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.     

Estimation of Leakage Rates Through Flexible Membrane Liners

Leakage rate calculations for both low- permeability soil liners and composite liners using flexible membrane liners (FMLs) overlying low-permeability soil are developed. Latin-Hypercube simulations with uncertainly assigned to the soil liner hydraulic conductivity value and the spatial frequency of FML holes are used to examine the variability in the liner leakage rates. The low-permeability soil hydraulic conductivity is the parameter with the greatest effect on landfill liner leakages rates. Composite liners have a significant impact on reducing leakage rates through the landfill liner.     

Foraminifera from the Vectis Formation (Wealden Group, Lower Cretaceous) of the Wessex Sub-basin, southern England: a preliminary account

Foraminifera are documented from the uppermost part of the essentially lagoonal Vectis Formation (Barremian to possibly early Aptian) of the Isle of Wight, southern England. Monospecific and low-diversity influxes of indigenous agglutinated taxa are identified from claystones of mudflat or subaqueous origin, and their palaeoecological significance is assessed. In contrast, reworked Upper Jurassic foraminifera are associated with coarser-grained bioclastic deposits and indicate the proximity of the Wessex Sub-basin margin, immediately to the north.     

Isotope shifts in the Late Permian of the Delaware Basin,Texas, precisely timed by varved sediments

Closely spaced samples (285 in number) of varved sediments from the Upper Permian in Delaware Basin, Texas, have been analyzed for δ¹³C_carb, δ¹³C_org, δ¹⁸O_carb, C_org, C_carb, and calcite/dolomite. δ¹³C records a dramatic rise from ?2.8 to +5.7‰ in only 4400 years, detected in three sections across the basin, extrapolating smoothly through a 600-year interruption by a local (west side of the basin) fresh-water inflow evidenced by low δ¹⁸O. This continuity and low C_org within the basin, both indicate that the excess net deposition of C_org, necessary to generate the rise in δ¹³C, took place in the ocean external to the Delaware Basin. Correlation with similar records from the Zechstein Basin suggest that the event was world-wide, although this poses obvious difficulties for the carbon cycle. The rate of rise of δ¹³C, and its sustained high level, must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved.     

Level of Lake Lahontan during deposition of the Trego Hot Springs tephra about 23,400 years ago

The Trego Hot Springs tephra bed is a silicic tephra about 23,400 yr old, found at several localities in pluvial lake sediments in northern Nevada, southern Oregon, and northeastern California. It has been characterized petrographically, by the major and minor element chemistry of its glass, and by its stratigraphic position with respect to other tephra layers. At a newly described locality on Squaw Creek, northwest of Gerlach, Nevada, at the north end of the Smoke Creek Desert, Trego Hot Springs tephra has been found in sediments of the Sehoo and Indian Lakes formations. The depositional environments of these sediments show that when the tephra fell, pluvial Lake Lahontan stood between 1256 and 1260 m, and that immediately thereafter the lake rose to at least 1275 m. These data corroborate earlier findings by Benson (Quaternary Research9, 300–318) from radiometric dating of calcareous tufa. However, the Lake Lahontan area has been affected by isostatic subsidence and rebound in response to changing water loads, so that caution is required in the use of lakeshore elevations in correlation.     

Upriver migration and abundance of naked goby (Gobiosoma bosci) larvae in the Patuxent River estuary,Maryland

Larvae of the naked goby,Gobiosoma bosci, were collected during the spring and early summer of 1977 in the upper tidal Patuxent River, Maryland. Larvae first appeared in the collections on May 5. Weekly night sampling at 26 stations covering 28 km of the Patuxent illustrated the upriver movement of larvae, at an estimated rate of about 1 km per day. Larval densities quickly reached high levels, with a maximum density of more than 6,000 larvae per 100 m³ at one station on June 16. By June 23, the mean larval density for the entire 28 km stretch of the river was 1,825 larvae per 100 m³. Length-frequency distributions of the larvae illustrate the growth of the larvae, continual recruitment into the population, and a gradient in mean population length over the sampling transect that was due to the presence of the smallest larvae in the lower stations.     

Experimental paleotemperature equation for planktonic foraminifera

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups.Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO₃ indicate that the foraminifera precipitate their CaCO₃ in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craig's (1965) equation yields: $\text{t = ?0.07 + 1.01}\text{t}\text{?}\text{(r= 0.95)}$ where t is the actual growth temperature and $\text{t}\text{?}$ Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer.Second order regression of the culture temperature and the delta difference (δ¹⁸Oc ? δ¹⁸Ow) yield a correlation coefficient of r = 0.95: $\text{t}\text{?}\text{= 17.0 ? 4.52(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow) + 0.03(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow)}{}^2$$\text{t}\text{?}\text{, δ}{}^{18}\text{Oc}$ and δ¹⁸Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively.A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.     

Hafnium isotope results from mid-ocean ridges and Kerguelen

¹⁷⁶Hf/¹⁷⁷Hf ratios are presented for oceanic volcanics representing both extremes of the range of mantle HfNdSr isotopic variation. Hf from critical mid-ocean ridgebasalts shows that ¹⁷⁶Hf/¹⁷⁷Hf does indeed have a greater variability than ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr in the depleted mantle. This extra variation is essentially of a random nature, and can perhaps be understood in terms of known Rb/SrSm/NdLu/Hf fractionation relationships. At the other extreme of mantle isotopic composition, ¹⁷⁶Hf/¹⁷⁷Hf ratios for igneous rocks from the Indian Ocean island of Kerguelen show a closely similar variation to published ¹⁴³Nd/¹⁴⁴Nd ratios for the same samples. Comparison of HfNdSr c relationships for Tristan da Cunha, Kerguelen and Samoa reveals divergences in the mantle array for ocean island magma sources, and perhaps suggests that these irregularities are largely the result of an extra component of ⁸⁷Sr/⁸⁶Sr variation.     

Evolution of continental crust and mantle heterogeneity: Evidence from Hf isotopes

We present initial ¹⁷⁶Hf/¹⁷⁷ Hf ratios for many samples of continental crust 3.7-0.3 Gy old. Results are based chiefly on zircons (1% Hf) and whole rocks: zircons are shown to be reliable carriers of essentially the initial Hf itself when properly chosen on the basis of U-Pb studies. Pre-3.0 Gy gneisses were apparently derived from an unfractionated mantle, but both depleted and undepleted mantle are evident as magma sources from 2.9 Gy to present. This mantle was sampled mainly from major crustal growth episodes 2.8, 1.8 and 0.7 Gy ago, all of which show gross heterogeneity of ¹⁷⁶Hf/¹⁷⁷Hf in magma sources from _Hf=0 to +14, or about 60% of the variability of the present mantle.The approximate _Hf=2_Nd relationship in ancient and modern igneous rocks shows that ¹⁷⁶Lu/¹⁷⁷Hf fractionates in general twice as much as ¹⁴⁷Sm/¹⁴⁴Nd in mantle melting processes. This allows an estimation of the relative value of the unknown bulk solid/liquid distribution coefficient for Hf. D_Lu/D_Hf= 2.3 holds for most mantle source regions. For garnet to be an important residual mantle phase, it must hold Hf strongly in order to preserve Hf-Nd isotopic relationships.The ancient Hf initials are consistent with only a small proportion of recycled older cratons in new continental crust, and with quasi-continuous, episodic growth of the continental crust with time. However, recycling of crust less than 150 My old cannot realistically be detected using Hf initials. The mantle shows clearly the general positive _Hf resulting from a residual geochemical state at least back to 2.9 Gy ago, and seems to have repeatedly possessed a similar degree of heterogeneity, rather than a continuously-developing depletion. This is consistent with a complex dynamic disequilibrium model for the creation, maintenance and destruction of heterogeneity in the mantle.