Temporal trends in grain-size measures on a linear sand dune

Within aeolian dune systems spatial patterns of grain-size variation have been recognized, but little has been said about temporal changes. Increasingly it is becoming clear that linear dunes are associated with bi-directional wind regimes which are often seasonal. In the Namib Sand Sea, where linear dunes are aligned roughly north-south, winds blow from the west in summer and from the east in winter. In response to this regime, sand is eroded from the west slopes and deposited on the east slopes in summer, and eroded from the east slopes and deposited on the west slopes in winter. Preliminary evidence from a study of a single Namib linear dune reported here confirms that this seasonal aeolian regime induces seasonal responses in some grain-size measurements due to the dynamics of sand transport on the dune, the characteristics of the sand source immediately upwind of the sample point and the nature of the deposit. Thus, time of sampling is crucial to the results obtained.     

Organic films on particulate matter in surface waters off eastern Asia

SEM examination of suspended material collected by filtration from samples of surface waters over continental shelves and deeper areas off eastern Asia reveals the presence of irregular organic films that are longer, cover more filter area, and have more tapered edges in samples from nearshore than offshore regions. Associated diatoms include species diagnostic of coastal environments. Films and coastal diatoms are most abundant in waters above continental shelves where river discharges cause the waters to be more dilute than 33.5‰ salinity. Farther from shore, both films and skeletal elements are broken and partly dissolved. Skeletal elements, faecal matter, and other debris are trapped or adhere to the films, which therefore provide a concentrated food source for small organisms beyond nearshore regions of high primary productivity. The films contribute an unknown percentage of the total organic matter that reaches bottom sediments.     

The Regional Research Laboratory initiative A progress report

Abstract

This paper outlines the origins and objectives of the four multidisciplinary Regional Research Laboratories (RRLs) established in Great Britain by the Economic and Social Research Council at Cardiff, Edinburgh, London and Newcastle, and describes the work undertaken in the first 6 months of the trial phase. The RRLs will have four main functions, viz., data management, software development, spatial analysis and research training. An example is given of the work undertaken at each RRL, viz., a general purpose system for the display and query of large spatially-referenced data sets, an integrated spatial database for south-east England, a health care planning information system for the County of Avon and a target marketing system. The trial phase of this initiative is then evaluated in terms of its laboratory, research and regional dimensions     

A late Quaternary bio- and climatostratigraphy for marine sediments in the north-central part of the North Sea

BOREAS Harland, R., Gregory, Diane M., Hughes, M. J. & Wilkinson, I. P. 1978 06 01: A late Quaternary bio- and climatostratigraphy for marine sediments in the north-central part of the North Sea. Boreas, Vol. 7, pp. 91–96. Oslo. ISSN 0300–9483.
Micropalaeontological studies of three boreholes in the north-central North Sea have led to the erection of a bio- and climatostratigraphy for the area. Palaeoenvironmental interpretations have depended largely upon oceanographic concepts and changes in the micropalaeontological assemblages have been related to postulated alterations in water mass regimes. The biostratigraphy can then be utilized as a climatostratigraphy since such water mass changes are most probably linked to alterations in the circulation of the North Atlantic, and in particular to the positions of the climatically important North Atlantic Current and Polar Front. The North Sea sequences are compared to similar sections in Europe and related to the commonly accepted standard chronostratigraphy.     

MALDI analysis of presolar nanodiamonds: Mass spectrometric determination of the mass distribution of nanodiamonds from meteorites and a technique to manipulate individual nanodiamonds

Abstract— This paper describes the use of matrix‐assisted laser desorption and ionization (MALDI) to measure the mass distribution of nanodiamonds extracted from meteorites. The techniques used to prepare and mass analyze nanodiamond samples from the Murchison (CM2) and Allende (CV3) meteorites are described. The mass spectra of nanodiamonds (peaking at between 1 times 10⁴‐1.5 times 10⁴ Daltons) are compared with size distributions obtained by point‐counting transmission electron microscopy (TEM) images obtained elsewhere and reasonable agreement is found. The implications of the ability to produce and mass analyze a beam of nanodiamonds are explored.     

Biotites as Indicators of Fluorine Fugacities in Late-Stage Magmatic Fluids: the Gardar Province of South Greenland

The major element chemistry and fluorine contents of biotitesfrom the Gardar alkaline province of South Greenland providean insight into the F contents of late-stage fluids associatedwith the magmatism. Biotites were taken from composite intrusionsranging from alkali gabbro to syenites, nepheline syenites andalkali granites. In each complex they show a large range ofFe/(Fe+Mg) (from 0•2 to 1) and exhibit strong Fe-F avoidance.There is considerable variation in F for any value of Fe/(Fe+Mg)but for each centre maximum F values plotted against Fe/(Fe+Mg)define a nearly straight line of characteristic slope towardslow or zero F at pure annite. Micas in the SiO₂ undersaturatedcentres have higher F contents than those from oversaturatedcentres. Cl is low (0•69 wt%) except in the Kûngnâtintrusion, where it reaches 1•4 wt%. Phase equilibriumand textural considerations suggest that most or all biotitesgrew subsolidus in a pervasive deuteric fluid. ¹⁸O values suggestthat these fluids were largely magmatic in character and thatextensive reactions with envelope fluids did not occur. Metasomaticresetting of F in biotites in early intrusive units in the aureoleof later units can be demonstrated. Experimental data of Munoz (Mineralogical Society of America,Reviews in Mineralogy 13, 469–494, 1984) were used tocalculate families of curves showing variation in F with Fe/(Fe+Mg)for biotites in equilibrium with fluids of fixed fugacity ratio,f(HF)/f(H₂O), at fixed P and T. The resulting curves cut sharplyacross the maximum fluorine lines observed in the natural examples.As it seems highly unlikely that changes in fluid compositionand T, acting together, could produce the observed linear relationship,we conclude that the partitioning of F between fluid and micain the plutonic environment is not well modelled by the experiments.Possible explanations are short-range order (SRO) of Fe andMg on octahedral sites in biotite (Mason, Canadian Mineralogist30, 343–354, 1992) or effects resulting from differentF speciation in alkaline fluids. If perfect Fe-F avoidance isassumed, Fe-Mg SRO can increase maximum F content. The F levelsseen in the silica-saturated centres are broadly consistentwith a cooling-rate related control. It is possible that thehigher F in biotites in the undersaturated centres reflectsdifferent speciation in the fluid rather than higher F contents,with strongly bound SiF₄° complexes more common. KEY WORDS: biotites; Gardar; fluorine; alkaline rocks; fluids     

The oxygen isotopic properties of olivines in the Semarkona ordinary chondrite

Abstract— In order to explore the origin of chondrules and the chondrites, the O isotopic compositions of nine olivine grains in seven chondrules from the primitive Semarkona LL3.0 chondrite have been determined by ion microprobe. The data plot in the same general region of the three-isotope plot as whole-chondrule samples from ordinary chondrites previously measured by other techniques. There are no significant differences between the O isotopic properties of olivine in the various chondrule groups in the present study, but there is a slight indication that the data plot at the ¹⁶O-rich end of the ordinary chondrite field. This might suggest that the mesostasis contains isotopically heavy O. The olivines in the present study have O isotopic compositions unlike the ¹⁶O-rich olivine grains from the Julesburg ordinary chondrite. Even though olivines in group A chondrules have several properties in common with them, the ¹⁶O-rich Julesburg olivines previously reported are not simply olivines from group A chondrules.     

The hydrodynamics of particle clusters and sediment entrapment in coarse alluvial channels

ABSTRACT Particles projecting from the bed of an alluvial channel distort the fluid stream to produce a distinctive pressure field. This has considerable significance for both the entrapment and entrainment of other particles and is a primary cause of the widespread occurrence of pebble clusters and boulder shadows. Lift and drag forces are determined on clustered hemispherical particles of varying size. In the wake of an obstructing particle both forces are shown to vary directly with particle separation in a linear fashion. On the stoss side of the cluster, drag is uniform regardless of the separation of the component particles, but lift is shown to increase when particle separation is small, so affecting stability. This mutual interference of neighbouring clustered bed particles is a vital consideration of incipient motion and is shown by field evidence to cause a wide range in transport stage for particles of similar size and shape. On average, 46% of clustered particles are entrained by flood flow compared to 87% of particles in open plane-beds. The influence of clusters is a major determinant of sedimentary sorting.     

Reconstruction of late Quaternary sea-level change in southwestern British Columbia from sediments in isolation basins

Bracketing ages on marine—freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about —15 m from 14000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 in a ^-1, similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a^-1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet.