bluuebunny/crossref_metadata_2025 huggingface dataset:
On the effect of mid‐air collisions on aeolian saltation
Authors: SØRENSEN MICHAEL , McEWAN IAN
Published: June 2006

The effect of mid‐air collisions on aeolian saltation is investigated using concentration profiles and grain velocities predicted by a numerical saltation model. The probability of a mid‐air collision is found to be greater at high wind speeds. It is also found that mid‐air collisions tend to reduce the number of grain/bed impacts and thus reduce the number of ejecta near the bed; this, in turn, reduces the intensity of mid‐air collisions. It is suggested that this feed‐back mechanism significantly influences transport rates at high wind speeds.
Sediment flux distribution in the Southern Brazil Basin during the late Quaternary: the role of deep‐sea currents
Authors: MASSÉ L. , FAUGÈRES J. C. , PUJOL C. , PUJOS A. , LABEYRIE L. D. , BERNAT M.
Published: June 2006

Detailed sedimentological and stratigraphic analyses were carried out on seven Kullenberg cores collected across the Brazilian continental margin during the French cruises Byblos and Apsara III, in order to highlight the factors controlling the sediment flux distribution in the Southern Brazil Basin during the late Quaternary. On the continental slope and upper continental rise above 3000 m depth, sediment fluxes are important and highly variable (4·2–14·2 g cm−2 10−3 yr). The sediments show a pelagic or turbiditic character, depending on the width of the shelf and proximity of canyons. The material is characterized by high kaolinite contents, and originates from the coastal rivers draining the South American continent north of Rio de Janeiro. On the middle continental rise between 3000 and 4000 m depth, sediment fluxes are the lowest observed in the area (0·9 g cm−2 10−3 yr), because terrigenous input is trapped at shallower depths on the São Paulo Plateau. Pelagic settling is the dominant process. In the deep domains, below 4000 m depth, contouritic accumulations are developed on the path of the northwards moving Antarctic bottom water (AABW) currents. The deposits consist of fine‐grained silty‐clayey muds with very low carbonate contents. The sediment fluxes (1·45 g cm−2 10−3 yr) are higher than on the middle continental rise, as a consequence of fine‐grained terrigenous supply derived from higher latitudes (Argentine Basin and Southern Ocean), and transported in the basin through the Vema Channel by the AABW currents. This material is characterized by high smectite and chlorite contents. These data reveal large sediment flux variations which are linked to distinct depth‐related domains. Such a distribution is the consequence of the presence of two available sources of terrigenous sediments: (1) the Brazilian continental areas with a downslope material transport and a sediment distribution controlled by the morphology of the margin, and (2) the Argentine Basin with an alongslope material transport by deep‐sea currents which dominate the sedimentation in the abyssal domains.
Groundwater dolocretes in a lake‐marginal environment: an alternative model for dolocrete formation in continental settings (Danian of the Provence Basin, France)
Authors: COLSON JELENA , COJAN ISABELLE
Published: June 2006

In the long continental history of the Provence Basin which extended from Santonian to Oligocene times, a major period of palaeosol development occurred in the Danian. Dolocretes developed within floodplain silts, and partly from palustrine limestones. Dolocretes are overlain by pedogenic facies: calcretes and palustrine limestones. Gradational lower and upper limits of profiles, succession of nodular, coalescent and massive horizons, the epigenesis of quartz by dolomite, the unimodal crystal size and the euhedral dolomite fabric, as well as the absence of biogenic structures and vadose cements show that dolocretes formed in the phreatic zone.

The exclusive occurrence of dolocretes around the palaeolake or playa suggests that dolocrete formed by the mixing of groundwaters and lake brines, which infiltrated the phreatic zone during periods of strong evaporation and lake level lowering. The term halo dolocrete is proposed to describe this type of dolocrete deposit.

Subsequent alteration of the dolocrete includes leaching of the central core of dolomite crystals and calcitization. Calcitization was either fabric‐destructive (type I) or fabric‐preserving (type II) and took place during very early diagenesis, i.e. concomitant with calcrete formation or palustrine limestone deposition. Fabric‐destructive calcitization is attributed to a drop in the lake level, when the upper part of the dolocrete was subjected to vadose zone processes, whereas the fabric‐preserving calcitization resulted from reactions with dilute lake and groundwaters during rise in lake level.
Fields in the spectrum of channel style
Authors: WOOLFE KEN J. , BALZARY JAMES R.
Published: June 2006

The classification of channel styles has to date proved difficult, with most schemes having been constructed around a series of geomorphological end‐members which are inherently unable to describe the continuum of channel morphologies. We present a framework that accommodates all possible channel‐interchannel configurations and facilitates the continued use of existing channel classification schemes. By considering the relative rates of channel and interchannel accumulation, a model has been derived with the potential to predict bed geometry and preservation potential for the entire spectrum of aggrading and eroding channels. The model identifies stability fields for all potential configurations of channel and interchannel areas. Significantly, the model predicts that the transition from aggrading to eroding systems need not be accompanied by a change from raised to incised channels.
Flow and sediment transport over large subaqueous dunes: Fraser River, Canada
Authors: KOSTASCHUK RAY , VILLARD PAUL
Published: June 2006

Large symmetric and asymmetric dunes occur in the Fraser River, Canada. Symmetric dunes have stoss and lee sides of similar length, stoss and lee slope angles <8°, and rounded crests. Asymmetric dunes have superimposed small dunes on stoss sides, sharp crests, stoss sides longer than lee sides, stoss side slopes <3° and straight lee side slopes up to 19°. There is no evidence for lee side flow separation, although intermittent separated flow is possible, especially over asymmetric dunes. Dune symmetry and crest rounding of symmetric dunes are associated with high sediment transport rates. High near‐bed velocity and bed load transport near dune crests result in crest rounding. Long, low‐angle lee sides are produced by deposition of suspended sediment in dune troughs. Asymmetric dunes appear to be transitional features between large symmetric dunes and smaller dunes adjusted to lower flow velocity and sediment transport conditions. Small dunes on stoss sides reduce near‐bed flow velocity and bed load transport, causing a sharper dune crest. Reduced deposition of suspended sediment in troughs results in a short, steep lee slope. Dunes in the Fraser River fall into upper plane bed or antidune stability fields on flume‐based bedform phase diagrams. These diagrams are probably not applicable to large dunes in deep natural flows and care must be taken in modelling procedures that use phase diagram relations to predict bed configuration in such flows.
Stratigraphic architecture resulting from Late Quaternary evolution of the Riverine Plain, south‐eastern Australia
Authors: PAGE K. J. , NANSON G. C.
Published: June 2006

The Riverine Plain of south‐eastern Australia is the result of prolonged Cenozoic fluvial activity. Single thread, anabranching and distributary channels and floodplains, and associated aeolian dunes, characterize the uppermost sequences. Based on detailed interpretations of Late Quaternary fluvial sedimentation and surficial stratigraphy for this 77 000‐km2 basin, earlier ‘prior stream’ and ‘ancestral stream’ models of fluvial deposition, deduced from limited stratigraphic and chronological evidence, are replaced with aggradational palaeochannel and migrational palaeochannel models. Thermoluminescence dating reveals four distinct phases of palaeochannel activity between 105 and 12 ka; the first (Coleambally phase) late in Oxygen Isotope Stage 5, the second (Kerarbury phase) in Stage 3, the third (Gum Creek phase) before and the fourth (Yanco phase) after the Last Glacial Maximum (LGM) in Stage 2. The first three of these phases were characterized by mixed‐load laterally migrating sinuous palaeochannels with occasional transitions to a straighter bedload‐dominated mode, and vice versa. The first two phases concluded with a bedload‐dominated episode resulting in aggradational palaeochannels on the surface of the Plain, and the third phase (prior to the LGM) did also in its downstream reaches. The phase following the LGM was characterized entirely by large mixed‐load sinuous migrational palaeochannels. These exhibited no terminating bedload episode, because the onset of Holocene climates reduced the size of the flood peaks, greatly diminished the supply of bedload from the upper catchments and resulted in streams evolving to their present highly sinuous suspended load form. The result is a complex stratigraphic architecture consisting of vertically and laterally accreted units extending over hundreds of kilometres in the form of channel‐sand stringers, sand sheets and derivative aeolian dunes partially or wholly encased in overbank fines.
Climatic control of fluvial‐lacustrine cyclicity in the Cretaceous Cordilleran Foreland Basin, western United States
Authors: DRUMMOND CARL N. , WILKINSON BRUCE H. , LOHMANN KYGER C.
Published: June 2006

Tectono‐stratigraphic models of foredeep sedimentation have generally presumed a direct link between changing rates of tectonism and concomitant sedimentological response as manifested by change in thickness, composition or depositional environment of sediment accumulating in adjacent basins. Lacustrine limestone units within the early Cretaceous fluvial/lacustrine Gannett Group of western Wyoming exhibit systematic variation in several geochemical proxies of relative rates of precipitation and evaporation, indicating that lakewater chemistry was controlled by variation in regional climate.

Change in proportion of allochthonous terrigenous clastic vs. autochthonous carbonate deposition, as well as carbonate Mg/Ca ratio and stable isotopic composition, occurs at two scales. Metre‐scale alternation of micritic limestone and argillaceous marl is accompanied by mineralogical and isotopic variation within individual beds, indicating preferential carbonate accumulation during intervals of decreased regional meteoric precipitation relative to lake‐surface evaporation. Limestone deposition began during intervals of maximum aridity, and decreased as increased meteoric precipitation‐driven flux of terrigenous clastic sediment overwhelmed sites of carbonate accumulation. Similar upsection variation in limestone mineralogy and isotopic composition at a scale of tens of metres reflects the multiple processes of long‐term increase in meteoric precipitation and lakewater freshening prior to influx of terrigenous sediment, across‐basin fluvial‐deltaic progradation, and renewed accumulation of riverine terrigenous units. Such trends suggest that formation‐scale alternation between fluvial clastic and lacustrine carbonate deposition was controlled by climate change.
Palaeoceanography of organic‐rich rocks of the Loma Chumico Formation of Costa Rica, Late Cretaceous, eastern Pacific
Authors: ERLICH R. N. , ASTORGA A. , SOFER Z. , PRATT L. M. , PALMER S. E.
Published: June 2006

The Late Cretaceous (late Cenomanian‐Campanian) Loma Chumico Formation consists of laminated to massive bedded siliceous shales, cherts, ash fall tuffs/volcanic glass beds and volcaniclastic sandstones. The Loma Chumico Formation is at least 630 m thick (core data) in the Tempisque Basin, and can be subdivided in the subsurface into organic‐rich and organic‐lean (total organic carbon <1%) facies. Rock‐Eval total organic carbon (TOC) data show that TOC in the organic‐rich facies averages 15·5%, with values as high as 33%. Inorganic geochemical, petrological and sedimentological analyses indicate that all the lithologies of the Loma Chumico Formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc.

The organic geochemistry and palaeontology of the Loma Chumico Formation help constrain the factors that controlled biological productivity in the region during the Late Cretaceous. Biomarkers, identified in organic‐rich facies by gas chromatography/mass spectrometry (GC/MS), show a high abundance of total steranes relative to hopanes in the Morote‐1 core, indicating algal‐dominated organic input. The hopane‐to‐sterane ratio of the extract from the Manzanillo‐1 core indicates a relatively high bacterial component to the organic matter.

Upwelling and extrusive volcanism were the most important factors that controlled nutrient supply (including silica flux) and biological productivity within the Loma Chumico Formation depositional system. Episodic radiolarian, dinoflagellate or diatom ‘blooms’, instigated by rapid infusions of volcanogenic silica, may have resulted in expansion of the oxygen minimum zone (OMZ), enhancing the preservation of organic matter. Productivity appears to have been uniform, even during deposition of the organic‐lean facies.

The findings of this study suggest that ocean‐wide anoxia in the eastern Pacific was unlikely during the Late Cretaceous. High TOC contents of organic‐rich radiolarites from central Caribbean Deep Sea Drilling Project (DSDP) sites may be related to upwelling produced in the eastern Pacific by convergence of the easterly Trade Winds (Eastern Pacific Equatorial Upwelling Zone), or may be part of a more complex Pacific‐Atlantic Ocean interaction.

The end of deposition of organic‐rich rocks began near the end of the latest Santonian‐earliest Campanian in the central Caribbean and Costa Rica.

Palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the North Atlantic‐South Atlantic seaway may explain this observation. This may represent the influx of a previously unrecognized source of colder, oxygenated intermediate/bottom water (proto‐Antarctic Intermediate Water) into the Late Cretaceous central Atlantic and eastern Pacific oceans.
Pyroclastic surges of the Pleistocene Monte Guardia sequence (Lipari Island, Italy): depositional processes
Authors: COLELLA A. , HISCOTT R. N.
Published: June 2006

The 20–16 ka Monte Guardia sequence of Lipari island, southern Italy, is a complex succession of silicic pyroclastic surge deposits produced, in part, by hydromagmatic explosions near sea level. Most surges were directed to the east, north‐east and north of the vent, and climbed the 12° southern slopes of Monte Sant’Angelo in the central part of the island.

A series of thin, distinctive key bed‐sets containing oxidized ash and accretionary lapilli allow a detailed correlation of sections and the lateral tracing of deposits of single pyroclastic surges across the island. Facies analysis reveals that the proximal‐to‐distal facies changes are different from those suggested by a previous study based on a statistical approach to lateral facies distribution. Single dry surge deposits evolve downcurrent from (1) beds of disorganized medium‐ to coarse‐grained lapilli containing scattered blocks, to (2) bipartite disorganized/stratified beds of fine‐ to coarse‐grained lapilli with ash matrix, to (3) dunes formed of coarse‐grained ash to medium‐grained lapilli, to (4) planar beds of fine‐grained lapilli. This facies sequence is similar to published models for some Korean surge deposits, and records decelerating surges which experienced a downflow decrease in turbulence, particle concentration and suspended‐load fall‐out rate, and an increase in traction processes.

As the Monte Guardia surges climbed the opposing slopes of Monte Sant'Angelo, they bifurcated into eastern and western tongues, which experienced rapid deceleration leading to a rapid downcurrent thinning and fining of the surge deposits. Two fluid‐dynamical approaches suggest that Monte Guardia surges travelled at speeds of more than 75–85 m s ‐1 before climbing Monte Sant’Angelo. Flows with this vigour and distribution are capable of destroying animal and plant populations on Lipari.
Numerical simulation of turbidity current flow and sedimentation: I. Theory
Authors: ZENG JIANJUN , LOWE DONALD R.
Published: June 2006

A computer‐based numerical model of turbidity current flow and sedimentation is presented that integrates geological observations with basic equations for fluid and sediment motion. The model quantifies those aspects of turbidity currents that make them different from better‐understood fluvial processes, including water mixing across the upper flow boundary and the interactions between the suspended‐sediment concentration and the flow dynamics and sedimentation. The model includes three numerical components: (1) a layer‐averaged three‐equation flow model for tracing downslope flow evolution using continuity and momentum equations, (2) a sedimentation/fluidization model for tracing sediment‐size fractionation in sedimenting multicomponent suspensions and (3) a concentration‐viscosity model for quantifying the changes in resistance of such suspensions toward fluid and sediment motion. The model traces the evolution of a model turbidity current in terms the layer‐averaged flow velocity, flow thickness, sediment concentration distribution, and the rate of sedimentation and sediment size fractionation. It generates synthetic turbidites with downslope variations in thickness and grain‐size structuring at each point along the flow path. This study represents an effort to evaluate quantitatively the effects of basin geometry, sediment supply and sediment properties on the mechanics of turbidity current flow and sedimentation and on the geometry and grain size characteristics of the resulting deposits.
Sedimentology and isotopic composition of Upper Palaeocene to Eocene non‐marine stromatolites, eastern Ebro Basin, NE Spain
Authors: ZAMARREÑO I. , ANADÓN P. , UTRILLA R.
Published: June 2006

Stromatolites are abundant in Upper Palaeocene to Eocene fluvial deposits from the Eastern Ebro Basin, whereas they are scarce in the lacustrine facies. The fluvial stromatolites display a variety of growth forms: oncoids, domes, laminated crusts and locally irregular bioherms. These morphologies are related to the hydrological behaviour of the fluvial systems. Elongate domes, dome heads and ovoid to subspherical oncoids accreted in flowing water. Laminated crusts and small‐sized cylindrical to lenticular oncoids formed during low‐discharge and ponding phases. In the lacustrine environments only small‐sized ovoid oncoids occur.

The main characteristics of the Ebro Basin non‐marine stromatolites are: (1) laminations and concentric banding exhibited by all morphologies; (2) the occurrence of well‐preserved cyanobacterial filaments in several laminae, suggesting that these microbiotas are the major contributors in growth; (3) the asymmetrical growth of cortices in domes and oncoids with polar thickening on the upper side suggesting in situ growth under low energy conditions.

δ13C values of carbonate stromatolites range from ‐ 11.3%o (Late Palaeocene) to — 4.4%o (Middle‐Late Eocene). During the Late Palaeocene, under tectonically quiescent conditions, the δ13C values mainly reflect the influence of soil‐derived CO2. During the Eocene, the progressive uplift of the surrounding catchment areas led to an increase of exposures of Mesozoic rocks. Consequently, the δ13C values of the Eocene stromatolites reflect the influence of the CO2 derived from the dissolution of Mesozoic marine carbonates.

There is a 2.5%o shift in δ18O values of stromatolites from the Late Palaeocene to Middle‐Late Eocene which is consistent with the variation in δ18O of precipitation due to changes in altitude of the catchment area during this time.

The isotopic values of all Middle‐Upper Eocene laminated crust samples show distinct covariant trends, suggesting that these stromatolites were formed either in ponding zones of fluvial channels or in disconnected pools developed during low‐discharge episodes.
Spheroidal dolomites in a Visean karst system – bacterial Induced origin?
Authors: NIELSEN P. , SWENNEN R. , DICKSON J. A. D. , FALLICK A. E. , KEPPENS E.
Published: June 2006

Spheroidal dolomite crystals occur in the karstified top of a Dinantian dolomite sequence in eastern Belgium. The spheroidal dolomite crystals are best developed at the base of the karst system. The dolomite crystals are characterized by a spherulitic or dumb‐bell inclusion pattern, and are overgrown by dolomite cements with a rhombohedral outline. They are considered to be bacterially related precipitates based on, (1) textural similarities with documented bacteriogenic precipitates, (2) the presence of ‘bacterial’microspheres and framboidal pyrite embedded within the dolomite, and (3) their general geological setting. The geochemical characteristics of the dolomites and associated minerals support a bacterial origin. The ubiquity of framboidal pyrite, depleted in 34S (δ34S=— 22.4 to — 25.5%oCDT), testifies to a period of bacterial sulphate reduction. The isotopic composition of the spheroidal dolomites (δ13C=— 2.4 to ‐ 3.2%oPDB and δ18O=— 3.8 to ‐ 3.4%oPDB) suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction. Sulphate reduction may also result in a concomitant 18O depletion if the system is nearly closed. It is however, evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open. The 18O depletion of the spheroidal dolomite crystals (δ18O=— 3.8 to — 3.4%oPDB) and their occurrence adjacent to, and within karst cavities suggests a mixing zone origin, with a significant proportion of freshwater in it. The rhombohedral cement‐overgrowths have calculated δ18O values in the range of 0 to +5.3%oPDB, which reflect precipitation from normal to slightly evaporated contemporaneous seawater.
The upper Hawkesbury River, New South Wales, Australia: a Holocene example of an estuarine bayhead delta
Authors: NICHOL SCOTT L. , ZAITLIN BRIAN A. , THOM BRUCE G.
Published: June 2006

Holocene deposits of the Hawkesbury River estuary, located immediately north of Sydney on the New South Wales coast, record the complex interplay between sediment supply and relative sea‐level rise within a deeply incised bedrock‐confined valley system. The present day Hawkesbury River is interpreted as a wave‐dominated estuarine complex, divisible into two broad facies zones: (i) an outer marine‐dominated zone extending 6 km upstream from the estuary mouth that is characterized by a large, subtidal sandy flood‐tidal delta. Ocean wave energy is partially dissipated by this flood‐tidal delta, so that tidal level fluctuations are the predominant marine mechanism operating further landward; (ii) a river‐dominated zone that is 103 km long and characterized by a well developed progradational bayhead delta that includes distributary channels, levees, and overbank deposits. This reach of the Hawkesbury River undergoes minor tidal level fluctuations and low fluvial runoff during baseflow conditions, but experiences strong flood flows during major runoff events. Fluvial deposits of the Hawkesbury River occur upstream of this zone.

The focus of this paper is the Hawkesbury River bayhead delta. History of deposition within this delta over the last c. 12 ka is interpreted from six continuous cores located along the upper reaches of the Hawkesbury River. Detailed sedimentological analysis of facies, whole‐core X‐ray analysis of burrow traces and a chronostratigraphic framework derived from 10 C‐14 dates reveal four stages of incised‐valley infilling in the study area: (1) before 17 ka BP, a 0–1 m thick deposit of coarse‐grained fluvial sand and silt was laid down under falling‐to‐lowstand sea level conditions; (2) from 17 to 6·5 ka BP, a 5–10 m thick deposit composed of fine‐grained fluvial sand and silt, muddy bayhead delta and muddy central‐basin deposits developed as the incised valley was flooded during eustatic sea‐level rise; (3) during early highstand, between 6·5 and 3 ka BP, a 3–8 m thick bed of interbedded muddy central‐basin deposits and sandy river flood deposits, formed in association with maximum flooding and progradation of sandy distributary mouth‐bar deposits commenced; (4) since 3 ka BP, fluvial deposits have prograded toward the estuary mouth in distributary mouth‐bar, interdistributary‐bay and bayhead‐delta plain environments to produce a 5–15 m thick progradational to aggradational bayhead‐delta deposit. At the mouth of the Hawkesbury estuary subaqueous fluvial sands interfinger with and overlie marine sands. The Hawkesbury River bayhead‐delta depositional succession provides an example of the potential for significant variation of facies within the estuarine to fluvial segment of incised‐valley systems.
Numerical modelling of a mid‐sized gravity flow: the 1979 Nice turbidity current (dynamics, processes, sediment budget and seafloor impact)
Authors: MULDER T. , SAVOYE B. , SYVITSKI J. P. M.
Published: June 2006

The 1979 Nice turbidity current is modelled using a visco‐plastic analysis of flow velocity because the initial flow concentrations are expected to have been very high. The complete history of the failed sediment from debris flow to turbidity current plume is therefore addressed. The turbidity current portion is considered as a steady state flow divided into a dense bottom flow and an upper plume. Model results show that a dense flow can be generated from the debris flow by the disaggregation of the initial slide. The dense flow would be strongly erosive and able to create and maintain a low‐density plume at its surface. The depth of erosion of the channel floor by the dense flow is predicted to reach 6–11 m in overconsolidated sediments, with the main erosion taking place in Var Canyon and the Upper Fan Valley. The eroded volume (108 m3) provides additional material to the sediment mass of the initial failure. The dense flow appears able to inject fine sand and silt into the overlying plume during 90 km, and would disintegrate before being able to deposit sediment. The extensive sand layer along the travel path of the turbidity current may have been deposited from the tail of the trailing plume: a result of the velocity difference between the plume and the dense flow. Observations on sedimentary structures, erosion features and distribution of the sand deposit are quite in agreement with our modelling approach. For example, gravel waves can be generated when loose deposits are reworked by the supercritical dense flow. The methodology and equations presented here provide a good estimate of the geological consequences of a high‐velocity gravity flow undergoing rheological transition.
Erosional marks on consolidated banks and slump blocks in the Rupen River, north‐west India
Authors: GIBLING M. R. , TANDON S. K.
Published: June 2006

Erosional marks, including grooves, current crescents and flutes, are present on banks and slump blocks of the Rupen River on the semi‐arid plains of north‐west India. The channel has a width:depth ratio of 6, and is incised up to 8 m through well consolidated, fine‐grained aeolian sediment dated at ∼ 20–60 ka. Pedogenic carbonate nodules embedded in the channel walls have localized scour, and reworked carbonate particles probably promoted corrasion during strong seasonal flow. Similar erosional marks are apparently scarce on modern river banks, and a distinctive combination of conditions, including a consolidated substrate and strong flow in a confined channel, is probably required for their generation and preservation on channel walls and on slump blocks.
Jurassic aeolian oolite on a palaeohigh in the Sundance Sea, Bighorn Basin, Wyoming
Authors: KILIBARDA ZORAN , LOOPE DAVID B.
Published: June 2006

Aeolian limestones are widespread in the Quaternary record and have been identified in outcrops and cores of late Palaeozoic strata. These rocks have been interpreted as a low latitude signal of glacio‐eustatic sea level fluctuations and have not been previously reported from the Mesozoic or from other episodes of earth history generally believed to have been non‐glacial. Numerous lenticular bodies of cross‐stratified oolite lie near the contact between the lower and upper members of the mudstone‐dominated lower Sundance Formation (Middle and Upper Jurassic) in the Bighorn Basin of north‐central Wyoming, USA. The lenses, up to 12 m thick, contain sedimentary structures diagnostic of aeolian deposition. Inversely graded laminae within thick sets of cross‐strata were deposited by climbing wind ripples. Adhesion structures and evenly dispersed lag granules are present in flat‐bedded strata at the bases of several of the oolite bodies. Thin sections reveal abundant intergranular micrite of vadose origin. The lenses appear to represent virtually intact, isolated aeolian bedforms that migrated across a nearly sand‐free deflation surface. When the Sundance Sea transgressed the dunes, a thin (<1 m thick), wave‐rippled, oolite veneer formed on the upper surface of the aeolianite. Previous workers, primarily on the basis of sedimentary structures in the veneer, interpreted the oolite lenses as tidal sand bodies.

The dunes provide clear evidence of widespread subaerial exposure on the crest and north flank of the Sheridan Arch. This structural high was delineated by previous workers who demonstrated thinning of pre‐upper‐Sundance Formation strata and localized development of ooid shoals. Ooids that formed in shoals on the windward (southern) side of the palaeohigh were exposed and deflated during lowstand. Thin, scour‐filling ooid grainstone lenses that crop out in the southern part of the study area represent remnants of the marine beds that sourced the aeolianites. Farther north (down‐wind), oolitic dunes prograded over thinly laminated lagoonal silts. When relative sea level began to rise, the uncemented dunes were buried under fine‐grained marine sediment as the lee side of a low‐relief island was inundated.
PLASTID DEVELOPMENT IN THE PRIMARY LEAF OF PHASEOLUS VULGARIS: VARIATIONS BETWEEN DIFFERENT TYPES OF CELL
Authors: WHATLEY JEAN M.
Published: June 2006

Summary

During the period of cellular differentiation, plastids in all cells throughout the primary leaf of Phaseolus vulgaris undergo the same sequence of structural changes. However plastids in different types of cell can, at an early stage, be distinguished from each other quantitatively, i.e. in size, in the amount of starch accumulated, and, later, in the extent of their thylakoid systems. These quantitative differences depend in part on the position of the cell within the lamina and in part on the type of cell involved, and they persist throughout development. Further modifications in plastid structure affect only a few specialized types of cell. These later modifications in plastid structure take place only as the cells become fully differentiated.

Plastid division occurs in two separate phases, during seed development on the parent plant and during germination. It is probable that differing rates of plastid division and cell division in epidermal, palisade and mesophyll cells during early stages of germination are responsible for the characteristically different numbers of plastids present in each type of cell in the mature leaf.
ENDOGENOUS AUXIN AND CYTOKININ CHANGES DXJRING EMBRYOID DEVELOPMENT IN CELERY TISSUE CULTURES
Authors: AL‐ABTA SAHERA , COLLIN H. A.
Published: June 2006

Summary

Embryoids as embryonic cell masses, globular, heart and torpedo forms were grown on medium in the presence and absence of the growth regulators, 2,4‐dichlorophenyoxyacetic acid (2,4‐D) and kinetin. The early phase, up to the globular stage of development, was dependent on a supply of 2,4‐D and kinetin for continued cell division and growth, whereas the later stages did not require an external supply of growth regulators and their development was in fact inhibited if an external supply was provided. The early dependent phase and the later independent phase in the embryoids corresponded to the heterotrophic and autotrophic phases of embryo development in the intact plant. An analysis of endogenous auxin and cytokinin in the different stages of embryoid development showed a relatively low auxin content with little change at each stage. The cytokinins however showed both quantitative and qualitative changes with an increase in total cytokinin in the mature embryoids and plantlets then a decline in the intact plant.
EFFECTS OF LIGHT AND GROWTH REGULATORS ON GERMINATION AND RADICLE GROWTH OF LETTUCE SEEDS HELD UNDER HIGH‐TEMPERATURE STRESS AND WATER STRESS
Authors: HEGARTY T. W. , ROSS HEATHER A.
Published: June 2006

Summary

Seeds of two cultivars of lettuce (Lactuca sativa L.), untreated or soaked in acetone containing kinetin and gibberellic acid (K + GA3), were germinated in light or dark at a range of (high) temperatures and at a range of water potentials. In addition, untreated and treated seeds were germinated at 20°C in the light and then transferred to the same high temperatures or to low water potentials. In both cvs light and K + GA3 promoted germination at high temperatures and at low water potentials, although the cvs differed quantitatively in their responses. The upper temperature limit of germination in the light, and of radicle growth after germination, were similar in treated and untreated seeds respectively, suggesting that light and K + GA3 in combination may have completely removed the specific high‐temperature block to germination. Although light and K + GA3 increased the tolerance of germination to water stress, germinated, untreated seeds were able to grow at even lower water potentials. The K + GA3 treatment, whilst promoting germination under high temperature or water stress, reduced radicle growth subsequent to germination, thus providing support for the possibility that, in germination, the initiation of cell elongation has a degree of metabolic independence of the other processes associated with growth.
SOME ASPECTS OF CARBON METABOLISM AND TRANSLOCATION IN ONIONS
Authors: STEER B. T. , DARBYSHIRE B.
Published: June 2006

Summary

In the first six leaves of plants of Allium cepa L. cv. Creamgold grown from seed, the carbohydrate content per unit fresh weight within the leaf is highest in the leaf base and lowest at the tip. Soluble protein content is highest at the leaf tip and decreases down the leaf. The activity of ribulose bisphosphate carboxylase per unit fresh weight is constant in the upper leaf but is lower in the leaf sheath.

During growth, ribulose bisphosphate carboxylase activity reaches a maximum when leaves are at about 50 % of final size. Thereafter activity decreases even though leaf growth continues. After short exposures to 14CO2, 80 % of 14C in the leaf is recovered in sucrose. Carbon is rapidly translocated from the upper leaf to the leaf base and to a lesser extent to roots and unemerged leaves. The rapid carbon translocation is consistent with the absence of non‐structural polysaccharide pools in the upper leaf segments.
MOVEMENTS OF ABAXIAL AND ADAXIAL STOMATA
Authors: PEMADASA M. A.
Published: June 2006

Summary

A comparative study was made of diurnal movements, and responses to a range of light intensities, of abaxial and adaxial stomata on normal and inverted leaves of Stachytarpheta indica by microscopic examination of epidermal strips fixed in absolute ethanol. Additional observations were made on Coreopsis grandifiora, Crotalaria retusa and Tridax procumbens. The natural diurnal movements in the field and light‐induced opening in the laboratory and accompanied changes in concentrations of starch and potassium in the guard cells were all substantially more pronounced in the shaded abaxial stomata than in the exposed adaxial stomata on normal leaves. The effect of leaf inversion was to accentuate these differences considerably. Carbon dioxide‐free air was not effective in overcoming the differences in opening ability of abaxial and adaxial stomata. The differential behaviour of abaxial and adaxial stomata is related, to a great extent, to differential changes in concentrations of starch and potassium in abaxial and adaxial guard cells. The greater photosensitivity of abaxial stomata is a widespread phenomenon occurring in both monocotyledons and dicotyledons irrespective of differences in stomatal density; the adaptive significance of this phenomenon is briefly mentioned.
THE EFFECT OF EMBRYONAL AXIS ON THE DEVELOPMENT OF PHOTOSYNTHETIC ACTIVITY IN APPLE SEEDLINGS
Authors: MACIEJEWSKA U.
Published: June 2006

Summary

The development of photosynthetic activity in cotyledons from non‐dormant apple embryos and embryos in a state of dormancy was studied during the culture of intact embryos, of single cotyledon with axis, and of isolated cotyledons. The embryonal axis was found to stimulate the development of photosynthetic activity in the cotyledons. In non‐dormant embryos the influence of the axis on the assimilation of CO2 by cotyledons became apparent at an early stage of culture; in the dormant embryos it was noted first after 10 to 12 days. No influence of the embryonal axis was observed on chlorophyll biosynthesis in cotyledons. The photosynthetic rate was always higher in cotyledons from non‐dormant embryos than in those from dormant ones. However, the chlorophyll content was similar in cotyledons from both groups of embryos. It is concluded that the interaction of the embryonal axis and cotyledons in the development of photosynthetic activity in seedlings depends on the physiological state of the embryo.
WATER RELATIONS OF WHEAT ALTERNATED BETWEEN TWO ROOT TEMPERATURES
Authors: KIRKHAM M. B.
Published: June 2006

Summary

Water potentials, osmotic potentials and stomatal resistances were measured daily in a growth room during a 16‐day period, in growing leaves of a drought‐sensitive and a drought‐resistant winter wheat (Triticum aestivum L. em. Thell.), which had the roots maintained under one of three root‐temperature treatments: (1) constant temperature of 24°C (about the optimum); (2) constant temperature of 34°C (10° above the optimum and near the high temperature limit for growth); and (3) alternating temperature of 24 h at 24°C followed by 24 h at 34°C. Air temperature was constant at 24°C.

Water and osmotic potentials, stomatal resistances, and height of plants maintained at the 34°C root temperature were intermediate between those grown at 24°C (highest potentials, lowest resistances, tallest) and those alternated daily between the two temperatures (lowest potentials, highest resistances, shortest). Previous work showed that potentials, stomatal resistances, and growth of wheats subjected to constant root temperatures of 25, 29 and 33°C were linearly related to root temperature with lowest potentials, highest resistances, and least growth at the high temperature. Even though alternated plants in this experiment were at an average root temperature of 29°C, they grew the poorest. The wheat plants, therefore, did not integrate a root temperature stress in the same manner over ‘time’ as they did over ‘space’.

The results showed that the stomatal resistance, water and osmotic potentials, and height of wheat seedlings, maintained at a constant root temperature 10°C higher than the optimum, were about halfway between those of plants grown at the optimum and those alternated daily between the optimum and the optimum‐plus‐10 °C root temperature.
DESICCATION EFFECTS AND CATION DISTRIBUTION IN BRYOPHYTES
Authors: BROWN D. H. , BUCK G. W.
Published: June 2006

Summary

Analysis of the cations in a range of bryophytes, using a differential ion displacement technique, has shown that potassium is mainly soluble within the cells, calcium is bound, exchangeably, to sites in the cell wall and is insoluble within the cell and magnesium is present in all three locations. After desiccation, soluble ions either leak into the rehydrating solution (e.g. potassium and some magnesium) or become bound to the cell‐wall exchange sites (e.g. most of the magnesium). Leakage of intracellular ions can be used as a measure of membrane damage. An index of desiccation resistance (based on potassium retention within the cells after storage at 52 and 100% r.h.) is related to the availability of water in each bryophyte's habitat and is significantly correlated with the total potassium content of the plant. Reduced cation leakage occurred after material was transferred from either 52 or 0% r.h. to 100% r.h., indicating the ability of bryophytes to recover from such desiccation stress. An index of recovery is presented which shows that most bryophytes, unless excessively stressed, are able to repair the damage caused by desiccation.
CYTOCHEMICAL LOCALIZATION OF GLUTAMATE DEHYDROGENASES DURING CARPOPHORE DEVELOPMENT IN COPRINUS CINEREUS
Authors: ELHITI M. M. Y. , BUTLER R. D. , MOORE D.
Published: June 2006

Summary

The NAD‐ and NADP‐linked glutamate dehydrogenases were detected in frozen sections of carpophore tissues by means of tetrazolium salt. Material at all stages of development was examined. From the earliest stages NAD‐glutamate dehydrogenase was uniformly distributed in the basidial cells of the hymenium, and as the carpophore developed an increasing proportion of cells of the subhymenium came to express enzyme activity. The NADP‐glutamate dehydrogenase (NADP‐GDH) was initially limited to basidial cells in isolated patches of the hymenium. As development proceeded the proportion of basidia exhibiting NADP‐GDH activity increased, as did the proportion of subhymenial cells showing this enzyme activity. No NADP‐GDH activity was detectable in sections of stipe tissue.
THE UPTAKE OF UREA BY THE DIATOM, PHAEODACTYLUM
Authors: REES T. A. V. , SYRETT P. J.
Published: June 2006

Summary

Urea‐grown cells of Phaeodactylum absorbed [14C]urea by an active mechanism. Most of the urea taken up was present in the cells as free urea and the ratio of internal to external concentration could exceed 3000. The activity of the transport mechanism was greatly increased by depriving the cells of nitrogen for up to 24 h. The uptake mechanism had a high affinity for urea, the half‐saturation constant being about 1·0 μM. Active uptake of urea occurred in darkness, particularly in nitrogen‐deprived cells, but uptake was markedly stimulated by light. Uptake was not inhibited by DCMU but was abolished almost completely by 10−4m CCCP. It is concluded that active uptake is driven by phosphorylation. Uptake of [14C]urea continued until a constant level within the cells was attained, the plateau value probably resulting from a balance between rate of active uptake and rate of passive loss by diffusion.

The transport mechanism was absent from cells grown with ammonium as nitrogen‐source. The urea uptake mechanism developed in such cells when they were deprived of nitrogen; cycloheximide prevented the development of the mechanism. The mechanism was lost when urea‐grown cells were incubated in ammonium medium for 24 h but ammonium (at concentrations up to 10 mM) did not inhibit short‐term uptake of urea into urea‐grown cells.
THE UPTAKE OF UREA BY CHLORELLA
Authors: BEKHEET I. A. , SYRETT P. J.
Published: June 2006

Summary

The uptake of 14C by urea‐grown cells of Chlorella (strain 211/8p) supplied with [14C]urea was studied. Uptake was rapid in light with an apparent half‐saturation value (Km) for urea of 16·5 μM. Uptake was inhibited competitively by thiourea. Uptake of 14C was inhibited by 6 × 10−6 DCMU in light and was very much slower in darkness; nevertheless, under these conditions, rate of loss of 14C from the medium was much the same as in illuminated non‐inhibited cultures. [14C]urea was metabolized rapidly by the cells and, in illuminated cells after a 5 min exposure to [14C]urea, less than 50 % of the soluble 14C within the cells was in [14C]urea. It is concluded that much of the measured 14C uptake may have been due to conversion of [14C]urea to 14CO2 followed by photosynthetic 14CO2 fixation. Nevertheless, when [14C]urea in the cells was extracted and separated by thin‐layer chromatgraphy, there was clear evidence of accumulation at a concentration above that in the external medium and of light stimulation of uptake. It is suggested that, in view of the rapid metabolism of [14C]urea by Chlorella, it may be preferable to study the uptake mechanism of this organism by using the urea analogue, thiourea.
THE OCCURRENCE OF A HYPERSENSITIVE REACTION IN THE PLANKTONIC DIATOM ASTERIONELLA FORMOSA HASSALL PARASITIZED BY THE CHYTRID RHIZOPHYDIUM PLANKTONICUM CANTER EMEND., IN CULTURE*
Authors: CANTER HILDA M. , JAWORSKI G. H. M.
Published: June 2006

Summary

Culture work has shown that cells of the diatom Asterionella formosa Hassall may undergo a hypersensitive death reaction in response to infection by the chytrid Rhizophydium planktonicum Canter emend. In the clone of Asterionella studied most of the infected cells exhibited this fatal reaction. On these incompatible cells the fungus died and the encysted zoospore did not enlarge into a sporangium. However, in very rare instances a compatible cell bearing a sporangium was found. An investigation of this mainly incompatible, hypersensitive host‐parasite relationship was conducted using light microscopy and experimentation.
ULTRASTRUCTURE OF DRY SEED TISSUE AFTER A NON‐AQUEOUS PRIMARY FIXATION
Authors: THOMSON WILLIAM W.
Published: June 2006

Summary

A primary fixative of formaldehyde and glycerol is presented as an essentially non‐aqueous medium for the preservation of dry material, such as seeds, for electron microscopic studies. Good preservation of the ultrastructure of the parenchyma cells of cotyledons of dry seeds of mungbean was obtained with this fixative. In these cells the nuclei, plastids, protein bodies and mitochondria were easily identified. In some parenchyma cells, stacked arrays of ribosomes were observed that were similar to ordered arrays of rough endoplasmic reticulum although the membrane elements were poorly defined. In general, all membranes including the plasmaiemma were ill defined, suggesting that, in dry seeds, membranes are disorganized from the topical bilayered structure.
ULTRASTRUCTURE OF PHLOEM IN YOUNG RUNNER‐BEAN STEM: DISCOVERY, IN OLD SIEVE ELEMENTS ON THE BRINK OF COLLAPSE, OF PARIETAL BUNDLES OF P‐PROTEIN TUBULES LINKED TO THE PLASMALEMMA
Authors: LAWTON D. M. , NEWMAN Y. M.
Published: June 2006

Summary

Thin sections of the oldest uncrushed sieve elements in two vascular bundles have been examined by electron microscopy. They are shown to contain bundles of about 50 P‐protein tubules which are no different in appearance from tubules in immature sieve elements. Tubules in these old sieve elements have remained interlinked with ‘side‐arms’ throughout the time that the sieve elements were translocating. The accumulation of callose on each sieve element pore, which signifies senescence, may incidentally protect the tubules from changes in pressure whilst they are fixed. The generally held conclusion that P‐protein tubules change into narrow striated filaments and disperse from their parietal positions as the sieve element reaches maturity is re‐examined.

In the development of the sieve element the central body of the P‐protein crystal is shown to be present very early, at a stage when the sieve element and the companion cell are otherwise still difficult to distinguish.