Late Carboniferous foreland basin formation and Early Carboniferous stretching in Northwestern Europe: inferences from quantitative subsidence analyses in the Netherlands

The large thickness of Upper Carboniferous strata found in the Netherlands suggests that the area was subject to long-term subsidence. However, the mechanisms responsible for subsidence are not quantified and are poorly known. In the area north of the London Brabant Massif, onshore United Kingdom, subsidence during the Namurian–Westphalian B has been explained by Dinantian rifting, followed by thermal subsidence. In contrast, south and east of the Netherlands, along the southern margin of the Northwest European Carboniferous Basin, flexural subsidence caused the development of a foreland basin. It has been proposed that foreland flexure due to Variscan orogenic loading was also responsible for Late Carboniferous subsidence in the Netherlands. In the first part of this paper, we present a series of modelling results in which the geometry and location of the Variscan foreland basin was calculated on the basis of kinematic reconstructions of the Variscan thrust system. Although several uncertainties exist, it is concluded that most subsidence calculated from well data in the Netherlands cannot be explained by flexural subsidence alone. Therefore, we investigated whether a Dinantian rifting event could adequately explain the observed subsidence by inverse modelling. The results show that if only a Dinantian rifting event is assumed, such as is found in the United Kingdom, a very high palaeowater depth at the end of the Dinantian is required to accommodate the Namurian–Westphalian B sedimentary sequence. To better explain the observed subsidence curves, we propose (1) an additional stretching event during the Namurian and (2) a model incorporating an extra dynamic component, which might well explain the very high wavelength of the observed subsidence compared with the wavelength of the predicted flexural foreland basin.     

Rockfall Hazard Analysis for Hong Kong Based on Rockfall Inventory

Summary ¶This paper compiles and analyzes the rockfall data in Hong Kong in the last fifty years. A simple rockfall hazard analysis is presented based on this rockfall inventory. A frequency-magnitude relation, which is analogous to the Gutenberg-Richter relation for earthquake occurrence, is proposed for rockfall, and direct correlation between rockfall frequency and the daily rainfall is observed. Data analysis shows that a threshold daily rainfall of about 150–200mm is expected in order to trigger rockfall events in Hong Kong. Among the 368 rockfall events in the 13 year period from 1984 to 1996 in Hong Kong, 35% of the incidents lead to blockage of or damage to roads, 22% lead to damages or evacuation of squatter huts, 21% lead to blockage of pedestrian pavement and footpath, and 15% affect buildings, such as housing apartments and schools. Only 15% of these rockfalls fell onto open space and caused negligible effects on human activities. Most of these rockfall events occurred during heavy rain and when landslide warning should has been issued by the Hong Kong Observatory, thus only 6% of these events led to injury or casualty, car damages, and damages to public utilities. Rockfall hazard zonation maps in terms of the spatial distribution of previous rockfalls are proposed for both Kowloon Peninsula and Hong Kong Island.     

Sea flux of trace metals in Saanich Inlet

The sea fluxes of trace metals, POC, and settled material were studied in anoxic seawater, Saanich Inlet, B. C., Canada with sediment traps. This paper discusses the change of mass fluxes of sediment, trace metals and POC for various seasons and depths. The annual mean of settled material is 1.56 g.m⁻².a⁻¹, 84.6 mg. m⁻².a⁻¹ for POC, 60.0 mg. m⁻².a⁻¹ for Cu, 16.5 mg.m⁻².a⁻¹ for Pb, 189 mg.m⁻².a⁻¹ for Zn, 2.20 mg.m⁻².a⁻¹ for Cd, 699 mg.m⁻².a⁻¹ for Fe, 38.8 mg.m⁻².a⁻¹ for Co, and 84.6 mg.m⁻².a⁻¹ for Ni. The relations between the average fluxes of trace metals and POC, the fluxes of trace metals and settled matter, and the sea fluxes of trace metals and Fe are in linear progression. The resident times of elements as calculated from sea flux, are 1.1 a. for Cu, 0.014 a. for Pb, 0.50 a. for Zn, 3.8 a. for Cd, 0.16 a. for Fe, 0.39 a. for Co, and 1.14 a. for Ni. The order of resident times is as follows: Pb−Fe−Co−Zn−Cu−Ni−Cd. The metal resident times in Saanich Inlet are shorter than the values estimated for the open ocean. It illustrates that the biochemical processes in shallow Saanich Inlet are faster than those in the open ocean, and that debries of plankton and fecal pellets of zooplankton play an important role in vertical transport of organic carbons. Contribution No. 1650 from the Institute of Oceanology, Academia Sinica.     

Extended-aperture underwater acoustic multisource azimuth/elevationdirection-finding using uniformly but sparsely spaced vector hydrophones

Aperture extension is achieved in this novel ESPRIT-based two-dimensional angle estimation scheme using a uniform rectangular array of vector hydrophones spaced much farther apart than a half-wavelength. A vector hydrophone comprises two or three spatially co-located, orthogonally oriented identical velocity hydrophones (each of which measures one Cartesian component of the underwater acoustical particle velocity vector-field) plus an optional pressure hydrophone. Each incident source's directions-of-arrival are determined from the source's acoustical particle velocity components, which are extracted by decoupling the data covariance matrix's signal-subspace eigenvectors using the lower dimensional eigenvectors obtainable by ESPRIT. These direction-cosine estimates are unambiguous but have high variance; they are used as coarse references to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector-hydrophone spacing exceeds a half-wavelength. In one simulation scenario, the estimation standard deviation decreases with increasing intervector-hydrophone spacing up to 12 wavelengths, effecting a 97% reduction in the estimation standard deviation relative to the half-wavelength case. This proposed scheme and the attendant vector-hydrophone array outperform a uniform half-wavelength spaced pressure-hydrophone array with the same aperture and slightly greater number of component hydrophones by an order of magnitude in estimation standard deviation. Other simulations demonstrate how this proposed method improves underwater acoustic communications link performance. The virtual array interpolation technique would allow this proposed algorithm to be used with irregular array geometries     

Okadaic acid, a causative toxin of diarrhetic shellfish poisoning, in green-lipped mussels Perna viridis from Hong Kong fish culture zones: method development and monitoring

Green-lipped mussels (Perna viridis) were collected from seven fish culture zones (FCZs) in Hong Kong and analyzed for okadaic acid (OA). A conventional HPLC method was modified by incorporating a proteinase K digestion step. Results suggest that a higher recovery (2.5 times higher) of OA was obtained from spiked samples after the addition of 1.08 mg proteinase K in comparison with samples incubated without the proteolytic enzyme. For the hepatopancreas (HP) of individual field-collected mussels, the additional digestion step can enhance OA extraction by 3.1 times. Spatial and temporal variations in OA concentrations in the mussels from various FCZs were investigated. The highest concentration of OA in mussel HP samples was 1164.9 ng/g HP wet wt. With respect to OA concentrations in whole mussel tissues from seven sites and four seasonal samplings, the concentrations were between 70.0 and 131.0 ng/g wet wt., which did not exceed the generally recognized international regulatory criteria (>200 ng/g) for OA.     

A case study on fuel oil contamination in a mangrove swamp in Hong Kong

Mangroves commonly found along tropical and subtropical coastlines are susceptible to oil pollution. In December 2000, around 500 1 m tall Kandelia candel saplings at the age of 3–5 years old located at the foreshore region of Sheung Pak Nai swamp, Hong Kong SAR, were found to be damaged by oil pollution. More than 80% of the saplings were either dead or washed away and leaving less than 5% healthy saplings with dense green leaves. Elevated concentrations of light n-alkanes (ranging from n-C₁₄ to n-C₂₀), pristane and phytane were recorded in surface sediments collected in December 2000. The ratio between light and total n-alkanes was 0.4. The total petroleum hydrocarbons (60–80 μg g⁻¹ TPH) and unresolved complex mixtures (60–70 μg g⁻¹ UCM) were higher than the background values of other mangrove sediments in Hong Kong, which were 40 and 20 μg g⁻¹, respectively. In certain root zone sediments, TPH concentrations were above 1000 μg g⁻¹. These results suggest that surface sediments in Sheung Pak Nai were contaminated by petroleum oil, most likely by illegal discharge of fuel oil which occurred between 1998 and 2002. One year later, in December 2001, unhealthy saplings had recovered and re-grown. The concentrations of TPH and UCM in sediments declined to around 40 μg g⁻¹, pristane and phytane dropped by 80%, and the ratio of light to total n-alkanes was 0.15, suggesting that residual oil in sediments was weathered leading to a remarkable recovery of the unhealthy saplings.     

Evaluation of landslide triggering mechanisms in model fill slopes

Hong Kong is particularly susceptible to landslide risk due to the steep natural topography and prolonged periods of high intensity rainfall. Compounding the risk of slope failure is the existence of loose fill slopes which were constructed prior to the 1970s by end-tipping. A clear understanding of the underlying triggering mechanisms of fast landslides in fill slopes is required to analyse landslide risk and to optimise slope stabilisation strategies. The work described here had the objective of evaluating two candidate triggering mechanisms—static liquefaction and the transition from slide to flow due to localised transient pore water pressures—against observations of slope behaviour obtained from highly instrumented centrifuge model tests. These results indicate that static liquefaction is unlikely to occur if the model fill is unsaturated and the depth to bedrock large, as the high compressibility and mobility of air in the unsaturated void spaces allows the model fill slope to accommodate wetting collapse without initiating undrained failure. In contrast, high-speed failures with low-angle run-outs are shown to be easily triggered in model fill slopes from initially slow moving slips driven by localised transient pore water pressures arising from constricted seepage and material layering.     

Studying fractal geometry on submicron length scales by small-angle scattering

Recent studies have shown that internal surfaces of porous geological materials, such as rocks and lignite coals, can be described by fractals down to atomic length scales, In this paper, the basic properties of self-similar and self-affine fractals are reviewed and how fractal dimensions can be measured by small-angle scattering experiments are discussed.This paper was presented at Emerging Concepts, MGUS-87 Conference, Redwood City, California, 13–15 April 1987.     

The oxidation state diagram: Additional comments

The oxidation state diagram provides additional information that cannot be readily discerned from an activity ratio—pE diagram. A theoretical framework for explaining the existence of thermodynamically unstable species becomes available.     

A Two-Dimensional Spectrum for Bistatic SAR Processing Using Series Reversion

This letter derives the two-dimensional point target spectrum for an arbitrary bistatic synthetic aperture radar configuration. The method described makes use of series reversion, the method of stationary phase, and Fourier transform pairs to derive the point target spectrum. The accuracy of the spectrum is controlled by keeping enough terms in the two series expansions, and is verified with a point target simulation