Basin analysis palaeo-landscape modelling: Testing the critical controls using experimental design constrained by a real 3D geological model,Gippsland Basin,Australia

The main controlling variables for palaeo-landscape evolution are investigated to assess their relative importance using the Gippsland Basin geological history. Palaeo-landscape reconstruction is a complicated process controlled and affected by multiple variables, including tectonic, palaeo-environment, sea-level change, rainfall, sediment erosion, transportation, deposition, etc. The Basin and Landscape Dynamics software (Badlands) software was used with an efficient experimental design (ED) to guide the selected scenarios, process the results, and generate the multi-variate equations that define and identify the important controlling variables. The ED was used to test and identify the main uncertainties and their possible ranges, based on actual field data, while at the same time ensuring that the full multi-dimensional space for those variables was covered to enable the computation of multivariate equations from the minimum number of scenario runs. A full suite of 3D forward palaeo-landscape models of the Gippsland Basin was built to reconstruct the basin history from its formation to the present (Early Cretaceous to Holocene, 137-0 Ma). The models are compared to the corresponding full 3D realistic structural and stratigraphic model of the basin that has been built in Petrel (Schlumberger software). This constrains the sedimentary, stratigraphic, burial and thermal histories to the relative subsidence rates and basin-fill for each geological sequence by using the model isopachs input to the Badlands modelling. The ED required only 22 scenarios to fit 12 identified variables and test for possible interactions with each other. The most significant variables are those that control sediment supply including non-marine erodibility, rainfall, (Rainfall × Area) exponent m, Slope and critical slope while maximum % Marine Deposition and marine dispersal are also required to fill the marine accommodation space. Sea Level and subsidence only become significant when rapid enough to outpace sediment supply. The controlling factors change over time with basin development from rift to post-rift phases and interactions are highly significant.     

Measurement of arrival time of particles in extensive air showers using TDC32

Arrival time of particles in an extensive air shower (EAS) is a key physical parameter to determine its direction. EAS direction is useful for studies of anisotropy and composition of cosmic rays, and search for multi-TeV γ-rays sources. Accurate timing may be used to search exotic phenomena such as production of new particles at extremely high energies available during early stages of development of EAS and also for detecting sub-relativistic hadrons in EAS. Time to digital converters (TDCs) are used to perform this task. Traditional TDCs operate in the START-STOP mode with limited dynamic range and single-hit capability. With the advent of high luminosity collider LHC, need for TDCs with large dynamic range, multi-hit capability and TRIGGERED mode of operation became necessary. A 32 channel TDC was designed for the GRAPES-3 experiment on a CAMAC platform around TDC32, an ASIC developed by micro-electronics group at CERN, Geneva. Four modules were operated in the GRAPES-3 experiment. Here, we present details of the circuit design and their performance over several years. The multi-hit feature of this device was used to study the time structure of particles in the EAS on time scale of ~1 μs. The distribution of time intervals in the multi-hit data shows an exponential profile with a time constant of ~370 ns. These delayed particles are likely to be neutrons produced in the EAS core that were recorded in the scintillator detectors following the relativistic EAS front.     

Surface heat flow and probable evolution of Deccan volcanism

In the light of surface heat-flow observations, as well as other related geological and geophysical data, the origin of the Deccan basalts has been examined. The Indian lithosphere, after its detachment from Gondwanaland, apparently traversed a rising plume at La Réunion, which virtually bored through the lithosphere to emerge as the Deccan Trap volcanism on the surface. Subsequent volcanic and plutonic activity appears to have continued not only up to the Oligocene, as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features — the West Coast faults, the Narmada-Son-Tapti lineament, and the Cambay Graben — but also up to the Mio-Pliocene, as indicated by the heat flow and gravity data over the Cambay Graben. The dyke-swarms and sills, which are mostly post-trappean, evolved from the lithosphere after the Indian Plate moved away from the hot spot.     

Use of P coda for determination of yield on nuclear explosions

Summary. Spectral analysis of P and P coda from NTS explosions recorded at NORSAR shows that magnitudes based on spectral integration of P coda provide a significantly more precise measure of yield than those based on the initial P . Coda amplitudes and spectra are considerably less sensitive to near-source variations than the direct P . A plot of P -coda magnitude, after correcting for the effects of attenuation in the upper mantle and the source spectrum based on knowledge of approximate yield or m_b , versus log yield appears to have a slope of unity. This implies that P coda from several stations (with different but known t * values) can be combined to improve the yield determinations further. Single station P coda from Soviet explosions can also be used to determine relative yields that appear to be at least as precise as those from Lg based on a network of stations.     

First megafossil evidence of Cyatheaceous tree fern from the Indian Cenozoic

A part of the compressed tree fern axis with leaf and adventitious root scars in unusual arrangement from Plio–Pleistocene sediments of Arunachal Pradesh, India is described as Cyathea siwalika sp. nov. This record suggests that Cyathea was an important component of tropical evergreen forest in the area during the Plio–Pleistocene and this group subsequently declined in importance within the local vegetation.     

Geochemistry of groundwater,Burdwan District,West Bengal,India

Hydrogeochemical investigations are carried out in the different blocks of Burdwan district, West Bengal, India in order to assess its suitability for drinking as well as irrigation water purpose. Altogether 49 representative groundwater samples are collected from bore wells and the water chemistry of various ions viz. Ca²⁺, Mg²⁺, Na⁺, K⁺, CO₃²⁻, HCO₃⁻, Cl⁻, SO₄²⁻ and NO₃⁻ are carried out. The chemical relationships in Piper and Gibbs diagram suggest that the groundwater mainly belongs to alkali type and Cl⁻ group and are controlled by rock dominance. A comparison of groundwater quality in relation to drinking water quality standards proves that most of the water samples are suitable for drinking water purpose whereas groundwater in some areas of the district has high salinity and high sodium adsorption ratio (SAR), indicating unsuitability for irrigation water and needs adequate drainage.     

Teleseismic P-wave residual investigations at Shillong,India

The northeast India region is seismically very active and it has experienced two large earthquakes of magnitude 8.7 during the last eight decades (1897 and 1950). We have analysed teleseismic P-wave residuals at Shillong, the only reliable seismic station operating in the region, to investigate a possible association of travel-time residual anomaly with earthquake occurrence. The period covered is from October 1964 through March 1976. The total number of events is 9479, including 1767 events with depth >/ 100 km. Six-monthly average residuals have been calculated. The standard deviations are less than 0.10 sec for these data sets. During the period of investigations, no major earthquake took place close to Shillong. The earthquake of June 1, 1969 with a magnitude (M_b) of 5.0, at an epicentral distance of 20 km from Shillong is the only significant event. This earthquake is found to be associated with a travel-time increase with a maximum amplitude of 0.4 sec. It appears that, in general, the P-wave velocity has decreased in the neighbourhood of Shillong since 1969. A quadrant-wise analysis of residuals indicates that the residual anomaly is most prominent in the SE quadrant from Shillong.     

El Niño/Southern Oscillation (ENSO) Related Variations in Particulate Export Fluxes in the Western and Central Equatorial Pacific

Time-series data from sediment trap moorings intermittently deployed during 1991–1999 show that the fluxes of biogenic material (carbonate, opal and organic matter, including amino acids) and other related parameters are temporally and spatially distinct across the Western Pacific Warm Pool (WPWP). These variations resulted from the El Niño and La Niña conditions, which alternately prevailed over the equatorial Pacific Ocean during the mooring deployments. The westernmost WPWP (a hemipelagic region) recorded relatively high average total mass and amino acid fluxes during the El Niño event. This was in sharp contrast to the eastern part of the WPWP (oligotrophic and weak upwelling regions) which recorded higher flux values during the La Niña event. Settling particulate organic matter was rich in labile components (amino acids) during La Niña throughout the study area. Relative molar ratios of aspartic acid to β-alanine together with relative molar content of non-protein amino acids β-alanine and γ-aminobutyric acid) suggested that organic matter degradation was more intense during La Niña relative to that during El Niño in the WPWP. This study clearly shows that during an El Niño event the well documented decrease in export flux in the easternmost equatorial Pacific is accompanied by a significant increase in export flux in the westernmost equatorial Pacific Ocean.     

Stochastic stability of tethered buoyant platforms

A moment method for analysing the stochastic stability of the surge motion of a tethered buoyant platform (TBP) in a random sea is examined. In the differential equation describing the surge motion the variation of tether tension caused by the vertical component of the wave forces is random-time dependent in form. The asymptotic moment behaviour of the solution is determined and approximated in terms of an integral equation. Under the assumption of a narrow band process imposed upon the random coefficient, the stability results are obtained with the aid of deterministic stability theory. The mean square stability is studied and criteria for stability are obtained in terms of the damping coefficient and the auto-correlation function of the random sea.