Tufa Accumulations in Ephemeral Streams: Observations from The Kimberley,north-west Australia

Four types of tufa occur along creeks draining the Oscar Range in the Kimberley region of Western Australia; stream-bed tufa, tufa dams, stream-bed tufa waterfalls, and rimstone pools. Well-developed tufa dam and waterfall formations occur at significant breaks of slope within the channel long profile. This suggests that disruption of the hydraulic flow regime and increased turbulence at these points has an important role to play in determining the location of tufa deposits. However, the best-developed stream-bed tufa deposits are located immediately upstream of dam and waterfall formations, which indicates that the evaporation of water ponded behind these flow obstructions may lead to calcium carbonate precipitation during the dry season. The presence of plant and cyanobacterial communities on, and the incorporation of organic material into, the best-developed tufa formations indicates that biological activity may have an important role to play in determining both the rate of tufa deposition and the internal structure of the resulting accumulations.     

Sea Levels and Western Boundary Flow Near a Tectonic Zone in the Northern Pacific

This article concerns an interrelation between the sea levels and the western boundary flow near a tectonic boundary in a local zone in the Northwestern Pacific. In this zone, sea level variations at stations located on the coast facing the Pacific are studied to find the interrelation between variations of the Kurosio flow as an index of the distance of the flow axis off a specific coast. The result is discussed after data processing of the monthly means of the sea levels, and a notice is taken of variations caused by active crustal upheavals during a seismic event, a local earthquake.     

Sea Levels and Western Boundary Flow Near a Tectonic Zone in the Northern Pacific

This article concerns an interrelation between the sea levels and the western boundary flow near a tectonic boundary in a local zone in the Northwestern Pacific. In this zone, sea level variations at stations located on the coast facing the Pacific are studied to find the interrelation between variations of the Kurosio flow as an index of the distance of the flow axis off a specific coast. The result is discussed after data processing of the monthly means of the sea levels, and a notice is taken of variations caused by active crustal upheavals during a seismic event, a local earthquake.     

A case of successful soil geochemistry: the Rubiales Zn-Pb orebody (NW Spain)

The Rubiales Zn-Pb orebody (NW Spain) is a blind deposit developed in a vertical shear zone during the Variscan Orogenesis. It is about 1200 m long in a N-S direction, with an average thickness of 30 m, and is hosted by lower Cambrian limestones and slates, with some quartzite beds. The deposit has a large hydrothermal alteration aureole. The silicified halo contain sphalerite and galena disseminations, with grades between 0.2 and 3% Pb + Zn.The Rubiales orebody was discovered in the late 60s following a soil geochemical survey. In the regional phase of the survey, 28,622 samples were collected in 57 lines; two of the lines over the Rubiales zone yielded 1400 ppm Pb and 1550 ppm Zn. In a local phase, centred on the anomalous zone, 1716 samples were collected in 21 lines. This local survey defined the geochemical anomalies that were subsequent drill-hole targets. Based on 38 surface-holes, geological ore reserves of 18.6 million tons, with 8.6% Zn + Pb, were estimated.Residual soil geochemical anomalies of Zn and Pb were developed over the silicification zone. The Zn anomaly has a greater extent than the Pb anomaly, due to the greater Zn mobility in surficial environments. The Zn and Pb anomalies exhibit an asymmetrical morphology, with greater extent to the south, due to the down slope creep of residual anomalies. The main cross-faults present in the deposit also control the morphology of the anomalies, as a result of Zn and Pb mobilisation and transport by ground waters along the cross-faults. The Cu anomaly defines two maxima over the feeder zones to the orebody. The two feeder zones, also in the silicification zone, are extensively brecciated and contain the highest grades of the deposit (∗> 20% Zn + Pb) and disseminated chalcopyrite.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Influence of Sedimentation on the Geomorphology of the Northwestern Continental Margin of India

Based upon the analysis of about 10,000 line km of echosounding and bathymetric data and variations in mass accumulation rate along the NW continental margin of India (between Kori creek and Mumbai), we have deduced that in the northern region (in the vicinity of the River Indus) the shelf-break occurs at a shallower depth and the slope is shallower, has the steepest gradient (<1:20), is smoother with no major features, and has reduced width (slope edge at 1450 m; width 19 km than off Mumbai). The width and depth of the slope edge gradually increases southwards, and is at maximum off DamanMumbai (slope edge depth 2900 m; width 84 km). The intensity of the occurrence of physiographic features also increases southwards. The shelf edge off Saurashtra is undulating and on the slope, regional notches and benches (the most prominent at 560 m) are observed. Further southwards off Khambhat-Mumbai, the slope is characterized by the presence of bathymetric highs and lows. We have also observed numerous features on the shelf, with a variable depth of the shelf-break. The gradient of the continental slope is also reduced from the northern region to the southern region. The variations in the gradient of the slope and the presence of distinct physiographic features in this area are examined vis-a-vis fluvial supply of the sediments into the region.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.