A 24,700-yr paleolimnological history from the Peruvian Andes     

Rachel Hillyer  Bryan G. Valencia  Miles R. Silman 《Quaternary Research》2009,71(1):71-126

A new paleolimnological dataset from Lake Pacucha (13 °S, 3095 m elevation) in the Peruvian Andes provides evidence of changes in lake level over the past 24,700 yr. A late-glacial highstand in lake level gave way to an early-Holocene lowstand. This transition appears to have paralleled precessional changes that would have reduced insolation during the wet-season. The occurrence of benthic/salt-tolerant diatoms and CaCO₃ deposition suggest that the lake had lost much of its volume by c. 10,000 cal yr BP. Pronounced Holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c. 8300 to 5000 cal yr BP. While a polymictic lake formed at c. 5000 cal yr BP. These relatively wet conditions were interrupted by a series of drier events, the most pronounced of which occurred at c. 750 cal yr BP. Paleolimnological changes in the Holocene were more rapid than those of either the last glacial maximum or the deglacial period.  相似文献   

Provenance and pathways of late Quaternary turbidites in the deep-water Agadir Basin,northwest African margin     

Michael Frenz  Russell B. Wynn  Aggeliki Georgiopoulou  Vera B. Bender  Gayle Hough  Douglas G. Masson  Peter J. Talling  Bryan T. Cronin 《International Journal of Earth Sciences》2009,98(4):721-733

A series of individual turbidites, correlated over distances >100 km, are present in the recent fill of the Agadir Basin, offshore northwest Africa. The aim here is to unravel multiple turbidite source areas and flow pathways, and show how turbidite provenance studies contribute to interpretation of flow processes. Agadir Basin turbidites are sourced from four main areas, with the majority originating from the siliciclastic Morocco Shelf; their sand-mud distribution is strongly controlled by flow sediment volume, with relatively low-volume flows dying out within the Agadir Basin and large-volume flows bypassing significant sediment volumes to basins further downslope. Two large-volume volcaniclastic turbidites are attributed to a Canary Islands landslide source, while several small mud-dominated turbidites are interpreted to be locally sourced from hemipelagic-draped seamounts (e.g. Turbidite AB10). Finally, Turbidite AB1 (∼1 ka) is only present in the western Agadir Basin, and is linked to recent “re-activation” of the Sahara Slide headwall. The muddy suspension clouds of three large-volume flows, all linked to large-scale landslides, have covered huge areas of seafloor and flowed along or even slightly upslope for long distances. It is proposed that northeastwards-flowing bottom currents have aided transport of these dilute flow fractions into and across the Agadir Basin.  相似文献   

A New Ectasian Event of Basitic Magmatism in the Southern Siberian Craton     

Gladkochub  D. P.  Donskaya  T. V.  Ernst  R. E.  Hamilton  M. A.  Mazukabzov  A. M.  Pisarevsky  S. A.  Kamo  S. 《Doklady Earth Sciences》2019,486(1):507-511

Doklady Earth Sciences - On the basis of U–Pb dating of zircon and baddeleyite from gabbro–dolerite of the Goloustnaya dyke swarm (southern margin of the Siberian Craton), the age of...  相似文献   

A commentary on coastal research in New Zealand universities     

Paul S. Kench  Karin R. Bryan  Deirdre E. Hart  David M. Kennedy  Michael J. Hilton 《New Zealand geographer》2008,64(2):93-104

Abstract:    University research in coastal geomorphology, processes and management has made a major contribution to the fundamental understanding of coastal systems in New Zealand over the past 43 years. This article examines the growth in university-based coastal research since 1964 and discusses the geographical pattern and themes of this research. Data indicate a significant geographical concentration of research effort and focus on a narrow range of research themes. Underlying reasons for these characteristics of New Zealand coastal research are explored and challenges facing university based research are discussed. Such challenges can be overcome through a more coordinated research effort to realize the huge potential to undertake coastal science of national relevance and international significance.  相似文献   

Pressure-dependent Production Efficiency of an Enhanced Geothermal System (EGS): Stimulation Results and Implications for Hydraulic Fracture Treatments     

Günter Zimmermann  Torsten Tischner  Björn Legarth  Ernst Huenges 《Pure and Applied Geophysics》2009,166(5-7):1089-1106

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Empirical Assessment of Ground Water–to-Indoor Air Attenuation Factors for the CDOT-MTL Denver Site     

P.C. Johnson  R.A. Ettinger  J.P. Kurtz  R. Bryan  J.E. Kester 《Ground Water Monitoring & Remediation》2009,29(1):153-159

The area surrounding the Colorado Department of Transportation Materials Testing Laboratory in Denver was the subject of intense investigation, involving the collection of thousands of ground water, soil-gas, and indoor air samples in order to investigate indoor air impacts associated with a subsurface release of chlorinated solvents. The preremediation portion of that data set is analyzed and reduced in this work to ground water–to-indoor air attenuation factors (α_gw= the ratio of the measured indoor air concentration to the soil-gas concentration predicted to be in equilibrium with the local ground water concentration). The empirical α_gw values for this site range from about 10⁻⁶ to 10⁻⁴ with an overall average of 3 × 10⁻⁵ (μg/L indoor air)/(μg/L soil gas). The analysis of this data set highlights the need for a thorough data review and data screening when using large data sets to derive empirical relationships between subsurface concentrations and indoor air. More specifically, it is necessary to identify those parts of the data that contain a strong vapor intrusion pathway signal, which generally will require concentrations well above reported detection levels combined with spatial or temporal correlation of subsurface and indoor concentrations.  相似文献   

Seismicity in the outer rise offshore southern Chile: Indication of fluid effects in crust and mantle   总被引：1，自引：0，他引：1  

Frederik J. Tilmann  Ingo Grevemeyer  Ernst R. Flueh  Torsten Dahm  Jürgen Goßler 《Earth and Planetary Science Letters》2008,269(1-2):41-55

We examine the micro-earthquake seismicity recorded by two temporary arrays of ocean bottom seismometers on the outer rise offshore southern Chile on young oceanic plate of ages 14 Ma and 6 Ma, respectively. The arrays were in operation from December 2004–January 2005 and consisted of 17 instruments and 12 instruments, respectively. Approximately 10 locatable events per day were recorded by each of the arrays. The catalogue, which is complete for magnitudes above 1.2–1.5, is characterized by a high b value, i.e., a high ratio of small to large events, and the data set is remarkable in that a large proportion of the events form clusters whose members show a high degree of waveform similarity. The largest cluster thus identified consisted of 27 similar events (average inter-event correlation coefficient > 0.8 for a 9.5 s window), and waveform similarity persists far into the coda. Inter-event spacing is irregular, but very short waiting times of a few minutes are far more common than expected from a Poisson distribution. Seismicity with these features (high b value, large number of similar events with short waiting times) is typical of swarm activity, which, based on empirical evidence and theoretical considerations, is generally thought to be driven by fluid pressure variations. Because no pronounced outer rise bulge exists on the very young plate in the study region, it is unlikely that melt is accessible from decompression melting or opening of cracks. A fluid source related to processes at the nearby ridge is conceivable for the younger segment but less likely for the older one. We infer that the fluid source could be seawater, which enters through fractures in the crust. Most of the similar-earthquake clusters are within the crust, but some of them locate significantly below the Moho. If our interpretation is correct, this implies that water is present within the mantle. Hydration of the mantle is also indicated by a decrease of P_n velocities below the outer rise seen on a refraction profile through one of the arrays [Contreras-Reyes, E., Grevemeyer, I., Flueh, E.R., Scherwath, M., Heesemann, M., 2007. Alteration of the subducting oceanic lithosphere at the southern central Chile trench-outer rise. Geochem., Geophys. Geosyst. 8, Q07003.]. The deepest events within the array on the 6 Ma old plate occur where the temperature reaches 500–600 °C, consistent with the value observed for large intraplate earthquakes within the mantle (650 °C), suggesting that the maximum temperature at which these fluid-mediated micro-earthquakes can occur is similar or identical to that of large earthquakes.  相似文献   

Soil erodibility and processes of water erosion on hillslope   总被引：14，自引：0，他引：14  

Rorke B. Bryan   《Geomorphology》2000,32(3-4)

The importance of the inherent resistance of soil to erosional processes, or soil erodibility, is generally recognized in hillslope and fluvial geomorphology, but the full implications of the dynamic soil properties that affect erodibility are seldom considered. In Canada, a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility. This paper aims to place this work in an international framework of research on water erosion processes, and to identify critical emerging research questions. It focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales, essential for event-based soil erosion prediction. Results show that many components of erosional response, such as partitioning between rill and interrill or surface and subsurface processes, threshold hydraulic conditions for rill incision, rill network configuration and hillslope sediment delivery, are strongly affected by spatially variable and temporally dynamic soil properties. This agrees with other recent studies, but contrasts markedly with long-held concepts of soil credibility as an essentially constant property for any soil type. Properties that determine erodibility, such as soil aggregation and shear strength, are strongly affected by climatic factors such as rainfall distribution and frost action, and show systematic seasonal variation. They can also change significantly over much shorter time scales with subtle variations in soil water conditions, organic composition, microbiological activity, age-hardening and the structural effect of applied stresses. Property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and, therefore, both short and long-term hillslope erosional response. Similar property changes, linked to climatic conditions, may also significantly influence the stability and resilience of plant species and vegetation systems. Full understanding of such changes is essential if current event-based soil erosion models such as WEPP and EUROSEM are to attain their full potential predictive precision. The complexity of the interacting processes involved may, however, ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics.  相似文献   

Kuroshio pathways in a climatologically forced model     

Elizabeth M. Douglass  Steven R. Jayne  Frank O. Bryan  Synte Peacock  Mathew Maltrud 《Journal of Oceanography》2012,68(5):625-639

A high-resolution ocean model forced with an annually repeating atmosphere is used to examine variability of the Kuroshio, the western boundary current in the North Pacific Ocean. A large meander (LM) in the path of the Kuroshio south of Japan develops and disappears in a highly bimodal fashion on decadal timescales. The modeled meander is comparable in timing and spatial extent to an observed feature in the region. Various characteristics of the LM are examined, including relative vorticity, transport, and velocity shear. The many similarities between the model and observations indicate that the meander results from intrinsic oceanic variability, which is represented in this climatologically forced model. Each LM is preceded by a smaller “trigger” meander that originates at the south end of Kyushu, moves up the coast, and develops into the LM. However, there are also many meanders very similar in character to the trigger meander that do not develop into LMs. Formation of an LM only occurs when a deep anticyclone associated with the trigger meander forms near Koshu Seamount. Furthermore, the major axis of that deep anticyclone must be oriented away from the coast, rather than alongshore. In the specific case of interaction of a trigger meander with a deep anticyclone with major axis oriented away from the coastline, LM formation occurs.  相似文献   

Microseismicity induced during fluid-injection: A case study from the geothermal site at Groß Schönebeck,North German Basin   总被引：1，自引：1，他引：0  

Grzegorz Kwiatek  Marco Bohnhoff  Georg Dresen  Ali Schulze  Thomas Schulte  Günter Zimmermann  Ernst Huenges 《Acta Geophysica》2010,58(6):995-1020

The technical feasibility of geothermal power production in a low enthalpy environment will be investigated in the geothermal site at Groß Schönebeck, North German Basin, where a borehole doublet was completed in 2007. In order to complete the Enhanced Geothermal System, three massive hydraulic stimulations were performed. A seismic network was deployed including a single 3-component downhole seismic sensor at only 500 m distance to the injection point. Injection rates reached up to 9 m³/min and the maximum injection well-head pressure was as high as ～60 MPa. A total of 80 very small (?1.8 < M _W < ?1.0) induced seismic events were detected. The hypocenters were determined for 29 events. The events show a strong spatial and temporal clustering and a maximum seismicity rate of 22 events per day. Spectral parameters were estimated from the downhole seismometer and related to those from other types of induced seismicity. The majority of events occurred towards the end of stimulation phases indicating a similar behavior as observed at similar treatments in crystalline environments but in our case at a smaller level of seismic activity and at lower magnitudes.  相似文献