The Stability of Sodalite in a Synthetic Syenite plus Aqueous Chloride Fluid System   总被引：2，自引：0，他引：2  

WELLMAN  THOMAS ROBERT 《Journal of Petrology》1970,11(1):49-72

Natural feldspathoidal syenites may be approximated by assemblagescontaining some or all of the phases sodalite, nepheline, oneor two alkali feldspars, and aqueous chloride fluid in the systemNaAISi₃O₈-KAISi₃O₈-NaAISiO₄-KAISiO₄-NaCI-KCI-H₂O. The stabilityof sodalite in these assemblages was studied in the range 500–700°C and 600–2000 bars fluid pressure. Sodalite appears to be a stable phase on the vapor-saturatedliquidus in this system over a wide range of pressure. At or near the vapor-saturated liquidus minimum in this system,three distinct types of sodalite-bearing syenite can crystallize.Nepheline-sodalite-one alkali feldspar rocks, nepheline-sodalite-twoalkali feldspars rocks and sodalite-analcime-bearing rocks crystallizebelow 1600 bars, between 1600 and 2750 bars and above 2750 barsfluid pressure, respectively. The effects of closed-system cooling on the assemblage sodalite-nepheline-twoalkali feldspars-aqueous fluid are different and distinguishablefrom the effects of metasomatism. Closed-system cooling resultsin replacement of K-feldspar by albite, feldspathoids remainingnearly unchanged, while metasomatism generally results in sismultaneousenrichment or impoverishment in sodalite plus K-feldspar.  相似文献   

SELECTION OF SEISMIC PICKING BASED UPON THE DIP,MOVE-OUT AND AMPLITUDE OF EACH EVENT*     

ROBERT GAROTTA 《Geophysical Prospecting》1971,19(3):357-370

The general use of continuous CDP seismic lines means that the neighbourhood of each depth point can be considered according to two sets of co-ordinates: — the co-ordinates of the abscissa on the seismic lines and the reflection time, which allow investigation of the local dip of coherent events; — the co-ordinates of the reflection time and the move out, which allow investigations of the average velocity for these same events. The combination of both investigations for each coherent event is a very convenient operation for the seismologist, and can provide some useful interpretation aids such as velocity profiles, or information on the interval velocities. The principles which we use consist in the examination of a large range of possibilities, of which only the most coherent are chosen. Some examples are shown.  相似文献   

LONGITUDINAL DUNES OF THE NORTHWESTERN EDGE OF THE SIMPSON DESERT, NORTHERN TERRITORY, AUSTRALIA, 1. GEOMORPHOLOGY AND GRAIN SIZE RELATIONSHIPS   总被引：3，自引：0，他引：3  

ROBERT L. FOLK 《Sedimentology》1971,16(1-2):5-54

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Bedform and stratification characteristics of some modern small-scale washover sand bodies   总被引：3，自引：0，他引：3  

ROBERT K. SCHWARTZ 《Sedimentology》1982,29(6):835-849

Washover sand bodies commonly develop along microtidal coastlines in beach/barrier island or spit settings. Wave runup, usually in conjunction with an abnormally high water level, may overtop the most landward berm of the beach and the foredune crest, if one exists, to produce overwash and subsequent runoff across the more landward subaerial surface. Two main elements of the resulting deposit are the washover fan and runoff channel. Newly formed, small-scale washover deposits were examined along the Outer Banks, North Carolina, near Pt Mugu, California, and at Presque Isle (Lake Erie), Pennsylvania. The fans were formed in response to unidirectional landward transport, and the runoff channels in response to unidirectional flow usually in a landward direction, but sometimes in shore-parallel then seaward direction. Where overwash carried across the fan surface and entered a pond or lagoon, a small-scale delta (microdelta) developed. In this case, the washover fan consisted of two subfacies, the wetted, but ‘subaerial’ part of the fan and the subaqueous washover delta. Flow associated with the development of the fan and runoff channel produced distinctive sets of bedforms and internal stratification. High velocity discontinuous surges moving across the fan surface resulted in the development of a plane bed and subhorizontal to low-angle (landward dipping) planar stratification which comprised the major part of the fan. Similarly, rhomboid forms were produced by high velocity sheet flow across the fan surface. Where flow carried into a standing body of water, delta-type foreset strata developed. For this case, the lateral structural sequence was subhorizontal, planar stratification merging landward into landward dipping, delta (tabular) foreset strata. In the runoff setting, where flow became channelized and continuous, both upper-flow and lower-flow regime currents were typical. Upper-flow regime bedforms included antidunes, standing waves, and plane beds. The most commonly observed lower-flow regime bedforms included microdelta-like bars, low-amplitude bars, linguoid ripples, and sinuous-crested current ripple trains. The sets of sedimentary structures comprising modern washover sand bodies provide criteria for the identification of similar deposits in ancient sediments and for more specific interpretation of the environment.  相似文献   

Neogene non-marine sedimentation and tectonics in small pull-apart basins of the San Andreas fault system, Sonoma County, California   总被引：1，自引：0，他引：1  

ROBERT J. McLAUGHLIN  TOR H. NILSEN 《Sedimentology》1982,29(6):865-876

The San Andreas fault system in northern California forms an 80–90 km wide zone of right-lateral shear. Extensional tectonism within this broad shear zone is indicated by both Neogene silicic volcanic rocks that gradually young in the direction of shear propagation to the north-west and by numerous Neogene faultbounded structural basins filled with thick non-marine sequences. The Little Sulphur Creek basins, three well-exposed 1·5–2 km wide pull apart basins within this shear system, have sedimentation patterns analogous to those of much larger pull-apart basins. They were formed and subsequently deformed by east-west extension and by north-west to south-east-orientated right-slip concurrently with basin filling. Palaeocurrent and maximum-clast size data indicate both lateral sediment transport from fault-bounded basin margins and longitudinal transport down the basin axes. The basins are filled primarily with coarse alluvial-fan and streamflow deposits derived from a surrounding igneous, sedimentary, and metamorphic provenance. Two of the basins contain basin-plain-type lacustrine turbidites that grade laterally into distal alluvial fan, fan-delta, and sublacustrine delta deposits. Talus deposits along the south-west margin of the basins contain megabreccia indicative of active uplift. Structures indicative of dewatering, liquefaction, and slumping suggest penecontemporaneous tectonism.  相似文献   

A Holocene palaeomagnetic record and a geomagnetic master curve from Ireland   总被引：1，自引：0，他引：1  

ROY THOMPSON  KEVIN J. EDWARDS 《Boreas: An International Journal of Quaternary Research》1982,11(4):335-349

Magnetic analyses have been carried out on sediments collected from Lough Catherine. Northern Ireland, as part of a wider environmental study. The sediments span the whole of the Holocene. Radiocarbon and pollen dating of the palaeomagnetic signature locked in the sediments form the basis of an Irish Holocene geomagnetic master curve. The mineral magnetic characteristics of the sediments correspond with environmental changes, such as eighteenth century landscaping and the elm decline as revealed by pollen analyses. Both marginal and central sediments have been analysed. The sediments can be correlated by using either magnetic, pollen, or 14 C measurements. These three independent core correlation methods all agree extremely well with each other. A mathematical method is described which can be used to calculate continuous accumulation rates and influxes.  相似文献   

Late Miocene Halimeda alga-microbial segment reefs in the marginal Mediterranean Sorbas Basin, Spain   总被引：1，自引：0，他引：1  

JOSÉ M. MARTÍN  JUAN C. BRAGA  ROBERT RIDING† 《Sedimentology》1997,44(3):441-456

A ～6 Ma Messinian (late Miocene) Bioherm Unit on the southern slope of the Sorbas Basin, SE Spain, contains numerous biotically diverse lensoid patch reefs that formed on a shelf to basin slope during a cycle of relative sea-level change. Halimeda reefs are the largest and most complex of the patch reefs and are divisible into core, cap, and flank facies. On the upper and midslope they are up to 40 m thick and 400 m long. They become smaller downslope. The core consists of jumbled Halimeda segments, released by spontaneous disaggregation of the alga. The segments were stabilized close to their sites of growth and rapidly lithified by micritic and peloidal microbial crusts. Residual cavities were further veneered by isopachous marine cements. Flank facies, consisting of bedded packstones to rudstones, form wedge-shaped units lateral to the mounds. Cap facies consist of bioclastic calcarenites/calcirudites and microbial carbonates. Synsedimentary lithification assisted rapid accretion and inhibited off-mound export of sediment. Allochthonous reef-derived blocks on the mid-slope reflect penecontemporaneous rigidity of the Halimeda bioherms. Proximal Porites coral frame patch reefs associated with calcarenites were located near the shelf margin during the initial lowstand stage. Halimeda segment reefs associated with calcarenites and silty marls developed on the midslope and bivalve-bryozoan-serpulid reefs formed on the lower slope in silty marls with occasional turbidites. During the transgressive stage, coral patch reefs near the shelfbreak were overgrown by Halimeda. During highstand progradation, cap facies spread basinward as a sheet connecting many of the midslope patch reefs. These ancient analogues differ from most modern Halimeda reefs in being discrete laterally restricted patch reefs, surrounded by marly sediment, and located on a slope. They are, however, broadly comparable in biota, thickness, and depositional depth. Intense early lithification by microbial crusts and marine cements is an important feature of these Messinian segment reefs. It has not been reported from modern examples.  相似文献   

Early Cambrian braid-delta deposits, MacKenzie Mountains, north-western Canada   总被引：2，自引：0，他引：2  

ROBERT B. MACNAUGHTON  ROBERT W. DALRYMPLE  GUY M. NARBONNE 《Sedimentology》1997,44(4):587-609

Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a pre-vegetation braid-delta depositional system. Depositional environments represented in the succession include braided fluvial and braid-delta distributary channels, aeolian dune fields and interdistributary lagoons/bays, as well as mouth bar, beach to shoreface, and prodelta to distal shelf settings. Three formations have been investigated: the Ingta Formation formed in wave-dominated nearshore to offshore shelf environments with little or no apparent deltaic influence, whereas the overlying Backbone Ranges and Vampire formations contain an extensive record of braid-delta deposits ranging from braidplain to distal prodelta facies. On the braid-plain, river channels reached widths of up to several kilometres. Such channels terminated seaward in braid deltas that showed some shoreline protuberance and were characterized by fluvial-dominated mouth-bar deposition with lesser wave influence; wave-dominated deltaic successions are rare in the succession. Interdeltaic areas were characterized by wave-dominated prograding shorelines. Interdistributary lagoons probably formed primarily in abandoned distributary channels. Delta-front/prodelta deposits are silt-rich and contain abundant soft-sediment deformation, including slumps. The deposits in these formations illustrate the significantly different nature of sedimentation prior to the advent of land plants. This is illustrated in the dominance of braided fluvial deposition and of silt-rich offshore facies that may have resulted from enhanced aeolian transport of loess. The non-actualistic effects of limited bioturbation and extensive microbial binding apparently exerted relatively little control on the distribution of facies. However, the absence of extensive bioturbation is manifest in pristine preservation of primary sedimentary structures, while the hypothesized latest Proterozoic-earliest Cambrian decline in microbial binding may be reflected in the upward increase in the abundance of sole marks in the succession.  相似文献   

THE MAGNETISM OF MIAMI: SEGMENTED PATHS IN CUBAN MIGRATION*     

KEVIN E. McHUGH  INES M. MIYARES  EMILY H. SKOP 《Geographical review》1997,87(4):504-519

ABSTRACT. Miami is the primate city in a system of urban settlements that make up a Cuban ethnic archipelago in the United States. The city is also a national magnet, attracting Cuban migrants from metropolitan regions across the archipelago. Four large secondary cores of Cubans outside Florida serve as major “feeders” to the Miami enclave: northern New Jersey, New York City, Los Angeles, and Chicago. Currents of migration to Miami are especially strong among older, foreign-born, and disadvantaged Cubans, an indication of segmented paths in Cuban assimilation. Although concentration in Metropolitan Miami has been the Cuban story over the past three decades, processes of deconcentration now may well be under way.  相似文献   

PHOTOGRAPHIC BEACH MEASUREMENTS     

ROBERT DOLAN 《Sedimentology》1967,8(1):77-80

An automated photographic method is described for recording short-interval changes in sand levels on a natural beach. Results of photographic technique are compared with profiles obtained by conventional surveying methods. Lapse-time photography offers a wide range of possibilities for accurate and efficient beach measurements when information in large amounts is required.  相似文献