Evolution of the West Andean Escarpment at 18°S (N. Chile) during the last 25 Ma: uplift, erosion and collapse through time

The geological record of the Western Andean Escarpment (WARP) reveals episodes of uplift, erosion, volcanism and sedimentation. The lithological sequence at 18°S comprises a thick pile of Azapa Conglomerates (25–19 Ma), an overlying series of widespread rhyodacitic Oxaya Ignimbrites (up to 900 m thick, ca. 19 Ma), which are in turn covered by a series of mafic andesite shield volcanoes. Between 19 and 12 Ma, the surface of the Oxaya Ignimbrites evolved into a large monocline on the western slope of the Andes. A giant antithetically rotated block (Oxaya Block, 80 km×20 km) formed on this slope at about 10–12 Ma and resulted in an easterly dip and a reversed drainage on the block's surface. Morphology, topography and stratigraphic observations argue for a gravitational cause of this rotation. A “secondary” gravitational collapse (50 km³), extending 25 km to the west occurred on the steep western front of the Oxaya Block. Alluvial and fluvial sediments (11–2.7 Ma) accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall, indicating further shortening between 8 and 6 Ma. Flatlying Upper Miocene sediments (<5.5 Ma) and the 2.7 Ma Lauca–Peréz Ignimbrite have not been significantly shortened since 6 Ma, suggesting that recent uplift is at least partly caused by regional tilting of the Western Andean slope.     

Mineral-chemical studies of metamorphosed hydrothermal alteration in the Kristineberg volcanogenic massive sulfide district,Sweden

Mineralium Deposita - The massive sulfide deposits of the Kristineberg area, Sweden, occur within a 2- to 3-km-thick succession of felsic volcaniclastic rocks belonging to the Skellefte Group. The...     

Groundwater in fractured crystalline rocks, the Clara mine, Black Forest (Germany)

The chemical composition of water sampled in a 700 m deep underground barite-fluorite mine in the crystalline basement of the Black Forest area (SW Germany) varies systematically with depth and the length of flow paths trough, the fracture porosity of the gneiss matrix. Calcium and sulfate increase as a result of a combined sulfide oxidation and plagioclase alteration reaction. The gneiss contains andesine–plagioclase (An₂₀–An₄₀) and is rich in primary sulfide. As an effect of Ca and SO₄ release by the prime water–rock reaction, dissolved oxygen decreases and the waters become more reduced. The waters have Cl/Br mass ratios of about 50, which is very close to that of experimentally leached gneiss powders indicating that the rock matrix is the source of the halogens. The waters are undersaturated with respect to calcite in the upper parts of the mine. With increasing reaction progress, calcite saturation is reached and carbonate forms as a reaction product of the prime reaction that also controls the partial pressure of CO₂ to progressively lower values. The chemical evolution of groundwater in fractured basement of the Clara mine suggests that the partial pressure of CO₂ is an internally buffered parameter rather than a controlling external variable.     

Shoreline development and Swedish colonisation of north-west Estonia during the Middle Ages

This paper focuses on how landscape development in areas of land uplift has come to direct the primary human colonisation on the coastal areas in north-western Estonia. A Swedish-speaking minority population has at least since medieval times settled these areas. On the basis of an estimation of the rate of land uplift, the shoreline development and topography of a section of the coast was reconstructed. In this respect, it appears that large changes have occurred in that during the Middle Ages, the coast was much steeper but also much longer than today, full of little bays and points. This means that the drainage of near-shore areas was more intensive and that it was possible to find suitable landing places and well-sheltered harbours in some locations. These locations appear to have been primary settlements of the Swedish-speaking colonists and are very similar to coastal settlements of the same age along other coasts of the central Baltic Sea basin. Thus, the results presented in the paper allow the selection of primary research sites for field studies of the early settlement history of this ancient Estonian minority. This revised version was published online in July 2006 with corrections to the Cover Date.     

Movements,failure and climatic control of the Veslemannen rockslide,Western Norway

On September 5, 2019, the Veslemannen unstable rock slope (54,000 m³) in Romsdalen, Western Norway, failed catastrophically after 5 years of continuous monitoring. During this period, the rock slope weakened while the precursor movements increased progressively, in particular from 2017. Measured displacement prior to the failure was around 19 m in the upper parts of the instability and 4–5 m in the toe area. The pre-failure movements were usually associated with precipitation events, where peak velocities occurred 2–12 h after maximum precipitation. This indicates that the pore-water pressure in the sliding zones had a large influence on the slope stability. The sensitivity to rainfall increased greatly from spring to autumn suggesting a thermal control on the pore-water pressure. Transient modelling of temperatures suggests near permafrost conditions, and deep seasonal frost was certainly present. We propose that a frozen surface layer prevented water percolation to the sliding zone during spring snowmelt and early summer rainfalls. A transition from possible permafrost to a seasonal frost setting of the landslide body after 2000 was modelled, which may have affected the slope stability. Repeated rapid accelerations during late summers and autumns caused a total of 16 events of the red (high) hazard level and evacuation of the hazard zone. Threshold values for velocity were used in the risk management when increasing or decreasing hazard levels. The inverse velocity method was initially of little value. However, in the final phase before the failure, the inverse velocity method was useful for forecasting the time of failure. Risk communication was important for maintaining public trust in early-warning systems, and especially critical is the communication of the difference between issuing the red hazard level and predicting a landslide.

     

Research, Extension and Industry – Working Together Can Achieve Results

Over recent decades, research has been directed to assessing the impacts of land uses on valuable natural assets, such as the Great Barrier Reef. Land managers in adjacent areas are expected to adopt practices to minimize any adverse affects on downstream environments. Conversely, researchers are being pressed to provide answers to the problems. In response, researchers and environmental managers are bombarding land managers with information regarding the potential environmental implications of their practices. Is this an effective mode to achieve on-ground change?

Collaboration between all groups – research, industry and extension – may be more effective in developing and implementing practical solutions to these more complex issues. A change from the research and extension models currently used may be needed to achieve positive resource management outcomes.

Research, development and extension initiatives underway in the Australian sugar industry to improve farm practice and reduce the potential for adverse impacts on downstream environments are discussed. Case studies provide some insights into how science and extension skills work best together and how an industry group can respond to a community concern.     

Permeability distribution in the Quaternary of the Upper Rhine glacio-fluvial aquifer

An extraordinarily large and geographically extensive 3D dataset has allowed us to relate permeability to detailed geological features. Permeability data derived from several thousand pumptests in Quaternary sediments (thickness < 120 m) of the Upper Rhine valley vary from K = 4.5 × 10⁻⁷ m s⁻¹ to K = 2.7 × 10⁻¹ m s⁻¹. The geometric mean of the data is K = 2.25 × 10⁻³ m s⁻¹. The permeability distribution maps for four different stratigraphic levels show that the highest values are found in sections beneath recent and historic fluvial systems. Fossil fans of small rivers from the Black Forest can be identified in the Rhine valley on the basis of the permeability pattern. The average hydraulic conductivity decreases S–N along the flow direction which corresponds to a decrease in grain-size of the fluvial sediments.     

Spatial and compositional variations within finely laminated mineral crusts at Carpenter's Gap,an archaeological site in tropical Australia

Mineralogical and geochemical variations in ten rock surface crusts are described from a large rock shelter known as Carpenter's Gap 1 in the southern Kimberley, formed at the junction between a sandstone floor and an overlying limestone roof. The finely laminated crusts, containing quartz, clays, oxalate and phosphate minerals, and sulfate salts (bassanite, gypsum, epsomite), formed over quartz‐rich sandstones. Mineralogical analyses of crusts, determined by X‐ray diffraction, and major element geochemical trends, in the form of element maps of cross sections, show a complex distribution of hemi‐, mono‐, and dihydrated sulfate and oxalate minerals vertically and laterally within the shelter. These mineralogical changes have occurred under fluctuating moisture and temperature regimes, which follow a general drying trend spatially with distance from the back wall and temporally over a period of about 20,000 years. Documenting these mineralogical changes is a first step in understanding the nature of microclimatic controls on the formation of rock surface coatings in shelters and their implications for palaeoenvironmental reconstructions and for dating engravings covered by these crusts. © 2001 John Wiley & Sons, Inc.