bluuebunny/crossref_metadata_2025 huggingface dataset:
Terminal settling velocity of commonly occurring sand grains
Authors: HALLERMEIER ROBERT J.
Published: June 2006

Published measurements of terminal settling velocity for commonly occurring sands are used to develop three equations which join into a single segmented curve of dimensionless form. Results are noticeably different from those for spheres of similar diameter, and permit calculation of the settling velocity for usual sand grains without specification of exact grain shape. For quartz in water, the three equations of different settling regimes correspond approximately to: very fine sand; fine to coarse sand; and very coarse sand.
New evidence of scroll‐bar formation on the Beatton River
Authors: NANSON GERALD C.
Published: June 2006

In recent work, two hypotheses were proposed to explain the formation of distinct scroll bars and subsequent floodplain ridges on the Beatton River. These hypotheses are reassessed here in the light of recent field observations, which suggest that an initial scroll bar may form around a stranded dead tree that acts as a sedimentation nucleus on a point‐bar platform.
Sediment dispersal and palaeohydraulics of Oligocene rivers in the eastern Ebro Basin
Authors: ALLEN PHILIP , MANGE‐RAJETZKY MARIA
Published: June 2006

Mapping of heavy mineral associations and diagnostic accessories in Oligocene sediments of the eastern Ebro Basin has revealed two major provinces and several sub‐provinces. The Pyrenean Province is characterized by an apatite‐tourmaline‐garnet association with diagnostic staurolite in the west (western Pyrenean Sub‐Province) and micaceous composite grains plus chloritoid in the east (eastern Pyrenean Sub‐Province). The Catalanides Province is characterized by an ultrastable angular brown tourmaline‐staurolite association with kyanite in the south‐west (Montsant Sub‐Province), faceted garnets and rounded tourmalines in an intermediate position (St Miquel del Montclar Sub‐Province) and in the north‐east rounded and green tourmalines admixed with clinopyroxene, apatite and micas derived from the Pyrenees (Montserrat Sub‐Province).

Palaeodischarges have been estimated from 30 channels distributed throughout both major provinces. A gradual decrease in river discharge through Oligocene times is indicated for the rivers of Catalanides parentage, although the discharges of high‐sinuosity streams alone remain uniform. This decrease through time of Catalanides drainage competitiveness is reflected in the greater areal extent of the Pyrenean petrological province together with a progressive displacement south or south‐eastwards of basinal lacustrine facies. The increasing dominance of Pyrenean drainage during the Oligocene may be due to more prolonged tectonic activity in the Pyrenees compared to the more quiescent Catalanides.
The initiation of sedimentary furrows by standing internal waves
Authors: DYER K. R.
Published: June 2006

Longitudinal helical vortices are generally considered to be the cause of longitudinal sedimentary bedforms. In tidal oscillatory flows, however, it is not clear how a regular system of vortices will become fixed for long enough to establish the bedforms.

It is proposed that the presence of standing internal waves, with axes parallel to the tidal current, have provided the basic flow pattern on which longitudinal helical vortices develop in Southampton Water. The observed furrows then developed in a pattern determined by the standing internal waves.
Temporal and spatial variation in intertidal sedimentation rates
Authors: CARLING P. A.
Published: June 2006

Sediment deposition and erosion rates are reported for an intertidal zone in the Burry Inlet, South Wales.

Measured deposition rates over the salt marsh are compared with deposition rates calculated from observed suspended sediment concentrations. Notably, it is concluded that residual turbulence at slack water should not be discounted when calculating deposition rates.

Grain‐size distributions of suspended sediments over the marsh surface, during flood and ebb tides, contrast with the grain‐size distribution of deposited marsh sediments, the latter being significantly coarser. These data in conjunction with mass budget calculations are used to relate total annual deposition and sediment supply by tidal action during settled meteorological periods. The analysis suggests that episodic storm‐induced sediment transport is probably an important mechanism for introducing coarse sediment on to the marsh surface.

Finally, it is noted that seasonal reworking of the sandy non‐cohesive sediments may be related to variations in the intensity of wave‐breaking throughout the year.
Bedform climbing in theory and nature
Authors: RUBIN DAVID M. , HUNTER RALPH E.
Published: June 2006

Where bedforms migrate during deposition, they move upward (climb) with respect to the generalized sediment surface. Sediment deposited on each lee slope and not eroded during the passage of a following trough is left behind as a cross‐stratified bed. Because sediment is thus transferred from bedforms to underlying strata, bedforms must decrease in cross‐sectional area or in number, or both, unless sediment lost from bedforms during deposition is replaced with sediment transported from outside the depositional area. Where sediment is transported solely by downcurrent migration of two‐dimensional bedforms, the mean thickness of cross‐stratified beds is equal to the decrease in bedform cross‐sectional area divided by the migration distance over which that size decrease occurs; where bedforms migrate more than one spacing while depositing cross‐strata, bed thickness is only a fraction of bedform height.

Equations that describe this depositional process explain the downcurrent decrease in size of tidal sand waves in St Andrew Bay, Florida, and the downwind decrease in size of transverse aeolian dunes on the Oregon coast. Using the same concepts, dunes that deposited the Navajo, De Chelly, and Entrada Sandstones are calculated to have had mean heights between several tens and several hundreds of metres.
Quantitative relationships between numbers of fluvial cycles, bulk lithological composition and net subsidence in a Scottish Namurian basin
Authors: READ WILLIAM A. , DEAN J. MICHAEL
Published: June 2006

This detailed quantitative basin analysis of fluvial deposits in a subsiding Namurian structural basin is aimed at discovering underlying statistical relationships between numbers of fluvial cycles, bulk lithological composition and net subsidence which could be used as a background to future sophisticated computer simulation experiments and would also facilitate comparison with other ancient basins. The succession studied lies between two widespread marine bands, one of Arnsbergian (E2) and one of Kinderscoutian (R1) age, and is dominated by upward‐fining cycles: 94% of the semi‐cycles containing sand, here termed grain‐size cycles, are upward‐fining and the ratio of fine members (mudstone+siltstone) to coarse members ranges from 0·23 to 5·0.

Trend‐surface analysis reveals basement structures, which influenced sedimentation, including a Caledonoid graben. Correlation coefficient values and results of principal component analysis demonstrate that the numbers of rooty horizons and grain‐size cycles, together with the total thicknesses of sandstone and of mudstone+siltstone, all tend significantly towards a linear relationship with the total thickness of strata and hence net subsidence. The average thickness of grain‐size cycles tends towards an inverse linear relationship with net subsidence. This probably reflects the presence of stacked, relatively thin, channel‐fills within persistent channel belts. These belts tend to be localized in the areas of greatest subsidence within the basin and follow courses basically similar to channels already discovered in the underlying deltaic sediments. The highest concentrations of mudstone+siltstone tend to lie on the flanks of the basin, but high local sand concentrations found at points on the margin where channels entered the basin from the NW and NE and left to the SW, effectively disrupt any significant relationship between net subsidence and the proportion of sand.

Coal has been selectively preserved on the flanks of the basin and the number of rooty horizons is greatest in an area of low subsidence which lay somewhat remote from the main channel belts.
Some effects of compaction and geological time on the pore parameters of argillaceous rocks
Authors: BORST ROGER L.
Published: June 2006

Graphical statistics have been applied to the pore‐size distribution curves of argillaceous rocks to characterize the changes in pore parameters that result from compaction and geological time. The most striking characteristic of recently deposited sediment is the high variability in mean pore size and in the sorting and skewness of the pore system. The mean pore size ranges from 15 to 980 nm, sorting ranges from very well sorted to poorly sorted, and skewness varies from systems in which small pores predominate over large ones to systems in which large pores predominate. This high variability in pore structure represents the many environmental and mineral‐related variables that affect the pore system of newly deposited sediment.

The mean pore size of shales decreases with increasing compaction and approaches a limiting value of about 3·5 nm at depth. Within a geological time span of 50 m.y. and/or depth of burial of about 1200 m, most sediments have reached an irreversible, well sorted pore‐size distribution. Early diagenetic processes apparently affect the skewness of pore systems more than compaction, such that within about 50 m.y. the pore system is negatively skewed, with small pores predominating over large.

Sediments buried to a depth of 500 m or less exhibit a porosity range of 40‐‐85%; below 500 m, porosity decreases linearly with burial depth. No correlation exists between the surface area of shale pore systems and depth of burial, geological age, and the pore parameters mean pore size, sorting, and skewness.
Sedimentation in the Conway Trough, a deep near‐shore marine basin at the junction of the Alpine transform and Hikurangi subduction plate boundary, New Zealand
Authors: CARTER L. , CARTER R.M. , GRIGGS G.B
Published: June 2006

The Conway Trough is a 40 km × 10 km, 1000 m deep, rectangular, tectonically controlled sedimentary basin situated on an active plate boundary. The basin lies at the junction of the Alpine transform and Hikurangi subduction sectors of the Indo‐Australian/Pacific plate boundary. It is incised into Cainozoic sedimentary rocks and contains a thick fill of late Neogene sediment.

Study of the continental shelf near the Conway Trough indicates: (1) that transport mechanisms operate in a net north‐easterly direction, and (2) that the neritic sediment drift system is confined to within a few kilometres of the shoreface, with the result that (3) large areas of the shelf south of the trough comprise bare bedrock, or relict late Pleistocene sediment. Despite reaching to within 3 km of shore, the Conway Trough receives little modern bedload sediment, as indicated by a paucity of sand fill. However, the trough has intercepted some Holocene bedload, since the main channel contains redeposited graded gravel and sand with a C‐14 age of 4670 yr. Satellite imagery and piston cores reveal that abundant mud is provided to the trough, much of it from river sources up to 200 km to the south. Some of this sediment is inferred to move by turbid layer transport through Conway Trough and out via Kaikoura Canyon into nearby Hikurangi Trough. Nonetheless, sedimentation rates in the Conway Trough may be as high as 1‐7 m (1000 yr) 1.

The Conway Trough forms a modern example of a transform basin, varying Neogene examples of which are found widely in north‐eastern South Island. Sedimentation models are constructed to compare transform and transduction basins, particularly with respect to the effects of Pleistocene sea‐level changes.
Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland
Authors: PRATT BRIAN R. , JAMES NOEL P.
Published: June 2006

Bioherms are common in the St George Group, a sequence of shallow‐water carbonate rocks deposited on the western continental shelf of Iapetus Ocean. They range from small heads and metre‐sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent. The cores of these bioherms are principally composed of thrombolites (unlaminated, branching, columnar stromatolites), structures quite distinct from laminated stromatolites which are common in intertidal beds. Associated with thrombolites is a diverse fauna of burrowing invertebrates, trilobites, nautiloids, pelmatozoans, brachiopods, gastropods, rostroconchs and archaeoscyphiid sponges.

On the basis of framework‐building components, three main bioherm types are distinguished: (1) thrombolite mounds, (2) thrombolite‐Lichenariaor ‐sponge mounds and (3) thrombolite‐Lichenaria‐Renalcisreef complexes. The framework of the last is the most complex, with abundant cavities and a demonstrably uneven growth surface of thrombolites, corals and free‐standingRenalcisheads, walls and roofs. Some cavities were active sediment conduits while others were protected, their roofs draped withRenalcisand their walls coated by cryptalgal laminites.

These bioherms possess the attributes of shallow‐water ecologic reefs. They span a critical time gap in the development of reefs, the transition period from algal‐dominated bioherms of the Precambrian and Cambrian to the metazoan‐dominated bioherms of the Middle Ordovician and remaining Phanerozoic.
The use of settling velocity in defining the initiation of motion of heavy mineral grains, under unidirectional flow
Authors: COLLINS M. B. , RIGLER J. K.
Published: June 2006

The results of critical threshold experiments on four commonly occurring heavy minerals are described. The data are presented, in conjunction with comparable quartz data, using the non‐dimensional Shields’ Curve and the Movability Number (U*/ws). The results indicate that critical shear stress for material of high density is overestimated by use of Shields’ Curve, under smooth boundary conditions. Grain settling velocity is found to be a good indicator for the critical shear stress for grains of a wide density range. A physical explanation for the results is proposed.
Distribution of chlorite and kaolinite in eastern Atlantic sediments off North Africa
Authors: LANGE HEINZ
Published: June 2006

Chlorite in the Atlantic sediments is predominantly derived from the Atlas Mountains, kaolinite originates in the southern Sahara and Sahel zone. These minerals may be used to reconstruct the tracks of two superimposed wind systems (Trade Winds and Harmattan Wind). A modified method for determining relative abundances of chlorite and kaolinite is presented.
Oncolites from lacustrine sediments in the Cretaceous of north‐eastern Spain
Authors: FREEMAN TOM , ROSELL JUAN , OBRADOR ANTONIO
Published: June 2006

Compact micritic oncolites up to 8 cm in maximum diameter occur within Maestrichtian (Upper Cretaceous) Garumniense continental marls of Sierra del Montsec (Lerida Province) of north‐eastern Spain. Synsedimentary development is documented by patches of terrigenous quartz that occur among oncolitic protuberances. Soluble nuclei (limestone fragments and bivalves) further suggest an origin through accretion, rather than that of soil pisolite. Similarities between the petrography and isotopic compositions of the oncolites and those of interbedded Garumniense limestones suggest similar sedimentary origins. However, these lacustrine oncolites, like modern counterparts described by others, probably developed through in situ metabolic precipitation of calcium carbonate. Evidence of this origin is their high degree of concentricity, which is unlikely to have developed through sedimentary accretion, inasmuch as the oncolites ‘float’ in quiet‐water marls.
Experimental investigation of silt formation by static breakage processes: the effect of temperature, moisture and salt on quartz dune sand and granitic regolith
Authors: PYE K. , SPERLING C. H. B.
Published: June 2006

ABSTRACT Weathering simulations carried out using a climatic cabinet have demonstrated that diurnal temperature and humidity variations typical of those occurring in warm desert environments are ineffective in causing static breakage of quartz dune sand and polymineralic regolith sand grains. Wetting and drying combined with temperature variations was also found to be a relatively ineffective weathering process. These results suggest that ‘crack tip’ processes are insignificant where mineral grains are not subject to static loading. Sodium sulphate weathering was found to cause slight damage to quartz dune sand grains and major damage to first cycle regolith grains. Feldspars and mica in the regolith sands were more susceptible to salt action than quartz. Salt weathering of the regolith sands produced substantial quantities of silt in the size range typically found in natural loess deposits.
Sedimentation in a deep glacier‐fed lake—Lake Tekapo, New Zealand
Authors: PICKRILL R. A. , IRWIN J.
Published: June 2006

ABSTRACT Surface sediments, cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in Lake Tekapo. Sedimentation is dominated by the Godley River which forms an extensive delta in the northern third of the lake. Delta growth accounts for 55% of annual sediment deposition. In winter sandy muds are deposited at the top of the delta slope, where they may move under gravity as a surficial slide. Oversteepening of the upper slope also generates deep seated failures. The entire 20 km2 of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment. Down the delta slope sedimentation rates decrease, surface sediments get finer and varves become better developed.

In the lake basin sediments are parallel bedded varves, which contain typical winter‐summer annual cycles as well as minor, non‐annual flood varves. Annual varve thickness and semi‐annual varve frequency are determined by variations in the discharge of the Godley River. Sedimentation in the basin accounts for 40% of the budget and sedimentation rates decrease with distance from the delta, except at the distal end of the basin, where turbid underflows are stopped by the rising lake floor. Beyond the basin, sedimentation rates decrease abruptly. Coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore. The remaining 5% of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement, which occasionally slumps to the basin floor.
Interpretation of moment measures derived from water‐lain sediments
Authors: SLY P. G. , THOMAS R. L. , PELLETIER B. R.
Published: June 2006

ABSTRACT Although mean size provides a useful value for characterizing sediments, it is an inadequate expression of the interaction between sediments and hydraulic regimes and many authors have explored the significance of other statistical moment measures in different parts of the particle size spectrum. Few publications, however, have described such relationships over a very wide range of particle sizes. Using a combined data base (of marine and lacustrine sediments) we have been able to demonstrate the following:

The distributions of standard deviation (and entropy) values are repeated in similar form on either side of the sand size class, describing mixtures between sands and gravel and sands and clay.

Skewness is modified by the hydraulic response of the sediment and a skewness divide is present at about 2.7 φ, where it coincides with the minimum shear velocity required to initiate particle motion. This divide may be used to distinguish between high and low energy regimes.

Kurtosis, like standard deviation, is a measure of the mixing of end member populations but it is more sensitive to changes in the tails of distribution curves. The maximum positive peak of kurtosis, at about 2.5 φ, lies close to the skewness divide (in our data).

By using skewness/kurtosis plots it is possible to define separate field distribution for sediments which, to a greater or lesser degree, appear to conform to hydraulic equilibrium.

By using sediments which are close to equilibrium (and lie at or close to our skewness/kurtosis boundary curves, it should be possible to define hydraulic shear velocities, at the time of formation. Values may be established by empirical relationships or by defining the break‐point (traction and intermittent suspension) between linear components of individual sample φ size/probability distribution plots. Such relationships should be enhanced by using hydraulic equivalent diameters instead of sieve diameters.

In fine sediments, the use of fractional (silt: clay) ratios offers sensitivity at a level comparable to that of skewness/kurtosis plots and may be more easily computed.
Lithofacies types and vertical profile models; an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences
Authors: EYLES NICHOLAS , EYLES CAROLYN H. , MIALL ANDREW D.
Published: June 2006

ABSTRACT Increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills. These are based to a large degree on theoretical considerations of likely depositional processes. The classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in Quaternary and Pre‐Quaternary successions. This situation is compounded in many Quaternary terrains by the continued description of ‘tills’ in terms of laboratory‐derived analytical data only, reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment. Detailed sedimentological logging of lithofacies is rarely undertaken. There is thus considerable confusion as to what is being described or sampled when analytical data are presented for many Pleistocene ‘tills’. The same remarks apply to Pre‐Pleistocene ‘tillites’.

A lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites; the term‘till’is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice. Use of a four part code, in conjunction with codes already published for fluvial sediments, allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work. The value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late Pleistocene glacigenic sequence at Scarborough Bluffs, Ontario.
Experiments on the production of transverse grain alignment in a sheared dispersion
Authors: REES A. I.
Published: June 2006

ABSTRACT A series of experiments was designed to investigate grain orientation in flows with concentrations of granular solids in the range from 0.5 to 15%. Fourteen experiments were carried out in which sand‐sized material was dispersed in liquid plaster of paris and the dispersion allowed to flow down a slope until it came to rest. The preferred orientation of the grains was then estimated by measuring the anisotropy of magnetic susceptibility of specimens cut from the solidified flows.

Five of the experiments showed signs of deformation, both in the gross characteristics of the flow and in the grain alignment. The remaining nine had grain alignment dependent on grain concentration. At concentrations of 1.2% and less and 11.1% and more, by volume, alignment of long axes was parallel to flow. These observations were consistent with the existing theories for low concentrations, in which preferred alignment is shown to result from the varying rate of rotation of grains in a shearing flow, and for high concentrations, in which preferred alignment results from the transfer of angular momentum between colliding grains.

At some intermediate concentrations transverse alignment was observed. A theoretical explanation combining the theories of the extreme cases is suggested. The observation of transverse alignment is compared with a similar observation in some turbidites.
Chalcedonic quartz and occurrence of quartzine (length‐slow chalcedony) in pelagic sediments
Authors: KEENE J. B.
Published: June 2006

ABSTRACT Chalcedony is the most abundant form of quartz in silicified pelagic sediments from the North Pacific. Varieties of chalcedonic quartz present in chert of deep‐sea origin include chalcedony (length‐fast and zebraic), quartzine (length‐slow), and lutecite.

These occurrences of quartzine in known pelagic sediments emphasize the dangers of using quartzine as an indicator of former evaporitic environments. Quartzine is a diagenetic mineral and does indicate pore fluids rich in sulphate and magnesium. In pelagic sediments, it is always associated with authigenic barite and in many cases with authigenic dolomite. Quartzine should not be used, by itself, as an indicator of any particular environment of deposition.
On the dynamics of sediment suspension by residual Reynolds stresses—confirmation of Bagnold's theory
Authors: LEEDER M. R.
Published: June 2006

ABSTRACT Bagnold's dynamic theory for sediment suspension requires that the immersed weight of suspended grains over unit bed area is supported by an upward‐directed residual Reynolds stress, τyy, arising from asymmetrical shear turbulence. The present paper presents an analysis of previously published turbulence data which confirms the existence of this residual stress and indicates its generation in the lowermost part of the buffer layer of turbulent shear flows. The magnitude of τyy is estimated as about 0.3τyx. Calculations from experimental data on suspended fine sand transport over upper phase beds reveals that τyy, is in approximate equilibrium with the weight stress due to the suspended load.
Turbidite depositional patterns and flow characteristics, Navy Submarine Fan, California Borderland
Authors: PIPER DAVID J. W. , NORMARK WILLIAM R.
Published: June 2006

The late Pleistocene and Holocene stratigraphy of Navy Fan is mapped in detail from more than 100 cores. Thirteen 14C dates of plant detritus and of organic‐rich mud beds show that a marked change in sediment supply from sandy to muddy turbidites occurred between 9000 and 12,000 years ago. They also confirm the correlation of several individual depositional units. The sediment dispersal pattern is primarily controlled by basin configuration and fan morphology, particularly the geometry of distributary channels, which show abrupt 60° bends related to the Pleistocene history of lobe progradation. The Holocene turbidity currents are depositing on, and modifying only slightly, a relict Pleistocene morphology.

The uppermost turbidite is a thin sand to mud bed on the upper‐fan valley levées and on parts of the mid‐fan. Most of its sediment volume is in a mud bed on the lower fan and basin plain downslope from a sharp bend in the mid‐fan distributary system. Little sediment occurs farther downstream within this distributary system. It appears that most of the turbidity current overtopped the levée at the channel bend, a process referred to as flow stripping. The muddy upper part of the flow continued straight down to the basin plain. The residual more sandy base of the flow in the distributary channel was not thick enough to maintain itself as gradient decreased and the channel opened out on to the mid‐fan lobe.

Flow stripping may occur in any turbidity current that is thick relative to channel depth and that flows in a channel with sharp bends. Where thick sandy currents are stripped, levée and mid‐fan erosion may occur, but the residual current in the channel will lose much of its power and deposit rapidly. In thick muddy currents, progressive overflow of mud will cause less declaration of the residual channelised current. Thus both size and sand‐to‐mud ratio of turbidity currents feeding a fan are important factors controlling morphologic features and depositional areas on fans. The size‐frequency variation for different types of turbidity currents is estimated from the literature and related to the evolution of fan morphology.
Interaction of the Western Boundary Undercurrent with the continental margin off Newfoundland
Authors: CARTER LIONEL , SCHAFER CHARLES T.
Published: June 2006

Sedimentation on the Newfoundland rise is strongly influenced by the Western Boundary Undercurrent (WBU). The upper rise (2600‐2800 m) is swept by a rapid (Ū= 8·5 cm sec−1), south‐flowing core of the WBU which has generated a sandy contourite facies characterized by coarse gravelly, sandy sediments; current‐induced bedforms such as scour moats, lineations and lee drifts; ferro‐manganese‐stained gravel clasts; a high proportion of broken foraminiferal tests and a diagnostic benthic foraminiferal assemblage. The overlying nepheloid layer, when compared to adjacent waters, is thickest (800 m), most sediment laden (80 μg 1−1), contains the highest proportion of terrigenous sediment and exhibits the best developed bottom mixed layer (∼ 15 m thick). Comparisons with earlier data from the same area imply the dimensions and sediment load of the nepheloid layer vary with time. Empirical considerations, based on near‐bottom current meter records from Labrador and Newfoundland, suggest the WBU is capable of transporting bedload with threshold friction velocities (u*) of around 0·87‐1·14 cm sec−1 for between 1 and 15% of the time. The prevailing transport direction is southwards along the rise, but this may be punctuated periodically by brief incursions to the north.

The erosional regime of the upper rise is bordered by a regime of fine‐grained deposition typified by muddy contourites. Both the lower slope and lower rise are mantled by bioturbated muds, the former zone having terrigenous mud and the latter, biogenic calcareous mud. The accompanying nepheloid layer is thin, biogenic‐rich and devoid of an identifiable mixed layer.
Post‐glacial seismic stratigraphy, central Great Barrier Reef, Australia
Authors: JOHNSON D. P. , SEARLE D. E.
Published: June 2006

A regional programme of continuous seismic (boomer) profiling in the central Great Barrier Reef Province has identified a widespread shallow seismic discontinuity (reflector A) which is interpreted as the pre‐Holocene surface.

Nine seismic facies units are distinguished primarily on the basis of the seismic records, but also with the aid of additional criteria such as location and surface sediment types. Two units underlie reflector A and are pre‐Holocene. These units are interpreted as: (a) Permo‐Carboniferous bedrock, and (b) Pleistocene/? Tertiary sediments, consisting of both shelf‐wide terrigenous units, and carbonate mounds and platforms under present reefs. Seven units are post‐glacial and overlie reflector A. These units are interpreted as: (c) fluvial/estuarine channel fill, (d) relict delta‐front deposits, (e) relict transgressive veneer, (f) coastal coarse and (g) fine deposits, (h) modern reef and (i) reef talus.

In general post‐glacial sediment cover is very thin and in many places on the mid‐shelf the pre‐Holocene units crop out. Substantial post‐glacial accumulations are limited to protected coastal embayments and to offshore reef masses.
‘SLABBER’: a useful device for subsampling box cores
Authors: BENGGIO BRADFORD L. , NELSEN TERRY A.
Published: June 2006

ABSTRACT

The ‘SLABBER’, a plexiglass device designed for subsampling box cores, was used at sea with excellent results. The SLABBER allowed visual inspection of any existing sedimentary features, and also provided storage, when necessary for subsamples. When the features were present, X‐radiography of the SLABBER subsamples clearly showed sediment layering, evidence of bioturbation and orientation of shell material, all with apparent minimal disturbance of these structures.
Geomorphic evolution and stratigraphy of Price and Capers Inlets, South Carolina
Authors: TYE ROBERT S.
Published: June 2006

A three‐dimensional model for a tidal inlet‐barrier island depositional system was constructed through examination of 37 vibracores and 10 auger drill holes on Capers and Dewees Islands, South Carolina. Two cycles of southerly inlet migration and subsequent abandonment resulted in beach ridge truncation on the northern ends of both barriers. Historical evidence indicates that these tidal inlets migrated 1.5 km to the south owing to a dominant north‐south longshore transport direction. The hydraulic inefficiency of these over‐extended inlet channels caused shorter, more northerly‐oriented channels to breach through the ebbtidal deltas. After inlet reorientation, large wave‐formed swash bars migrated landward closing former inlet channels. Weakened tidal currents through the abandoned channels permitted clay plugs to form thick impermeable seals over active channel‐fill sand and shell.

Price and Capers Inlets formed during the onset of the Holocene transgression following submergence of the ancestral Plio‐Pleistocene Santee River drainage system. Coarse, poorly sorted inlet‐deposited sand disconformably overlies Pleistocene estuarine clay and is capped by a dense clay plug. Shoreline reorientation and landward retreat of a primary barrier island chain occurred between the first and second cycles of inlet‐channel migration and abandonment. Beach ridges prograded seaward over the first inlet sequence. A second cycle of inlet migration truncated the northernmost portion of these beach ridges and scoured into the clay plug of the earlier inlet deposit. Abandonment of this channel resulted in deposition of a second abandoned inlet‐channel clay plug. Abandoned tidal inlet channels exhibit U‐shaped strike and crescentic‐ to wedge‐shaped dip geometries. Basal, poorly sorted inlet sands are sealed beneath impermeable, abandoned‐channel silt and clay, washover deposits, and salt marsh. Multiple episodes of inlet migration and abandonment during a rising sea‐level deposited stacked inlet‐fill sequences within the barrier islands.

The resultant stratigraphy consists of interlayered, fining‐upward, active inlet‐fill sand overlain by thicker abandoned inlet‐fill clay plugs. These clay plugs form impermeable zones between adjacent barrier island sand bodies. Shoreline transgression would remove the uppermost barrier island deposits, sealing the inlet‐fill sequences between Pleistocene estuarine clay and shoreface to shelf silt and clay.
Organic films on particulate matter in surface waters off eastern Asia
Authors: EMERY K. O. , JOHNS IAN A. , HONJO SUSUMU
Published: June 2006

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.
Lateritization and ground water alteration phenomena in the Triassic Budra Formation, south‐western Sinai
Authors: GOLDBERY R. , BEYTH M.
Published: June 2006

Field and laboratory investigations of the Triassic Budra Formation of Wadi Budra, south‐west Sinai, have demonstrated the existence of surface pedogenic laterites developed within‘overbank facies’of fluviatile sediments during times of hiatus. The laterite profiles, up to 7 m thick, comprise a zone of high‐iron concentrations (21.47–73.17%) which includes a concretionary unit and either overlies a zone of slightly mottled host rock or rests directly upon unaltered sandstone; a pallid zone is noticeably absent. The primary depositional horizontal fabric of the finely laminated sediments of the‘overbank facies’ has strongly influenced the final fabric of the laterite. The pronounced alternations of iron‐rich pisolitic and iron‐deficient laminae highlight the influence of inherent fabric (primary bedding) on pedogenesis. The micromorphology of the laterites is characterized by bimasepic plasmic fabrics, abundant elongate voids partially infilled with cryptocrystalline kaolinite and an abundance of randomly oriented skew planes. Illuviation of clay minerals to considerable depths is evident. Sesquioxidic and kaolinitic glaebules, concentrated within the concretionary units of the laterite have a flattened ellipsoidal shape and occur as both massive and concentrically structural varieties.

At Gebel Mussaba Salama to the north, zoned iron mineralization occurs at various levels within the fluviatile sandstones which underlie the‘overbank facies’. This is interpreted as being a non‐pedogenic, ground water alteration phenomenon induced by a rising water table within the buried alluvial channels. Iron mineralization, probably records minor fluctuations of the water table during standstill periods.

Lateritization in the Triassic Budra Formation provides important evidence that the widely recorded late Triassic lateritization and bauxitization event of the neighbouring East Mediterranean countries, extended south to the continental areas bordering the Tethyan Ocean.
Sedimentology of the Minette oolitic ironstones of Luxembourg and Lorraine: a Jurassic subtidal sandwave complex
Authors: TEYSSEN T. A. L.
Published: June 2006

The oolitic ironstones of the Minette were deposited during Toarcian/Aalenian times in a nearshore environment of the Paris Basin. The sedimentary sequence comprises up to 13 coarsening upward depositional cycles. The development of the cycles and different facies types are described. The iron ooids accumulated in a subtidal environment under the effects of tidal currents. Sand waves, which form an important part of the Minette sediments, were deposited under both time‐velocity symmetrical and time‐velocity asymmetrical tides. From the study of their internal structures the time‐velocity patterns of the currents, current speeds (up to 0±9m s−1) and net transport rates have been estimated (29 g m−1 s−1 in the case of large‐scale sand waves controlled by time‐velocity symmetrical tides). Sand wave heights and calculated near‐bed current speeds suggest a mesotidal regime. Sedimentary facies include large‐scale and waves, subtidal shoals with channels and an offshore muddy shelf. Conclusions as to bathymetry are drawn from ichnofaunal associations and from the study of wave ripple marks. Finally a depositional model of the Minette iron formation is proposed which may be applicable to other oolitic ironstones.
A regressive coastal sequence from the Upper Eocene of Hampshire, southern England
Authors: PLINT A. G.
Published: June 2006

The Lower Headon and Upper Barton Beds of Hampshire, southern England, consist of fine sands, silts and clays, often fossiliferous, with lignitic and carbonate horizons. They accumulated in a coastal environment following deposition of the marine Lower and Middle Barton Beds. A variety of distinctive facies can be defined on faunal and lithological grounds, and these permit palaeoenvironments to be defined with some precision. Littoral marine, barrier island shoreface, storm washover and barrier flat, brackish lagoon, distributary channel and floodplain lake environments are recognized. The evidence suggests that a barrier island or spit developed offshore, enclosing a sheltered inshore region of lagoons in which deposition of relatively fine‐grained sediments took place. Lagoonal sediments show a general trend towards reduction of salinity with time. With the eventual exclusion of marine influence, the area underwent a gradual transition to river‐dominated sedimentation in shallow flood‐plain lakes. While the sequence as a whole shows a progressive reduction in salinity, several brief periods of increased salinity are recognized and these reflect the very low topography of the region and its susceptibility to marine incursion.
Bedload stresses and sediment transport theory—a correction
Authors: LEEDER MICHAEL R.
Published: June 2006

A previous proposal (Leeder, 1977) to test the magnitude of the solid‐transmitted stresses due to bedload transport failed to confirm Bagnold's theory because the applied fluid stress contribution was not corrected for sidewall drag. Once this correction is made there is a reasonable correspondence of theory and experiment.
Variations in wind velocity and sand transport on the windward flanks of desert sand dunes
Authors: LANCASTER N.
Published: June 2006

The magnitudes of increases in wind velocity, or speed‐up factors, have been measured on the windward flanks of transverse and linear dunes of varying height. On transverse dunes, velocity speed‐up varied with dune shape and height. For linear dunes, speed‐up factors varied principally with wind direction relative to the dune, with dune shape and dune height. The main effect of velocity speed‐up on the windward flanks of dunes is to increase potential sand transport rates considerably in crestal areas. This is greatest for large dunes, with winds of moderate velocity blowing at a large angle to the dune. Changing ratios of base to crest sand‐transport rates on transverse dunes tend to reduce dune steepness as overall wind velocities increase. On linear dunes, the tendency for crestal lowering is counteracted by deposition in this area when winds reverse in a bi‐directional wind regime.
Platform and off‐platform carbonates of the Upper Cambrian of western Maryland, U.S.A.
Authors: DEMICCO ROBERT V.
Published: June 2006

Upper Cambrian carbonates in western Maryland are comprised of platform facies (Conococheague Limestone) west of South Mountain and basin facies (Frederick Limestone) east of South Mountain. Conocheague platform carbonates contain interbedded non‐cyclic and cyclic facies. Non‐cyclic facies consist of cross‐stratified grainstones, thrombolitic bioherms, and graded, thin‐bedded dolostones. These were deposited in shallow, subtidal shelf lagoons. Cyclic facies are composed of repeated sequences of cross‐stratified grainstone; ribbon‐rock; wavy, prism‐cracked laminite; and planar laminated dolostone. The cyclic facies are shallowing‐upward cycles produced by lateral progradation of tidal flats over shallow, nearshore subtidal environments. Cyclic and non‐cyclic facies are interbedded in the Conococheague in a layer cake fashion, but no higher‐order cyclicity can be found.

The Frederick Limestone is dominated by monotonously thick sequences of graded, thin‐bedded limestones, interbedded with massive peloidal grainstones and beds of breccia up to 10 m thick in the lower Frederick. The breccias contain transported megaclasts of Epiphyton‐Girvanella boundstones. The basal Frederick was deposited in a slope‐to‐basinal setting east of a rimmed shelf. An Epiphyton‐Girvanella marginal reef along the shelf edge was the source of the blocks in the breccias. The upper Frederick Limestone formed on a carbonate ramp.
Characteristics of two Pleistocene channel‐fill deposits and their implication on the interpretation of megasequences in ancient sediments
Authors: LAJOIE JEAN , ST‐ONGE DENIS A.
Published: June 2006

Two Pleistocene channel fills located in two different geological settings, on Guadeloupe in the lesser Antilles and along the Coppermine River in the Northwest Territories of Canada, have different clast compositions, scale, and origin of fragmentation but have similar depositional characteristics. Massive bedding or absence of structures caused by traction, sharp non‐erosive contacts, reverse coarse‐tail grading, matrix‐supported clasts together indicate a debris‐flow mechanism in which mixtures of fine and coarse sediments moved downslope by laminar flow. Field evidence suggests subaqueous deposition for both deposits. Both bed thickness (BTh)/maximum grain size (MGS) ratios and correlations appear characteristic of subaqueous masses capable of flowing on slopes less than 1°.

The two channel fills have random BTh and MGS variations, they do not thin and fine up‐section. It is suggested that fills originating from laminar mass transport could normally have random BTh and MGS up‐section variations. In flysch and volcaniclastic sequences, where coarse sediments interpreted as laminar flow deposits are common, up‐section BTh and MGS variations may result from processes related to source, slope, and flow characteristics rather than from the environment in which the sediments accumulate (channel).
Seasonal succession and microlamina formation in a meromictic lake displaying varved sediments
Authors: DICKMAN MIKE
Published: June 2006

In a small meromictic lake near Toronto, Canada, a mass mortality of photosynthetic bacteria followed the ventilation of the chemocline during fall (autumn) and resulted in 3–8 g m‐2 day‐1 of organic matter being deposited as a dark layer in sediment traps which were suspended in the permanently anaerobic zone. This mass mortality of photosynthetic bacteria occurred in late autumn following the annual thermal destratification of the lake's mixolimnion. Wind mixing during this period of homeothermy resulted in the introduction of low levels of dissolved oxygen into the lake's chemocline. The ensuing mass mortality of photosynthetic bacteria resulted in the release of elemental sulphur as the sulphur‐rich bacteria decomposed and sank to the bottom of the lake. The ferrous ions in the water below a depth of 15 m in Crawford Lake reacted with this sulphur to form black ferrous sulphides and pyrite which formed a dark microlamina on the lake floor. Each dark microlamina was overlain by a light coloured (calcite‐rich) layer which was deposited each spring and summer during the 3 yr period of this study.

The mechanism of microlamina formation elucidated here has been based on the examination of bi‐weekly sediment trap information. This approach has permitted an explanation of the mechanisms by which specific events such as calcite precipitation and phytoplankton seasonal succession are transcribed into the sediment record.