Morphology and surface texture of quartz grains from ODP Site 105-645

The shapes and surface textures of sand-sized quartz grains from the sediments cored at Site 645 in southern Baffin Bay during ODP Leg 105 were studied to characterize the terrigenous materials and the settling processes involved in the deposition of these sediments. Here, we show a homogeneous sand fraction that results from mixing grains from various provenances. The characteristics inherited from terrestrial processes (varying degrees of wear; fluviatile, aeolian, and diagenetic features) dominate the characteristics that result from evolution in a high-energy marine environment. Thus, the influence of the last stage of sedimentation in a deep-marine environment was difficult to distinguish. However, fluctuations in the relative proportions of particular features reveal that the terrigenous material derived from sedimentary formations of Baffin Island and East Greenland or from direct abrasion of the crystalline shield, which changed through time as the dominant settling processes evolved. In particular, this study confirms the onset of major ice rafting as old as late Miocene.

Particel size distribution and microstructures of sediments from ODP Leg 205 sites (Table 1)

Ocean Drilling Program Legs 170 and 205 offshore Costa Rica provide structural observations which support a new model for the geometry and deformation response to the seismic cycle of the frontal sedimentary prism and decollement. The model is based on drillcore, thin section, and electron microscope observations. The decollement damage zone is a few tens of meters in width, it develops mainly within the frontal prism. A clear cm-thick fault core is observed 1.6 km from the trench. The lower boundary of the fault core is coincident with the lithological boundary between the frontal prism and the hemipelagic and pelagic sediment of the Cocos plate. Breccia clast distributions in the upper portion of the decollement damage zone were studied through fractal analysis. This analysis shows that the fractal dimension changes with brecciated fragment size, implying that deformation was not accommodated by self-similar fracturing. A higher fractal dimensionality correlates with smaller particle size, which indicates that different or additional grain-size reduction processes operated during shearing. The co-existence of two distinct fracturing processes is also confirmed by microscopic analysis in which extension fracturing in the upper part of the damage zone farthest from the fault core is frequent, while both extension and shear fracturing occur approaching the fault core. The coexistence of extensional and shear fracturing seems to be best explained by fluid pressure variations in response to variations of the compressional regime during the seismic cycle. During the co-seismic event, sub-horizontal compression and fluid pressure increase, triggering shear fracturing and fluid expulsion. Fractures migrate upward with fluids, contributing to the asymmetric shape of the decollement, while slip propagates. In the inter-seismic interval the frontal prismrelaxes and fluid pressure drops. The frontal prismgoes into diffuse extension during the intervalwhen plate convergence is accommodated by creep along the ductile fault core. The fault core is typically a barrier to deformation, which is explained by its weak, but impermeable, nature. The localized development of a damage zone beneath the fault core is characterized by shear fracturing that appears as the result of local strengthening of the detachment.

Sediment constituents and quartz in the sand-sized fraction, West Florida slope and Mississippi Fan sediments

The interval between 488.2 and 513.7 m below seafloor at Deep Sea Drilling Project (DSDP) Site 615 is interpreted as a single carbonate gravity-flow deposit. The deposit has characteristics of both a debris flow and a high-density turbidity current. Comparison of the sedimentary constituents in 15 samples from this site with samples from 26 core tops from the upper West Florida continental slope and eastern Mississippi Fan shows many similarities. Shallow-water indicators, such as mollusk and echinoid fragments, occur in both suites of samples. The West Florida continental margin, therefore, is a potential provenance area. The Yucatan slope is also a possible source, but data from it are limited. The recognition of carbonate gravity-flow deposits intercalated within the Mississippi Fan refines our understanding of Pleistocene sedimentation within the Gulf basin. Deposition in the deep Gulf is dominated by the construction of the Mississippi Fan. However, this marine terrigenous depocenter is located between two large carbonate depocenters, the West Florida continental margin on the east and the Yucatan peninsula on the southwest. Periodically, the carbonate slope in these two regions fails, injecting carbonate gravity flows into the accreting terrigenous deep-sea fan.

Sediment microstructures of ODP Leg 105 holes

Possible genetic relationships between syn- and post-depositional processes and sediment microstructure were investigated. Samples from cores at Sites 646 and 647 of Ocean Drilling Program (ODP) Leg 105 included examples of bottom current deposition (contourites), turbidity current deposition, consolidation, and diagenesis. Examination of nearly 200 micrographs of 14 samples from Site 646 and 13 samples from Site 647 leads to the conclusion that sedimentation processes do not appear to have an obvious influence on fabric. The effects of post-depositional processes, such as bioturbation, coring disturbance, and even remolding, appear to be less significant than one might expect as a result of the relatively coarse grain size of the sediments studied. Consolidation resulting from increased overburden stress results in increased particle alignment and compression of fabric elements with depth. The transition from open, random fabric in shallow samples to preferred orientation at depth represents the only change in these sediments that can be ascribed directly to a specific depositional or post-depositional process. Mineralogical variations, owing to changes in weathering processes and growth of authigenic/diagenetic minerals, also have a pronounced effect on sediment fabric.

Tongass National Forest (N.F.), Quartz Hill road access, bulk sampling permit D,Dapp,Dsup,F,Fapp; Draft mining development concepts B1; Mining development concepts : environmental impact statement.

Mode of access: Internet.

Fused-quartz fibers : a survey of properties, applications, and production methods /

Bibliography: p. 18-26.

High temperature infra-red transmission studies of ultrasil fused quartz for Project FIRE /

Photocopy.

Quartz from the uplands,

Published anonymously in 1905; now issued with slight alterations.

Rapport sur la mine de quartz aurifere de Santa Ernestina (en Cunapiru) Departamente de Tacuarembo, Republique Orientale de l'Uruguay

Mode of access: Internet.

Method for determining reaction rate of mild steel containers during melting of magnesium-aluminium alloys and effect of aluminium content on directionally solidified microstructures

A magnesium alloy of eutectic composition (33 wt-'%Al) was directionally solidified in mild steel tubes at two growth rates, 32 and 580 mum s(-1,) in a temperature gradient between 10 and 20 K mm(-1). After directional solidification, the composition of each specimen varied dramatically, from 32'%Al in the region that had remained solid to 18%Al (32 mum s(-1) specimen) and 13%Al (580 mum s(-1) specimen) at the plane that had been quenched from the eutectic temperature. As the aluminium content decreased, the microstructure contained an increasing volume fraction of primary magnesium dendrites and the eutectic morphology gradually changed from lamellar to partially divorced. The reduction in aluminium content was caused by the growth of an Al-Fe phase ahead of the Mg-Al growth front. Most of the growth of the Al-Fe phase occurred during the remelting period before directional solidification. The thickness of the Al-Fe phase increased with increased temperature and time of contact with the molten Mg-Al alloy. (C) 2003 Maney Publishing.

Metalorganic chemical vapor deposition of GaAsN epilayers: microstructures and optical properties

In this article, we investigate the parameters used in the MOCVD growth of GaAsN epilayers on GaAs substrates and some of their microstructures and optical properties. The N incorporation was found to mainly depend on the growth temperature and the fractional 1,1-dimethylhydrazine molar flow. A thin highly strained interface layer was observed between GaAsN and GaAs, which, contrary to previously published results, was not N enriched. The low-temperature (10 K) photoluminescence spectra were composed of several emissions that we attribute to a combination of interband transition and transitions involving localized defect states. (C) 2004 Elsevier B.V. All rights reserved.