bluuebunny/crossref_metadata_2025_split huggingface dataset:
Petrology of glacial sand: implications for the origin and mechanical durability of lithic fragments
Authors: SLATT ROGER M. , EYLES NICHOLAS 
Published: June 2006

ABSTRACTThe petrology of first cycle (unmodified) and second cycle (reworked) sand at the termini of eleven valley glaciers eroding coarse‐ to fine‐grained bedrock types is determined in order to evaluate the origin and mechanical durability of lithic sands. First cycle sands are coarse‐ to medium‐grained, poorly sorted, fine‐skewed, non‐modal lithic sands with an average composition of Q21F6L73. Grain‐size distributions do not vary with composition or source rock types, although sands derived from finer grained source rocks contain more lithic fragments than sands from coarser grained sources. By contrast, second cycle sands are medium‐grained, poorly sorted, fine‐ to coarse‐skewed arkosic to lithic sands with an average composition of Q19F40L41, and contain fewer lithic fragments than do first cycle sands.We propose that the origin, mechanical durability and survival potential of lithic fragments are related to the types and abundances of their internal planes of weakness, and the particular stress field of the transporting medium. As a result of abrasion, glacial clasts and lithic fragments are subjected to shear stress so that fractures propagate along intracrystal and intercrystal planes of weakness resulting in a continuous grain‐size spectrum of lithic fragments and monomineralic grains irrespective of the type of source rock. Upon subsequent aqueous transport in the proglacial environment lithic fragments are subjected to point‐loading during saltation in addition to shear stress. Point‐loading produces extensional fractures which preferentially propagate along intercrystal planes of weakness, so the lithic fragments break into smaller monomineralic grains and/or lithic fragments.Lithic fragments of very coarse sand‐size are abundant in first cycle sands, thus refuting, at least for glacial sands, the widely held view that grains of this size are deficient in nature. The presence of fewer grains of this size in second cycle sands indicates that very coarse sand‐size lithic fragments can survive recycling, but in greatly reduced proportions due to breakage.
Biosedimentological zonation of Boundary Bay tidal flats, Fraser River Delta, British Columbia
Authors: SWINBANKS DAVID D. , MURRAY JAMES W. 
Published: June 2006

ABSTRACTBoundary Bay tidal flats on the inactive southern flank of the Fraser Delta have surface sediments consisting almost entirely of very fine to fine, well to very well sorted sands which show a gradual fining‐shorewards trend. Five floral/sedimentological zones form distinct biofacies. These are, from the shoreline seaward, the saltmarsh, algal mat, upper sand wave, eelgrass and lower sand wave zones. The lower limit of the saltmarsh lies at a constant level above which the maximum duration of continuous exposure rises abruptly from ∼ 12 to 40 days. Similarly, at the lower limit of the algal mat zone the maximum duration of continuous exposure jumps from 1 to ∼ 2 days, and at the upper limit of the eelgrass zone from ∼ 0·5 to ∼ 0·8 days. These correlations between exposure and zonation are suggested to be causal.In the algal mat and eelgrass zones microtopography of biogenic origin, only a few centimetres high, creates lateral heterogeneity within the zonal biofacies. In the upper sand wave zone, very low amplitude (a∼ 0·1 m) symmetrical sand waves (λ∼ 30 m) of probable storm‐wave origin have a similar effect. In the lower sand wave zone, sand waves (a∼ 0·5 m, λ∼ 60 m) are formed by tidal currents or wave action and physical sedimentary structures dominate over biogenic ones.The densities of the following macrofaunal organisms which produce distinctive biogenic sedimentary structures were determined on two surveyed transects: Callianassa californiensis and Upogebia pugettensis, both thalassinidean shrimps; three polychaete worms, Abarenicola sp., Spio sp. and Clymenella sp.; the bivalve Mya arenaria and the gastropods Batillaria attramentaria and Nassarius mendicus. Callianassa excavate unlined temporary feeding burrows, whereas Upogebia build mud‐lined permanent dwelling burrows. Upogebia are restricted to below mean sea‐level where continuous exposure is < 0·5 days, whereas Callianassa extend up to a level, just below mean higher high water, where maximum continuous exposure rises abruptly from 4 to 9 days. This difference in range is probably due to the latter's greater anoxia tolerance—a necessary adaptation for life in an unlined feeding burrow.
Static breakage of granitic detritus by ice and water in comparison with breakage by flowing water
Authors: MOSS A. J. , GREEN PATRICIA , HUTKA J. 
Published: June 2006

ABSTRACTTemperature cycling between −4·5±1·0°C and 13·0±2·0°C in the presence of added water caused significant breakage of granitic detritus. Because cycling with only adsorbed water present also caused breakage, fragmentation is attributed to both the combined action of ice and adsorbed water and to the latter acting alone. Breakage evidently resulted from the gradual tensile opening of pre‐existing cracks, weakening then splitting grains. Surviving unbroken grains show evidence of a fatigue effect. Quartz split dominantly along pre‐existing subplanar microfractures whereas feldspar and biotite split along crystal cleavages.Degree of breakage and product size distribution depend on the crystalline nature of the parent material, its previous history, and the nature and duration of the breakage process. With the first two factors the same, size distributions from adsorbed water breakage alone and from that due to adsorbed water plus ice differ slightly. Both contrast strongly with those of simulated fluviatile breakage. Whereas the latter preferentially produced 2–20 μm particles (probably debris of inter‐particle collisions), static breakage split coarser grains wherever major weaknesses occurred, producing less selective product size distributions with greater proportions of loess‐sized material (about 20‐‐60 μ). Characteristic inflections in the size distribution curves of our experimentally produced debris are also shown by samples from the sola of some frost‐affected soils.Partially healed microfractures in plutonic quartz are normally spaced at about 1–10 μ—approaching the downward asymptotic comminution limit for brittle solids (about 1 μ). Surficial physical processes are capable of reducing only a small proportion of plutonic quartz to this size before its storage in sediments.
Evolution of a classic sand ridge field: Maryland sector, North American inner shelf
Authors: SWIFT DONALD J. P. , FIELD MICHAEL E. 
Published: June 2006

ABSTRACTThe ridge and swale topography of the Middle Atlantic Bight is best developed on the Delaware‐Maryland inner shelf. Here sand ridges can be seen in all stages of formation. Several aspects of the ridge field are pertinent to the problem of ridge genesis. The first is ridge morphology. There is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges, which reflects the changing hydraulic regime. As successively more seaward ridges are examined, maximum side slope decreases, the ratio of maximum seaward slope to maximum landward slope decreases, and the cross‐sectional area increases. These changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the Holocene transgression.A second aspect is the change in bottom sediment characteristics that accompanies these large‐scale morphologic changes. Megaripples, sand waves and mud lenses appear in the troughs between nearshore and offshore ridges. These changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector, and that the role of high‐frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea‐floor.A third aspect is the systematic relationship of grain size to topography. Grain size is 90° out of phase with topography, so that the coarsest sand lies between the axis of the landward trough and the ridge crest, while the finest sand lies between the ridge crest and the axis of the seaward trough. This relationship is characteristic of large‐scale bedforms.Finally, flow was measured and transport calculated on the same ridge during a one‐month period (November 1976). Threshold was exceeded only during storm events. Mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline. These flow measurements are in conformity with the pattern of smaller bedforms. A 43‐year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion, seaward flank deposition, and seaward crest migration.Sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress. The relationship between grain size and topography supports this model, but does not account directly for the oblique angle of the ridge with respect to the coastline. This feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge, and the relationship between this migration rate, and the rate of shoreface retreat.
The control of cathodoluminescence in dolomite by iron and manganese
Authors: PIERSON BERNARD J. 
Published: June 2006

ABSTRACTVariations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese (Mn2+) as the most important activator, and iron (Fe2+) as the main inhibitor of luminescence. Interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages (Cambrian to Cretaceous) and a wide geographical distribution (North America and Europe).Iron and manganese are positively correlated in the dolomites, with the former showing a greater range of variation. Very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm Mn2+ is present in highly luminescing samples. The intensity of luminescence is not proportional to the manganese concentration. Iron begins to quench luminescence as its concentration reaches 10,000 ppm. Above that level, luminescence is rapidly lost and total extinction occurs among samples containing more than 15,000 ppm Fe2+, regardless of the manganese concentration.
De glauconiarum origine
Authors: ODIN GILLES S. , MATTER ALBERT 
Published: June 2006

ABSTRACTThe glauconitic facies is widespread on present‐day continental shelves from 50° S to 65° N and at water depths between 50 and 500 m, and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m. It is also common in many ancient rocks of post‐late Precambrian age.It occurs as sand‐ to pebble‐sized, essentially green particles (granular facies) but also as a surface coating on particles and hardgrounds and as a diffuse impregnation (film and diffuse facies). We suggest the replacement of the term ‘glauconite’, which has been interchangeably used to designate a morphological form and a specific mineral, by glaucony (facies) and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family.The widely accepted model of Burst and Hower for glauconitization requires a degraded, micaceous (2: 1 layer lattice structure) parent clay mineral. However, detailed analysis of numerous samples of Recent glaucony reveals that such a parent substrate is exceptional. The model therefore requires modification. Generally the parent material is carbonate particles, argillaceous (kaolinitic) faecal pellets, infillings of foraminiferal tests, various mineral grains and rock fragments, that pass gradually into the commonly occurring green grains.We show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate, accompanied by progressive alteration and replacement of the substrate. It is this two‐fold evolution that causes the ‘verdissement’of granular substrates, macrofossils and hardgrounds. The authigenic mineral is an iron‐rich and potassium‐poor glauconitic smectite. While new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium, producing decreasingly expandable minerals with a non‐expandable glauconitic mica as the end member. This mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony. Four categories, nascent, little‐evolved, evolved and highly‐evolved glaucony are distinguished.Glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro‐environment and ambient open marine sea water. The optimum conditions for glauconitization are those of semi‐confinement. As a result the interior of a grain is more glauconitized than its less confined periphery. Similarly, for identical substrate types, large grains (500μm) provide more favourable substrates for glauconitization than lesser confined small grains.On a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing. Low accumulation rates expose grains to the open marine environment for sufficiently long times (105‐106 years for highly‐evolved glaucony).
Significance of interdune deposits and bounding surfaces in aeolian dune sands
Authors: KOCUREK GARY 
Published: June 2006

ABSTRACTBounding surfaces and interdune deposits provide keys for detailed interpretations of the development, shape, type, wavelength and angle of climb of aeolian bedforms, as well as overall sand sea conditions. Current alternate interpretations of bounding surfaces require very different, but testable models for sand sea deposition.Two perpendicular traverses of Jurassic Entrada Sandstone, Utah, reveal relations among cross‐strata, first‐order bounding surfaces, and horizontal strata. These field relations seem explicable only as the deposits of downwind‐migrating, climbing, enclosed interdune basins (horizontal strata) and dune bodies consisting of superimposed smaller crescentic dunes (cross‐stratified deposits). A 1.7 km traverse parallel to the palaeowind direction provides a time‐transgressive view showing continuous cosets of cross‐strata, first‐order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree. Changes occur in the angle of climb, cross‐strata structure, and interdune deposits; these reflect changes in depositional conditions through time. A 1.5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first‐order bounding surfaces and interdune deposits forming flat, laterally discontinuous lenticular bodies. The distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins, such as those on Padre Island, Texas.Hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg. The presence of three orders of bounding surfaces indicates dune bodies consisting of smaller, super‐imposed dunes. The geometry of first‐order bounding surfaces is a reflection of the shape of the inter‐dune basins. Second‐order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type. Third‐order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes. The presence of only two orders of bounding surfaces indicates simple dunes.Modern and Entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet, damp, and dry conditions. Interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions.
Methods of computation of suspended load from bed materials and flow parameters
Authors: GHOSH J. K. , MAZUMDER B. S. , SENGUPTA S. 
Published: June 2006

ABSTRACTComputation of the grain‐size distribution of the suspended load above a sand bed must take into consideration: (1) sorting processes from the bed to the bed layer and (2) sorting between the bed layer and suspension. Grain‐size distributions of the bed layers above sand beds of three different types have been computed in this work, both by the Einstein and the Gessler methods. Using these as references, suspended load distributions have been obtained in each case by the Rouse suspension equation. A new formula has also been developed in partial modification of Hunt's method for direct computation of bed load and suspended load from a bed's grain‐size distribution and flow parameters.Comparison of the computed data with actual observations in laboratory flumes show that no one method is particularly superior to the others, but the present method is advantageous because it affords direct computation of the suspended load from a bed's grain‐size distribution, without going through an intermediate stage (bed load). The possible sources of error in each of the methods have been discussed.
La sédimentation argileuse depuis l'Eocène sur le plateau Vøring et à son voisinage, d'après le Leg 38 DSDP (Mer de Norvège)
Authors: FROGET CLAUDE 
Published: June 2006

ABSTRACTThe study of clays from sites 338 to 343 enables the main lines of the palaeogeographical evolution of the Vøring plateau, off Norway, to be determined. The following stages are proposed:(1) In early Eocene sediments, clays provide evidence of erosion of the Scandinavian shield; detrital primary minerals (illite, chlorite) derived from crystalline rocks are dominant. This erosion results from tectonic movements coeval with the opening of the Norwegian basin. The rejuvenation of marginal relief hinders pedogenesis, which is only indicated by the presence of minerals coming from the few soils which are developed.(2) From the Middle Eocene, primary minerals decrease while smectite becomes dominant. This trend increases through the late Eocene and at the beginning of the Middle Oligocene, where only smectite is present. During this period the basin margins are stabilized after the initial movements. In essentially pelagic marine sediments, the smectite seems to be derived from volcanic rocks.(3) During the Middle Oligocene and early to Middle Miocene, smectite is always dominant, but primary minerals reappear, with mixed‐layers indicating a moderate continental alteration. This composition suggests a modification of the climate, mainly marked by an increase in humidity.(4) In Pliocene and Plio‐Pleistocene sediments, primary minerals are dominant, while smectite decreases. The glacial climate is responsible for this mineralogy. Detrital minerals would come from the erosion of Scandinavian moraines and from rafting by icebergs.
Wind sedimentation tunnel experiments on the origins of aeolian strata
Authors: FRYBERGER STEVEN G. , SCHENK CHRISTOPHER 
Published: June 2006

ABSTRACTThe origins and sedimentary features of grainfall‐, avalanche‐, and ripple‐produced strata have been studied experimentally in a wind sedimentation tunnel. Rate of deposition, wind velocity and wind duration have been shown to control specific sedimentary features of these types of strata.Grainfall‐produced strata were deposited on a horizontal surface, and surfaces sloping up to the angle of initial yield for dry sand (about 34°). Thickness of a grainfall‐produced stratum depended upon rate of deposition and duration of a specific wind event. Grainfall‐produced strata were both non‐graded and graded. Graded strata were produced by changes in wind velocity which controlled size of sand in transport and flying distances of individual grains. Distinctive features of grainfall‐produced strata are: (a) gradual thinning, or tapering downwind (e.g. down the simulated slipface and across the simulated interdune; (b) extreme variability of thickness from less than 1 mm (wind gusts of a few seconds) to 10 cm or more (sustained gusts).Aeolian avalanche‐produced strata were formed when grainfall‐produced strata steepened above the angle of initial yield and sheared downslope. A rapid transition in sedimentary features from top to bottom of the slipface characterized avalanche‐produced strata of the slump degeneration type in dry sand derived from grainfall deposition. Fadeout laminae formed near the top of the simulated slipface and about 1 m farther down the slipface were flame structures and drag folds. Near the base of the slipface, the avalanche truncated and then overrode grainfall‐produced deposits. Distinctive features of avalanche‐produced strata for a 2.5 m long slipface are the deformation structures, a thickness of 1 or 2 cm, sandflow toes, and steep dip (34°). Each avalanche‐produced stratum was roughly tabular in cross‐section parallel to wind direction, with gradual pinchout upslope.Aeolian ripple‐produced strata were deposited on horizontal surfaces, and surfaces sloping to as much as 28°. Thickness of a ripple‐produced stratum depended upon rate of deposition, morphology of the ripple, and rate of ripple migration. A maximum thickness of several centimetres was observed for a single ripple‐produced stratum. Shape and attitude of ripple foresets was controlled by ripple morphology. Distinctive features of aeolian ripple‐produced strata are: (a) presence of ripple foresets; (b) abrupt changes in thickness of a stratum or pinchout over downwind distances of a few centimetres; (c) low average foreset‐to‐diastem angle (10–15°); (d) low ripple‐climb angle (<10°).
Transmission electron microscope study of quartz microstructures produced by aeolian bombardment
Authors: VEBLEN DAVID R. , KRINSLEY DAVID H. , THOMPSON MARK 
Published: June 2006

ABSTRACTThe near‐surface structure produced by laboratory aeolian bombardment of Brazilian quartz has been studied with transmission electron microscopy (TEM). Thin specimens of the abraded surface were prepared by a one‐sided ion etching technique, and control specimens of unabraded material were prepared by standard ion etching methods. The abraded sample exhibited a vastly larger number of defects than the unabraded specimen. The abraded sample contained areas with very little surface disruption, presumably where pieces of material up to several tens of microns in diameter had broken away. Other areas of the abraded surface were extremely disrupted, with open and closed microcracks spaced from a few tens of angstroms to a few microns apart. Electron diffraction indicated significant rotation among submicron blocks bounded by the fractures. These observations suggest that surface disruption occurs primarily by a mechanism involving brittle fracture, rather than plastic deformation.This study demonstrates the feasibility of studying the effects of abrasion on near‐surface structure with TEM. The degree and scale of fracturing also suggest a mechanism for forming submicron particles in quantity during aeolian abrasion.