Regional atmospheric circulation change in the North Pacific during the Holocene inferred from lacustrine carbonate oxygen isotopes, Yukon Territory, Canada     

Lesleigh Anderson  Mark B. Abbott  Bruce P. Finney  Stephen J. Burns 《Quaternary Research》2005,64(1):21-35

Analyses of sediment cores from Jellybean Lake, a small, evaporation-insensitive groundwater-fed lake, provide a record of changes in North Pacific atmospheric circulation for the last ∼7500 yr at 5- to 30-yr resolution. Isotope hydrology data from the southern Yukon indicate that the oxygen isotope composition of water from Jellybean Lake reflects the composition of mean-annual precipitation, δ¹⁸O_p. Recent changes in the δ¹⁸O of Jellybean sedimentary calcite (δ¹⁸O_ca) correspond to changes in the North Pacific Index (NPI), a measure of the intensity and position of the Aleutian Low (AL) pressure system. This suggests that δ¹⁸O_p variability was related to the degree of fractionation during moisture transport from the Gulf of Alaska across the St. Elias Mountains and that Holocene shifts were controlled by the intensity and position of the AL. Following this model, between ∼7500 and 4500 cal yr B.P., long-term trends suggest a predominantly weaker and/or westward AL. Between ∼4500 and 3000 cal yr B.P. the AL shifted eastward or intensified before shifting westward or weakening between ∼3000 and 2000 cal yr B.P. Rapid shifts eastward and/or intensification occurred ∼1200 and 300 cal yr B.P. Holocene changes in North Pacific atmospheric circulation inferred from Jellybean Lake oxygen isotopes correspond with late Holocene glacial advances in the St. Elias Mountains, changes in North Pacific salmon abundance, and shifts in atmospheric circulation over the Beaufort Sea.  相似文献   

On ‘mantled feldspars from the Golden Horn batholith,Washington’     

Richard N. Abbott 《Lithos》1979,12(4):347-348

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Degradation of 5α-cholestane into dimethylperhydrophenanthrenes: an experimental and theoretical study     

Mark A. Sugden  Adri C. T. van Duin  Geoffrey D. Abbott   《Organic Geochemistry》2004,35(11-12):1337

A tetradeuteriated cholestane was heated with kerogen isolated from the Messel oil shale at 350 °C for 25 different time periods (ranging from 0.5 to 80 h) in borosilicate vessels. Three isomers of tetradeuteriated dimethylperhydrophenanthrene were formed and one of these was the major saturated hydrocarbon product under most conditions. The stereochemistry for these isomers was unknown but if the stable 5α,8β,9α(H),10β(CH₃) sterane configuration is inherited from the cholestane then there are four possible isomers namely: I and II [13β(H) and 13α(H) diastereomers, respectively, of 10,13-dimethylperhydrophenanthrene] as well as III and IV [14β(H) and 14α(H) diastereomers, respectively, of 10,14-dimethylperhydrophenanthrene]. Molecular mechanics revealed that I is the most stable form and therefore is the component that dominated the saturated hydrocarbon degradation products. The identification of only three isomers of deuteriated dimethylperhydrophenanthrene in the pyrolysis experiments is supported by the calculated stabilities (ΔΔG) as isomer IV is considerably more unstable (by 1.7 kcal/mol) than II which is the least stable of I, II and III. If these compounds can be detected in crude oils their distributions may be useful maturity indicators in oils that have been generated at high thermal maturity.  相似文献   

Permo–Triassic intraplate magmatism and rifting in Eurasia: implications for mantle plumes and mantle dynamics     

A. M. Nikishin  P. A. Ziegler  D. Abbott  M. -F. Brunet  S. Cloetingh 《Tectonophysics》2002,351(1-2)

At the transition from the Permian to the Triassic, Eurasia was the site of voluminous flood-basalt extrusion and rifting. Major flood-basalt provinces occur in the Tunguska, Taymyr, Kuznetsk, Verkhoyansk–Vilyuy and Pechora areas, as well as in the South Chinese Emeishen area. Contemporaneous rift systems developed in the West Siberian, South Kara Sea and Pyasina–Khatanga areas, on the Scythian platform and in the West European and Arctic–North Atlantic domain. At the Permo–Triassic transition, major extensional stresses affected apparently Eurasia, and possibly also Pangea, as evidenced by the development of new rift systems. Contemporaneous flood-basalt activity, inducing a global environmental crisis, is interpreted as related to the impingement of major mantle plumes on the base of the Eurasian lithosphere. Moreover, the Permo–Triassic transition coincided with a period of regional uplift and erosion and a low-stand in sea level. Permo–Triassic rifting and mantle plume activity occurred together with a major reorganization of plate boundaries and plate kinematics that marked the transition from the assembly of Pangea to its break-up. This plate reorganization was possibly associated with a reorganization of the global mantle convection system. On the base of the geological record, we recognize short-lived and long-lived plumes with a duration of magmatic activity of some 10–20 million years and 100–150 million years, respectively. The Permo–Triassic Siberian and Emeishan flood-basalt provinces are good examples of “short-lived” plumes, which contrast with such “long lived” plumes as those of Iceland and Hawaii. The global record indicates that mantle plume activity occurred episodically. Purely empirical considerations indicate that times of major mantle plume activity are associated with periods of global mantle convection reorganization during which thermally driven mantle convection is not fully able to facilitate the necessary heat transfer from the core of the Earth to its surface. In this respect, we distinguish between two geodynamically different scenarios for major plume activity. The major Permo–Triassic plume event followed the assembly Pangea and the detachment of deep-seated subduction slabs from the lithosphere. The Early–Middle Cretaceous major plume event, as well as the terminal–Cretaceous–Paleocene plume event, followed a sharp acceleration of global sea-floor spreading rates and the insertion of new subduction zone slabs deep into the mantle. We conclude that global plate kinematics, driven by mantle convection, have a bearing on the development of major mantle plumes and, to a degree, also on the pattern of related flood-basalt magmatism.  相似文献   

A Late Glacial–Holocene Tephrochronology for Glacial Lakes in Southern Ecuador     

Donald T. Rodbell  Stefan Bagnato  Jeffrey C. Nebolini  Geoffrey O. Seltzer  Mark B. Abbott 《Quaternary Research》2002,57(3):343

Despite the presence of numerous active volcanoes in the northern half of Ecuador, few, if any, distal tephras have been previously recognized in the southern one third of the country. In this article, we document the presence of thin (0.1–1.0-cm-thick) distal tephras comprising glass and/or phenocrysts of hornblende and feldspar in sediment cores from five glacial lakes and one bog in Las Cajas National Park (2°40′–3°00′S, 79°00′–79°25′W). The lake cores contain from 5 to 7 tephras, and each has a diagnostic major element geochemistry as determined from electron microprobe analysis of 710 glass shards and 440 phenocrysts of feldspar and hornblende. The loss of sodium with exposure to the electron microbeam causes a 10±7 wt.% (±1σ) reduction in Na content, which we empirically determined and corrected for before correlating tephras among the sediment cores. We use a similarity coefficient to correlate among the sediment cores; pair-wise comparison of all tephras generally yields an unambiguous correlation among the cores. Six tephras can be traced among all or most of the cores, and several tephras are present in only one or two of the cores. Twenty-six accelerator mass spectrometry ¹⁴C dates on macrofossils preserved in the sediment cores provide the basis for establishing a regional tephrochronology. The widespread tephras were deposited 9900, 8800, 7300, 5300, 2500, and 2200 cal yr B.P. The oldest tephras were deposited 15,500 and 15,100 cal yr B.P., but these are not found in all cores. Two of the tephras appear correlative with volcaniclastic strata on the flanks of Volcán Cotopaxi and one tephra may correlate with strata on the flanks of Volcán Ninahuilca; both volcanoes are in central Ecuador. The absence of tephras in sediment cores correlative with the numerous eruptions of active volcanoes of the past two millennia implies that the earlier eruptions, which did deposit tephras in the lakes, must have been either especially voluminous, or southerly winds must have prevailed at the time of the eruption, or both.  相似文献   

AuroralH-emission and interplanetary neutral hydrogen     

W. N. Abbott 《Pure and Applied Geophysics》1960,45(1):167-174

Summary Auroral spectra taken from within the auroral zone reveal H-emission as not limited to the magnetic zenith but as extending over the sky. The surface brightness forH andH may tentatively be estimated to a few airglows. The assumption is made that some of this emission may extend to the very low gm latitudes and be practically universal and the possible mode of excitation of neutral hydrogen in space is speculated upon. At the earth's orbit the density number of the cosmic, infalling, hydrogen accreted from beyond the solar system towards the sun is about 10² neutral atoms cm^–3 and coronal plasma contributions cannot encrease this number by more than a factor of two. If an exceptionally violent solar disturbance ejects stream-electrons attaining velocities-of 2,200 km sec^–1 corresponding to the threshold energy forH excitation of 12.8 eV and if these electrons, at the earth's orbit, have a density number of 10³ cm^–3, then a shell about 100,000 km thick may contributeH emission having a surface brightness of about 0.1 airglow this being the higher probable value. Such anH-emission could be detectable from all latitudes during, or, most probably, just before the occurence of an auroral storm.  相似文献   

The geochemistry and petrogenesis of K-rich alkaline volcanics from the Batu Tara volcano,eastern Sunda arc   总被引：8，自引：0，他引：8  

A. J. Stolz  R. Varne  G. E. Wheller  J. D. Foden  M. J. Abbott 《Contributions to Mineralogy and Petrology》1988,98(3):374-389

Mineralogical, major and trace element, and isotopic data are presented for leucite basanite and leucite tephrite eruptives and dykes from the Batu Tara volcano, eastern Sunda arc. In general, the eruptives are markedly porphyritic with phenocrysts of clinopyroxene, olivine, leucite ±plagioclase±biotite set in similar groundmass assemblages. These K-rich alkaline volcanics have high concentrations of large-ion-lithophile (LIL), light rare earth (LRE) and most incompatible trace elements, and are characterized by high ⁸⁷Sr/⁸⁶Sr (0.70571–0.70706) and low ¹⁴³Nd/ ¹⁴⁴Nd (0.512609–0.512450) compared with less alkaline volcanics from the Sunda arc. They also display the relative depletion of Ti and Nb in chondrite-normalized plots which is a feature of subalkaline volcanics from the eastern Sunda arc and arc volcanics in general. Chemical and mineralogical data for the Batu Tara K-rich rocks indicate that they were formed by the accumulation of variable amounts of phenocrysts in several melts with different major and trace element compositions. The compositions of one of these melts estimated from glass inclusions in phenocrysts is relatively Fe-rich (100 Mg/(Mg + Fe²⁺)=48–51) and is inferred to have been derived from a more primitive magma by low-pressure crystal fractionation involving olivine, clinopyroxene and spinel. Mg-rich (mg 90) and Cr-rich (up to 1.7 wt. % Cr₂O₃) zones in complex oscillatory-zoned clinopyroxene phenocrysts probably also crystallized from such a magma. The marked oscillatory zoning in the clinopyroxene phenocrysts is considered to be the result of limited mixing of relatively evolved with more primitive magmas, together with their phenocrysts, along interfaces between discrete convecting magma bodies.  相似文献   

Drainage-basin evolution and aquifer development in a karstic limestone terrain South-Central Texas,U.S.A.     

C. M. Woodruff  Patrick L. Abbott 《地球表面变化过程与地形》1979,4(4):319-334

The Edwards artesian aquifer occurs in cavernous limestones of Cretaceous (Albian) age within the Balcones fault zone in south-central Texas. The major recharge and discharge zones of the aquifer are contained within the upper reaches of three river systems: the Nueces, the San Antonio, and the Guadalupe. Within these watersheds, recharge dominates in the semiarid Nueces basin to the west while most discharge occurs farther east from wells in the subhumid San Antonio basin and from springs in the subhumid Guadalupe basin. This long-distance transfer of ground water (up to 240 km) is a result of several factors: depositional and early diagenetic history of the limestone host rock, geometry and magnitudes of fault displacement, and physiographic responses to faulting. The loci of greatest discharge from the aquifer occur in an area that was exposed subaerially with concomitant porosity enhancement due to dissolution of limestone during late Early Cretaceous time. This area also was subjected to the greatest fault displacement during Miocene time. Thus, faults and associated joints superimposed additional avenues for porosity and permeability development onto an area that already had considerable secondary porosity. Further determinants on aquifer properties resulted from late Tertiary and Quaternary drainage evolution in response to faulting along the Balcones trend. The strike of the fault zone lay at acute angles to the courses of the main trunk streams in the ancestral Guadalupe and San Antonio River systems, whereas in the Nueces basin the trend of the fault zone was normal to the courses of the main streams. Thus, as a fault-line scarp began to form in the eatern basins, scarp-normal streams were incised rapidly into northwest-trending canyons. These steep-gradient streams captured the eastward-flowing major streams in the easten watersheds. These pirate streams incised into the aquifer at the lowest topographic levels within the region because of: 1. The sudden acquisition of extensive catchment areas in a subhumid area; and 2. Steep stream gradients that reflected the larger fault displacement in the east. The low topographic points of discharge became the loci of major springs. Recharge is dominant in the Nueces basin mainly because streams cross permeable limestone units at higher topographic levels than in the San Antonio and Guadalupe basins. The topographic characteristics of the Nueces watershed resulted from a combination of diverse factors: lesser fault displacement, no major stream piracy, and less vigorous erosion because of a semiarid climate.  相似文献   

Geochemistry of quaternary volcanism in the Sunda-Banda arc, Indonesia, and three-component genesis of island-arc basaltic magmas   总被引：1，自引：0，他引：1  

G.E. Wheller  R. Varne  J.D. Foden  M.J. Abbott 《Journal of Volcanology and Geothermal Research》1987,32(1-3)

Volcanic rocks of the Sunda and Banda arcs range from tholeiitic through calcalkaline and shoshonitic to leucititic, the widest compositional span of mafic magmatism known from an active arc setting.Mafic rocks in our data set, which includes 315 new analyses of volcanic rocks from twelve Quaternary volcanoes, including Batu Tara in the previously geochemically unknown Flores-Lembata arc sector, are generally similar to those from other island arcs: most contain <1.3 wt. % TiO₂ and 16–22 wt. % Al₂O₃, and have characteristically high K/Nb and La/Nb values. Abundances of P, Ba, Rb, Sr, La, Ce, Nd, Zr and Nb increase sympathetically with increasing K₂O contents of mafic rocks but those of Na, Ti, Y and Sc vary little throughout the geochemical continuum from low-K tholeiitic to high-K leucititic rocks.Excluding Sumatra and Wetar, which possess mainly dacitic and rhyolitic volcanics, the Sunda-Banda arc is divisible into four geochemical arc sectors with boundaries that correlate with major changes in regional tectonic setting and geological history. From west to east, the West Java, Bali and Flores arc sectors each comprise volcanoes which become progressively more K-rich eastwards, culminating in the leucitite volcanoes Muriah, Soromundi and Sangenges, and Batu Tara, respectively. In the most easterly Banda sector, the volcanics vary from high- to low-K eastwards around the arc.Correlations between geochemistry and ⁸⁷Sr/⁸⁶Sr values show separate trends for each of the four arc sectors, believed to be the result of involvement of at least three geochemically and isotopically distinct components in the source regions of the arc magmatism.A dominant source component with a low K content and a low ⁸⁷Sr/⁸⁶Sr value, and common to all sectors, is probably peridotitic mantle. A second component, with low K content but high ⁸⁷Sr/⁸⁶Sr value, appears to be crustal material. This component is most apparent in the Banda sector, in keeping with that sector's tectonic setting close to Precambrian Australian continental crust, but it is also present to lesser extents in the West Java and Flores sectors.However, the most marked geochemical and isotopic variations shown by the arc volcanics are primarily due to the involvement of a third component, which is rich in K-group elements but has relatively low ⁸⁷Sr/⁸⁶Sr values. This component appears to be mantle-derived and is least overprinted by crustal material in the Bali sector volcanics where the Pb, Be, U-Th and O isotope characteristics of the rocks support the suggestion that their genesis has not involved incorporation of recently subducted, continent-derived sialic material.The high, regionally persistent, Th/U value (about 4.3) of the Sunda subarc mantle, obtained from U-Th isotopic data, suggests a close association could exist between the K-rich component and the southern hemisphere ‘DUPAL’ mantle isotopic anomaly.  相似文献   

Phytoplankton pigment distribution in relation to silicic acid, iron and the physical structure across the Antarctic Polar Front, 170°W, during austral summer     

C. Mengelt  M. R. Abbott  J. A. Barth  R. M. Letelier  C. I. Measures  S. Vink 《Deep Sea Research Part II: Topical Studies in Oceanography》2001,48(19-20)

In order to study the factors controlling the phytoplankton distribution across the Antarctic Polar Frontal Region (PFR), surface pigment samples were collected during austral summer (January/February 1998) near 170°W. Both the Polar Front (PF) and the Southern Antarctic Circumpolar Current Front (SACCF) were regions of enhanced accumulation of phytoplankton pigments. The mesoscale survey across the PF revealed two distinct phytoplankton assemblages on either side of the front. The phytoplankton community was dominated by diatoms south of the PF and by nanoflagellates (primarily by prymnesiophytes) to the north. Surprisingly, chlorophyll a concentrations did not correlate with mixed-layer depths. However, an increase of the dominance of diatoms over prymnesiophytes was observed with decreasing mixed-layer depths. Despite this relationship, we conclude that the average light availability in the mixed layer was not an important factor influencing the shift in phytoplankton composition across the PF. Although no correlation was found between the surface distribution of the major phytoplankton taxa and dissolved iron or silicic acid concentrations, the location of the strongest vertical gradient in silicic acid and iron concentration coincides with the maximum abundance of diatoms. We conclude that the difference in taxonomic composition is a result of increased silicic acid and iron flux to the upper mixed layer as a result of the increased vertical gradient of these key nutrients south of the front.  相似文献