bluuebunny/crossref_metadata_2025 huggingface dataset:
A trough cross‐stratified glaucarenite: a Cambrian tidal inlet accumulation
Authors: CHAFETZ H. S.
Published: June 2006

The upper part of the Riley Formation, Cambrian of central Texas, is primarily composed of a sequence of thoroughly trough cross‐stratified deposits. The dominant lithologies range from fossiliferous glaucarenite to highly glauconitic bio‐sparrudite. These cross‐stratified deposits accumulated within a tidal inlet and associated lagoonal tributary and distributary channels. Tidal inlet‐fill strata are underlain by shallow, open marine oosparites and biomicrites and are overlain by parallel bedded glaucarenites which accumulated as part of a barrier island complex. The parallel bedded deposits exhibit large scale, gently inclined strata, ripple cross‐stratification, and a minor amount of vertical burrows.

Some glaucarenite units within the tidal inlet‐fill have local concentrations of skeletal material, primarily trilobite carapaces. These concentrations are most abundant in the bottoms of troughs. Cementation by bladed to fibrous spar between the carapaces has resulted in the nodular appearance of these skeletal accumulations. Calcite clasts, with relict evaporite textures, occur within the carbonate nodules and surrounding glaucarenite. These clasts were eroded from the shallow subsurface of the barrier island as the tidal inlet migrated. The presence of the former evaporite clasts attest to an arid climate at the time of their formation.
A note on the estimation of sedimentation rates in the Gulf of Elat (= Gulf of Aqaba), by the use of Foraminifera
Authors: LARSEN ARNE ROSENKRANDS
Published: June 2006

Abundance fluctuations of Amphistegina in the upper 4–5 cm of a few small cores from the Gulf of Elat look somewhat like rainfall fluctuations in the hinterland. To correlate the two patterns, a sedimentation rate of 2.2–3.3 mm/year must be assumed. A similar rate is obtained from estimates of annual production of Amphistegina.
The use of slump structures as palaeoslope orientation estimators
Authors: WOODCOCK N. H.
Published: June 2006

The two main methods of estimating palaeoslope direction from slump structure orientation data are reviewed. The mean axis method takes the downslope direction as the perpendicular to the mean slump fold axis. The separation are method estimates the downslope direction by the bisector of a planar separation angle between groups of slump folds with opposite downplunge asymmetry. The advantages and disadvantages of each method are considered in detail, by reference first to idealized slump fold distributions and then to a compilation of sixty natural slump fold axis distributions, mostly from published data.

Among the advantages of the mean axis method are the ease of deriving confidence limits for estimates and its applicability where fold asymmetry data are unavailable. The main advantage of the separation are method is its validity for strongly skewed fold axis samples. The statistical robustness of the mean axis method, however, due to its reliance on average properties of data, makes it more generally reliable than the separation arc method which depends on extreme properties of data. A procedure for determining palaeoslope directions is suggested which reflects the respective strengths of the two methods.
Storm surge turbation
Authors: LINDSTRÖM MAURITS
Published: June 2006

Sand ridges along the coast of northern Brittany contain alternating beds of coarse and fine to medium sand 4–10 m above normal reach of highest spring tides. They were deposited in the Holocene, largely during the last centuries, by sand charged storm surges. Deformation structures at many levels in these beds have amplitudes of 2–25 cm. Fine‐grained beds were folded in a manner that suggests relative competency of transmitting horizontally directed stress. Coarse‐grained beds, by yielding, permitted folding to die out vertically. It is suggested that a transitional zone existed between the storm surge and the underlying sediment. This zone consisted of a mixture of water and sand. Deformation occurred at the moment movement in this zone was arrested. Comparison with published data on deformed bedding indicates that the described structures may be environment specific.
Patch or pinnacle reefs of Cretaceous age exposed on western margin of Dead Sea (Israel)
Authors: FRIEDMAN GERALD M. , ARKIN YAACOV , AHARONI E.
Published: June 2006

For a petroleum geologist knowledge of the density of the distribution of subsurface Cretaceous reefs is a matter of practical interest. Hence, the discovery in the Judean Desert of Israel, near the western margin of the Dead Sea, of an exhumed sea bottom below an erosional unconformity is of particular interest, because it reveals the original distribution of such reefs, and thus may provide a clue to their subsurface distribution. In this desert, newly described Turonian (Upper Cretaceous) reefs are the dominant geomorphic features, as in their original habitat on the Cretaceous sea bottom. These reefs can be traced on aerial photographs: they are generally 5‐15 m in diameter and 1‐2.5 m in vertical dimension. Generally, reefs occur within 100‐200 m of one another; in many places they are less than 50 m apart. The shapes of the patch or pinnacle reefs are almost circular, as are those occurring in the Edwards Limestone (Comanchean, Lower Cretaceous) in central Texas (Roberson, 1972).

The hard, resistant, ring‐like outer rims of these exposed reefs weather out as raised rims. A central depression within such structures consists, in places, of Senonian soft chalky or friable material that has been interpreted as a diagenetic product of the vadose zone. The massive reef core consists of porous dolomite. The flanking strata which dip away from the reef core at angles of approximately 15‐25° are composed of a probable original grainstone which has been diagenetically changed to a micritic fabric.
Errors in measuring uniform aeolian sand flow by means of an adjustable trap
Authors: JONES J. R. , WILLETTS B. B.
Published: June 2006

A vertical‐slot sand trap was constructed incorporating a device to adjust the freedom of flow through the trap. Using a dune‐sand of equivalent diameter 0.25 mm, measurements of sand transport were made with this flow so adjusted that no change of sand surface geometry detectable by eye occurred upstream of the trap; this was considered to be a correct procedure. Further measurements were taken with the flow through the trap deliberately set to be (a) more vigorous and (b) less vigorous than the correct setting. In the latter case very significant differences were observed in measured transport rates of sand compared with the ‘correct’measurements. The disparities are of interest because it is commonly assumed that sand grains have enough ‘penetration’to enter a slot trap freely despite a degree of stagnation upstream of it. This does not appear to be a prudent assumption and substantial errors may result from lack of attention to the provision of free air flow through the trap.
Sedimentation in the latest Messinian at Capo Rossello (Sicily)
Authors: CITA M. B. , COLOMBO L.
Published: June 2006

Ten samples from a Late Messinian section measured at Capo Rossello, a few hundred metres laterally from and stratigraphically immediately below the Miocene/ Pliocene boundary stratotype, have been investigated by various techniques: carbonate content, grain‐size analysis, loss on ignition, clay mineral composition, frequency of euryhaline ostracods. Two lithological sub‐units. with different palaeoenvironmental implications, are recognized. Both sub‐units were deposited after the termination of evaporitic conditions, and immediately after deposition of an ash fall tuff. The lower unit is the Congeria marl which yields the ‘lago‐mare’faunal assemblage, the autochthony of which is supported by biometrical analysis of Cyprides agrigentina, indicating brackish, shallow‐water conditions with Paratethyan affinities, and the upper, the Arenazzolo, a thin sandy unit indicating a higher energy environment whose duration is estimated at some thousand years. Marine faunas yielded by the Arenazzolo are interpreted as allochthonous. Sedimentary structures suggest a littoral setting at the edge of the lake, or a delta lobe.

The main environmental change occurs at the base of the immediately overlying Trubi Formation, where open marine conditions indicative of oceanic depths mark the termination of the Messinian salinity crisis.
Origin of authigenic carbonates in sediment from the deep Bering Sea
Authors: HEIN JAMES R. , O'NEIL JAMES R. , JONES MARJORIE G.
Published: June 2006

Forty beds of authigenic carbonate were identified from the deep Bering Sea in cores taken on Leg 19 of the Deep Sea Drilling Project. Carbonate minerals were mainly high‐magnesium calcite and protodolomite, less commonly siderite, rhodo‐chrosite, low‐magnesium calcite, and manganosiderite. Authigenic carbonates cement and replace diatom ooze, ash and bentonite beds, and, less commonly, clastic beds. Replacement zones are as much as 60 cm thick. Eighty‐five per cent of carbonate beds occurred below 400 m sub‐bottom depth and 70% in sediment older than 4 m.y. δ13C values averaged ‐17.200/00 PDB and δ18O ranged from 18.59 to 34–110/00SMOW. The carbon was derived from oxidation of organic matter under anaerobic conditions during bacterial reduction of sulphate, or from CO2 produced in concert with CH4 during degradation of organic matter. The cations (Ca, Mg, Fe, Mn) were derived from alteration of ash beds. In Bering Sea deposits, ash beds altered to smectite within about 3–5 m.y. Carbonate precipitated simultaneously at different stratigraphic levels within the 627–1057 m sections at temperatures of 7–85°C. No apparent calcite precursor of biogenic origin was found for these authigenic carbonates.
Multiple slump scars in the Tortonian type area (Piedmont Basin, northwestern Italy)
Authors: CLARI PIERANGELO , GHIBAUDO GUIDO
Published: June 2006

Multiple intraformational discordances, recognized in the Tortonian (Upper Miocene) type area, occur at the top of a shelf sequence, directly overlain by slope sediments. The discordances display smooth, concave upward lower surfaces and are covered by sediments identical to the surrounding strata. Inferred lateral extent of single discordances is 500–700 m. Thickness of sediments overlying the discordances ranges from 5 to 25 m. The intraformational discordances are interpreted as scars formed by downslope sliding of whole packets of strata. The slumps may have been triggered by tectonic oversteepening of shelf sediments due to tilting of the sea floor. The slump scars appear comparable in position and size to some small scale modern examples recorded on margins near the shelf‐break.
Authigenic weddellite in sediments from the Coral Sea Basin
Authors: LINGEN GERRIT J. VAN DER
Published: June 2006

Euhedral, tetragonal, dipyramidal crystals of weddellite, an authigenic calcium oxalate, occur in samples from the topmost core of Deep Sea Drilling Project Site 210 in the Coral Sea Basin. Opinions in the literature differ as to whether weddellite is formed in situ or during sample storage. Comparison of smear‐slides made of samples after a 4 year storage period with shipboard smear‐slides made immediately after core retrieval, indicates that weddellite was formed in situ. Possible further growth during storage is not obvious. The presence of many corroded crystals, and the absence of weddellite in deeper cores, suggest that weddellite is formed soon after deposition, but dissolves again in time and with increased burial, due to changing geochemical parameters.
Distributary channels, sand lobes, and mesotopography of Navy Submarine Fan, California Borderland, with applications to ancient fan sediments
Authors: NORMARK WILLIAM R. , PIPER D. J. W. , HESS GORDON R.
Published: June 2006

The deep‐tow instrument package of Scripps Institution of Oceanography provides a unique opportunity to delineate small‐scale features of a size comparable to those features usually described from ancient deep‐sea fan deposits. On Navy Fan, the deep‐tow side‐scanning sonar readily detected steep channel walls and steps and terraces within channels. The most striking features observed in side‐scan are large crescentic depressions commonly occurring in groups. These appear to be large scours or flutes carved by turbidity currents. Four distinct acoustic facies were mapped on the basis of qualitative assessment of reflectivity of 4 kHz reflection profiles. There is a distinct increase in depth of acoustic penetration, number of sub‐bottom reflectors, and reflector continuity from the upper fan‐valley to the lower fan. These changes are accompanied by a decrease in surface relief.

Navy Fan is made up of three active sectors. The active upper fan is dominated by a single channel with prominent levees that decrease in height downstream. The active mid‐fan region or suprafan is where sand is deposited. Well defined distributary channels with steps, terraces, and other mesotopography terminate in depositional lobes. Interchannel areas are rough, containing giant scours as well as other relief. The active lower fan accumulates mud and silt and is without resolvable surface morphology.

The morphological features seen on Navy Fan other than levees, interchannel areas, and lobes are principally erosional. The distributary channels are up to 0.5 km wide and 5–15 m deep. Such features, because of their large size and low relief, are rarely completely exposed or easily detectable in ancient rock sequences. Some flute‐shaped scours are larger than channels in cross section but many are 5‐30 m across and 1‐2 m deep. If observed in ancient rocks transverse to palaeo‐current direction, they would perhaps be indistinguishable from channels. Surface sediment distribution combined with fan morphology can be used to relate modern sediments to facies models for ancient fan sediments. Gravel and sand occur in the upper valley, massive sand beds in the mid‐fan distributary channels, classical complete Bouma sequences on depositional lobes, incomplete Bouma sequences (lacking division a) on the lower mid‐fan, and Bouma sequence with lenticular shape or other limited extent on mid‐fan interchannel areas and on levees.
Surface suspended matter off western Africa: relations of organic matter, skeletal debris and detrital minerals*
Authors: EMERY K.O. , HONJO SUSUMU
Published: June 2006

Components of suspended matter in surface waters between western Africa and the Mid‐Atlantic Ridge were removed by filtration and measured by scanning electron and optical microscopy. Skeletal debris from diatoms, dinoflagellates, and other plankton are most concentrated in Antarctic surface water and in regions of coastal upwelling. Detrital mineral grains are most concentrated in nearshore regions, from discharge of major rivers, erosion of sea cliffs, and deposition from offshore winds. Farther offshore are high concentrations of mineral grains brought by trade winds from deserts in both northern and southern Africa. The winds also bring freshwater diatoms and woody tissue. The remaining component on the filters is marine organic matter, mostly in thin films. These films trap skeletal debris and mineral grains. Presumably, animals that graze upon the films further concentrate the grains into faecal pellets whose rapid settling carries the grains into deeper waters and to the bottom. The films were found in all other areas of the world ocean from which surface samples were spot‐checked: off eastern Asia, off eastern North America, and the central Pacific. Thus they appear to be a major factor in marine sedimentation. In areas of upwelling off western Africa, the total suspended matter in surface waters averages about 0.1 mg/1 of filtrate, about five times that present in the open ocean. It consists of about 70% organic matter, 29.6% skeletal debris, and 0.4% mineral grains, in contrast with concentrations in the open ocean of 90%, 8% and 2%, respectively.
On the threshold of transport of sand‐sized sediment under the combined influence of unidirectional and oscillatory flow
Authors: HAMMOND T. M. , COLLINS M. B.
Published: June 2006

While the transport of sediment by unidirectional currents or by oscillatory (wave‐induced) currents has been investigated, very little attention has been paid to the problem of the threshold of transport under the two mechanisms combined. Studies were carried out using cohesionless sand‐sized (mean diameters: 142, 363, 771 and 1134 μm) quartz grains in a unidirectional flume, within which an oscillatory carriage had been installed. The experiments were carried out under unidirectional velocities ranging between 0 and 27 cm s‐1, combined with simulated wave‐induced currents (at periods of 5 and 15 s) ranging from 0 to 35 cm s‐1. The threshold of transport was assessed, by visual observation, using the Yalin Criterion for unidirectional flow. This criterion permitted critical conditions to be estimated subjectively by observation of incipient transport from the flat beds. The results indicated the dependence of the critical threshold velocity combination on grain size and wave period. Thresholds tend to increase with increasing grain size or decreasing period. The grain‐size dependence is predictable from existing empirical relationships for the separate mechanisms; statistical fluctuations in near‐bed stress (bursting) however, are invoked to explain the wave period dependence. The latter effect acts in a reverse manner for wave and current combinations than for waves alone. Graphs are presented, relating grain size to critical threshold velocity combinations, to aid in the sedimentological interpretation of field data.
Geological significance of Coorong dolomites
Authors: BORCH C. C. VON DER , LOCK D.
Published: June 2006

Microcrystalline dolomite and related carbonate minerals have been forming throughout the Quaternary in shallow ephemeral alkaline lakes on the coastal plain of the Coorong area in southern Australia. These Coorong dolomites differ significantly from sabkha‐type dolomites. They form in areas where evaporation rates during summer months exceed groundwater inflow rates to a series of alkaline lakes. This results in the lakes becoming desiccated during summer months. Brines resulting from this drying phase are then refluxed out of the system into seaward‐flowing groundwaters of an unconfined coastal aquifer. Dolomites and other fine‐grained carbonates remain behind, whilst saline and sulphate evaporite minerals are flushed out of the system. Progressive restriction by sedimentation in and around the Holocene coastal dolomite lakes results in an upward‐shoaling sedimentary cycle. Basal sediments which formed in a restricted marine environment pass upwards to lacustrine dolomites or magnesites exhibiting desiccation and groundwater resurgence structures such as mudcracks and teepees. The upper Proterozoic Skillogallee Dolomite Formation, an early rift basin unit of the Adelaide Supergroup, contains dolomites which show many of the features characteristic of the peculiar groundwater hydrology which plays an important role in Coorong dolomite genesis. These features include aphanitic dolomites which lack relict saline or sulphate evaporite minerals. The Skillogallee Dolomite Formation in some areas overlies an earlier dolomitic unit, informally named the Callanna Beds, typified by abundant pseudomorphs after sulphate minerals. Sabkha style dolomites characterizing the Callanna Beds are replaced up‐section by the Coorong‐type dolomite of the Skillogallee Dolomite Formation. This implies the development of an increasingly more active groundwater regime. The ultimate source and mode of concentration of the necessary Mg required to form both the modern and ancient dolomites remain imperfectly understood.
Particulate calcium carbonate in New England shelf waters: result of shell degradation and resuspension*
Authors: FITZGERALD M. G. , PARMENTER C. M. , MILLIMAN J. D.
Published: June 2006

Aragonite and calcite needles, 30–500 μm long, were found to be prominent visual components throughout the water column in some areas of the New England (northeastern U.S.A.) continental shelf during winter months. Further investigation showed these‘needles’to be laths derived from the degradation of mollusc shells which were resuspended from bottom sediments during winter storms. Such degradation and subsequent transport/dissolution of carbonate particles may help explain why the terrigenous 'starved’shelf sediments off New England contain such small amounts of calcium carbonate.
A small cliff‐bound estuarine environment: Sandyhaven Pill in South Wales
Authors: KING C. J. H.
Published: June 2006

Sandyhaven Pill is a ‘drowned valley’ type of estuary. Thus the deposits differ from most other described estuarine deposits which are of ‘tidally influenced river’ type. The surface sediments may be divided broadly into wave‐dominated deposits (22% of area), tide‐dominated deposits (65%), deposits related to marginal cliff collapse (12%) and river‐dominated deposits (1%). Further subdivision shows that the subenvironments are nested in a progression up the estuary with trends to finer sediment size, reduced sorting and increased biogenic activity. The latter relates to a marine to estuarine faunal change and a strong relationship between the distributions of biota and depositional subenvironments. Over a 29 day period, reduction in wave height was reflected in wave‐dominated areas by shoreward movement of some subenvironment boundaries and by improved definition of symmetrical ripples. The tidal cycle had only a limited effect on the tide‐dominated sediments. The most reliable indicators of estuary trend are channels and asymmetrical ripples; but coring shows that ripples and other minor structures are rarely preserved. Heavy mineral analysis indicates that most of the estuarine sand came from offshore. Gradual sediment build‐up will result in a regressive sequence. If this were preserved under a later transgression, the resultant deposit would be an elongate sediment body bounded laterally by a coarse marginal facies. The sediment sequence would be inward and upward fining with diachronous facies boundaries sloping upwards towards the offshore end and towards the axis of the body.
Flows above oscillatory ripples
Authors: HONJI H. , KANEKO A. , MATSUNAGA N.
Published: June 2006

The flows above ripples of glass beads and ripple models have been visualized in an oscillatory water tunnel. Some ripples were observed to form without flow separation. Two types of vortices, the standing vortices without flow separation and the separation vortices have been observed, and their similarity is discussed.
Little known but important papers on grain‐size analysis
Authors: SOCCI ANTHONY , TANNER W. F.
Published: June 2006

Some important papers have apparently gone unnoticed by most sedimentologists, as shown by their absence from bibliographies of recent texts. These papers concern sample size, permissible number of splits, sieving time, and sieve‐vs‐settling tube comparisons. These papers were published where sedimentologists would not ordinarily see them, but should be required reading for students.
The shape of rock particles, a critical review
Authors: BARRETT P. J.
Published: June 2006

An attempt was made to distinguish aspects of the shape of rock particles, and to discover by analysis and empirical considerations the most appropriate parameters for describing these aspects. The shape of a rock particle can be expressed in terms of three independent properties: form (overall shape), roundness (large‐scale smoothness) and surface texture. These form a three‐tiered hierarchy of observational scale, and of response to geological processes. Form can be represented by only two independent measures from the three orthogonal axes normally measured. Of the four pairs of independent measures commonly used for bivariate plots, the two sphericity/shape factor pairs appear to be more efficient discriminators than simple axial ratios. Of the two, the most desirable pair is the maximum projection sphericity and oblate‐prolate index for both measures show an arithmetic normal distribution for the range investigated. A measure of form that is independent of the three orthogonal axes, and measures derived from them, is the angularity measure of Lees. Roundness has measures of three types, those estimating average roundness of corners, those based on the sharpest corner, and a measure of convexity in the particle outline. Although each type measures a different aspect, they are not independent of each other. Only roundness from corners is considered in detail. As neither average nor sharpest corner measures are inherently more objective or more quantitative, purpose should determine which is more appropriate. Of the visual comparison charts for average roundness, Krumbein's appears best. The Modified Wentworth roundness is the most satisfactory for estimating roundness from the sharpest corner. The Cailleux Roundness index should not be used because it includes aspects of roundness and form. Shape is a difficult parameter to use for solving sedimentological problems. Even the best of the commonly used procedures are limited by observational subjectivity and a low discriminating power. Unambiguous interpretation of particle shape in terms of source material and processes will always be made difficult by the large number of natural variables and their interactions. For ancient sediments satisfactory results can be expected only from carefully planned studies or rather unusual geological situations.
Large transverse bedforms and the character of boundary‐layers in shallow‐water environments
Authors: ALLEN J. R. L.
Published: June 2006

Theoretical work, laboratory studies, and field observations indicate that the oscillatory boundary layers generated by the tidal wave differ fundamentally in dynamics and kinematic structure from the unidirectional boundary layers of rivers. Unique to the former are mass‐transport currents attributable to: (1) the wave motion itself, and (2) bed curvature in the presence of the oscillatory flow. The implication of this difference for bed‐material transport is that the larger flow‐transverse bedforms of shallow‐water environments are divisible hydraulically between two major classes: (A) those related to tidal conditions, under which the fluid reverses in direction of flow with each reversal of the tide, permitting the initiation and maintenance of bed features by the spatially reversing, curvature‐related mass transport, and (B) those related strictly to rivers and river‐like flows, in which the fluid motion is unidirectional, and therefore the only mechanisms available for bedform initiation and maintenance are those creating a finite spatial lag between the transport rate and the bed waviness. Forms of Class B are best called dunes and bars, and only those attributable to Class A should be termed sand waves. The latter, restricted to oscillatory boundary layers of tidal origin, apparently correspond to the very much smaller; but also commonly symmetrical, ripple marks produced in wind‐wave oscillatory boundary layers.
Rhythms in deep sea, fine‐grained turbidite and debris‐flow sequences, Middle Ordovician, eastern Tennessee
Authors: SHANMUGAM GANAPATHY
Published: June 2006

Rhythms in fine‐grained sediments have not previously been studied because of their complex depositional cycles and diagenetic changes. Examination of nearly 9000 layers in outcrops, polished slab samples, and thin sections has led to recognition of rhythms in the Middle Ordovician Whitesburg, Blockhouse, and Sevier formations of east Tennessee. Rhythms have been described in four orders based on relative magnitude. First order cycles (basin‐fill sequences, hundreds of metres thick)are composed of thinning upward debris‐flow sequences and thickening upward turbiditic shale sequences. Second order cycles (multiple sedimentation units, tens of centimetres thick) consist of: (1) thinning upward cycles; (2) symmetrical cycles; (3) thickening upward cycles; (4) minor multiple cycles; (5) uniform cycles; and (6) dubious cycles. Third order cycles (single sedimentation unit, tens of millimetres thick) have thinning upward and asymmetrical cycles. Fourth order portrays the grain‐size variations within a single layer of the third order. First order rhythms were controlled by tectonism and progradation of a deep‐sea fan system. Second and third order rhythms were controlled by depositional processes, bottom topography, and sediment source. Depositional processes, sediment source, and bioturbation were the dominant controlling factors in the fourth order. A deep‐sea fan model is proposed for the fine‐grained turbidites in which channels and lobes coexist in the lower fan. The lower fan/mid fan boundary is marked by the presence of a channel cycle near the top of a lobe sequence. The basin plain/lower fan boundary is suggested by the appearance of minor lobe cycles over the non‐cyclic basin plain sequence.
A modification of Burger's phi‐normal approximation for the moments of grain‐size data
Authors: BEAUDOIN YVES
Published: June 2006

This paper gives a modification of Burger's method of approximation for the moments of grain‐size data. It is shown that formal integration can be carried out in conjunction with Burger's phi‐normal interpolation scheme. This approach obviates Burger's recourse to a discrete numerical integration procedure because exact integration yields a computationally more efficient approximation formula for the moments.
The resuspension of underwater sediment by rain
Authors: GREEN T. , HOUK D.
Published: June 2006

The rain‐induced resuspension of bottom sediment in shallow water is measured in a simple laboratory experiment, and found to increase significantly with increasing drop size and rain intensity, and decreasing water depth.
Calcrete profiles in the Eyam Limestone (Carboniferous) of Derbyshire: petrology and regional significance
Authors: ADAMS A. E.
Published: June 2006

Calcrete profiles (caliche) have been recognized in the Eyam Limestone from the Lower Carboniferous in the area around Monyash, Derbyshire. They occur at the top of the flank facies surrounding carbonate‐mud buildups (‘knoll reefs’). Four units make up the complete profile. These are from base to top: (1) grain‐supported sediment with rhizocretions, (2) matrix‐supported sediment with alveolar texture, (3) pelleted calcrete, (4) laminar calcrete. Commonly one or more units are missing from the profile. Calcretes indicate subaerial exposure. The carbonate buildups of the Eyam Limestone were completely exposed soon after deposition, requiring a fall in sea‐level probably in excess of 10 m. This discovery demands a review of previous regional palaeoenvironmental studies.
Clay mineral distribution patterns as influenced by depositional processes in the Southeastern Levantine Sea
Authors: MALDONADO ANDRÉS , STANLEY DANIEL JEAN
Published: June 2006

Analysis of the clay minerals in stratigraphically defined cores (23,000 years BP to the present) in the southeastern Levantine‐Nile Cone sector of the eastern Mediterranean indicates that depositional processes are very significant in determining the distribution of clay assemblages. The interplay of long‐distance transport by water mass circulation, downslope mass gravity transport and wind dispersal is recorded by the clay assemblages in each of the stratigraphic layers. The temporal variations and spatial distribution of smectite, the dominant clay mineral of the River Nile, can be related closely to downslope gravity‐related processes and to deposition from water mass flow. Increased kaolinite, in part of wind‐blown origin from North Africa, correlates with areas receiving low terrigenous input but influenced by enhanced suspended sediment transport. Illite and chlorite distributions are most closely associated with a northern Levantine provenance and dispersal by the circulation of eastern Mediterranean water masses. Climatically induced changes may have altered the clay minerals in the region and minor diagenetic changes may have occurred, but these factors do not fully explain observed vertical clay mineral changes in the Late Quaternary. We conclude that palaeoclimatic interpretations based on vertical clay mineralogical changes at single core localities should be approached cautiously in small ocean basins such as the Mediterranean.
Bed shear stress over subaqueous dunes, and the transition to upper‐stage plane beds
Authors: BRIDGE JOHN S.
Published: June 2006

Plane beds that replace small bedforms (e.g. ripples) on the backs of subaqueous dunes are dynamically similar to upper‐stage plane beds. Local bed shear stresses at the position on dunes where plane beds develop may be two to three times larger than on a completely plane bed under the same general hydraulic conditions. These observations help explain the transition from dunes to a wholly upper‐stage plane bed.
Mineralogy of arc‐derived sediment: siliciclastic sediment on the insular shelf of Puerto Rico
Authors: BREYER JOHN A. , EHLMANN ARTHUR J.
Published: June 2006

Siliciclastic sediments on the insular shelf of Puerto Rico are derived from a volcanic arc. The sands are feldspatholithic and subquartzose. They confirm predictions about sandstones of arc derivation in the following ways. The quartz content is low, usually less than 25 %. Feldspar is more abundant than quartz, but less so than lithic fragments. If mud rip‐up clasts are excluded from the lithic suite, the ratio V/L (volcanic lithic grains to total unstable lithic grains) assumes values near 0.75. Most of the volcanic lithic grains have textures suggesting intermediate volcanics as source rocks. Ratios of plagioclase to total feldspar are high. Values of the parameter C/Q (stable lithic fragments to total lithic grains) are higher than expected for sandstones of volcanic provenance.

Four compositionally and areally distinct assemblages of clay minerals are recognized. Clay suites characterized by major concentrations of both halloysite and smectite are found off the north‐west coast. Sediments off the north‐central and north‐east coasts contain major concentrations of halloysite and lesser amounts of smectite, illite and chlorite. Major concentrations of kaolinite are present off the south‐east coast. An assemblage of poorly crystallized smectite with lesser amounts of illite and chlorite occurs off the south‐west and south‐central coasts. Variation in the mineralogic composition of clays around the perimeter of the island reflects changes in the intensity of chemical weathering and the type of rock exposed in the immediate source area and, in instances, either early diagenetic alteration or, more likely, sorting within the clay fraction by currents on the shelf.
Origin and diagenetic evolution of Ca–Mg–Fe carbonates in some coalfields of Japan
Authors: MATSUMOTO RYO , IIJIMA AZUMA
Published: June 2006

Carbonate concretions, lenses and bands in the Pleistocene, Palaeogene and Upper Triassic coalfields of Japan consist of various carbonate minerals with varied chemical compositions. Authigenic carbonates in freshwater sediments are siderite > calcite > ankerite > dolomite >> ferroan magnesite; in brackish water to marine sediments in the coal measures, calcite > dolomite > ankerite > siderite >> ferroan magnesite; and in the overlying marine deposits, calcite > dolomite >> siderite. Most carbonates were formed progressively during burial within a range of depths between the sediment‐water interface and approximately 3 km. The mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial. Based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies, three diagenetic stages of carbonates are proposed. Carbonates formed during Stage I (< 500 m) strongly reflect the initial sedimentary facies, e.g. low Ca‐Mg siderite in freshwater sediments which are initially rich in iron derived from lateritic soil on the nearby landmass, and Mg calcite and dolomite in brackish‐marine sediments whose pore waters abound in Ca2+ and Mg2+ originating in seawater and calcareous shells. Carbonates formed during Stage II (500–2000 m) include high Ca‐Mg siderite, ankerite, Fe dolomite and Fe–Mg calcite in freshwater sediments. The assemblage of Stage II carbonates in brackish‐marine sediments in the coal measures is similar to that in freshwater sediments. This suggests similar diagenetic environments owing to an effective migration and mixing of pore water due to the compaction of host sediments. Carbonates formed during Stage III (> 2000 m) are Fe calcite and extremely high Ca‐Mg siderite; the latter is exclusively in marine mudstones. The supply of Ca is partly from the alteration of silicates in the sediments at elevated burial temperatures. After uplift, calcite with low Mg content precipitates from percolating groundwater and fills extensional cracks.
Geochemistry and mineralogy of marine and non‐marine Namurian black shales from the Tansley Borehole, Derbyshire
Authors: SPEARS D. A. , AMIN M. A.
Published: June 2006

The Namurian black shales studied have a good palaeontological control. Pyrite, illite and organic matter are higher in the marine shales, and siderite and kaolinite are higher in the non‐marine shales. The distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity. The same control could account for the observed clay‐mineral distribution by differential flocculation. The major element geochemistry closely reflects the above mineral variation. Mn and Zr are higher in the non‐marine shales due to siderite and zircon respectively. Co, Cr, Rb, Y and Ba are not significantly different and a detrital source, mainly clay minerals, is suggested. In the marine shales the elements Pb, Cu, V, Ni, Sr and Zn are significantly higher. Using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated. The present element locations are thought, from correlation analysis, to be pyrite and organic matter. By analogy with experimental work and modern environments, the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors. The element enrichment cannot be related directly to seawater concentrations, unlike some black shales, and the accumulation rates for Pb and Cu are thought to be unusually high.
Diagenesis of aragonite from Upper Cretaceous ammonites: a geochemical case‐study
Authors: BUCHARDT BJØRN , WEINER STEPHEN
Published: June 2006

Shell aragonite from ammonites collected in the Upper Cretaceous of West Greenland was investigated by means of macroscopic/microscopic visual evaluation, analyses of calcite/aragonite ratios, carbon and oxygen isotopic compositions and Sr and Mg concentrations of shell carbonate and of amino acid compositions of organic matrices. The results are:

(1) Material visually classified as well preserved may have suffered diagenetic modifications of mineralogical and chemical composition. (2) Of the chemical and mineralogical parameters studied, amino acid composition, calcite/aragonite ratios and magnesium concentrations were found to be most sensitive to post‐depositional modifications, while oxygen isotope composition and strontium concentrations showed detectable diagenetic modifications only after more pronounced alterations. (3) Based on the Mg/Ca ratios and calcite concentrations of the shell aragonite, a diagenetic classification has been proposed grouping the material into well preserved, moderately preserved and poorly preserved. (4) The chemical and mineralogical composition of the best preserved material suggests that the Upper Cretaceous ammonites had a shell composition similar to that of modern Nautilus and other aragonite‐shelled molluscs.
Nepheloid and suspended particulate matter in south‐eastern Lake Michigan*
Authors: CHAMBERS RICHARD L. , EADIE BRIAN J.
Published: June 2006

A persistent benthic nepheloid layer with high total suspended matter (TSM) and high total particulate surface area was observed in south‐eastern Lake Michigan. The layer thickens from a few metres near the shelf‐slope boundary to greater than 10 m at the base of the slope. When compared to the hypolimnion, TSM increases by a factor of 2‐20 at 1 m above the bottom, the greatest increase detected at the slope‐basin boundary. Sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom, suggesting that a large fraction of the collected material came from resuspension. A nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period, apparently through the action of weak but persistent currents. This layer is supplemented by lakeward transport of fine particles resuspended near the shelf‐slope boundary due to impingement of the thermocline on the bottom, or during higher energy events.
The effects of soluble salts on the threshold shear velocity of fine sand
Authors: NICKLING W. G. , ECCLESTONE M.
Published: June 2006

Wind tunnel tests were carried out to investigate the effects of two soluble salts (NaCl and KCI) on the threshold shear velocity of a well‐sorted, fine sand. A sensitive laser monitoring system was used to detect initial grain motion during the tests. Results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement‐like bonds formed between grains that tend to hold individual particles in place. However, with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity. This is indicated by increased scatter of data on the threshold shear velocity‐surface salt concentration plots for both NaCl and KCl. Although data scatter is evident, significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case.
Distribution, morphology, and origin of sedimentary furrows in cohesive sediments, Southampton Water
Authors: FLOOD ROGER D.
Published: June 2006

Patches of sedimentary furrows are developed at several locations in the cohesive estuarine sediments of Southampton Water (water depth 1–12 m). These furrows apparently result from short periods of erosion followed by long periods of deposition. Although all the furrows are similar, regularly spaced, parallel troughs, 0.5–15 m wide aligned with the dominant current, furrows in different patches have different characteristics. In some areas furrow width is 1/5–1/15 of furrow spacing (termed ‘narrow’), whereas in other areas furrow width is about 1/2 of the spacing (termed ‘wide’). Narrow furrows have developed where sediment accumulation rates are greater than 3–6 cm yr−1; wide furrows where accumulation rates are lower. Cockle shells, and other coarse sediments, concentrated on the furrow floors and on floors of smaller (2–10 cm wide) minifurrows, play an important role in furrow formation and evolution as they act to widen the furrows when mobilized during current episodes. Uniform sedimentation across the profile during slack periods tends to narrow the furrow. Some of the larger furrows have remained in the same position for 12 years, while mini‐furrows have duration scales of a few months or less. Well‐developed furrows are also found in a recently dredged channel. Bedforms similar to those described here may be preserved in the sedimentary record. While no analogues to the larger furrows are presently known, minifurrows may be morphologically similar to the ‘gutter casts’ described from ancient rocks.
Carbonate ramp‐to‐deeper shale shelf transitions of an Upper Cambrian intrashelf basin, Nolichucky Formation, Southwest Virginia Appalachians
Authors: MARKELLO J. R. , READ J. F.
Published: June 2006

The Nolichucky Formation (0–300 m thick) formed on the Cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton. Lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp.

Peritidal facies of the regional shelf are cyclic, upward‐shallowing stromatolitic carbonates. These grade toward the intrashelf basin into shallow ramp, cross‐bedded, ooid and oncolitic, intraclast grain‐stones that pass downslope into deeper ramp, subwave base, ribbon carbonates and thin limestone conglomerate. Ribbon limestones are layers and lenses of trilobite packstone, parallel and wave‐ripple‐laminated, quartzose calcisiltite, and lime mudstone arranged in storm‐generated, fining upward sequences (1–5 cm thick) that may be burrowed. Shallow basin facies are storm generated, upward coarsening and upward fining sequences of green, calcareous shale with open marine biota; parallel to hummocky laminated calcareous siltstone; and intraformational flat pebble conglomerate. There are also rare debris‐flow paraconglomerate (10–60 cm thick) and shaly packstone/wackestone with trace fossils, glauconite horizons and erosional surfaces/hardgrounds. A 15‐m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin.

Understanding the Nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the Lower Palaeozoic elsewhere. The study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation. Finally, recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks, whose trends may be unrelated to regional shelf‐edge trends.
Relationships between lithology and diagenesis in a limeston—marl facies transition: an electron microprobe study
Authors: REECKMANN SARAH ANNE
Published: June 2006

A 3 km long lateral facies transition from Oligo‐Miocene skeletal grainstones into packstones and mudstones displays systematic variation in carbonate skeletal fragment alteration and secondary carbonate mineral composition.

Within the skeletal grainstone end‐member all aragonitic grains have dissolved, all Mg‐calcite skeletal fragments have altered to calcite, and calcite has been precipitated as both void‐filling spar and as syntaxial overgrowths on echinoid fragments. Within the transitional grainstone‐packstone lithologies some skeletal fragments show preservation of their original mineralogy, while calcite, ferroan calcite spar and dolomite have precipitated in void spaces. Within the packstone‐mudstone end‐member of the transition, aragonitic grains have been preserved and Mg‐calcite skeletal fragments have retained most of their magnesium. Thin, originally porous grainstone layers within the pack‐stone‐mudstones contain sideroplesite and ferroan calcite spar in void spaces, and iron has been incorporated in skeletal fragments which were originally Mg‐calcite. In these grains iron has been incorporated at the expense of magnesium until the grains approach the composition of the surrounding ferroan calcite cement.

The lateral variation in diagenetic alteration across this facies transition is a function of differing groundwater movement and composition, controlled ultimately by the composition, porosity and permeability of the host lithologies.
Fossil remnants of up‐turned debris bands in Pleistocene glacial deposits of Poland
Authors: RUSZCZYŃSKA‐SZENAJCH HANNA
Published: June 2006

Fossil remnants of up‐turned debris‐rich bands of glacial ice are recorded from three localities in the Polish Lowlands. In each case the fossil debris bands occur in proximal parts of hills built of glacitectonically disturbed sediments. The characteristics of these remnants and of the associated deposits and structures are described, and they are compared to present‐day examples from Spitsbergen.