bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrothermal origin of Late Proterozoic bedded chert at Gusui, Guangdong, China: petrological and geochemical evidence
Authors: ZHOU YONGZHANG , CHOWN E. H. , GUHA JAYANTA , LU HUANGZHANG , TU GUANGZHI
Published: June 2006

The Late Proterozoic bedded chert from Gusui in Guangdong Province, southern China, is characterized by bedded, laminated, massive and pseudobrecciated structures. The chert is depleted in TiO2, Al2O3 and most trace elements. However, it is enriched in Ba, As, Sb, Hg, and Se. In Al‐Fe‐Mn ternary diagrams, it falls into the ‘hydrothermal field’. Factor analysis shows that many elements show up in the principal trace element factor suggesting their enrichment results from leaching of the country rock by hydrothermal solutions. The chert has low REE concentrations and displays an REE pattern consistent with a hydrothermal origin. It may have formed in a Late Proterozoic rift or extension zone developed within the Yunkai continental margin back‐arc basin, with a fault system linking it to an unknown heat source at depth.
Field experiments of aeolian dust accumulation on rock fragment substrata
Authors: GOOSSENS DIRK
Published: June 2006

The effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long‐term field experiment in the Negev desert of Israel. Four parameters were studied: pebble eccentricity, pebble size, pebble flattening and cover density. The effect of these parameters on the accumulation of dust on the pebbles, on the accumulation of dust between and underneath the pebbles, and on total dust accumulation (pebbles+interpebble space) was measured separately. Accumulation on the pebbles increased as the pebbles became larger, less flattened and more elongated, and as cover density increased. Accumulation between and underneath the pebbles increased as the pebbles became smaller, more flattened and more elongated, and as cover density increased (although the accumulation area available became smaller). Total dust accumulation increased as the pebbles became smaller, more flattened and more elongated, and as cover density increased.

Rock fragments act as a dust trap as dust accumulation on pebble‐covered surfaces is several tens of times larger than dust accumulation on similar but pebble‐free surfaces. However, less than 20% of the initially settled dust is protected from further erosion.

In the Negev desert, dust erosion by wind is of the order of 10 times larger than dust erosion by water. The rate of long‐term dust accumulation in the Negev is of the order of 15–30 g.m−2.yr−1. This is considerably lower than the rates proposed elsewhere in the literature, which are based upon over optimistic dust retainment percentages.
Sedimentary dynamics and evolutionary history of a Late Carboniferous Gondwanic lake in north‐western Argentina
Authors: BUATOIS LUIS ALBERTO , MANGANO MARIA GABRIELA
Published: June 2006

Lacustrine deposits are well represented in the lower part of the Late Carboniferous Agua Colorada Formation in the north‐west Sierra de Narváez, Catamarca Province, Argentina. Lake Narváez was one of the several water bodies formed in the region immediately after the Gondwana glaciation.

The lacustrine transport system has been divided into three distinct zones: delta, shallow lake and deep lake. Delta progradation proceeded from the ESE. Coarse‐grained delta plain and turbidite delta front deposits suggest that the delta was formed close to the headwaters (‘short‐headed stream delta’type). During periods of high discharge, river mouths acted as bypass zones and fine and very fine sands were transported further into the lake by underflow currents. The clastic material supplied by the deltaic system was partially reworked by wave action. Sands accumulated in unstable conditions at the upper delta front as a consequence of delta progradation. As a result of the addition of clastics in the steep delta front, turbidity currents were formed, spreading their load along the lower delta slope. Deep lacustrine deposits are typically stacked, forming two different kinds of progradational turbidite lobe sequences. Type I lobes were formed in a basinal setting and were probably detached from their feeder systems as a result of sediment‐bypassing in a shallow lake during periods of low lake level. These turbidite lobes are replaced upwards by type II lobes, which were formed on the delta slope during periods of lake level rise that allowed the onset of delta progradation. The presence of highly deformed sandstone bodies suggests rapid depositional rates in a high slope setting, whereas the occurrence of hummocky cross‐stratified sandstones indicates wave reworking of the sands initially emplaced by turbidity currents. Therefore, the inner part of type II lobes was formed above storm wave base. The depositional history of Lake Narváez can be traced through four evolutionary stages: lake transgression, formation of type I lobes, formation of type II lobes and delta progradation. Tectonic activity was probably important at the early stage of lake evolution, but the subsequent depositional history was mainly controlled by fluctuations of lake level.
Carbonate pond deposits related to semi‐arid alluvial systems: examples from the Tertiary Madrid Basin, Spain
Authors: SANZ M. E. , ZARZA A. M. ALONSO , CALVO J. P.
Published: June 2006

Carbonate pond deposits occur associated with alluvial sediments in Miocene sequences of the Madrid Basin, central Spain. The ponds developed near the basin margins, either in floodplain environments (north) or mud‐flat settings (south). Three main facies assemblages are recognized: (1) floodplain/mud‐flat, (2) palaeosols and (3) pond deposits.

In the northern part of the basin, ponds developed on the floodplain of terminal fluvial systems. The floodplain facies are typically red mudstones with interbedded sandstones and siltstones. Palaeosols associated with the ponds show a pedofacies relationship, the maturity of soils increasing with distance from the main channel. Carbonate pond deposits consist mainly of limestones, which display typical ‘palustrine’features. The formation and further accumulation of carbonate in the ponds took place in periods of reduced clastic sediment input and it is suggested that recharge into the pond areas was mainly from groundwater.

In the south, ponds developed on mud‐flats located between sheet‐flood‐dominated alluvial fans and evaporite lakes. Mud‐flat facies consist of red mudstone that exhibits evidence of progressive soil development near both edges and beneath the carbonate pond lenses. Carbonate in the ponds is mainly dolomite and comprises two subfacies, mottled and laminated dolomicrites. This mineralogy, together with the presence of gypsum crusts below and in the lower part of the carbonate body, suggests higher evaporation rates and/or more saline waters filling the ponds in this part of the basin.

In spite of differences in depositional setting and, to some extent, climatic conditions between the two areas of the basin, both facies associations and the sequential arrangement of the ponds show strong similarities that allow the proposal of a facies model for carbonate pond deposits related to semi‐arid alluvial systems. The sequences recognized from the pond deposits record a set of facies clearly different to those forming in swampy lakes associated with many permanent fluvial systems developed in more humid climates.
Two hundred million years of karst history, Dachstein Limestone, Hungary
Authors: JUHÁSZ E. , KORPÁS L. , BALOG A.
Published: June 2006

Platform carbonates of the Upper Triassic Dachstein Limestone in Naszály Hill have been karstified extensively over the past 200 million years. They provide an excellent example of polyphase karstic diagenesis that is probably typical of many subaerially exposed carbonate sequences.

Seven karstic phases are recognized in the area, each of which include polyphase karstic events. The first karst phase was associated with the Löfer cycles. Meteoric waters caused dissolution; enlarged fractures and cavities, were filled by marine and/or vadose silts and cement.

The second karst phase was caused by local tectonic movements. Bedding‐plane‐controlled phreatic caves were formed, and filled by silts.

The third karst phase lasted from the end of the Triassic to the Eocene. This was a regional, multiphase karstic event related to younger composite unconformities. Bauxitic fill is the most characteristic product of this phase. The karst terrain reached its mature or senile stage with very little porosity.

Narrow veins and floating rafts of white calcite marks karst phase 4, which resulted from hydrothermal activity associated with Palaeogene magmatism. The early Rupelian phase of Alpine uplift caused large‐scale rejuvenation of the former karst terrain (karst phase 5). Subsequently Naszály Hill was buried as an area of juvenile karst with significant porosity. A second period of hydrothermal activity in the area (karst phase 6) was induced by Miocene volcanism, which resulted in wide, pale green calcite veins. Finally karst phase 7 was of tectonic origin. Following the most recent, Miocene uplift of the Naszály Hill, the carbonates have again become the site of vadose karst development.
Facies architecture and sequentiality of nearshore and ‘shelf’sandbodies; Haystack Mountains Formation, Wyoming, USA
Authors: MELLERE DONATELLA , STEEL RONALD J.
Published: June 2006

The Haystack Mountains Formation (Campanian, Mesaverde Group, US Western Interior Basin, Wyoming) contains a series of shallow‐marine sandbodies, extending tens of kilometres out from a basin margin. The study succession (around 200 m thick) is composed of eight major sandstone tongues (Bolten Ranch, O'Brien Spring, Seminoe 1–2–3–4, Hatfield 1 and 2 members), each partially encased within marine shale intervals. The Formation is ‘sequential’at several scales. At the largest scale, the whole succession presents an aggradational to basinward‐stepping stacking pattern of the sandstone tongues. At a lower level, each tongue (member) is characterized internally by two different types of lithosome: the first represents shoreface progradation with hummocky cross‐strata passing up to swaley and trough cross‐stratified sandstones. This lithosome is erosively truncated at its top in most cases, and has a general sheet‐like geometry along strike, whereas down dip it displays a series of sharp‐bounded clinothems. The latter sometimes indicate a downward as well as a basinward shift through time, as suggested by the occurrence of coarser and/or shallower facies at a lower level in the shoreface profile. The second type of lithosome is sheet‐ or wedge‐like and sharply overlies the shoreface deposits. The lithosome consists of laterally widespread units of planar tabular to trough cross‐bedded medium sandstones passing laterally (in a dip direction) into bioturbated sandstones. The lower part of this lithosome is progradational, becoming retrogradational into the overlying shales. The facies within the cross‐bedded lithosome suggest a tidally dominated delta front to estuarine depositional setting.

The two types of lithosome are not related genetically. The erosion surface separating the two lithosomes is a sequence boundary separating forced‐regressive (relative sea‐level fall) shoreface deposits from lowstand to transgressive (early relative sea‐level rise), cross‐bedded deposits. The uppermost part of the cross‐stratified lithosome shows a landward‐stepping of component parasequences and is abruptly blanketed by open‐marine shales.

The most widespread cross‐bedded lithosomes are apparently best developed in the lowermost members of the Haystack Mountains Formation, i.e. in the aggradational part of the large‐scale progradational succession. In the uppermost, highly progradational sandstone tongues, the shoaling‐upward shoreface lithosome dominates, whereas the cross‐bedded lithosome occurs in narrow, lensoid belts, or is absent. The middle portion of the succession shows intermediate characteristics. The vertical variation in geometry, thickness and progradational extent of successive cross‐bedded lithosomes results from greater confinement of the incised nearshore systems both in space (landward direction) and in time (from the aggradation to the progradation architecture). The latter is a consequence of a decreasing rate of accommodation creation through time.
Sedimentary structures and sediment transport across the continental slope of Israel from piston core studies
Authors: ALMAGOR GIDEON , SCHILMAN BETTINA
Published: June 2006

The continental terrace of Israel consists of Nile‐derived sediments. They are classified into three major groups, according to their structures: (1) irregularly to wavy laminated, coarse‐grained sediments (quartz and skeletal debris) of the flat outer shelf and upper bend of the slope (10–20% of the bulk) which are influenced by currents. These sediments are bioturbated to various degrees. Smectitic silty clays (80–90%) form two structural groups: (2) laminated, turbiditic sediments which accumulate on the slope, particularly in the canyons of the northern slope. Irregular, wavy, thickly laminated, coarse‐grained sediments of the upper slope and canyon heads merge downslope with parallel, thinly laminated, fine‐grained sediments. Toward the foot of the slope and on the adjacent deep‐sea floor lamination becomes indistinct and the sediment is visually homogeneous. (3) Slump‐generated mud lumps of various size which accumulate on the lower slope and along the transport axes of the canyons. These are the most visible evidence for large‐scale slumping mass movement.

Transportational and depositional processes are far more intensive over the steep northern continental slope of Israel, and especially in its canyons than over the gentle southern slope.

Very stiff overconsolidated sediments unconformably overlain by the ubiquitous recent silty‐clayey sediment were cored on steep sections of the middle continental slope and along the canyon walls. Their preconsolidation stress values suggest that these sections were formerly overlain by more than 40 m of sediment and now are exposed by slumping. The downsliding slabs usually disintegrated into small fragments although several huge fragments could be identified along the canyon axes.
Megaripple dynamics and sediment transport in a mesotidal mangrove creek: implications for palaeoflow reconstructions
Authors: LARCOMBE P. , RIDD P. V.
Published: June 2006

An experiment was conducted to study megaripple morpho dynamics on a sandy intertidal shoal in a mesotidal mangrove creek (Gordon Creek, Townsville, Australia). Tidal current velocity and depth were recorded with S4 current meters over a period of 35 tides. The tidal megaripples were 0.06–0.2 m in height and 1–2 m in wavelength, and their movement was monitored by (1) electromagnetic bed‐elevation probes (which automatically recorded bed level every 2 min at three positions along the survey transect) and (2) daily surveying for 8 days around spring tidals.

The tidal currents in Gordon Creek are ebb‐dominated, with maximum depth‐mean current velocities for the flood and ebb tides of 0.62 and 0.98 m s−1respectively. Significant bedload transport occurs only during spring tides, and only on the larger of the unequal semi‐diurnal tides. Bedload transport is overwhelmingly in the ebb direction. Megaripple migration rates reach 5.6 m per tide in the ebb direction and up to 0.1 m min−1within individual tides. Within‐tide ‘bedform transport rates’are up to 0.29 kg m−1s−1.

The results suggest that for reconstruction of palaeoflows from deposits of preserved fine‐ to medium‐grained sandy tidal megaripples, it is valid to use a depth‐averaged velocity of 0.5–0.6 m s−1as the migration threshold. Velocity thresholds associated with partial or complete reversal of megaripple asymmetry are invalid.
Late Pleistocene morainal bank facies at Greystones, eastern Ireland: an example of sedimentation during ice marginal re‐equilibration in an isostatically depressed basin
Authors: MCCABE A. MARSHALL , O'COFAIGH COLM
Published: June 2006

A late Pleistocene morainal bank is sited in a depocentre to the lee of a major rock ridge, near Greystones, in the western Irish Sea Basin. During deglaciation the ridge provided a pinning point during tidewater wastage northwards. Sedimentation patterns and palaeocurrent data show morainal bank growth by discharge from a single basal efflux located to the east or south‐east of the ridge during ice marginal re‐equilibration.

The four lithofacies associations which are recognized from the western part of the formerly more extensive apron are related largely to variable jet and plume sedimentation. At the base of the 1.6 km long exposure, Lithofacies association 1 (massive mud, muddy diamict and laminated mud) was deposited from turbid plumes, variable ice rafting and traction current activity. Lenticular units of gravels within this mud bank record high energy pulses and sediment fluxes from the efflux jet. Lithofacies association 2 (sands, laminated muds and muddy diamict) is discontinuous and occurs within basins along a marked erosion surface cut in Lithofacies association 1. It is associated with a decrease in jet strength, traction currents and suspension sedimentation. Lithofacies association 3 is a tabular body of interbedded diamicts and gravels which is present along the entire section. It documents the decay phase of re‐equilibration as the ice margin disintegrated catastrophically and released large volumes of heterogeneous sediment which was resedimented by quasicontinuous mass flow. Lithofacies association 4 consists of stratified and massive gravels within distributary channels cut into underlying facies and represents the last phase of meltwater activity.

Sediment geometries, particularly sedimentary contrasts representing erosion surfaces at a variety of scales and abrupt textural contrasts are attributed to jet switching. Lithofacies association 1 (60%) and Lithofacies association 3 (30%) are the dominant facies. In favourable topographic settings this stratigraphic couplet is a signature for re‐equilibrated ice margins in isostatically depressed basins dominated by tidewater fronts, rapid ice flux and high relative sea level.

Morainal banks document rapid environmental change and in the Irish Sea Basin they form part of a deglacial event stratigraphy related to unstable tidewater margins and high relative sea level. Deglaciation was therefore controlled primarily by high relative sea level rather than climatic forcing. Facies variations should therefore not be used for stratigraphic correlations in place of direct stratigraphy. This type of situation may be more common than hitherto realized in Late Pleistocene, mid‐latitude shelves where most of the preserved stratigraphy is characterized by complex, interbedded sequences formed when isostatic depression exceeded sea‐level fall.
Basin dimensions and morphology as controls on amplification of tidal motions (the Early Miocene North Hungarian Bay)
Authors: SZTANÓ ORSOLYA , DE BOER POPPE L.
Published: June 2006

Following the Late Aquitanian sea‐level fall, tide‐influenced deposition started in the North Hungarian Bay, an embayment in the Paratethys open to the north‐east. The relatively narrow, funnel shape of the bay supported amplification of tidal movements, resulting in the generation of strong tidal currents. The length and the depth of the North Hungarian Bay and the connecting seaway through East Slovakia fell into the ‘Tidal Amplification Window’and thus fulfilled the conditions needed for resonant amplification of semidiurnal (M2) tides. Tide‐influenced deposits were formed at both sides of the North Hungarian Bay. They reflect dominant currents in opposite directions and of different strengths at either side of the basin. This difference was the result of bottom‐tide interactions. Cyclonic (anticlockwise) residual currents were induced above the asymmetrical central depression in the bay and were superimposed upon the tidal currents, producing an anticlockwise, time‐and‐velocity asymmetrical current system.

The North Hungarian Bay and other examples show that amplification of tidal motions and formation of tide‐influenced deposits may occur if basin dimensions pass through the ‘Tidal Amplification Window’. This window represents ideal conditions for resonant or amphidromic amplification of tidal currents. It determines an ideal length/depth or width/depth ratio relative to the wavelength of the astronomical tides. Thus signs of strong tidal influence in fossil basin fills can be used to reconstruct the dimensions (length, depth and width) of such basins.
An experimental study of multiple grain‐size ejecta produced by collisions of saltating grains with a flat bed
Authors: RICE M. A. , WILLETTS B. B. , McEWAN I. K.
Published: June 2006

Collision data are presented from coloured high‐speed films of three size fractions of sand grains saltating over a bed of the total grain population. Each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded. The results confirm earlier findings that V3/V1≅0.5–0.6, Vn/V1≅.08 and the rebound angle increases with decreasing grain size. Ejected grains are examined in relation to their size, the impactor size, ejection speed and angle and the number of ejecta per collision. In addition, changes in grain parameters are observed with time. For fine impactors, ejection speeds generally increase with a decrease in ejecta size, but the fine fraction does not follow this trend for the coarse and medium impactors. Ejection angles are typically between 40° and 60°, with coarse grains having shallower mean angles than fine ejecta. The number of ejections per collision increases with a decrease in particle size for each impactor size. The general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes. There is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains. Much of the forward momentum of the saltating grains is transfered to creeping grains. The composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud.
Sedimentary structures of cold‐climate coastal dunes, Eastern Hudson Bay, Canada
Authors: RUZ MARIE‐HÉLÈNE , ALLARD MICHEL
Published: June 2006

A study of sedimentary structures of cold‐climate coastal dunes along Eastern Hudson Bay, Canada, showed that in areas of very sparsely vegetated surfaces, tractional sedimentary processes are dominant while in partly and well vegetated areas, grainfall deposition is the dominant sedimentary process. Alternating fine and coarse sand strata are characteristic of the vegetated foredune ridge. Coarse strata are interpreted to be mainly related to niveo‐aeolian deposition. In poorly vegetated areas deformed strata associated with the melting of snow were preserved. A vaguely stratified strata interpreted as a dimpled surface as well as coarse lenses with irregular basal contact were found. Such distinctive sedimentary structures may represent good indicators of cold‐climate conditions and could serve as criteria to identify aeolianites that may have been deposited in similar cold‐climate environments in palaeoenvironmental reconstructions.
Sedimentary K‐Ar signatures in clay fractions from Mesozoic marine shelf environments in Israel
Authors: STEINITZ G. , KAPUSTA Y. , SANDLER A. , KOTLARSKY P.
Published: June 2006

The K‐Ar system in clay fractions from shallow marine carbonate shelf environments was investigated on silicate fractions (clay minerals, feldspar) separated from 20 Lower Jurassic to Upper Cretaceous sedimentary rocks, deposited in the southern Tethys ocean. The range of lithologies investigated included dolomite and chalk [IR (insoluble residue)<10%], marl, shale (IR= 70–85%) and sandstone (IR>90%). The results show that K‐bearing clay fractions often have K‐Ar ages similar to the suggested age of deposition, which means either supply of land‐derived authigenic K‐bearing clays or synsedimentary diagenetic authigenesis, or both. This K‐Ar synsedimentary signal is recorded in clay fractions from the whole range of studied lithologies and stratigraphic units. Among the clay minerals, the synsedimentary K‐Ar signature was recorded and retained in illite/smectite of the <2‐um and <0.2‐um fractions. A prominent synsedimentary signature is found in K‐feldspars, from shaly and especially from calcareous rocks, which is substantiated by their authigenic origin based on idiomorphic crystal morphology and their limited size distribution (4–10 um). Post‐depositional closure of the K‐Ar system is indicated by ages up to 15 Ma younger than the stratigraphic age in different lithologies from dispersed localities. A distinct late diagenetic (20–25 Ma younger) event is recorded in the formation of authigenic K‐feldspar within Upper Cretaceous chalk and shale. In the IR and >10‐um fractions the K‐Ar ages reflect the contribution of detrital mica and feldspar which accompanies the kaolinite‐dominated samples. The overall results differ considerably from K‐Ar age patterns observed in deep‐sea sediments, a difference which may be connected with the occurrence of brines in these shelf deposits. The findings indicate the potential in the K‐Ar dating of fine IR fractions of marine shelf sediments in terms of geochronological‐stratigraphic and palaeogeographical aspects as well as in the petrology of clay minerals themselves.
Stable isotope evidence for the origin of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel
Authors: AYALON AVNER , LONGSTAFFE FRED J.
Published: June 2006

The oxygen isotope compositions of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel, have been used to identify porewater types during diagenesis. Changes in porewater composition can be related to major geological events within southern Israel. In particular, saline brines played an important role in late (Pliocene‐Pleistocene) dolomitization of these rocks.

Diagenetic carbonates included early siderite (δ18OSMOW=+24.4 to +26.5‰δ13CPDB=−1.1 to +0.8‰), late dolomite, ferroan dolomite and ankerite (δ18OSMOW=+18.4 to +25.8‰; δ13CPDB=−2.1 to +0.2‰), and calcite (δ18OSMOW=+21.3 to +32.6‰; δ13CPDB=−4.2 to + 3.2‰). The petrographic and isotopic results suggest that siderite formed early in the diagenetic history at shallow depths. The dolomitic phases formed at greater depths late in diagenesis. Crystallization of secondary calcite spans early to late diagenesis, consistent with its large range in isotopic values.

A strong negative correlation exists between burial depth (temperature) and the oxygen isotopic compositions of the dolomitic cements. In addition, the δ18O values of the dolomitic phases in the northern Negev and Judea Mountains are in isotopic equilibrium with present formation waters. This behaviour suggests that formation of secondary dolomite post‐dates the tectonic activity responsible for the present relief of southern Israel (Upper Miocene to Pliocene) and that the dolomite crystallized from present formation waters. Such is not the case in the Central Negev. In that locality, present formation waters have much lower salinities and δ18O values, indicating invasion of freshwater, and are out of isotopic equilibrium with secondary dolomite. Recharge of the Inmar Formation by meteoric water in the Central Negev occurred in the Pleistocene, and halted formation of dolomite.
Early diagenesis and its relationship to depositional environment and relative sea‐level fluctuations (Upper Cretaceous Marshybank Formation, Alberta and British Columbia)
Authors: McKAY J. L. , LONGSTAFFE F. J. , PLINT A. G.
Published: June 2006

Early diagenesis of the Upper Cretaceous (late Coniacian to early Santonian) Marshybank Formation was controlled by depositional environment (composition of depositional water, Fe and organic content of the sediment, sedimentation rate, proximity to the shoreline) and influx of meteoric water related to relative sea‐level fall.

Five depositional environments, each characterized by a distinct early diagenetic mineral assemblage, have been recognized. Offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions, composed of ‘early’ calcite and siderite. Intense sulphate reduction, promoted by the dysaerobic depositional water, was the primary influence on early diagenesis. Offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions, composed of two generations of siderite (S1 and S2). In this environment, methanogenesis, rather than sulphate reduction, was more important. Early diagenesis of the inner shelf sands was generally limited. However, in sands deposited proximal to the shoreline, mixing of marine and meteoric waters promoted crystallization of Fe‐rich chlorite and siderite. The shoreface was characterized by dissolution of detrital minerals in the upper portion, and precipitation of kaolinite or illite/smectite in the lower portion. In the coastal plain environment, brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite. Ankerite, rather than siderite, is the typical early diagenetic carbonate.

The δ18O values of the earliest cements (i.e. ‘early’ calcite, siderite S1, inner shelf siderite) indicate crystallization from a low‐18O, marine‐derived porewater. Assuming crystallization at 25°C, a δ18O value of about −7‰ (SMOW) can be estimated for the seaway during Marshybank Formation time. Similar calculations for the overlying Dowling Member (Puskwaskau Formation) suggest that the δ18O value of the seaway increased to about −4% (SMOW), consistent with its transgressive nature. Very low δ18O values are exhibited by siderite S2. These results indicate crystallization during intermediate diagenesis (≥60°C) from meteoric water (≥− 15‰ SMOW) that entered the Marshybank Formation during sea‐level lowstand.
Early diagenetic siderite as an indicator of depositional environment in the Triassic Rewan Group, southern Bowen Basin, eastern Australia
Authors: BAKER JULIAN C. , KASSAN JOCHEN , HAMILTON P. JOE
Published: June 2006

Early concretionary and non‐concretionary siderites are common in subsurface Triassic sandstones and mudrocks of the Rewan Group, southern Bowen Basin. A detailed petrological and stable isotopic study was carried out on these siderites in order to provide information on the depositional environment of the host rocks. The siderites are extremely pure, containing 85–97 mol% FeCO3, and are commonly enriched in manganese. δ13C (PDB) values are highly variable, ranging from ‐ 18·4 to +2·9‰, whereas δ18O (PDB) values are very consistent, ranging from ‐ 14·0 to ‐ 10·2‰ (mean= ‐ 11·9 ± 1·0‰). The elemental and oxygen isotopic composition of the siderites indicates that only meteoric porewaters were involved in siderite formation, implying that host rocks accumulated in totally non‐marine environments. The carbon isotopic composition of the siderites is interpreted to reflect mixing of bicarbonate/carbon dioxide generated by methane oxidation and methanogenesis. Very low δ13C values demonstrate that, contrary to current views, highly 13C‐depleted siderite can be produced at shallow burial depths in anoxic non‐marine sediments.
A new, instantaneous aeolian sand trap design for field use
Authors: JACKSON D. W. T.
Published: June 2006

A new aeolian sediment trap is described which can give up to 1 Hz measurement frequency in field conditions. The trap adopts a circular, horizontal trap design with a load cell connection to give continuous, unobtrusive trap measurement of sediment flux. Simultaneous velocity recording is carried out using an anemometer. Trap construction costs are approximately £200. Initial results in field conditions using a direct comparison of wind velocity data, sampled at an equivalent frequency, have given a first‐order relationship between sediment flux and velocity. The trap enables simultaneous sampling of wind velocity and sediment flux at a sufficiently short interval to enable investigation of sediment transport dynamics under a variety of field conditions.
Anatomy and origin of toplap in a mixed carbonate‐clastic system, Seven Rivers Formation (Permian, Guadalupian), Guadalupe Mountains, New Mexico, USA
Authors: RANKEY EUGENE C. , LEHRMANN DANIEL J.
Published: June 2006

The Seven Rivers Formation exposed in Slaughter Canyon, Guadalupe Mountains, New Mexico, reveals complex relations between long‐ and short‐term relative changes in sea‐level, shelf configuration and sedimentation, which interacted to create a distinct toplap geometry. At least five sandstones diverge basinward from a prominent boundary unit marking the surface of toplap at the top of the Seven Rivers Formation and create a series of prograding, shingled clinoforms. The boundary unit is a horizontal, well‐sorted, quartz arenite underlain across the shelf by peritidal carbonate or by other merging sandstones. Preserved palaeotopography is indicated by facies changes downdip and the presence of horizontal geopetal indicators in inclined beds. Near the boundary unit (updip), merging sandstones contain rare sedimentary structures including evaporite moulds and irregular fenestrae and are bounded above and below by peritidal carbonate with microbial laminae, fenestral fabrics and mudcracks. Laterally (downdip), the sandstone‐bounding peritidal carbonate facies pass into subtidal carbonate facies (ooid‐peloid‐fusulinid‐dasyclad‐mollusc pack‐ and grainstone) and interbedded sandstones contain sedimentary structures such as ripple marks and trough to planar cross‐stratification, as well as ooids, fusulinids and other carbonate grains. Toplap is interpreted to have developed by sediment bypass across a subaerially exposed shelf while sedimentation continued in still‐submerged areas downdip from the shelf crest, and hence represents depositional toplap. Physical tracing of subaerial exposure surfaces suggests that the shoreline migrated up and down palaeoslope several times. The vertical component of five short‐term shoreline migrations decreased during formation of the toplap geometry. Sea‐level rose to approximately the same position following each fall to create the toplap geometry. This depositional toplap is the stratigraphic result of high‐‘frequency’ relative changes of sea‐level that combined to produce the larger‐scale geometry. We suggest that changing amplitudes of relative sea‐level may play a significant role in the stratigraphic evolution of platforms and that separating ‘short‐term’and ‘long‐term’relative sea‐level may be ambiguous in such instances.
Assessing the microped size distributions of desert soils erodible by wind
Authors: CHATENET B. , MARTICORENA B. , GOMES L. , BERGAMETTI G.
Published: June 2006

The microped size distribution of erodible soils is one of the main factors controlling the emissions of mineral aerosol. To date, the microped size distributions of desert soils in natural field conditions are not well known and thus the existing dust source models cannot be applied to natural sites. Based on dry sieving and elemental analysis of 26 soil samples collected in arid and semiarid regions, it is shown that the microped size distributions of these desert soil samples involve a combination of four major mass size populations. These four size populations correspond to salty soils, fine quartz sand, coarse dune sand and aluminosilicate silt. We show that the microped size distributions of the various desert soils, according to their mineralogical characteristics, can be calculated by a mixture involving two or three of these four populations. The main field of application for this scheme is the characterization of the erodible soil size distributions for modelling the atmospheric dust cycle.
A depositional model for storm‐ and tide‐influenced prograding siliciclastic shorelines from the Middle Devonian of the central Appalachian foreland basin, USA
Authors: PRAVE ANTHONY R. , DUKE WILLIAM L. , SLATTERY WILLIAM
Published: June 2006

A stratigraphic motif observed in many foreland basins is the development of basinward tapering siliciclastic wedges characterized by various scales of depositional cycles. The Middle Devonian (Givetian) Mahantango Formation in the central Appalachian foreland basin is such an example. It consists of both small‐and large‐scale thickening‐ and coarsening‐upward cycles; the small‐scale cycles are typically less than 10 m thick whereas larger‐scale cycles are generally a few tens of metres thick and commonly contain several of the smaller‐scale cycles. Outcrop‐based facies analyses indicate that the depositional cyclicity resulted from episodic progradation of a regionally straight, tide‐dominated shoreline onto a storm‐dominated, shallow marine shelf. The depositional model for this ancient shallow marine system consists of a vertical facies succession in which storm‐dominated offshore marine mudstone and fine sandstone pass gradationally upward into storm‐dominated nearshore marine shelf and shoreface sandstone overlain by, in proximal sections, tide‐dominated shoreline sandstone, pebbly sandstone and mudstone. Transgressively reworked lag deposits cap most of the thickening‐ and coarsening‐ upward packets. In this model, coarse‐grained rocks, rather than implying basinward shifts of facies, are a consanguineous part of the stacked shoaling cycles. Lateral facies relationships show that the dominance of storm‐ vs. tide‐generated sedimentary features is simply a function of palaeogeographical position within the basin; proximal sections contain tidally influenced sedimentary features whereas more distal sections only display evidence for storm‐influenced deposition. These results suggest caution when inferring palaeoceanographic conditions from sedimentological datasets that do not contain preserved examples of palaeoshorelines.
Sedimentation in a tropical, microtidal, wave‐dominated coastal‐plain estuary
Authors: ANTHONY E. J. , LANG J. , OYÉDE L. M.
Published: June 2006

The Mono estuary is an infilled, microtidal estuary located on the wave‐dominated Bight of Benin coast which is subject to very strong eastward longshore drift. The estuarine fill comprises a thick unit of lagoonal mud deposited in a ‘central basin’between upland fluvial deposits and estuary‐mouth wave‐tide deposits. This lagoonal fill is capped by organic‐rich tidal flat mud. In addition to tidal flat mud, the superficial facies overlying the ‘central basin’fill include remnants of spits resting on transgressive/washover sand, an estuary‐mouth association of beach, shoreface, flood‐tidal delta and tidal inlet deposits, and a thin sheet of fluvial sediments deposited over tidal flat mud.

After an initial phase of spit intrusion over the infilled central basin east of the present Mono channel, the whole estuary mouth became bounded by a regressive barrier formed from sand supplied by the Volta Delta during the middle Holocene eustatic highstand. Barrier progradation ceased late in the Holocene following the establishment of an equilibrium plan‐form shoreline alignment that allowed through‐drift of Volta sand to sediment sinks further downdrift. Over the same period, accretion, from fluvially supplied sediments, of the estuarine plain close to the limit of spring high tides, or, over much of the lower valley, into a fluvial plain no longer subject to tidal flooding, induced marked meandering of the Mono and its tidal distributaries in response to confinement of much of the tidal prism to these channels. The process resulted in erosion of spit/washover and regressive barrier sand, and in reworking of the tidal flat and floodbasin deposits. The strong longshore drift, equilibrium shoreline alignment and the year‐round persistence of a tidal inlet maintained by discharge from the Mono and from Lake Ahémé have resulted in a stationary barrier that is reworked by a mobile inlet.

The Mono example shows that advanced estuarine infill may result in considerable facies reworking, obliteration of certain facies and marked spatial imbrication of fluvial, estuarine and wave‐tide‐deposited facies, and confirms patterns of sedimentary change described for microtidal estuaries on wave‐influenced coasts. In addition, this study shows that local environmental factors such as sediment supply relative to limited accommodation space, and strong longshore drift, which may preclude accumulation of sediments in the vicinity of the estuary mouth, may lead to infilled equilibrium or near‐equilibrium estuaries that will not necessarily evolve into deltas.
Fabric characteristics of subaerial slope deposits
Authors: BERTRAN PASCAL , HÉTU BERNARD , TEXIER JEAN‐PIERRE , VAN STEIJN HENK
Published: June 2006

The clast fabrics of certain types of terrestrial slope deposits are reviewed and compared, including the deposits of rockfalls, solifluction, debris flows, dry grain flows, frost‐coated clast flows and run‐off. The analysis is based on modern deposits in active environments. The study shows that fabric characteristics allow discrimination between ‘collective’and individual movement of rock particles. The individual particle movement generally results in a random clast orientation, whereas the processes of ‘collective’movement typically create distinct preferred orientations. The highest fabric strengths together with low values of spherical variance are found in solifluction deposits. A survey of Pleistocene slope deposits indicates, however, that clast fabric has to be used with caution in the identification of past slope dynamics, because significant post‐depositional changes may occur during ageing and burial of deposits. The diagnostic significance of fabric characteristics may also be low due to the overlap of the statistical values that typify different processes.
Climatic significance of natric horizons in Permian (Asselian) palaeosols of north‐central Kansas, USA
Authors: McCAHON THOMAS J. , MILLER KEITH B.
Published: June 2006

Columnar structured horizons have been recognized in ancient coastal palaeosols of several Lower Permian (Asselian) stratigraphic units of north‐central Kansas. These strongly developed columnar, polygonal‐shaped peds are characteristic of sodium‐influenced (natric) argillic horizons, and are commonly indicative of semi‐arid to arid environments. Evaporite features above and below these palaeosols support the conclusion for a dry palaeoclimate. The columnar peds are typically 3–15 cm in diameter and exhibit domed tops. Fine clay fills the cracks between the columnar peds, and is generally of a darker colour than the peds. Each natric horizon has a low value and chroma colour, apparently the result of carbonate accumulation. The natric horizons in these Permian palaeosols appear to have been partially influenced by sodium‐rich groundwaters. Root traces and root moulds are found between peds in all natric horizons, indicating plant succession after columnar ped formation. These sodium‐influenced palaeosol profiles occur as part of a spectrum of palaeosol types that indicate cyclical climate change associated with glacioeustatic sea‐level fluctuations.
MYCORRHIZAL INFECTION ON GROWTH AND NITROGEN FIXATION OF PUERARIA AND STYLOSANTHES AND UPTAKE OF PHOSPHORUS FROM TWO ROCK PHOSPHATES
Authors: WAIDYANATHA U. P. de S. , YOGARATNAM N. , ARIYARATNE W. A.
Published: June 2006

Summary

Growth and nodulation of Pueraria and Stylosanthes, and also nitrogenase activity of Pueraria grown in methyl bromide treated soil were severely retarded unless the plants were infected with vesicular–arbuscular (VA) mycorrhiza or given large amounts (500 mg per kg of soil) of rock phosphate. Added rock phosphate further stimulated growth, nodulation and nodule activity of mycorrhizal plants. Mycorrhizae also enhanced uptake of phosphorus, which was increased further by the addition of rock phosphate.

The comparative levels of phosphorus in plants and growth responses were clearly different with respect to the two sources of rock phosphate in both mycorrhizal and non‐mycorrhizal plants.

These observations refer in particular to Pueraria; the treatment effects being less pronounced with Stylosanthes as the uninoculated plants were naturally contaminated with mycorrhizae, but to a lesser degree than those inoculated.
LOCALIZATION OF HEAVY METALS AND OTHER ELEMENTS ACCUMULATED IN THE LICHEN THALLUS
Authors: GARTY JACOB , GALUN MARGALITH , KESSEL MARTIN
Published: June 2006

Summary

This study demonstrates the extracellular deposition of particulate metallic fall‐out accumulated in the lichen Caloplaca aurantia with the aid of scanning and transmission electron microscopy and the application of energy dispersive X‐ray analyses. The elemental composition of particles integrated in the lichen tissue was compared with the elemental composition of dust particles collected from the surface of the lichen colonies.

The different effect of heavy metals in particulate form or in solution, as reflected by lichen's tolerance or sensitivity, is discussed.
Ultrastructural Alterations in the Right and Left Ventricular Myocardium Following Multiple Low Energy Endocardial Countershocks in Anesthetized Dogs
Authors: SCHIRMER UWE , HEMMER WOLFGANG , LINDNER KARL H. , ANHÄUPL THOMAS , WIESER THOMAS
Published: June 2006

Both high energy transthoracic and direct epicardial defibrillation can result in RV and LV myocardial damage, but little is known about the damage due to defibrillation using an endocardial RV electrode. Furthermore, disturbances in postdefibrillation oxidative metabolism have been reported and may be caused by primary injury of mitochondrial integrity and function, but information about ultrastructural mitochondrial alterations is rare. We therefore studied, in 13 fox hounds, RV and LV ultrastructural alterations following multiple low energy endocardial countershocks. Using an ICD and an endocardial defibrillation system a median of 54 (43–74) countershocks with a cumulative energy of 1,558 J (844–2,141 J) was delivered. After termination of countershocks, RV and LV myocardium was examined by electron microscopy. In both ventricles, severe myocardial alterations were found, including swollen mitochondria, disruption of mitochondrial crests, and loss of integrity of the mitochondrial inner and outer membranes. At the first time a semiquantitative score, originally developed for postischemic injury, was successfully used to grade the postcountershock mitochondrial alteration, which showed a more pronounced damage in the RV (2.69 ± 0.22 points) compared to the LV (2.18 ± 0.22; P = 0.021). We conclude that even the use of endocardial lead systems with low energy countershocks may lead to severe mitochondrial damage, especially in the RV.
Transient Right Bundle Branch Block Causing R Wave Attenuation Postdefibrillation
Authors: KAM RUTH M. L. , GARAN HASAN , McGOVERN BRIAN A. , RUSKIN JEREMY N. , HARTHORNE JOHN W.
Published: June 2006

Transient and significant decrease in R wave amplitude, associated with transient right bundle branch block, was noted to occur after defibrillation in a defibrillator patient. The mechanism is probably stunning of the right bundle branch, causing right intraventricular conduction delay and decrease in signal amplitude reaching the endocardial sensing dipoles.
Iatrogenic Pneumohemomediastinum Mimicking Cardiac Tamponade: A Complication of Catheter Ablation Procedure
Authors: VOCI PAOLO , TRITAPEPE LUIGI , CRITELLI GIUSEPPE
Published: June 2006

We describe a patient who developed cardiac tamponade during electrophysiological mapping aimed at ablating an atrioventricular accessory pathway. Transesophageal echocardiography showed compression of the left pulmonary veins due to pneumohemomediastinum secondary to left subclavian vein cannulation.