Chronostratigraphy and lake-level changes of Laguna Cari-Laufquén, Río Negro, Argentina     

Alyson Cartwright  Jay Quade  Scott Stine  Kenneth D. Adams  Wallace Broecker  Hai Cheng 《Quaternary Research》2011,76(3):430-440

Evidence from shoreline and deep-lake sediments show Laguna Cari-Laufquén, located at 41°S in central Argentina, rose and fell repeatedly during the late Quaternary. Our results show that a deep (> 38 m above modern lake level) lake persisted from no later than 28 ka to 19 ka, with the deepest lake phase from 27 to 22 ka. No evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake, before regressing to present levels. Laguna Cari-Laufquén broadly matches other regional records in showing last glacial maximum (LGM) highstands, but contrasts with sub-tropical lake records in South America where the hydrologic maximum occurred during deglaciation (17–10 ka). Our lake record from Cari-Laufquén mimics that of high-latitude records from the Northern Hemisphere. This points to a common cause for lake expansions, likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the LGM.  相似文献   

Isotopic tracers of paleohydrologic change in large lakes of the Bolivian Altiplano   总被引：2，自引：0，他引：2  

Christa J. Placzek  Jay Quade 《Quaternary Research》2011,75(1):231-244

We have developed an ⁸⁷Sr/⁸⁶Sr, ²³⁴U/²³⁸U, and δ¹⁸O data set from carbonates associated with late Quaternary paleolake cycles on the southern Bolivian Altiplano as a tool for tracking and understanding the causes of lake-level fluctuations. Distinctive groupings of ⁸⁷Sr/⁸⁶Sr ratios are observed. Ratios are highest for the Ouki lake cycle (120-95 ka) at 0.70932, lowest for Coipasa lake cycle (12.8-11.4 ka) at 0.70853, and intermediate at 0.70881 to 0.70884 for the Salinas (95-80 ka), Inca Huasi (~ 45 ka), Sajsi (24-20.5 ka), and Tauca (18.1-14.1 ka) lake cycles. These Sr ratios reflect variable contributions from the eastern and western Cordilleras. The Laca hydrologic divide exerts a primary influence on modern and paleolake ⁸⁷Sr/⁸⁶Sr ratios; waters show higher ⁸⁷Sr/⁸⁶Sr ratios north of this divide. Most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from Lake Titicaca. The Coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide. In contrast, the Ouki lake cycle was an expansive lake, deepest in the northern (Poópo) basin, and spilling southward. These results indicate that regional variability in central Andean wet events can be reconstructed using geochemical patterns from this lake system.  相似文献   

The Reaction Kinetics between CO2-bearing Fluid and Olivines/Hawaiian Picrites     

WANG Zhengrong  QIU Lin  ZHANG Shuang  KARATO Shun-ichiro  Kevin JOHNSON  Jay AGUE  Michael ORISTAGLIO  Edward BOLTON  David BERCOVICI 《《地质学报》英文版》2013,87(Z1):967-968

  相似文献   

Geophysical Finite-Element Simulation Tool (GeoFEST): Algorithms and Validation for Quasistatic Regional Faulted Crust Problems     

Jay Parker  Gregory Lyzenga  Charles Norton  Cinzia Zuffada  Margaret Glasscoe  John Lou  Andrea Donnellan 《Pure and Applied Geophysics》2008,165(3-4):497-521

GeoFEST (Geophysical Finite Element Simulation Tool) is a two- and three-dimensional finite element software package for the modeling of solid stress and strain in geophysical and other continuum domain applications. It is one of the featured high-performance applications of the NASA QuakeSim project. The program is targeted to be compiled and run on UNIX systems, and is running on diverse systems including sequential and message-passing parallel systems. Solution to the elliptical partial differential equations is obtained by finite element basis sampling, resulting in a sparse linear system primarily solved by conjugate gradient iteration to a tolerance level; on sequential systems a Crout factorization for the direct inversion of the linear system is also supported. The physics models supported include isotropic linear elasticity and both Newtonian and power-law viscoelasticity, via implicit quasi-static time stepping. In addition to triangular, quadrilateral, tetrahedral and hexahedral continuum elements, GeoFEST supports split-node faulting, body forces, and surface tractions. This software and related mesh refinement strategies have been validated on a variety of test cases with rigorous comparison to analytical solutions. These include a box-shaped domain with imposed motion on one surface, a pair of strike slip faults in stepover arrangement, and two community-agreed benchmark cases: a strike slip fault in an enclosing box, and a quarter-domain circular fault problem. Scientific applications of the code include the modeling of static and transient co- and post-seismic earth deformation, Earth response to glacial, atmospheric and hydrological loading, and other scenarios involving the bulk deformation of geologic media.  相似文献   

Dynamic characteristics and horizontal transports of internal solitons generated at the Columbia River plume front     

Jiayi Pan  David A. Jay 《Continental Shelf Research》2009

River plume front-generated internal solitons play an important role in the interaction between the plume and coastal waters. The internal solitons drive a non-harmonic velocity field, resulting in a horizontal transport that carries plume water seaward and redistributes nutrients and sediments. In this study, we present observations of internal solitons generated at the Columbia River plume front that separates the new, tidal plume, older plume and coastal waters. Scale analyses suggest that the plume front-generated internal solitons are highly non-linear waves, and their dynamic properties do not conform to any weakly non-linear theory. Thus, a high-order Korteweg–de Vries (KdV) theory is used to analyze the internal solitons. The comparison between theoretical values and cruise data shows that the high-order KdV model is much better than the weakly non-linear theories for prediction of the soliton dynamic parameters. Based on the model, we develop theoretical and numerical solutions of the soliton-induced upper layer horizontal transport and Lagrangian water parcel transport distance, which shows that the water particle drift, during the internal soliton passage, is as far as 1 km, and demonstrates the role of the internal solitons on the exchange between the plume and ambient coastal water. Energy fluxes caused by the internal solitons are estimated using the high-order KdV theory. The leading soliton fluxes 2.0×10³ W m⁻¹ per unit crest length, and carries energy of 4.2×10⁵ J m⁻¹. The total energy carried by the eight internal solitons is 1.6×10⁶ J m⁻¹, about 70% of the total frontal energy.  相似文献   

Geochemistry,chronology and stratigraphy of Neogene tuffs of the Central Andean region     

Christa Placzek  Jay Quade  Jason A. Rech  P.J. Patchett  Carlos Pérez de Arce 《Quaternary Geochronology》2009,4(1):22-36

Tuff layers are vital stratigraphic tools that allow correlations to be made between widely dispersed exposures. Despite their widespread occurrence in the central Andes, tuffs from both natural exposures and sedimentary cores extracted from the region's extensive salars (salt pans) are relatively unstudied. Here we lay the foundation for a tephrostratigraphic framework in the central Andes (14–28°S) by chemically and morphologically characterizing ash shards, and in some cases dating 36 Neogene distal tuffs. These tuffs occur in lacustrine and alluvial deposits from the southern Bolivian Altiplano and adjacent Atacama Desert. All tuffs are calc-akaline rhyolites, consistent with their setting in the Central Andean Volcanic Zone. Five of the older tuffs were ⁴⁰Ar/³⁹Ar dated and yield an age range of 6.63–0.75 Ma. Organic material associated with tuffs deposited into paleolake sediments, paleowetland deposits, or urine-encrusted rodent middens provide constraints on the age of several Late Pleistocene and Holocene tuffs.These tuffs provide key stratigraphic markers and ages for lake cycles and archeological sites on the Bolivian Altiplano and for assessing rates of surficial processes and archeology in both the Atacama and Altiplano. While modern climate, and consequently questions about geomorphic processes and climate change, differs in the hyperarid Atacama and the semi-arid Altiplano, the most extensive air-fall tuffs covered both regions, placing the Atacama and the Bolivian Altiplano in the same tephrostratigraphic province. For example, the Escara B tuff (～1.85 Ma), can be securely identified in both the Altiplano and Atacama. On the Altiplano, dates from the Escara B and E tuffs securely establish the age of the Escara Formation—representing the oldest expansive lake documented on the Bolivian Altiplano. By contrast, the presence of the Escara B tuff below ～6 m of alluvial sediment at the Blanco Encalado site in the Atacama desert yields information about sedimentation rates in this hyperarid region. Indeed, most tuffs from the Atacama Desert are older than 600,000 years, even though they occur within fluvial terraces immediately adjacent to the alluvial fans that are still active. Most of these geomorphic surfaces in the Atacama also possess well-developed saline soils that, when combined with the radiometric ages of the distal tuffs, suggest slow rates of geomorphic change and exceptional landscape stability for this area during the Quaternary.In contrast, younger tuffs are more abundant in the more recent lake records of the Altiplano. The Chita tuff was deposited at ～15,650 cal yr B.P., during the regressive phase of the region's deepest late Quaternary lake cycle—the “Tauca lake cycle”—which spanned 18.1–14.1 cal yr B.P. Two Holocene tuffs, the Sajsi tuff and the Cruzani Cocha tuff, are widespread. The Sajsi tuff was deposited just before 1700 cal yr B.P., whereas the Cruzani Cocha tuff appears to be mid-Holocene in age and shows some chemical affinities to a Holocene tuff (202B) deposited between 4420 and 5460 cal yr B.P. in a urine-encased rodent midden in the Atacama Desert.  相似文献   

Effects of soil layering on the characteristics of basin-edge induced surface waves     

Jay Prakash Narayan  Sanjay Kumar 《Acta Geophysica》2009,57(2):294-310

This paper presents the effects of soil layering on the characteristics of basin-edge induced surface waves and associated strain and aggravation factor. The simulated results revealed surface wave generation near the basin-edge. The first mode of induced Love wave was obtained in models having increasing velocity with depth and a large impedance contrast between the soil layers. Amplitude amplification or de-amplification of body waves was proportional to the impedance contrast between the soil layers. The average aggravation factor was inversely proportional to the impedance contrast between the soil layers in case of increasingvelocity models and proportional in case of decreasing-velocity basinedge models. On the other hand, the maximum strain was inversely proportional to the impedance contrast between the soil layers in both cases. On the average, strain was greater in case of increasing-velocity models but the average aggravation factor was greater in case of decreasingvelocity models.  相似文献   

AMS 14C age constraints on geoglyphs in the lower colorado river region,arizona and california     

Jay Von Werlhof  Harry Casey  Ronald I. Dorn  Glenn A. Jones 《Geoarchaeology》1995,10(4):257-273

Giant ground figures are widespread in the lower Colorado River area of southwestern North America, yet their chronology has remained unconstrained by numerical ages. Thirteen AMS ¹⁴C measurements reported here indicate that geoglyphs were made from before ˜A. D. 1200 to before ˜900 B. C. We account for potential contamination from prior organics in weathering rinds. All other potential errors point to ¹⁴C dates being minimum-limiting ages for the manufacturing of geoglyphs. Although these ages indicate considerable chronological complexity among geoglyphs, our data are consistent with the linguistic hypothesis that the Yuman people in the desert of southeastern California migrated from Baja California—rather than from the north. These results must, however, be placed under the cloud of uncertainty that hangs over the entire field of AMS dating of rock art: the untested assumption surrounding contemporeneity of organics in a surface context. © 1995 John Wiley & Sons, Inc.  相似文献   

Report of centimeter-sized tektites in Pima County,Arizona, cannot be verified     

David A. Kring  Alan R. Hildebrand  Michael J. Drake  H. Jay Melosh  Ann M. Vickery 《Meteoritics & planetary science》1995,30(1):110-112

Abstract— Glassy objects reportedly found in Pima County, Arizona, have been identified as tektites. A field survey of the area where they were said to occur, however, did not produce any other tektites, nor did it reveal any other geologic features that might indicate a nearby impact crater. The major-, minor-, and trace-element composition of one specimen is similar to those measured in indochinites, which suggests the objects reportedly from Pima County were instead transported to southern Arizona from Indochina by people.  相似文献   

Coronal images from the 1984 solar eclipse     

Jay M. Pasachoff  Kevin P. Reardon  John W. MacKenty 《Solar physics》1993,146(2):405-408

We present digitized photographs of the white-light solar corona taken during the total solar eclipse of 22–23 November, 1984, on both calibrated black-and-white film and on color film. Conditions on site in Hula, Papua New Guinea, were exceptionally clear. The color image was used to produce an isophotal map of the inner corona, from which a flattening coefficient of 0.23 was measured. The black-and-white image was enhanced through a digital radial filter. Our images are the best processed images available from the 1984 eclipse and so provide important data for synoptic observations.  相似文献