Orientation of framboidal pyrite in shale

Ordered framboids from Devonian Chattanooga Shale (U.S.A.) and Rammelsberg Banderz (Germany) show a common orientation in any one sample. This observation was made using a stereographic method of reconstruction in which the lineations within the framboids were measured on each of three planes cut mutually at right angles from the rock samples. The explanation for this preferred orientation is not yet known, but it may originate from crystal-growth during compaction of the shales.

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Zusammenfassung Pyrit-Himbeeren aus dem devonischen Chattanooga Shale (U.S.A.) und vom Rammelsberg Banderz zeigen bevorzugte Orientierungen ihrer inneren Struktur (Figure I) gegenüber der Sedimentschichtung. Diese Beobachtungen sind in stereographischen Projektionen aufgezeichnet. Der Vorgang der Orientierung mag auf die Kristallisation der Pyrit-Netzwerke während der Diagenese zurückzuführen sein.

     

Cyclic nature of lamination in the Tithonian Solnhofen Plattenkalk of southern Germany and its palaeoclimatic implications

In the Tithonian Solnhofen Plattenkalk (Malm + 2) of southern Germany, layers of purely micritic limestone are rhythmically interbedded with ones of marly micritic limestone. It appears that this alternation was formed under control of the Tithonian orbital variations. The Fourier spectral analysis shows that, on a decimetric to metric scale, the long-term cyclicities in the number of laminae per centimetre are in agreement with those found in the bed-thickness series, varying from 0.7 to 1.3 m cycles. The number of laminae of the Solnhofen Formation ranges from about 5,800 to about 12,800 laminae per main cycle. This indicates that, under an assumption that the main cycle of the Solnhofen Formation corresponds to the Tithonian precessional one, a single lamina represents a multi-year time interval. Particularly, in the short-term cyclic domain, the laminated sequence contains clearly millimetric cycles consisting of about two to three cyclic components. It implies that laminae formation may result from the composite effect of two or three distinct climatic processes.     

Deposition of coarse-grained sediments in the Korea Strait during late Pleistocene low sea level

The wide area of the Korea Strait shelf is covered by a thin veneer of gravelly sands, sands, or muddy sands. Most gravels are sub- to well-rounded and their content reaches up to 25%. These sediments were derived from the Korean Peninsula through the paleochannel of the Nakdong River, which extended onto the mid-shelf during late Pleistocene low sea level. The gravel distribution pattern suggests reworking and transport of the sediments by strong currents during times of low sea level.     

Computer Simulation of Coastal Acoustic Tomography by a Two-Dimensional Vortex Model

Computer simulation of coastal acoustic tomography with four, five, seven and nine stations was applied to two-dimensional vortex fields of horizontal domain 5 km × 5 km. Travel time data obtained in reciprocal directions between all pairs of acoustic stations were analyzed to reconstruct the vortex fields by the stochastic inverse method, reduced to the damped least squares method. The weighting factor appearing in the inverse analysis was determined by applying the L-curve method, in which a point making both the size of estimated error ‖y - Ex‖ and solution ‖x‖ as small as possible in a balance is specified as an optimum. The performance of this method was examined using two-dimensional vortex models which have different wavenumber spectra and adding the random error of different levels to the travel time difference data y. This study suggests that in the selection of the optimal weighting factor the horizontal section of the simulated tidal vortex fields can be well reconstructed by the coastal acoustic tomography system composed of five to seven acoustic stations located in the periphery of the vortex fields. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effects of drag reduction by ribbons attached to cylindrical pipes

This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to vertical pipes. Experiments were conducted in a circulating water channel to investigate the effects of the ribbon length and the direction of the flow on various current velocities. Drag on a vertical cylinder was measured by a resistance dynamometer. Flow visualizations were conducted using laser sheet beams. Laser Doppler Velocimetry (LDV) was used to measure the velocity field in the wake. This experiment demonstrates that attached ribbons can be used to reduce the drag force on vertical pipes for various directions of incoming flows. The ribbon-type device is very simple and easy to fabricate for field applications. The results are promising for the application to offshore structures.     

Distribution,provenance, and dispersal pattern of clay minerals in surface sediments,Bransfield Strait,Antarctica

Clay minerals of the surface sediments of Bransfield Strait, Antarctica, exhibit distinctive geographical distributions: kaolinite has the highest concentration near the shore of the South Shetland Islands in the northern strait (20%); chlorite, near Smith Island in the northwestern strait; illite, on the continental shelf off the Antarctic Peninsula in the southern strait (80%); and smectite, close to the Penguin and Bridgeman islands in the northeastern strait (25%). This distribution pattern, combined with hydrographic and climatic data for the strait, are used to infer clay mineral provenance and dispersal patterns.