Direct determination of⁷Be in sediments     

Ingvar L. Larsen  Norman H. Cutshall 《Earth and Planetary Science Letters》1981,54(3):379-384

Cosmic-ray produced⁷Be (53 days half-life) is directly measurable in freshly collected samples of river and coastal zone sediments using a lithium-drifted germanium detector. Calibration of the detector is discussed and an assessment of overall accuracy and sensitivity presented. The detection limit for a 250-g dry weight sediment sample contained in a Marinelli Beaker and counted for 200 minutes is approximately 0.4 pCi/g. Applications toward locating zones of rapid sedimentation as well as in understanding shallow-water sedimentation dynamics are suggested.  相似文献   

Glass-bearing gabbro inclusions in hyaloclastites from Tindfjallajökull,Iceland     

Jørgen Gutzon Larsen 《Lithos》1979,12(4):289-302

Gabbro inclusions from Tindfjallajökull are divided into two types: I. Panidiomorphic gabbros of non-cumulative origin composed of plagioclase + olivine ± clinopyroxene and interstitil vesicular glass. They have formed in equilibrium with the host magma and may either represent a marginal facies or a highly solidified magma body. In the latter case the host magma or part of it could be mobilized interstitial liquid. II. Allotriomorphic-hypidiomorphic tholeiitic olivine gabbro and diorite xenoliths with scarce Ti-pargasite which have undergone less than 10% partial melting in the host magma forming melts of alkali basaltic or Hekla andesite-like compositions dependent on the original mineral assemblage. Such liquids, enriched in K₂O and possibly other incompatible elements, may contaminate basaltic magmas rising slowly through a gabbroic lower crust. Large scale production of andesites by partial melting of such rocks is not possible but would need more hydrous or differentiated source rocks.  相似文献   

Geologic implications and potential hazards of scour depressions on bering shelf,Alaska     

Matthew C. Larsen  Hans Nelson  Devin R. Thor 《Environmental Geology》1979,3(1):39-47

Flat-bottomed depression 50–150 m in diameter and 60–80 cm deep occur in the floor of Norton Sound, Bering Sea. These large erosional bedforms and associated current ripples are found in areas where sediment grain size is 0.063–0.044 mm (4–4.5 φ), speeds of bottom currents are greatest (20–30 cm/s mean speeds under nonstorm conditions, 70 cm/s during typical storms), circulation of water is constricted by major topographic shoals (kilometers in scale), and small-scale topographic disruptions, such as ice gouges, occur locally on slopes of shoals. These local obstructions on shoals appear to disrupt currents, causing separation of flow and generating eddies that produce large-scale scour. Offshore artificial structures also may disrupt bottom currents in these same areas and have the potential to generate turbulence and induce extensive scour in the area of disrupted flow. The size and character of natural scour depressions in areas of ice gouging suggest that large-scale regions of scour may develop from enlargement of local scour sites around pilings, platforms, or pipelines. Consequently, loss of substrate support for pipelines and gravity structures is possible during frequent autumn storms.  相似文献   

Boccardia hamata (Polychaeta:spionidae): A potential pest of the American oyster in the James River,Virginia     

Peter F. Larsen 《Estuaries and Coasts》1978,1(3):183-185

During a comprehensive survey of fauna associated with James River oyster reefs in 1971–72, a large population of the spionid polychaeteBoccardia hamata was found. The abundance of this boring species was greater than that of the well-known oyster pestPolydora websteri. B. hamata has not been reported previously in the Chesapeake Bay system and its occurrence on the east coast of the United States is not common. The large numbers in 1971–72 and continued presence ofB. hamata in 1975 suggests that the species may be well established in the James River. This may have some implications to the oyster industry if the species is as harmful as other boring spionids.  相似文献   

CANADA'S LARGEST WATER WELL     

P. O. Bourgeois  J. D. Brownell  J. W. Kirk  C. H. Larsen 《Ground water》1974,12(1):39-46

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Early Diagenes. A Theoretical Approach | Robert A. Berner, 1980. Princeton University Press,Princeton, N.J., 241 pp., US$31.50 (cloth), US$12.00 (paper).     

G. Larsen 《Earth》1983,19(2):175-176

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Mixing rates in Shagawa Lake,Minnesota, sediments as determined from ¹⁰⁶Ru profiles     

John Van Sickle  Walter C. Weimer  David P. Larsen 《Geochimica et cosmochimica acta》1983,47(12):2189-2197

Rates of surficial sediment mixing and sediment burial are measured in Shagawa Lake, Minnesota, using radionuclide tracers. Based on ¹⁰⁶Ru profiles in 16 cores, mixing rates average 13 cm²/yr within the upper 9 cm of sediment. Two other nuclides, ²¹⁰Pb and ¹³⁷Cs, provide further evidence for calculation of mixing rates. In addition, ²¹⁰Pb profiles estimate sediment burial rates (about 0.4 cm/yr). Mixing estimates are shown to be fairly insensitive both to uncertainties in sediment burial rates and to temporal patterns of ¹⁰⁶Ru deposition.  相似文献   

Rapid uplift of southern Alaska caused by recent ice loss   总被引：3，自引：0，他引：3  

Christopher F. Larsen  Roman J. Motyka  Jeffrey T. Freymueller  Keith A. Echelmeyer  Erik R. Ivins 《Geophysical Journal International》2004,158(3):1118-1133

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Climatically driven pH changes in two Norwegian alpine lakes     

Jorunn Larsen  Vivienne J. Jones  Wenche Eide 《Journal of Paleolimnology》2006,36(2):175-187

Two alpine lakes in the south-central part of Norway have been studied for recent changes in diatom assemblages preserved in their sediments. Both lakes experience a post 1980 AD increase in diatom valve accumulation rates possibly reflecting an increase in lake productivity. In addition there is an overall increase in diatom-inferred pH at both sites. Recovery from lake acidification can be disregarded as a possible cause of increased pH as the lakes are situated in catchments with high buffering capacities in areas that have received low amounts of acid deposition. We suggest that recent climate warming has influenced both sites with the important effect of increasing mineralization in the catchments, resulting in greater fluxes of nutrients and base cations to the lakes, leading to an increase in diatom-inferred pH. Taxa that have increased in abundance include Achnanthes minutissima, Achnanthes nodosa, Cyclotella spp., Navicula schmassmannii, Staurosirella lapponica, and S. pinnata. In one of the lakes, the maximum diatom-inferred pH values reached at the top of the core are as high as pH values reconstructed from the diatom assemblages deposited at the end of the Mid-Holocene thermal maximum c. 4000 cal. BP.  相似文献   

Compaction bands and induced permeability reduction in Tuffeau de Maastricht calcarenite     

Theocharis Baxevanis  Euripides Papamichos  Olav Flornes  Idar Larsen 《Acta Geotechnica》2006,1(2):123-135

The mechanical behavior and permeability of the Tuffeau de Maastricht calcarenite were studied. Compactions bands were found to form in the “transitional” regime between brittle faulting and cataclastic flow. In order to predict the formation of compaction bands, bifurcation analysis was applied on a model developed by Lade and Kim. The numerical results proved to be in good agreement with the experimental ones where the localization point was identified to be the onset of shear-enhanced compaction (a threshold in differential stress after which significant reduction of porosity is induced). Before the onset of shear-enhanced compaction, permeability was primarily controlled by the effective mean stress, independent of the deviatoric stresses. With the onset of shear-enhanced compaction, however, coupling of the deviatoric and hydrostatic stresses induced considerable permeability and porosity reduction.  相似文献