process for the initiation of turbidity currents in other environments where there are steep slopes or high sedimentation rates. 相似文献
9.
An approach to extraction of viscoelastic parameters from seismic data is implemented and succesfully tested. Viscoelastic inversion is performed using adaptive damping factors to control the sensitivity of the viscoelastic parameters in relation to the τ-p seismic data. A priori information is incorporated through the damping factors as standard deviations of the data and of the viscoelastic model parameters. The stability of the inversion process is controlled by the variation of the damping factors as a function of the residual errors and parameter updates at each iteration. Tests on synthetic and real data show that P- and S-wave quality factors, Qp and Qs, in addition to P- and S-wave velocities and density Cp, Cs and p, can be extracted from τ-p seismic information. Singular value decomposition analysis demonstrates that estimated Qp and Qs values are more affected by the presence of data inaccuracies and noise than are those of Cp and p. Cs and Qs are not uniquely recovered due to the limited contribution of P-S converted waves. Knowledge of the viscoelastic parameters is of particular importance in accurately describing petrophysical properties of rocks and pore fluids existing in the subsurface; this is demonstrated with real data from the Gulf of Mexico. 相似文献
10.
GEORGE B.BARBOUR. 《地质学报》1923,2(1)
Ⅰ. INTRODUCTION. "One of the striking features in the Tsinan plain is a group ofisolated hillocks standing up boldly from it. Though mainly overgrown withvegetation, they are distinguishable by ther shape and dark colour from thelight-grey tabular limestone islands which for the last outposts pushedforward by the mountains lying to the south." 相似文献