Lithological heterogeneity in a back-barrier sand island: Implications for modelling hydrogeological frameworks

Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back-barrier sand island in southeast Queensland, Australia. The island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock. The stratigraphy is complex, recording the shift in depositional environments from fluvio-deltaic to strandplain, via estuarine stages of evolution. The back-barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east. Extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back-barrier island sediments is used to constrain the depositional age and chronology of the back-barrier island stratigraphy. The modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore-parallel back-barrier tidal lagoon. The lithological heterogeneity of the back-barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sea-level.Sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity. Post-depositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour. The derived hydrostratigraphy describes a vertically stacked, dual aquifer, island groundwater system consisting of a semi-confined palaeovalley aquifer overlain by an unconfined strand-plain aquifer.Hydrostratigraphic analysis based on sedimentary facies associations, integrated with post-depositional alteration characteristics reveals great complexity of groundwater systems within small island settings. The facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile.     

Evaluation of trace-metal enrichments from the 26 December 2004 tsunami sediments along the Southeast coast of India

The tsunami sediments deposited after the December 2004 tsunami were sampled immediately in the coastal environment of Tamil Nadu State on the southeast coast of India. Fifty-four sediment samples were collected and 14 representative samples were selected to identify the level of metal contamination in tsunami sediments. The results indicate that the sediments are mainly of fine to medium-grained sand and contain significantly high contents of dissolved salts in sediments (Na⁺, K⁺, Ca⁺², Mg⁺², Cl⁻) in water-soluble fraction due to seawater deposition and evaporation. Correlation of acid leachable trace metals (Cr, Cu, Ni, Co, Pb, Zn) indicate that Fe-Mn oxyhydroxides might play an important role in controlling their association between them. Enrichment of trace metals is observed in all the locations with reference to the background samples. High values of trace metals in the southern part of the study area are due to the large-scale industries along the coast, and they are probably anthropogenic in nature and of marine origin, which could cause serious environmental problems.     

Characterization of the shallow groundwater system in an alpine watershed: Handcart Gulch,Colorado, USA

Water-table elevation measurements and aquifer parameter estimates are rare in alpine settings because few wells exist in these environments. Alpine groundwater systems may be a primary source of recharge to regional groundwater flow systems. Handcart Gulch is an alpine watershed in Colorado, USA comprised of highly fractured Proterozoic metamorphic and igneous rocks with wells completed to various depths. Primary study objectives include determining hydrologic properties of shallow bedrock and surficial materials, developing a watershed water budget, and testing the consistency of measured hydrologic properties and water budget by constructing a simple model incorporating groundwater and surface water for water year 2005. Water enters the study area as precipitation and exits as discharge in the trunk stream or potential recharge for the deeper aquifer. Surficial infiltration rates ranged from 0.1–6.2×10^?5 m/s. Discharge was estimated at 1.28×10^?3 km³. Numerical modeling analysis of single-well aquifer tests predicted lower specific storage in crystalline bedrock than in ferricrete and colluvial material (6.7×10^?5–2.0×10^?3 l/m). Hydraulic conductivity in crystalline bedrock was significantly lower than in colluvial and alluvial material (4.3×10^?9–2.0×10^?4 m/s). Water budget results suggest that during normal precipitation and temperatures water is available to recharge the deeper groundwater flow system.     

Seasonal Variation in Guild Structure of the Puget Sound Demersal Fish Community

Identification of food web linkages is a major aim in ecology because it provides basic information on trophic flows and the potential for interspecific interactions. In addition, policy and restoration measures mandated to conform to ecosystem-based management principals can benefit from information on temporal and spatial variability in community-level interactions. Here, we analyzed guild structure of the demersal fish assemblage in Puget Sound, WA, a temperate estuarine system on the US west coast. Using diet information from 2,401 stomachs collected across three seasons (fall, winter, and summer), we identified guild membership for 21 fish species, examined seasonal guild switching, and tested for seasonal shifts in predation and for differences in the degree of diet overlap at the assemblage level. We accounted for ontogenetic variation in diet by dividing species into large (L) and small (S) size classes when appropriate. Using cluster analysis and a permutation approach, we identified seven significant guilds that were typified by predation on benthic invertebrates, pelagic invertebrates, and piscivory. Of the 18 species with more than one season of diet information, six switched guilds (Pacific sanddab L, sturgeon poacher, Pacific tomcod S, speckled sanddab, rex sole, and rock sole S). At the assemblage level, we tested for seasonal differences in prey use between seasons by performing an analysis of similarities based on Bray–Curtis diet similarities and found no significant difference. However, diet overlap was significantly higher in the summer than the fall and winter (with summer > fall > winter) indicating that diets within the assemblage converged in the summer. These results indicate that analyses of guild structure and diet overlap can reveal seasonal variation in community trophic structure and highlight intra-annual food web variation in the Puget Sound demersal fish community.     

Physics and Chemistry of sulfur lakes on Io

A model for a convecting sulfur lake, heated from below by a silicate magma chamber , is constructed and applied to major hot spot regions on Jupiter's satellite Io. We use a two-layer parametrized convection scheme for sulfur and silicates based on a local boundary layer analysis to calculate temperature profiles in the system and the maximum flux which can be extracted from the silicate magma in steady state. The results indicate that the highest-component temperature of some observed hot spots (J. S. Pearl and W. M. Sinton, 1982, In The Satellites of Jupiter (D. Morrison, Ed.), pp. 724–755. Univ. of Arizona Press, Tucson) is consistent with a convecting molten sulfur system, and the total flux from the most energetic spot, Loki Patera, is close to the maximum which can be extracted from molten silicates by convection. Simple hydrodynamic models of evaporative outflow from sulfur lakes indicate that the intermediate-component temperature of hot spots such as Loki can be identified with the evaporative sulfur flux which condenses in the atmosphere and over a wide area surrounding the lake(s). The ratio of warm to hot component fluxes for Loki and other hot spots is consistent with this interpretation, and evaporation sets a strong constraint on the maximum surface temperature for a steady-state lake. The Voyager IRIS continuum spectrum can be fitted by a sulfur lake model in which sulfur vapor condensing on the shore is assumed to radiate as a blackbody. The lifetime of such a lake, in steady state, based on evaporation and silicate cooling time scales is 1–100 years, implying long-term Earth-based observations could detect variations in the Loki thermal output. The model provides a useful interpretive tool for possible variability because it gives predictions for the relative thermal fluxes at different wavelengths. The sodium-sulfur phase diagram is also presented and used to show the evaporated lakes may leave behind a sodium-rich residue which could supply the torus with sodium. Finally, uncertainties in the model are assessed, including the lack of sulfur emission features in the Loki spectrum, and the alternative possibility that the SO₂ plume observed at Loki could be supplying the excess thermal flux.     

Intraplate uplift: new constraints on the Hoggar dome from the Illizi basin (Algeria)

Zones of anomalously high topography within continental interiors, distant from active plate boundaries, are interpreted as being either dynamically supported by viscous flow in the underlying mantle or influenced by plate tectonics. Constraining the models of their genesis requires accurate data on the timing and dimensions of such features. New apatite fission‐track and thermal maturity data from the Illizi Basin in Algeria quantify the magnitude and timing of kilometre–scale uplift and exhumation of the northern flank of the Hoggar swell in North Africa. The findings of this study, integrated with previously published thermochronological data, confirm that long‐wavelength regional uplift occurred during the Cenozoic extending over a distance in excess of 1500 km from north to south. The uplift, centred on the Hoggar Massif, significantly impacted the flanking Illizi and Tim Mersoï basins. The combination of thermal history modelling and regional stratigraphic observations indicates that the onset of exhumation of the Illizi Basin likely occurred during the Eocene, broadly coincident with magmatism on the Hoggar Massif to the south and the onset of tectonic shortening in the Atlasic belt to the north.     

Integrating Geospatial Technologies in Fifth-Grade Curriculum: Impact on Spatial Ability and Map-Analysis Skills

This study explores the effects of geographic information systems (GIS) curriculum on fifth-grade students' spatial ability and map-analysis skills. A total of 174 students from an urban public school district and their teachers participated in a quasi-experimental design study. Four teachers implemented a GIS curriculum in experimental classes over six weeks while three teachers continued with regular teaching in control classes. Both groups completed pre- and post-tests measuring spatial ability and map-analysis skills. Students in the GIS classes demonstrated more growth over time in spatial ability and map-analysis skills than did their peers in the control classes.     

Modelling water-table depth in a primary aquifer to identify potential wetland hydrogeomorphic settings on the northern Maputaland Coastal Plain,KwaZulu-Natal,South Africa

The primary aquifer on the Maputaland Coastal Plain in northern KwaZulu-Natal, South Africa, is the principal source of water for rivers, lakes and most of the wetlands in dry periods, and is recharged by these systems in wet periods. Modelling hydrologic conditions that control regional water-table depth can provide insight into the spatial patterns of wetland occurrence and of the persistence of wet conditions that control their character. This project used a groundwater model (MODFLOW) to simulate 10-year water-table fluctuations on the Maputaland Coastal Plain from January 2000 to December 2010, to contrast the conditions between wet and dry years. Remote sensing imagery was used to map “permanent” and “temporary” wetlands in dry and wet years to evaluate the effectiveness of identifying the suitable conditions for their formation using numerical modelling techniques. The results confirm that topography plays an important role on a sub-regional and local level to support wetland formation. The wetlands’ extent and distribution are directly associated with the spatial and temporal variations of the water table in relation to the topographical profile. Groundwater discharge zones in the lowland (1–50 masl) areas support more permanent wetlands with dominantly peat or high organic soil substrates, including swamp forest and most of the permanent open water areas. Most temporary wetlands associated with low-percentage clay occurrence are through-flow low-lying interdune systems characterised by regional fluctuation of the water table, while other temporary wetlands are perched or partially perched. The latter requires a more sophisticated saturated-unsaturated modelling approach.     

Hydrocarbon source potential of the Proterozoic Sirban Limestone Formation,NW Himalaya,Jammu

The Proterozoic Sirban Limestone Formation (SLFm) crops out as detached allochthons in the northwest Himalaya (Jammu region, India) and has its coeval equivalents laterally disposed in the west in Salt Range, in the northwest in Abbotabad (Pakistan) and in southeast in Himachal Pradesh (India). The oil and gas occurrences have been reported from the Proterozoic successions globally and the hydrocarbon potential of the SLFm cannot be ruled out.The interbedded shales and algal laminated dolostones within the SLFm have yielded microflora comparable to those reported in the North African Neoproterozoic sandstones and the Late Proterozoic carbonates of the giant oil and gas fields of the Siberian Platform. The SLFm contains a rich and diverse biota comprising ~ 10% of the rock volume in thin section. The rich organic assemblage justified a hydrocarbon source potential analysis of the SLFm, tested in this study by Rock Eval (RE) pyrolysis.RE pyrolysis yielded a total organic carbon (TOC) content of 0.02 to 1 wt. % with very low Hydrogen Index (HI) values for the shales and TOC content averaging 0.02 wt. % for the dolostones. The organically lean shales and dolostones exhibit T_max values indicative of immature to post mature stage. But, since these values are for the samples with complex thermal and tectonic history the results may be unreliable. The highly altered organic matter and kerogen present in the SLFm had the potential to generate hydrocarbons and presently indicates no significant source potential. This study is important for understanding the hydrocarbon occurrences in the SLFm particularly in light of the recent oil and gas discoveries from the coeval Proterozoic successions.