The tectono‐stratigraphic evolution of the Austral Basin and adjacent areas against the background of Andean tectonics,southern Argentina,South America

The Austral Basin (or Magallanes Basin) in southern Argentina is situated in a highly active tectonic zone. The openings of the South Atlantic and the Drake Passage to the east and south, active subduction in the west, and the related rise of the Andes have massively influenced the evolution of this area. To better understand the impacts of these tectonic events on basin formation to its present‐day structure we analysed 2D seismic reflection data covering about 95 000 km² on‐ and 115 000 km² offshore (Austral ‘Marina’ and Malvinas Basin). A total of 10 seismic horizons, representing nine syn‐ and post‐ rift sequences, were mapped and tied to well data to analyse the evolution of sedimentary supply and depocenter migration through time. 1D well backstripping across the study area confirms three main tectonic stages, containing (i) the break‐up phase forming basement graben systems and the evolution of the Late Jurassic – Early Cretaceous ancient backarc Austral/Rocas Verdes Basin (RVB), (ii) the inversion of the backarc marginal basin and the development of the foreland Austral Basin and (iii) the recent foreland Austral Basin. Synrift sedimentation did not exceed the creation of accommodation space, leading to a deepening of the basin. During the Early Cretaceous a first impulse of compression due to Andes uplift caused rise also of parts of the basin. Controlling factors for the subsequent tectonic development are subduction, balanced phases of sedimentation, accumulation and erosion as well as enhanced sediment supply from the rising Andes. Further phases of rock uplift might be triggered by cancelling deflection of the plate and slab window subduction, coupled with volcanic activity. Calculations of sediment accumulation rates reflect the different regional tectonic stages, and also show that the Malvinas Basin acted as a sediment catchment after the filling of the Austral Basin since the Late Miocene. However, although the Austral and Malvinas Basin are neighbouring basin systems that are sedimentary coupled in younger times, their earlier sedimentary and tectonic development was decoupled by the Rio Chico basement high. Thereby, the Austral Basin was affected by tectonic impacts of the Andes orogenesis, while the Malvinas Basin was rather affected by the opening of the South Atlantic.     

Geochemistry of Suspended Matter from Waters of the Amazon Basin

The geochemical study of the suspended matter in the waters of the Amazon River and its tributaries revealed that the chemical composition of this material ranges widely; however, generally, it is similar to the average composition of the suspended matter in the rivers and clayey sedimentary rocks around the world. Against this background, an essential regional Hg enrichment due to the anthropogenic factor is distinguished. The suspensions from the so-called clear waters from the tributaries of the Amazon River—Xingu and Trombetas—demonstrate the local enrichment in Pb, Sn, Zn, and organic carbon indicating the ore mineralization of the drainage basin, and points to the presence of metal-organic complexes.     

High-resolution ion-microprobe measurement of lead isotopes: Variations within single zircons from Lac Seul,northwestern Ontario

Selected-area measurements of lead-isotope ratios in zircons have been made at high mass resolution using a modified A.E.I. IM20 ion-microprobe. At a working resolution of 3200 it is shown that the important interfering molecular peaks generated from the zircon matrix may be separated from atomic lead peaks. Corrections for overlapping peaks, which are necessary in measurements of lead isotopes at low mass resolution, are then only required for ²⁰⁸Pb.Measurements on N.B.S. standards show no isotope discrimination within counting statistics. Determination of ²⁰⁷Pb/²⁰⁶Pb on 29 single zircon grains from a tonalite gneiss and a granite from Lac Seul, northwestern Ontario, give very variable ratios with mean values close to those of bulk separates. Peaks in the distribution of 207/206 ratios obtained from the tonalite gneiss may be interpreted as evidence for two stages of lead loss. High 207/206 ratios are shown to be significant for at least two zircons and probably record a minimum age of formation of 3.3 ± 0.1 b.y. for the gneiss.     

Automated co-registration of images from multiple bands of Liss-4 camera

Three multi-spectral bands of the Liss-4 camera of IRS-P6 satellite are physically separated in the focal plane in the along-track direction. The time separation of 2.1 s between the acquisition of first and last bands causes scan lines acquired by different bands to lie along different lines on the ground which are not parallel. Therefore, the raw images of multi-spectral bands need to be registered prior to any simple application like data visualization. This paper describes a method for co-registration of multiple bands of Liss-4 camera through photogrammetric means using the collinearity equations. A trajectory fit using the given ephemeris and attitude data, followed by direct georeferencing is being employed in this model. It is also augmented with a public domain DEM for the terrain dependent input to the model. Finer offsets after the application of this parametric technique are addressed by matching a small subsection of the bands (100×100 pixels) using an image-based method. Resampling is done by going back to original raw data when creating the product after refining image coordinates with the offsets. Two types of aligned products are defined in this paper and their operational flow is described. Datasets covering different types of terrain and also viewed with different geometries are studied with extensive number of points. The band-to-band registration (BBR) accuracies are reported. The algorithm described in this paper for co-registration of Liss-4 bands is an integral part of the software package Value Added Products generation System (VAPS) for operational generation of IRS-P6 data products.     

Deformability properties of model granular soils under true triaxial compression conditions

The study presents a review of modifications to the design of true triaxial test apparatuses and described a new mixed boundary apparatus to study the stress-strain behavior of coarse-grained soil under true triaxial compression conditions. It was shown that the deviatoric component plays an important role in affecting the volumetric compression of coarse-grained soil. The study analyzed the influence of different stress-strain characteristics on the development of lateral earth pressure.     

Tracking recent recovery from eutrophication in a high arctic lake (Meretta Lake, Cornwallis Island, Nunavut, Canada) using fossil diatom assemblages

Meretta Lake (Resolute Bay, Cornwallis Island, Nunavut, Canada) is a high arctic lake that received raw sewage for almost 50 years from the Canadian Department of Transport Base. The lake was sampled from 1968–72 during the International Biological Programme, as part of the Char Lake Project. As the number of users at the Transport Base declined throughout the 1990s, so too did the lake's nutrient levels, and Meretta Lake is now classified as oligotrophic. A previous diatom-based paleolimnological study revealed marked species assemblage shifts coincident with sewage inputs beginning in the late 1940s; however, because the core was taken at a time when nutrient levels were still relatively high (i.e., 1993), the diatom record did not yet track any signs of recovery. In this present study, we examined fossil diatom assemblages from a sediment core taken in 2001. Our results indicate a shift to the pre-impact diatom assemblages in the most recent sediments, indicating that the paleolimnological record is tracking the decreased nutrient inputs to this high arctic lake, and confirms that no significant lags exist in these largely ice-covered lakes.     

Modelling detrital cooling-age populations: insights from two Himalayan catchments

The distribution of detrital mineral cooling ages in river sediment provides a proxy record for the erosional history of mountain ranges. We have developed a numerical model that predicts detrital mineral age distributions for individual catchments in which particle paths move vertically toward the surface. Despite a restrictive set of assumptions, the model permits theoretical exploration of the effects of thermal structure, erosion rate, and topography on cooling ages. Hypsometry of the source‐area catchment is shown to exert a fundamental control on the frequency distribution of bedrock and detrital ages. We illustrate this approach by generating synthetic ⁴⁰Ar/³⁹Ar muscovite age distributions for two catchments with contrasting erosion rates in central Nepal and then by comparing actual measured cooling‐age distributions with the synthetic ones. Monte Carlo sampling is used to assess the mismatch between observed and synthetic age distributions and to explore the dependence of that mismatch on the complexity of the synthetic age signal and on the number of grains analysed. Observed detrital cooling ages are well matched by predicted ages for a more slowly eroding Himalayan catchment. A poorer match for a rapidly eroding catchment may result from some combination of large analytical uncertainties in the detrital ages and inhomogeneous erosion rates within the basin. Such mismatches emphasize the need for more accurate thermal and kinematic models and for sampling strategies that are adapted to catchment‐specific geologic and geomorphic conditions.