THE CARBONATE FRACTION OF BEACH AND DUNE SANDS   总被引：1，自引：0，他引：1  

ORRIN H. Pilkey    ROBERT W. MORTON  JOHN LUTERNAUER 《Sedimentology》1967,8(4):311-327

The sand size carbonate fractions of beach and dune sands from the southeastern U.S. Atlantic coast were investigated from the standpoint of mineralogy, roundness and size distribution. The carbonate fractions of beach-dune sands used in this study range in abundance from less than 1% to over 40% and average about 10%. Calcium carbonate is least abundant in Georgia beaches and increases slightly to the north and greatly to the south. The size distribution of the carbonate fraction is similar to that of the non-carbonate fraction since both have been distributed by the same processes. The variable flat shape of calcareous fragments causes the carbonate fraction to be usually coarser and more poorly sorted than the acid insoluble residues of the samples. No regional relationship between roundness and wave energies was found in sand size materials although field observations indicate high energies strikingly round gravel sized calcareous fragments. There is some tendency for angularity to increase with decreasing grain size in the sand sizes as with quartz grains. The mineralogy of beach sand carbonate fractions is characterized by the almost total absence of high My calcite. Aragonite is the dominant mineral.  相似文献   

OCCURRENCE OF HIGH-ANGLE STRATIFICATION IN LITTORAL AND SHALLOW NERITIC ENVIRONMENTS,CENTRAL GEORGIA COAST,U.S.A.1     

JOHN H. HOYT 《Sedimentology》1967,8(3):229-238

High-angle stratification (greater than 20°) is produced in several areas of shallow marine sedimentation along the barrier islands of the central Georgia coast. The maximum angle of inclination is 30° which is the angle of repose for the saturated, fine-grained, angular sand of this area. High-angle stratification forms in the following locations: (1) The depositional margin of tidal channel inlets. Under some wave and current conditions, sand accumulates near low tide level and steepens the depositional interface to the angle of repose. (2) The steep face of asymmetrical megaripples developed by tidal currents. Ripples with amplitudes as much as 3 ft. and wave lengths of 20–40 ft. commonly develop in channel inlets and other areas of sand sediments. (3) The steep face of sand waves formed in channel inlets. These large asymmetrical ripples have amplitudes as great as 12 ft. and wave lengths of ca. 300 ft. Lengths along the crests are over 600 ft. (4) The landward side of low bars developed on the beach. Bars and troughs (ridges and runnels) are common on the beaches of this area. The bars, which are as much as 5 ft. high, shift landward by deposition on the steep landward face. (5) The oceanward side of large sand waves at the mouth of offshore tidal channels. Large sand waves are located 6 miles offshore from Doboy Sound inlet in 20–25 ft. of water. The steep face of these asymmetrical sand waves is orientated toward the ocean. Amplitude of these large ripples is as much as 17 ft. and length along the crests is over 1/2 mile.  相似文献   

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines   总被引：1，自引：1，他引：1  

BRIAN J. TODD  PAGE C. VALENTINE  ODDVAR LONGVA  JOHN SHAW 《Boreas: An International Journal of Quaternary Research》2007,36(2):148-169

The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (<10 km long) also strike southwest-northeast. The mapped pattern of moraines implies that, shortly after the last maximum glaciation, the tidewater ice sheet began to retreat north from German Bank, forming De Geer moraines at the grounding line with at least one glacial re-advance during the general retreat. The results indicate that the Laurentide Ice Sheet extended onto the continental shelf.  相似文献   

New Chilean iron meteorites: Medium octahedrites from Northern Chile are unique     

JOHN T. WASSON  CLAUDIO CANUT DE BON 《Meteoritics & planetary science》1998,33(2):175-179

Abstract— We report data on three new iron meteorites from Northern Chile and propose names. All are unnamed iron meteorites from the meteorite collection at the Universidad de La Serena. For two, the provenance is unknown; for the third, the presumed discovery site is in the countryside east of Iquique. The three meteorites have been analyzed by instrumental neutron activation analysis (INAA) and their structures examined with a binocular microscope. La Serena is a complete 663 g iron, a new member of group IIICD; it is not paired with any other iron. Elqui has a mass of 260 g; two faces are fractures, possibly produced by human actions, but fusion crust appears to be present on some of the remaining surface. It is a hexahedrite and a member of group IIAB, but its composition differs from that of all other Chilean hexahedrites. The third iron, Pozo Almonte, is a medium octahedrite member of group IIIAB, one of the most common meteorite groups. To find out whether it is paired, we assembled a full set of IIIAB iron meteorites from Northern Chile. Our compositional data show that Pozo Almonte is not paired with any other IIIAB iron, and that there are no pairings within the full set with the possible exception of Joel's Iron and Sierra Sandon, which differ only in their contents of Ir, 0.39 and 0.34 μg/g, respectively. However, Buchwald's (1975) structural observations rule out this possible pairing. We find appreciable differences in Cu, As and Au between the previously paired IIIAB irons Chañaral and Ilimaës and conclude that these should not be paired.  相似文献   

MORAL GEOGRAPHY IN HIGH PLAINS HISTORY     

JOHN OPIE 《Geographical review》1998,88(2):241-258

ABSTRACT. When American society, through deliberate government action, intervenes to preserve the family farm as the locus of “good” human values and “authentic” environmental conditions, the result can be described as a moral geography. Nowhere is this clearer than in the protection of traditional farming on the High, or Great, Plains through federal funding and programs. Protection began during the Dust Bowl of the 1930s; federal support came to a close with the passage of the 1996 farm bill. These shifts deserve assessment of historic American interests in the protection of an agricultural institution and of a region at risk.  相似文献   

Thermal Emplacement Model for the Alpine Lherzolite Massif at Balmuccia, Italy   总被引：1，自引：0，他引：1  

SHERVAIS  JOHN W. 《Journal of Petrology》1979,20(4):795-820

The spinel lherzolite massif at Balmuccia, northwest Italy,forms an elongate north-south trending lens (4.5 x 0.5 x 1.1km) within the pre-Alpine granulite basement complex of theIvrea zone. The western contact is a mylonite fault zone formedduring late emplacement cataclastic flow near the Insubric line;to the east the lherzolite massif is separated from the granulitesby a magmatic sheath of layered pyroxenites, pyroxene pegmatitesand meta-gabbros. Pyroxene reaction zones on gabbro dikes indunite pods which lie east of the main lherzolite massif showthat emplacement occurred at pressures >9 kb, based on peridotiteequilibria studies. Phase chemistry calculations on pyroxenitesand granulites show ambient P–T conditions to have been850 °C (Cpx–Opx equilibria) and 10–13 kb (Opx–Gt;Plg–Gt–Sill–Qtz) during emplacement of thelherzolite massif. Temperature calculations on 12 peridotitesfrom throughout the massif suggest an earlier high-T stage (1200°C; Ol–Px–Sp) followed by partial re-equilibrationat lower T (850–950 °C; Cpx–Opx). The areaswithin the lherzolite massif with the highest calculated Ol–Px–Sptemperatures have the lowest Cpx–Opx temperatures, suggestingthat the apparent Cpx–Opx temperatures are due to re-equilibrationduring emplacement. The spinel lherzolite probably originatedat 12 and 20 kb, based on the mineral assemblage Ol + Opx +Cpx + Sp + Hnbd. The inferred P–T ranges put both themassif and the granulites on a geotherm that is high for continentalcrust and implies a high surface heat flow at the time of emplacement(2.2 µcal/cm² sec). The Balmuccia area later became thelocus of early Mesozoic rifting between the North and SouthAlpine plates. These relationships at Balmuccia are similarto the Great Basin of the western United States, where mantlexenoliths in young basalts that show P–T conditions of1100–1300 °C at 17–20 kb, occur in an area ofhigh heat flow (2.0 µCal/cm² sec average) and extension.This suggests an association between up-welling of mantle peridotitesbelow continents and ensialic tensional tectonics.  相似文献   

Description and hydraulic interpretation of grain size cumulative curves from the Platte River system     

J. P. VIARD  JOHN A. BREYER 《Sedimentology》1979,26(3):427-439

Log-probability plots of grain-size distribution from the Platte, North Platte, and South Platte rivers are composed of four or five straight line segments. The line segments are grouped, dividing each curve into three regions. These regions are interpreted as subpopulations moved by different transport mechanisms. Consideration of the criterion for suspension and calculation of shear velocities associated with dominant discharges support this interpretation. The grain size cumulative curves are similar to each other but distinct from curves of fluvial systems transporting only fine-grained material, the difference being the presence of a subpopulation of grains moved in traction transport. One of two possible relationships seems to exist between the grain-size distributions and flow conditions within the Platte River system. Estimated shear velocities derived by varying flow conditions within reasonable limits predict a range of grain sizes within which the break between the intermittent suspension and traction loads should occur. This break appears to be associated with intermediate shear velocities if truncated normal distributions are assumed; but if overlapping distributions are assumed, the ‘break'is associated with estimated maximum shear velocities.  相似文献   

A simulation model of alluvial stratigraphy   总被引：8，自引：0，他引：8  

JOHN S. BRIDGE  MICHAEL R. LEEDER 《Sedimentology》1979,26(5):617-644

The quantitative model presented simulates the development of a two-dimensional alluvial sedimentary succession beneath a floodplain traversed by a single major river. Several inter-related effects which influence the distribution of channel-belt sand and gravel bodies within overbank fines are accounted for. These are (a) laterally variable aggradation, (b) compaction of fine sediment, (c) tectonic movement at floodplain margins, and (d) channel avulsion. Selected experiments with the model show how the interconnectedness and areal density of channel-belt deposits decrease with increasing floodplain width/channel-belt size, mean avulsion period, and channel-belt aggradation rate. Separation of stream patterns based on interconnectedness and channel deposit density is difficult. Tectonic movements do not have a significant influence upon the successions unless a preferred direction of tilting is maintained (half-graben). Then channel-belt deposits showing offlap tendencies tend to cluster adjacent to the active floodplain margin, leaving dominantly fine-grained alluvium to accumulate on the inactive side. Individual channel-belt deposits thicken during aggradation, although a self-regulating limit to such thickening is likely to operate. ‘Multistorey’features resulting from aggradation may be difficult to tell apart from those arising through superposition of distinct channel-belt deposits of avulsive origin.  相似文献   

Holocene (Neoglacial) moraine and proglacial lake chronology, Barnes Ice Cap, Canada   总被引：1，自引：0，他引：1  

JOHN T. ANDREWS  D. MARTIN BARNETT 《Boreas: An International Journal of Quaternary Research》1979,8(3):341-358

Lichen diameters and radiocarbon dates from the western and southern margins of the Barnes Ice Cap yield a growth curve similar to that from southeastern Baffin Island. As a consequence, the moraine chronology of the northern and western Barnes Ice Cap needs revision, as does the chronology of the large proglacial lakes that existed north of the present Barnes Ice Cap. The revised chronology indicates that moraines were formed along the western margin of the Barnes Ice Cap during the following intervals: (1) less than 100 years ago; (2) 400–500 B.P.; (3) ca. 750 B.P.; (4) ca. 1000 B.P.; (5) ca. 1600 B.P.; (6) ca. 2100 B.P.; and (7) 2800 to 3100 B.P. As the western margin of the Barnes Ice Cap retreated, punctuated by stillstands and readvances, the northern margin of the Barnes Ice Cap lay athwart a series of westerly draining valleys, and a complex of proglacial lakes were dammed between the ice margin and the height of land. This sequence is traced by means of well-developed shorelines, lacustrine deltas, and spillways; specific lake levels are dated by lichenometry.
The Barnes Ice Cap moraine sequence is more complex than other Neoglacial records fringing mountain glaciers in Colorado, Alaska and Lappland. However, the chronology for the western Barnes Ice Cap closely resembles independent moraine chronology of mountain glaciers in Cumberland Peninsula, Baffin Island, and thus indicates that the difference between the Baffin Island climatic record and the general Neoglacial/Holocene climatic record (Denton & Karlén, Quaternary Research 7 , 1977) is real. Comparison of specific data from Swedish Lappland and Baffin Island shows substantial agreement. Although Neoglacial records may be globally synchronous, the case for a 2500 year periodicity of glacial fluctuations is not proven: a 300 to 600 year return interval is suggested for the period between 0 and 3000 B.P.  相似文献   

Instrumental Neutron Activation Analysis Of French Geochemical Reference Samples     

THEODORE J. BORNHORST  JOHN P. BALAGNA 《Geostandards and Geoanalytical Research》1979,3(2):177-180

Instrumental neutron activation analytical data, for eighteen trace elements (Ba, Co, Cr, Cs, Hf, Rb), Sb, Sc, Ta, Th, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu), Hd₂O and Fe₂0₃ in eleven French geoche-mical reference samples are presented and discussed briefly.  相似文献