A device to examine the in situ response of intertidal cohesive sediment deposits to fluid shear

A self-contained, field-portable recirculating seawater flume was designed and constructed in order to measure in situ the erodibility of cohesive estuarine muds. The flume can be easily deployed by one person and is designed for subaerial use only. Bed shear stresses up to 0.6 Nm⁻² can be generated by the flume. Rates of sediment erosion are assessed in terms of the mass of particulate material eroded with time. Flow calibrations yield a drag coefficient (C_D) of 4.5 × 10⁻³ which enables single mid-depth velocity measurements to be related directly to the imposed bed stress. Water motions within the flume are complex, but secondary (radial) circulations are not considered sufficiently competent to dominate sediment erosion. Stratification effects due to high levels of suspended sediment ( 1.5 gl⁻¹) are negligible. However, the drag-reducing properties of the sediment suspension are uncertain.     

The physical properties of quartz-micaschist and their application to freeze-thaw weathering studies in the maritime antarctic

As part of a study on freeze-thaw weathering in the maritime Antarctic an investigation was made of the physical properties of the local rock. Tests were made of point-load compressive strength, Schmidt hammer in situ rock strength, moisture content, indentor resistance and the size range of weathering products. The resulting data were used to consider the form of freeze-thaw weathering operative in the field and its relationship to laboratory simulations. A distinct difference between ‘massive rock’ and ‘intact rock’ is observed in the field. It is suggested that future studies should generate a greater database pertaining to rock properties as it is an invaluable aid in the study of mechanical weathering.     

Occurrence and distribution of shortnose sturgeon,Acipenser brevirostrum,in the upper tidal Delaware River

Sampling in the upper tidal Delaware River between Trenton, New Jersey, and Philadelphia, Pennsylvania, from July 1981 through December 1984 demonstrated the existence of a significant population of shortnose sturgeon. The sturgeon aggregate in the river channel during daylight hours, especially in the area between Trenton and Florence, New Jersey (river km 211.8 to 198.8). Occurrence in the river downstream of Florence appears to be restricted by poor water quality during summer months. Sturgeon were present in the study area throughout the year, but largest numbers were collected from May though November. No spawning was observed during this study, but presence of males with milt suggests that spawning possibly occurs in the Trenton area. Preliminary population estimates (Peterson, Schnabel and Seber-Jolly) indicate an adult population of approximately 6,000–14,000 shortnose sturgeon occupying the upper tidal Delaware River.     

Rapid deglaciation as an initiator of volcanic activity: An hypothesis

Volcanic activity on sub-Antarctic Marion Island is found to have occurred only during the interglacials. The present volcano distribution is associated with a radial and peripheral fault system, the location of which appears to be related to the former glacier distribution. An hypothesis is presented suggesting that the faulting is a result of deglaciation and that the specific location of the faults is due to the differential stresses occurring between ice-covered and ice-free areas during isostatic uplift. The faulting initiates volcanism due to the location of the island within a volcanic region.     

Carbon,hydrogen and nitrogen isotopes in solvent-extractable organic matter from carbonaceous chondrites

Solvent extractions were done on the carbonaceous chondrites Murray, Murchison, Orgueil and Renazzo, using CCl₄ and CH₃OH. Between 2 and 10% of the total carbon in these meteorites is extractable by ordinary techniques, most of it in CH₃OH. After demineralization with HF, perhaps as much as 30% of the total carbon in Murray may be extractable with CH₃OH. The extracts from Renazzo have isotopic ratios which suggest that they are mainly terrestrial organic matter, with lesser contributions from indigenous organics. The CH₃OH-soluble organic matter from Murchison and both untreated and HF-treated Murray has δ¹³C values of about +5 to + 10%. and δ¹⁵N values of about +90 to +100%., both of which are significantly higher than the bulk meteorite values. The Orgueil CH₃OH-extract also has a δ¹⁵N value well above the value in residual organic matter. Values for δD of +300 to +500%. are found for the CH₃OH-soluble organic matter. The combined data for C, H and N isotopes makes it highly unlikely that the CH₃OH-soluble components are derivable from, or simply related to, the insoluble organic polymer found in the same meteorites. A relationship is suggested between the event that formed hydrous minerals in CI1 and CM2 meteorites and the introduction of water-soluble (methanol-soluble) organic compounds. Organic matter soluble in CCl₄ has essentially no nitrogen, and δ³C and δD values are lower than for CH₃OH-soluble phases. Either there are large isotopic fractionations for carbon and hydrogen between different soluble organic phases, or the less polar components are partially of terrestrial origin.     

Middle-fan deposits from the late precambrian kongsfjord formation submarine fan,Northeast Finnmark,Northern Norway

The 3.2 km-thick late Precambrian Kongsfjord Formation Submarine Fan shows well-developed middle-fan facies-associations. Channel deposits are characterised by discrete packets of coarse-grained, medium to thick-bedded, amalgamated sandstone turbidites and other mass-flow deposits, generally 10 to 30 m thick. Individual beds, or packets of beds, wedge out and channel bases cut down by up to 11 m over a lateral distance of 150 m. Channel deposits often comprise a thinning-and-fining-upward sequence although they vary greatly in clarity. Interchannel deposits occur as packets, tens of centimetres to 25 m thick, of thin and very thin bedded Bouma T_cde siltstones and mudstones. Palaeocurrents within interchannel deposits commonly diverge from those of adjacent channel sandstones. Within the interchannel deposits, isolated beds or packets of beds occur that are both thicker bedded and coarser grained than the surrounding beds; these unusual deposits are sheet-like or fill small channels, and are interpreted as crevasse splays, lobes and channels. Packets, up to a few metres thick, of laterally discontinuous siltstone turbidites occur immediately above some of the channel sandstones, rarely below, and in some cases within interchannel deposits. These siltstones are thin to medium-bedded, show Bouma T_cd, with T_c often as climbing-ripple lamination, and commonly show soft-sediment deformation as slides, slumps, liquefaction and fluidisation structures. Palaeoflow within these packets, compared to adjacent channel sandstones, diverges by up to 90°, and in some cases channel sandstones are seen to pass laterally into these deposits with a swing in palaeocurrents from parallel to the inferred channel axis, to perpendicular to it. These deposits are thought to be levees. Channel-margin deposits are most distinctive, and they are recognised by extreme lateral wedging of channel sandstones, with concomitant thinning and fining of individual beds and their amalgamation towards the channel axis. Sliding and slumping of channel margin deposits is common. Throughout the Kongsfjord Formation Submarine Fan, channel sandstone palaeocurrents suggest a sediment-transport direction to the NE quadrant, although some channels funnelled sediment towards the southeast.     

Processes controlling precipitation of carbonate cement and dissolution of silica in reef and near-reef settings

Carbonate cementation in the surface layer of reefs and beachrock eliminates porosity and partially replaces detrital quartz grains. The uptake and release of CO₂ by photosynthesis and respiration in reef communities cause a shift in the carbonate buffer system of seawater. Field studies and experimentation simulating the natural settings show minimum values of CO₂ (1.9 mmoles 1^?1) and HCO₃^? (2.4 meq 1^?1) in association with maximum values of pH (9.8) and O₂ (> 100% oxygen saturation) in waters covering corals and algae prior to sunset. The converse is true for these variables prior to sunrise, when minimum values of pH (7.6) and O₂ (<66% oxygen saturation) occur with maximum values of CO₂ (2.7 mmoles 1^?1) and HCO₃^? (2.7 meq 1^?1). Experimental tanks containing plain seawater showed almost no diurnal variability in pH (a constant 7.5–7.6) or O₂ (80–90% oxygen saturation) measurements. Seawater adjacent to reef biomass, with elevated pH and supersaturated with calcium carbonate, is periodically pumped into the underlying reef and beach sediments due to pressure-buildups between the reef framework or algal zones and open waters. Carbonate precipitation and quartz dissolution follow. As the system equilibrates, pH values progressively decrease.     

The present day formation of apatite in Mexican continental margin sediments

Results of pore water and sediment analyses from the western Mexican continental margin strongly suggest the present day formation of apatite. The interstitial water phosphate and fluoride profiles indicate chemical removal at a depth which corresponds to a large maximum in the phosphorus content of the sediments. Apatite is identified within this maximum via X-ray diffraction but is elsewhere undetectable in the core. Radioisotopic thorium, uranium, and radium data support the conclusion that this deposit is modern. The present day depositional environment is consistent with those reported by other workers for phosphorite formation with the exception that pore water magnesium is not depleted below its seawater value.     

The Collision Manifold of the Collinear One-Bumper Two-Body Problem

We present a special model which is a caricature of the collinear three-body problem. Near triple-collision behavior for the model is governed by the collision manifold. We study the bifurcations of the dynamics on this manifold as we vary the ratio of masses. Both analytic and numerical results are presented.This revised version was published online in October 2005 with corrections to the Cover Date.