Modelling sea level surges in the Firth of Clyde,a fjordic embayment in south-west Scotland     

Alessandro D. Sabatino  Rory B. O’Hara Murray  Alan Hills  Douglas C. Speirs  Michael R. Heath 《Natural Hazards》2016,84(3):1601-1623

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Quantifying the tectono-metamorphic evolution of pelitic rocks from a wide range of tectonic settings: mineral compositions in equilibrium   总被引：1，自引：0，他引：1  

Mark J. Caddick  Alan B. Thompson 《Contributions to Mineralogy and Petrology》2008,156(2):177-195

Commonly used thermometer and barometer calibrations are sensitive to mineral assemblage and, thus, bulk-rock composition. Calculated mineral stabilities for an average pelitic rock over a pressure–temperature (PT) range appropriate for normal, thickened, heated and shallowly subducted continental crust (400–900°C at 0.1–3.0 GPa) reveal more than one hundred possible assemblages. Individual phase compositions are dependent on the assemblage in which they belong and combining isopleth sets to represent and reveals several PT-ranges where commonly used mineral thermobarometers are less effective. For example, the garnet-biotite thermometer becomes increasingly P dependent in the absence of muscovite in high T melt-bearing assemblages, and biotite and plagioclase are not stable at pressures appropriate for lower thickened continental crust. Compositional thermobarometers involving equilibration between alternative phases (namely garnet, phengite and omphacite) are presented. Although the equilibrium compositions of phases at any P and T may change significantly as a function of bulk-rock composition, compositional-ratio thermobarometers are typically insensitive to this, unless a pseudo-univariant reaction is crossed and the buffering assemblage is altered. Quantification of the limits of efficacy of various thermobarometers allows the mineralogy of metapelites to be used to precisely determine segments of PT paths and infer their likely tectonic controls. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

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Mark J. CaddickEmail:

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Late Pleistocene glaciers in Darhad Basin, northern Mongolia     

Alan R. Gillespie  Raymond M. Burke  Amgalan Bayasgalan 《Quaternary Research》2008,69(2):169-187

Late Pleistocene glaciers around Darhad Basin advanced to near their maximum positions at least three times, twice during the Zyrianka glaciation (at ∼ 17-19 ka and ∼ 35-53 ka), and at least once earlier. The Zyrianka glaciers were smaller than their predecessors, but the equilibrium-line altitude (ELA) difference was < 75 m. End moraines of the Zyrianka glaciers were ∼ 1600 m asl; ELAs were 2100-2400 m asl. ¹⁴C and luminescence dating of lake sediments confirm the existence of paleolake highstands in Darhad Basin before ∼ 35 ka. Geologic evidence and ¹⁰Be cosmic-ray exposure dating of drift suggests that at ∼ 17-19 ka the basin was filled at least briefly by a glacier-dammed lake ∼ 140 m deep. However, lake sediments from that time have not yet been recognized in the region. A shallower paleolake briefly occupied the basin at ∼ 11 ka, but between ∼ 11 and 17 ka and after ∼ 10 ka the basin was probably largely dry. The timing of maximum glacier advances in Darhad appears to be approximately synchronous across northern Mongolia, but different from Siberia and western Central Asia, supporting the inference that paleoclimate in Central Asia differed among regions.  相似文献   

High-resolution and precisely dated record of weathering and hydrological dynamics recorded by manganese and rare-earth elements in a stalagmite from Central China   总被引：2，自引：0，他引：2  

Houyun Zhou  Baoquan Chi  Michael Lawrence  Jianxin Zhao  Jun Yan  Alan Greig  Yuexing Feng 《Quaternary Research》2008,69(3):438-446

Manganese (Mn) and rare-earth elements (REEs) in a stalagmite (SJ3) collected from Central China were analyzed, using an ICP-MS method for the precise determination of > 40 trace elements in geological samples by enriched-isotope internal standardization. Unlike speleothem Mn and REEs investigated by cathodoluminescence, which may be incorporated into crystal lattice, the Mn and REEs analyzed in SJ3 should come largely from colloidal and particle phases in groundwater and may be associated with non-carbonate inclusions. The Mn and REEs in SJ3 vary significantly during the period between 20 and 10 ka. These elements show remarkable increases since  14.5 ka, suggesting enhanced weathering of the overlying soil layer and the host rock since the onset of the last deglaciation and the strengthening of the Asian summer monsoon. In addition, the Mn and REEs in SJ3 display significant centennial fluctuations which may reflect groundwater dynamics.  相似文献   

The motion of Adria during the Late Jurassic and Cretaceous: New paleomagnetic results from stable Istria     

Em&#x; Mrton  Vlasta &#x;osovi&#x;  Alan Moro  Sergej Zvocak 《Tectonophysics》2008,454(1-4):44-53

The motion of Adria, the largest lithospheric fragment in the Central Mediterranean region, has played an important role in the tectonic development of the surrounding mountain chains and even of distant areas, like the Eastern Alps or the Pannonian basin. The available paleomagnetic data were insufficient to constrain this motion, except in a general way. In this paper, new paleomagnetic results are presented from one of the stable parts of Adria which emerge from the Adriatic Sea. The results were obtained on weakly magnetic platform carbonates of the mud-supported type, collected from 21 geographically distributed localities.The results, combined with mean paleomagnetic directions from selected localities from a pioneer study in Istria that were chosen using statistical criteria, were divided into three age groups (Tithonian–Aptian, Albian–Cenomanian, Turonian–Coniacian). The paleomagnetic poles calculated for each of them (Tithonian–Aptian): λ(N) = 47°, (E) = 275°, k = 67, α₉₅ = 9.4°, N = 5; Albian-Cenomanian: λ(N) = 58°, (E) = 253°, k = 145, α₉₅ = 4.3°, N = 9; Turonian–Coniacian: λ(N) = 63°, (E) = 261°, k = 50, α₉₅ = 7.3°, N = 9) reveal a moderate shift during the Cretataceous, which is comparable with that calculated from the African reference poles. However, the Istrian apparent polar wander path is slightly displaced from the African curve, as a consequence of about 10° counterclockwise rotation of Istria, with respect to Africa. This rotation angle is more that 10° smaller than the difference measured for the Mid-Late Eocene between the paleomagnetic direction of platform carbonates from Istria and the African reference direction. This difference may be the consequence of a small clockwise rotation of Istria, with respect to Africa, most probably at the end of Cretaceous.  相似文献   

Deeper groundwater chemistry and geochemical modeling of the arsenic affected western Bengal basin,West Bengal,India   总被引：1，自引：0，他引：1  

Abhijit Mukherjee  Alan E. Fryar 《Applied Geochemistry》2008

A regional scale hydrogeochemical study of a ∼21,000-km² area in the western Bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers. Spatial trends of solutes and geochemical modeling indicate that carbonate dissolution, silicate weathering, and cation exchange control the major-ion chemistry of groundwater and river water. The main aquifer water has also evolved by mixing with seawater from the Bay of Bengal and connate water. The isolated aquifers contain diagenetically altered water of probable marine origin. The postoxic main aquifer water exhibits overlapping redox zones (metal-reducing, sulfidic and methanogenic), indicative of partial redox equilibrium, with the possibility of oxidation in micro-scale environments. The redox processes are depth-dependent and hydrostratigraphically variable. Elevated dissolved As in the groundwater is possibly related to Fe(III) reduction, but is strongly influenced by coupled Fe–S–C redox cycles. Arsenic does not show good correlations with most solutes, suggesting involvement of multiple processes in As mobilization. The main river in the area, the Bhagirathi–Hoogly, is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry. Arsenic in water of smaller streams (Jalangi and Ichamati) is probably introduced by groundwater discharge during the dry season.  相似文献   

Tertiary tectono-metamorphic evolution of the European margin during Alpine collison: example of the Leventina Nappe (Central Alps,Switzerland)     

Roger Rütti  Didier Marquer  Alan Bruce Thompson 《Swiss Journal of Geoscience》2008,101(1):157-171

The Leventina Nappe represents one of the lowermost exposed units in the Alpine nappe stack and corresponds to a slice of the European margin that was entrained into the Alpine continental accretionary prism during the Tertiary tectonic event. This study yields details regarding the tectonic and metamorphic history of the Leventina Nappe, through detailed analysis of structures and shear zone patterns, and the examination of the Si-content of white mica along a north-south profile. The Leventina Nappe underwent three phases of ductile deformation. Foliation S1 is mostly sub-parallel to the regionally dominant structural fabric (the S2 foliation). S2 foliation is penetratively developed in the structurally higher portions of the Leventina Nappe toward the Simano Nappe, while it is only weakly developed in the core of the Leventina Nappe. A 50 to 200 m wide mylonite zone, with a D2 top-to-NW sense of shear marks the boundary to the Simano Nappe. Throughout the Leventina Nappe only small-scale D2 shear bands (mm to cm wide) are observed, showing a top-to-NW sense of shear. Deformation phase D3 locally generated a vertical axial plane foliation (S3) associated with the large-scale D3 Leventina antiform.Microtextural evidence and phengite geobarometry were used to constrain the temperature and pressure conditions of equilibration of the Leventina Gneisses. Highest Si (pfu) values are preserved in the core of phengitic micas and reflect pressure and temperature conditions of around 8 kbar at 550 °C and 10 kbar at 650 °C in the northern and southern parts of the Leventina Nappe, respectively. Lower Si (pfu) values from the rims of white micas correspond to a metamorphic pressure of ca. 5 kbar during the exhumation of the unit. These metamorphic conditions are related to the underthrusting of the thinned European margin into the continental accretionary prism during late Eocene time. These new data allow us to propose a kinematic model for the Leventina Nappe during the Tertiary Alpine tectonics.  相似文献   

Water and soil quality at two eastern-Kentucky (USA) coal fires     

Trent Garrison  James C. Hower  Alan E. Fryar  Elisa D’Angelo 《Environmental Earth Sciences》2016,75(7):574

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Glacial lake levels and Eastern Great Lakes Palaeo‐Indians     

Lawrence J. Jackson  Christopher Ellis  Alan V. Morgan  John H. McAndrews 《Geoarchaeology》2000,15(5):415-440

This article investigates changing lake levels in the late Pleistocene eastern Great Lakes in order to gain insights into the Early Palaeo‐Indian occupations. Significant new information bearing on lake level history is provided, notably the first well‐documented deposits of a high water level above modern in the ca. 11,000–10,300 B.P. period in the southern Lake Huron basin. The lake level information, along with paleoenvironmental and site data, reinforces site age estimates to the 11th millennium B.P.; suggests significant numbers of sites have been inundated by rising water levels; provides specific information on the setting of archaeological sites such as placing the Parkhill site adjacent to a large lake estuary; indicates reasons for the attractiveness of shorelines to Palaeo‐Indians including persistence of more open areas conducive to higher game productivity; and points to ideal areas for future archaeological site survey, particularly in the Lake Erie drainage. © 2000 John Wiley & Sons, Inc.  相似文献   

Integer ambiguity resolution in precise point positioning: method comparison   总被引：24，自引：10，他引：14  

Jianghui Geng  Xiaolin Meng  Alan H. Dodson  Felix N. Teferle 《Journal of Geodesy》2010,84(9):569-581

Integer ambiguity resolution at a single receiver can be implemented by applying improved satellite products where the fractional-cycle biases (FCBs) have been separated from the integer ambiguities in a network solution. One method to achieve these products is to estimate the FCBs by averaging the fractional parts of the float ambiguity estimates, and the other is to estimate the integer-recovery clocks by fixing the undifferenced ambiguities to integers in advance. In this paper, we theoretically prove the equivalence of the ambiguity-fixed position estimates derived from these two methods by assuming that the FCBs are hardware-dependent and only they are assimilated into the clocks and ambiguities. To verify this equivalence, we implement both methods in the Position and Navigation Data Analyst software to process 1 year of GPS data from a global network of about 350 stations. The mean biases between all daily position estimates derived from these two methods are only 0.2, 0.1 and 0.0 mm, whereas the standard deviations of all position differences are only 1.3, 0.8 and 2.0 mm for the East, North and Up components, respectively. Moreover, the differences of the position repeatabilities are below 0.2 mm on average for all three components. The RMS of the position estimates minus those from the International GNSS Service weekly solutions for the former method differs by below 0.1 mm on average for each component from that for the latter method. Therefore, considering the recognized millimeter-level precision of current GPS-derived daily positions, these statistics empirically demonstrate the theoretical equivalence of the ambiguity-fixed position estimates derived from these two methods. In practice, we note that the former method is compatible with current official clock-generation methods, whereas the latter method is not, but can potentially lead to slightly better positioning quality.  相似文献