[en] Measurement of recent sediment accumulation rates using cesium-137 is discussed. Advantages and problems are considered and a comparison is made with other techniques

No abstract available

No abstract available

[en] Modern age samples from various depositional environments were examined for signal resetting. For 19 modern aeolian/beach samples all D_e values obtained were <0.5 Gy, with ∼70% having D_e<0.2 Gy. For 21 fluvial/colluvial samples, all D_e values were <5 Gy with ∼80% being <1 Gy. D_e as a function of illumination (OSL measurement) time (D_e(t)) plots were examined for all samples. Based on previous laboratory experiments, increases in D_e(t) were expected for partially reset samples, and constant D_e(t) for fully reset samples. All aeolian samples, both modern age and additional 'young' samples (<1000 years), showed constant (flat) D_e(t) while all modern, non-zero D_e, fluvial/colluvial samples showed increasing D_e(t). 'Replacement plots', where a regenerated signal is substituted for the natural, yielded constant (flat) D_e(t). These findings support strongly the use of D_e(t) as a method of identifying incomplete resetting in fluvial samples. Potential complicating factors, such as illumination (bleaching) spectrum, thermal instability and component composition are discussed and a series of internal checks on the applicability of the D_e(t) for each individual aliquot/grain level are outlined

[en] As sediments can accumulate unsupported lead-210 by different processes, there are uncertainties concerning the appropriateness of procedures for calculating lead-210 dates. The applicability of CRS (constant rate of Pb-210 supply) models and CIC (constant initial Pb-210 concentration) models is considered. Variants of both models can be devised to take account of postdepositional processes such as sediment mixing and redistribution. It is argued that the CRS model should be the primary dating model at a wide range of sites and that empirical testing should be built into dating strategies

[en] Like normal deltas, fan-deltas are composed of three parts, i.e., fan-delta plain, fan-delta front and pre-fin-delta, In-situ leachable uranium deposits are commonly distributed along the margins of in-land basins. The author analyzes the possible relationship between the basic characteristics of fan-delta sandstone bodies and uranium mineralization. Two examples, e.g., the fan delta depositional systems in the eastern part of Jungger basin and the southern part of Yili basin, are given to illustrate the fan-delta vertical sequence and planar distribution of sedimentary facies. It has been pointed out that the braided channel sandstone bodies on delta plain, sub-aqueous distributional channel sandstone bodies and delta front sandstone bodies may be the favourable host rocks for in-situ leachable sandstone uranium deposits

[en] From 1987 to 1992, Cd was added during the ice-free season to Experimental Lakes Area (ELA) Lake 382 at loadings of 1.7-4.2 mg·m^-2·year^-1. Cd was lost rapidly from the water column to sediments. Sediment cores (1987-1993) document increasing (from <1 to >5 mg·kg dry mass^-1) sediment Cd concentration over time, sediment storage accounting for 90-95% of added Cd. Sedimentation of Cd occurred in both depositional and erosional sediment zones. Sandy sediments at shallow sites, despite having low sediment Cd concentrations, were important sinks for Cd because of their great mass per unit area. Progressive transport of Cd into the mixed sediment layer (8-10 cm thick, mixing in a decade or more) at deep sites was another important sink. Selective extractions suggest weak surface adsorption of Cd to Mn and Fe oxyhydroxides in periphyton and sedimenting particles, with high K_d. Bottom sediments have lower K_d, although Cd tends to be associated with more strongly bound organic or sulfide fractions. This may indicate loss of easily mobilized Cd from bottom sediment during diagenesis. Because Cd is readily, released from fresh sediment, we hypothesize that recycling of sediment Cd to the water column will slow the recovery of Lake 382 to premanipulation conditions. (author)

No abstract available

[en] It is noticed that few geophysical studies have been carried out to decipher the crustal structure of southwestern part of the Northeast India comprising of Tripura fold belt and Bengal basin as compared to the Shillong plateau and the Brahmaputra basin. This region has a long history of seismicity that is still continuing. We have determined first-order crustal features in terms of Moho depths (H) and average V_P/V_S ratios (κ) using H-κ stacking technique. The inversion of receiver functions data yields near surface thick sedimentary layer in the Bengal basin, which is nearly absent in the Shillong plateau and Tripura fold belt. Our result suggests that the crust is thicker (38–45 km) in the Tripura fold belt region with higher shear-wave velocity in the lower crust than the Shillong plateau. The distribution of V_P/V_S ratio indicates heterogeneity throughout the whole region. While low to medium value of Poisson’s ratio (1.69–1.75) indicates the presence of felsic crust in the Shillong plateau of the extended Indian Archean crust. The medium to high values of V_P/V_S ratio (> 1.780) in the Bengal basin and the Tripura fold belt region represent mafic crust during the formation of the Bengal delta and the Tripura fold belt creation in the Precambrian to the Permian age. The depth of the sediments in the Bengal basin is up to 8 km on its eastern margin, which get shallower toward its northeastern and southeastern margins.

[en] All natural lakes and reservoirs whether on rivers, tributaries or off channel storages are doomed to be sited up. Pakistan has two major reservoirs of Tarbela and Managla and shallow lake created by Chashma Barrage. Tarbela and Mangla Lakes are losing their capacities ever since first impounding, Tarbela since 1974 and Mangla since 1967. Tarbela Reservoir receives average annual flow of about 62 MAF and sediment deposits of 0.11 MAF whereas Mangla gets about 23 MAF of average annual flows and is losing its storage at the rate of average 34,000 MAF annually. The loss of storage is a great concern and studies for Tarbela were carried out by TAMS and Wallingford to sustain its capacity whereas no study has been done for Mangla as yet except as part of study for Raised Mangla, which is only desk work. Delta of Tarbala reservoir has advanced to about 6.59 miles (Pivot Point) from power intakes. In case of liquefaction of delta by tremor as low as 0.12g peak ground acceleration the power tunnels I, 2 and 3 will be blocked. Minimum Pool of reservoir is being raised so as to check the advance of delta. Mangla delta will follow the trend of Tarbela. Tarbela has vast amount of data as reservoir is surveyed every year, whereas Mangla Reservoir survey was done at five-year interval, which has now been proposed .to be reduced to three-year interval. In addition suspended sediment sampling of inflow streams is being done by Surface Water Hydrology Project of WAPDA as also some bed load sampling. The problem of Chasma Reservoir has also been highlighted, as it is being indiscriminately being filled up and drawdown several times a year without regard to its reaction to this treatment. The Sediment Management of these reservoirs is essential and the paper discusses pros and cons of various alternatives. (author)