Modern sedimentation and hydrology in Lake Tyrrell,Victoria     

James T. Teller  J. M. Bowler  P. G. Macumber 《Australian Journal of Earth Sciences》2013,60(1-2):159-175

Lake Tyrrell is a large ephemeral salt lake, the level of which is controlled by climate and groundwater. Up to a metre of water fills the basin during the wetter and cooler winter season, but evaporates during the summer, precipitating up to 10 cm of halite. Each year essentially the same pool of ions is redissolved by this annual freshening. The small percentage of gypsum precipated (< 2%) in the surface salt crust reflects the low calcium content of the brine which, in turn, is a function of the negligible net discharge of calcium from the groundwater system. The small influx of fine‐grained clastic sediment to the lake floor comes from surface runoff, wind, and reworking of older sediment from the shoreline.

The Lake Tyrrell basin lies in a setting in which three different groundwater types, identified by distinct salinities, interact with surface waters. A refluxing cycle that goes from discharging groundwater at the basin margin, to surface evaporation on the lake floor, to recharge through the floor of the lake, controls the major chemical characteristics of the basin. In this process, salts are leached downward from the lake floor to join a brine pool below the lake. This provides an outlet from the lake, especially under conditions that have been both drier and wetter than those of today. Enhanced discharge occurs under drier conditions, when the enclosing regional groundwater divide is lowered, whereas a rise in lake level increases the hydraulic head over that of the sub‐surface brine and promotes an increase in brine loss from the lake.

Sulphate‐reducing bacteria in a zone of black sulphide‐rich mud beneath the salt crust help prevent gypsum from being incorporated into the recent sedimentary record. However, below the upper 5 to 10 cm zone of bacterial activity, discoidal gypsum is being precipitated within the mud from the groundwater. These crystals have grown by displacing the mud and typically “float” in a clay matrix; in some zones, they form concentrations exceeding 50% of the sediment. The occasional laminae of more prismatic gypsum that occur within the upper metre of mud have crystallised from surface brines. The scarcity of these comparatively pure prismatic‐crystal concentrations probably is a function of unfavourable chemical conditions in the lake brine and of the role that sulphate‐reducing bacteria have played.  相似文献   

A new Ordovician eurypterid (Arthropoda: Chelicerata) from southeast Turkey: Evidence for a cryptic Ordovician record of Eurypterida     

James C. Lamsdell  İzzet Hoşgör  Paul A. Selden 《Gondwana Research》2013,23(1):354-366

A new species of eurypterid, Paraeurypterus anatoliensis gen. et sp. nov., is described from the Upper Ordovician (Katian) ?ort Tepe Formation of southeast Turkey. The single specimen, preserving the carapace, mesosoma and fragments of appendages, appears morphologically intermediate between the eurypteroid families Dolichopteridae and Eurypteridae. P. anatoliensis retains the plesiomorphic conditions of crescentic eyes with enlarged palpebral lobes and a quadrate carapace with ornamentation consisting of small pustules but also displaying the derived characteristics of genal facets and a row of large acicular scales across the posterior of each tergite. Phylogenetic analysis incorporating each of the major eurypterine clades and all Eurypterina having a three-segmented genital operculum (the triploperculate condition) resolves eurypteroids to be an unnatural group, with Dolichopteridae and Eurypteridae forming part of a grade leading to diploperculate Eurypterina. P. anatoliensis is intermediate between the two eurypteroid families, as is ‘Eurypterus’ minor from the Pentland Hills of Scotland, which is shown to be a distinct genus and assigned to Pentlandopterus gen. nov. Using the phylogenetic topology to infer ghost ranges for each of the major eurypterid clades reveals that the majority of eurypterid superfamilies must have originated by the Katian, indicating a largely unsampled record of Ordovician eurypterids. The occurrence of poor dispersers such as Paraeurypterus in the Ordovician of Gondwana is puzzling, and it has been suggested that they dispersed to the continent during periods of sea level lowstand in the Sandbian and Hirnantian, however this does not explain the lack of Ordovician species in North America and Europe, given the well-sampled nature of these continents, and an alternative is proposed whereby eurypterids originated in Gondwana and radiated out to Laurentia and Baltica in the late Ordovician and early Silurian, thus explaining their sudden appearance in the European and North American rock record.  相似文献   

Delineating and defining the boundaries of an active landslide in the rainforest of Puerto Rico using a combination of airborne and terrestrial LIDAR data   总被引：1，自引：0，他引：1  

Guoquan Wang  James Joyce  David Phillips  Ramesh Shrestha  William Carter 《Landslides》2013,10(4):503-513

Light detection and ranging (LIDAR) is a remote sensing technique that uses light, often using pulses from a laser to measure the distance to a target. Both terrestrial- and airborne-based LIDAR techniques have been frequently used to map landslides. Airborne LIDAR has the advantage of identifying large scarps of landslides covered by tree canopies and is widely applied in identifying historical and current active landslides hidden in forested areas. However, because landslides naturally have relatively small vertical surface deformation in the foot area, it is practically difficult to identify the margins of landslide foot area with the limited spatial resolution (few decimeters) of airborne LIDAR. Alternatively, ground-based LIDAR can achieve resolution of several centimeters and also has the advantages of being portable, repeatable, and less costly. Thus, ground-based LIDAR can be used to identify small deformations in landslide foot areas by differencing repeated terrestrial laser scanning surveys. This study demonstrates a method of identifying the superficial boundaries as well as the bottom boundary (sliding plane) of an active landslide in National Rainforest Park, Puerto Rico, USA, using the combination of ground-based and airborne LIDAR data. The method of combining terrestrial and airborne LIDAR data can be used to study landslides in other regions. This study also indicates that intensity and density of laser point clouds are remarkably useful in identifying superficial boundaries of landslides.  相似文献   

Editorial     

Brian Horsfield  Ralf Littke  James J. Mori  G. S. Lynn Soreghan 《International Journal of Earth Sciences》2015,104(6):1497-1498

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Trace element residues in eggs of Little Egret (Egretta garzetta) and Black-crowned Night Heron (Nycticorax nycticorax) from Hong Kong, China     

Lam JC  Tanabe S  Wong BS  Lam PK 《Marine pollution bulletin》2004,48(3-4):390-396

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Development of Water Quality Index (WQI) model for the groundwater in Tirupur district, South India     

P.J.Sajil Kumar  E.J.James 《中国地球化学学报》2013,32(3):261-268

Groundwater quality of the Tiruppur district in Tamil Nadu was investigated in this study to develop a Water Quality Index (WQI) model. Hydrochemical parameters showed tremendous variation in certain location over the seasons. Ionic chemistry of groundwater suggested that textile industries and rock-water interaction are major threats to the water quality. Analysis of Na and Ca concentration indicates that direct as well as the inverse cation exchange controls the natural cation chemistry. NO3 concentration shows that the pre-monsoon samples were affected by the fertilizer usage in agricultural fields. Na-Cl type of the water was dominant throughout the study area except few locations. WQI showed that 55% of the pre-monsoon samples and the 47% of the post monsoon samples were classified as poor/very poor/unsuitable for drinking category. Leaching of the textile waste and their transport to the downstream was well observed during the post-monsoon season. The specific contribution of river Noyyal in the transport of the solutes to the discharge zones was proved by the hydrochemistry of the samples.  相似文献   

Photochemical and Microbial Transformations of Dissolved Organic Matter in Temperate Streams Associated with Land Use: Molecular Characterization Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry     

LI Xiaping  LU Yuehan  Rajaa MESFIOUI  James E. BAUER  Elizabeth A. CANUEL  R. M. CHAMBERS  Patrick G. HATCHER 《《地质学报》英文版》2013,87(Z1):640-640

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What biology can we learn from nucleus-like intracellular inclusions in Proterozoic cells?     

XIAO Shuhai  PANG Ke  James D. Schiffbauer  YUAN Xunlai 《《地质学报》英文版》2013,87(Z1):878-879

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Very high-frequency and seasonal cave atmosphere P_CO2 variability: Implications for stalagmite growth and oxygen isotope-based paleoclimate records     

James U.L. Baldini  Frank McDermott  Dirk L. Hoffmann  David A. Richards  Nicholas Clipson 《Earth and Planetary Science Letters》2008,272(1-2):118-129

Cave air P_CO2 at two Irish sites varied dramatically on daily to seasonal timescales, potentially affecting the timing of calcite deposition and consequently climate proxy records derived from stalagmites collected at the same sites. Temperature-dependent biochemical processes in the soil control CO₂ production, resulting in high summer P_CO2 values and low winter values at both sites. Large Large-amplitude, high-frequency variations superimposed on this seasonal cycle reflect cave air circulation. Here we model stalagmite growth rates, which are controlled partly by CO₂ degassing rates from drip water, by considering both the seasonal and high-frequency cave air P_CO2 variations. Modeled hourly growth rates for stalagmite CC-Bil from Crag Cave in SW Ireland reach maxima in late December (0.063 μm h^− 1) and minima in late June/early July (0.033 μm h^− 1). For well-mixed ‘diffuse flow’ cave drips such as those that feed CC-Bil, high summer cave air P_CO2 depresses summer calcite deposition, while low winter P_CO2 promotes degassing and enhances deposition rates. In stalagmites fed by well-mixed drips lacking seasonal variations in δ¹⁸O, integrated annual stalagmite calcite δ¹⁸O is unaffected; however, seasonality in cave air P_CO2 may influence non-conservative geochemical climate proxies (e.g., δ¹³C, Sr/Ca). Stalagmites fed by ‘seasonal’ drips whose hydrochemical properties vary in response to seasonality may have higher growth rates in summer because soil air P_CO2 may increase relative to cave air P_CO2 due to higher soil temperatures. This in turn may bias stalagmite calcite δ¹⁸O records towards isotopically heavier summer drip water δ¹⁸O values, resulting in elevated calcite δ¹⁸O values compared to the ‘equilibrium’ values predicted by calcite–water isotope fractionation equations. Interpretations of stalagmite-based paleoclimate proxies should therefore consider the consequences of cave air P_CO2 variability and the resulting intra-annual variability in calcite deposition rates.  相似文献   

Quantifying bank storage of variably saturated aquifers   总被引：1，自引：0，他引：1  

Li H  Boufadel MC  Weaver JW 《Ground water》2008,46(6):841-850

Numerical simulations were conducted to quantify bank storage in a variably saturated, homogenous, and anisotropic aquifer abutting a stream during rising stream stage. Seepage faces and bank slopes ranging from 1/3 to 100/3 were simulated. The initial conditions were assumed steady-state flow with water draining toward the stream. Then, the stream level rose at a constant rate to the specified elevation of the water table given by the landward boundary condition and stayed there until the system reached a new steady state. This represents a highly simplified version of a real world hydrograph. For the specific examples considered, the following conclusions can be made. The volume of surface water entering the bank increased with the rate of stream level rise, became negligible when the rate of rise was slow, and approached a positive constant when the rate was large. Also, the volume decreased with the dimensionless parameter M (the product of the anisotropy ratio and the square of the domain's aspect ratio). When M was large (>10), bank storage was small because most pore space was initially saturated with ground water due to the presence of a significant seepage face. When M was small, the seepage face became insignificant and capillarity began to play a role. The weaker the capillary effect, the easier for surface water to enter the bank. The effect of the capillary forces on the volume of surface water entering the bank was significant and could not be neglected.  相似文献