Precambrian volcanics associated with the taum Sauk Caldera,St. Francois Mountains,Missouri, U.S.A.     

A. W. Berry Jr.  M. E. Bickford 《Bulletin of Volcanology》1972,36(2):303-318

Petrological studies of 12 volcanic rock units in the northeast segment of the Taum Sauk Caldera, the major structural feature in the western part of the St. Francois Mountains, indicate that they were probably derived from the same magma chamber. These calc-alkalic rocks become progressively silica and alkali rich and calcium poor from the base to the top of the stratigraphic column. In the part of the northeast segment of the caldera studied in detail, the extrusives are over 5 thick and have a volume of over 500 km³. Rock units consisting of ash-flow tuffs, bedded airfall tuffs and lava flows were apparently deposited within a single episode of volcanic activity, since no signs of extensive erosion were observed among them. Although the rocks are completely devitrified, the preservation of pyroclastic and flow features is excellent. These volcanics are exposed representatives of a 1.3–1.4 b.y. old belt of volcanics and associated plutons which extends from southern Ohio to the Texas Panhandle any may represent a belt of continental accretion.  相似文献   

VEGETATION ANALYSIS OF A TYPICAL MANGROVE SWAMP──LAI CHI WO COAST OF HONG KONG     

卢昌义  黄玉山  谭凤仪  BerryRichard 《中国海洋湖沼学报》1998,(1)

INTRODUCTIONThemangroveswamPisaInaoransySteInwherespedallyadaptalplantSgrowintheintertidalbetattheinterfacebetweenlandandaninthetropiesandsub-tropies.ThernangrovefonstplaySrnanyrolessuchascoastalstabilizer,disperseroftheeneryofst0me,tida1boresandwinds,baniert0invasionofinlandarmbysaltwatCr,produoerofnutrientSandfoastresounasuchasfuel,chaimal,fodder,tirnberandsomeirnPor-tantanbeIsoferenoAncvalue.TheongoingintheiveandextenSivedestruCtion0frnangrovesbymankindseVereydarnagestemetrialandn…  相似文献   

The solubility control of rare earth elements in natural terrestrial waters and the significance of PO 4 3− and CO 3 2− in limiting dissolved rare earth concentrations: A review of recent information     

Kevin H. Johannesson  W. Berry Lyons  Klaus J. Stetzenbach  Robert H. Byrne 《Aquatic Geochemistry》1995,1(2):157-173

Rare earth element (REE) concentrations in alkaline lakes, circumneutral pH groundwaters, and an acidic freshwater lake were determined along with the free carbonate, free phosphate, and free sulfate ion concentrations. These parameters were used to evaluate the saturation state of these waters with respect to REE phosphate and carbonate precipitates. Our activity product estimates indicate that the alkaline lake waters and groundwaters are approximately saturated with respect to the REE phosphate precipitates but are significantly undersaturated with respect to REE carbonate and sulfate precipitates. On the other hand, the acidic lake waters are undersaturated with respect to REE sulfate, carbonate, and phosphate precipitates. Although carbonate complexes tend to dominate the speciation of the REEs in neutral and alkaline waters, our results indicate that REE phosphate precipitates are also important in controlling REE behavior. More specifically, elevated carbonate ion concentrations in neutral to alkaline natural waters tend to enhance dissolved REE concentrations through the formation of stable REE-carbonate complexes whereas phosphate ions tend to lead to the removal of the REEs from solution in these waters by the formation of REE-phosphate salts. Removal of REEs by precipitation as phosphate phases in the acid lake (pH=3.6) is inconsequential, however, due to extremely low [PO ₄ ^3– ] _F concentrations (i.e., 10^–23 mol/kg).  相似文献   

Late holocene paleoclimatic and paleobiologic records from sediments of Devils Lake,North Dakota     

Robert M. Lent  W. Berry Lyons  William J. Showers  Kevin H. Johannesson 《Journal of Paleolimnology》1995,13(3):193-207

An 84 cm sediment core collected from the center of Devils Lake, North Dakota, was analyzed at 1-cm intervals for,²¹⁰Pb,¹³⁷Cs, sediment conductivity, the concentrations of, biogenic silica, total organic carbon, carbon to nitrogen ratio, and the carbon and nitrogen isotopic composition of the organic fraction. Variations in²¹⁰Pb activities in the upper 20 centimeters indicate that sediment accumulations rates in Devils Lake are not constant, and that accumulation rates were highest during periods of high lake level. The mean sedimentation accumulation rate was calculated as 0.24 cm^–1 yr. The¹³⁷Cs profile is characterized by near-surface maximum concentrations, possibly the result of redistribution of¹³⁷Cs during salinity excursions.Biogenic silica is strongly correlated to lake level in Devils Lake. Periods of low lake level (characterized by high sediment conductivity) correspond to low biogenic silica concentrations. The trends in biogenic silica are attributed to variations in diatom productivity in the lake and to variations in sediment accumulation rates. Based on biogenic silica content and the composition of organic matter in the sediment (total organic carbon, carbon:nitrogen ratio and the ¹³C and ¹⁵N composition of total organic matter), paleobiologic conditions of Devils Lake during low lake stands were characterized by, (1) decreased primary productivity, (2) decreased input of detrital organic matter, and (3) increased nitrogen availability.During the 350 years of sediment accumulation represented by the 84-cm sediment core Devils Lake has experienced two periods of sustained high lake level; one between about 130 and 170 years ago (1820 to 1860 A.D.) and the second between 270 and 310 years ago (1680 to 1720 A.D.). Devils Lake experienced a period of intense drying about 260 years ago (1720 A.D.).  相似文献   

Probing discrete auroral arcs by ionospheric tomography     

J. Moen  S. T. Berry  L. Kersley  B. Lybekk 《Annales Geophysicae》1998,16(5):574-582

Optical observations of 557.7 nm and 630.0 nm emissions from discrete auroral arcs in the post-noon sector have been related to localised field-aligned enhancements in the spatial distribution of E- and F-layer electron density respectively seen in images reconstructed by ionospheric tomography. Results from two case studies are presented in which meridian scanning photometer and all-sky camera observations on Svalbard have been compared to electron-density structures found by tomographic inversion of measurements made by reception of radio signals at a chain of four stations at high latitude. The F-layer features are long-lived and show exact correspondence to the red-line emissions. Transient arcs in green-line intensity result in E-region structures that are resolved in one case, but not in another where the dynamic auroral forms are separated by less than one degree of latitude. The signature of an inverted-V precipitation event is clearly evident in one example.  相似文献   

Hypoxia in a Coastal Embayment of the Chesapeake Bay: A Model Diagnostic Study of Oxygen Dynamics     

Jian Shen  Taiping Wang  Julie Herman  Pam Mason  Gretchen L. Arnold 《Estuaries and Coasts》2008,31(4):652-663

Two distinct hypoxic patterns were revealed from high-frequency dissolved oxygen (DO) data collected from North Branch of Onancock Creek, a shallow coastal estuary of the Chesapeake Bay, from July to October 2004. Diurnal hypoxia developed associated with large DO swings during fair weather and hypoxia/anoxia developed for prolonged 2–5-day periods following rainfall events. A simplified diagnostic DO-algae model was used to investigate DO dynamics in the creek. The model results show that the modeling approach enables important features of the DO dynamics in the creek to be captured and analyzed. Large anthropogenic inputs of nutrients to the creek stimulated macroalgae blooms in the embayment. High DO production resulted in supersaturated DO in daytime, whereas DO was depleted at night as the high respiration overwhelmed the DO supply, leading to hypoxia. Unlike deep-water environments, in this shallow-water system, biological processes dominate DO variations. High macroalgae biomass interacting with low light and high temperature trigger the development of prolonged hypoxic/anoxic postrainfall events.  相似文献   

Sources and preservation of organic matter in Plum Island salt marsh sediments (MA, USA): long-chain n-alkanes and stable carbon isotope compositions     

X. -C. Wang  R. F. Chen  A. Berry 《Estuarine, Coastal and Shelf Science》2003,58(4):917-928

Elemental (TOC, TN, C/N) and stable carbon isotopic (δ¹³C) compositions and n-alkane (nC_16–38) concentrations were measured for Spartina alterniflora, a C₄ marsh grass, Typha latifolia, a C₃ marsh grass, and three sediment cores collected from middle and upper estuarine sites from the Plum Island salt marshes. Our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites. δ¹³C values of organic matter preserved in the upper fresh water site sediment were more negative (−23.0±0.3‰) as affected by the C₃ plants than the values of organic matter preserved in the sediments of middle (−18.9±0.8‰) and mud flat sites (−19.4±0.1‰) as influenced mainly by the C₄ marsh plants. The distribution of n-alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses S. alterniflora and T. latifolia, and nC₂₁ to nC₃₃ long-chain n-alkanes were the major compounds determined in all sediment samples. The strong odd-to-even carbon numbered n-alkane predominance was found in all three sediments and nC₂₉ was the most abundant homologue in all samples measured. Both δ¹³C compositions of organic matter and n-alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in Plum Island salt marsh sediments. This suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters.  相似文献   

Seismic stratigraphy of the central Scotian Rise: A record of continental margin glaciation     

J. A. Berry  D. J. W. Piper 《Geo-Marine Letters》1993,13(4):197-206

3.5-k Hz profiles from low channel levees on the Scotian Rise show transparent Holocene acoustic facies overlying stratified glacial facies, dated by Carbon-14 in cores. Corresponding acoustic facies in seismic records are correlated with glaciations by counting back from the present sea floor using sedimentation rates from Carbon-14 dating and biostratigraphy from wells as a guide. The regional thickness and character of the seismic units correlate with the duration and intensity of glacial periods inferred from the global isotopic record. Changes in glacial supply to the continental margin are interpreted using this chronology, which shows stage 12 as the first widespread erosional glacial event.  相似文献   

Countering Inequality: Brazil's Movimento Sem‐Terra          下载免费PDF全文

Rubia R. Valente  Brian J. L. Berry 《Geographical review》2015,105(3):263-282

Data from a national survey of formerly landless peasants residing in federal land‐reform settlements in Brazil (Pesquisa Nacional de Educação na Reforma Agrária—PNERA) confirm that the Landless Rural Workers Movement (Movimento dos Trabalhadores Rurais Sem‐Terra—MST) has been far more successful than other settlement movements in assuring a better quality of life for its members. This superior performance is attributed to an organizational structure that demands and assures membership involvement, and a commitment to participatory education in an environment that fosters and supports MST's goals and objectives. MST's members have higher self‐perceived social status than members of non‐MST movements, have better residential environments and more material possessions, and experience an education that emphasizes the movement's principles of social justice, radical democracy, and humanist and socialist values.  相似文献   

Modeling mixed exposures: an application to welding fumes in the construction trades     

Michael R. Flynn  Pam Susi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(3):377-388

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