bluuebunny/crossref_metadata_2025_split huggingface dataset:
Internal structure of aeolian dunes in Abu Dhabi determined using ground‐penetrating radar
Authors: BRISTOW CHARLIE , PUGH JONATHAN , GOODALL TIM 
Published: June 2006

ABSTRACTA ground‐penetrating radar survey of aeolian dunes in the Al Liwa area of Abu Dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures. The interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles. NNW— SSE‐orientated radar profiles, approximately parallel to the prevailing wind direction, show two sets of dipping reflectors which are interpreted as sets of cross‐stratification and second‐ and third‐order bounding surfaces. Radar profiles orientated WSW—ENE across the prevailing wind direction are dominated by concave‐up reflectors which are interpreted as trough‐shaped scours and sets of trough cross‐stratification produced by oblique progradation of barchanoid dunes. Nested troughs, with small sets of trough cross‐stratification within larger troughs, may be due to reactivation following wind reversal, or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes. Convex‐upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs. Overall there is a tendency for the larger second‐order bounding surfaces to dip downwind, which confirms Brookfield's ideas of the relative migration paths of dunes and draa.
Regional setting and role of meteoric water in dolomite formation and diagenesis in an evaporite basin: studies in the Zechstein (Permian) deposits of Poland
Authors: PERYT TADEUSZ M. , SCHOLLE PETER A. 
Published: June 2006

ABSTRACTThe Zechstein Basin of Poland was an area of widespread cyclical deposition of carbonates and evaporites during Late Permian time. The Zechstein shelves, along both the northern and the southern margins of the basin, were sites of shallow‐water sedimentation during the formation of the Main Dolomite and Platy Dolomite, two widespread carbonate units. These units consist of oolitic, peloidal, skeletal, micritic and evaporitic carbonates formed in depositional settings ranging from open marine to coastal (lagoonal, sabkha and salina). Although originally deposited as limestones, the Main Dolomite and Platy Dolomite are inferred to have been completely replaced by dolomite through very early stage (essentially penecontemporaneous) reflux of hypersaline brines.The dolomites of the two basin margins, however, have very different petrographic and isotopic characteristics. Many northern shelf dolomites show early stage calcitization (dedolomitization) and even, in some cases, evidence of a subsequent redolomitization event. These northern shelf samples also have a broad range of carbon and oxygen isotopic ratios (up to 12%0for oxygen). Samples from the southern shelf, on the other hand, are petrographically much simpler; they do not show complex calcitization and redolomitization patterns. Likewise, their isotopic values are much more tightly clustered, with only about a 5%0range of oxygen isotopic ratios.The differences between dolomites of the same age from the northern and southern margins are best explained by regional variations in river water influx during episodic exposure events associated with regional or global sea‐level fluctuations. The distribution of clastic terrigenous materials and palaeokarstic features indicate that areas of the northern shelf had extensive river input, an influx largely lacking on the southern shelf. Early formed dolomites appear to have been calcitized during sea‐level lowstands through the infiltration of meteoric fluids into the evaporitic dolomites created during the previous highstand. In some cases, redolomitization occurred when meteoric fluids were again replaced by hypersaline brines during subsequent sea‐level highstands.Although repeated sea‐level fluctuations are clearly evident in these strata, it is likely that associated climatic changes (rainfall variations) also played a role in forming these complex diagenetic patterns. Age‐equivalent strata from Texas and New Mexico (from sites at much lower palaeolatitudes) show no such alteration patterns; samples from Greenland (slightly higher palaeolatitudes) show even more intense diagenetic alteration during depositional cycles. Thus, the examination of patterns of diagenesis may be useful in interpreting ancient, palaeolatitudinally sensitive climate patterns.
Epitaxial salt reefs and mushrooms in the southern Dead Sea
Authors: TALBOT C. J. , STANLEY W. , SOUB R. , AL‐SADOUN N. 
Published: June 2006

ABSTRACTSalt usually accumulates in shallow ephemeral brines as simple flat beds. However, in permanent brines deepening in solar evaporation ponds in the southern Dead Sea, salt accumulation is complicated by the growth of isolated vegetable‐like salt structures and networks of polygonal salt walls. These walls divide large salt ponds, which are easily homogenized by wind, into thousands of small compartments that are less easy to mix. Instead, brines in the compartments stratify when a surficial layer about 10 cm thick supersaturates and floats above the cumulate floors on brines that are merely saturated.Salt reef growth in the southern Dead Sea has previously been attributed to mixing of ions common to brines already in the ponds and those pumped in from the northern basin (with or without subsurface brines rising through the pond floors). A new factor is emphasized here that, whatever the origins of the brines, salt reefs remain emergent by epitaxis, the in situ growth of crystalline substrates already in the surficial supersaturated layer.Epitaxis can be invisible in crystal clear brines and prolongs the obvious crystallization season by replacing sedimentation of grains nucleated and grown on the brine surface as the dominant mechanism of deposition. Salt reefs develop botryoidal overhangs that can merge into salt platforms that roof over deep brines. Salt shallows on the reef platforms and around the pond shores are both characterized by the deposition of the thin flat beds with vertical palisade textures well known from other ephemeral brines. Salt reefs are interpreted as tepee structures which have grown by epitaxis as fast as saturated brines have deepened around them. Epitaxis may also account for the rapid deposition of thick beds of pure salt in rifts that open to oceans.Local histories of salt reef compartmentalization can be read from the shapes of reefs that record their relative rates of growth and drowning. Rather than diminish evaporation area, damp emergent salt reefs act as giant transpirative pumps that accelerate salt crystallization and reconfigure the evaporation ponds into areas smaller than thought necessary by chemical engineers. The natural end of reef formation may be when shallow brines on hollow reef platforms become ephemeral on solid salt flats. Former salt reefs are likely to be distinguishable in the undeformed geological record by their botryoidal layers of nonvertical chevron crystals.
Transition from foreland‐ to piggyback‐basin deposition, Plio‐Pleistocene Upper Siwalik Group, Shinghar Range, NW Pakistan
Authors: PIVNIK DAVID A. , KHAN M. JAVED 
Published: June 2006

ABSTRACTPlio‐Pleistocene synorogenic deposits of the Upper Siwalik Group in the Shinghar Range (Trans‐Indus Salt Ranges) of north‐western Pakistan record the transition from foreland‐basin to piggyback‐basin deposition on the hangingwall of the Salt Range thrust. The Siwalik and Upper Siwalik Groups are over 4 km thick in the Shinghar Range. The lower 3 km consists of the Miocene Siwalik Group, which was deposited by a south‐flowing foreland trunk stream, the palaeo‐Indus River. The upper 1·5 km consists of the Upper Siwalik Group, which is herein divided into three members. The lowest member includes deposits of the south‐flowing palaeo‐Indus River and is distinguished from the underlying Siwalik Group by the first appearance of conglomerate. The transition from the lower member to the middle member is interpreted as recording uplift on the Salt Range thrust. As the Salt Range thrust was active, the palaeo‐Indus River was bifurcated to the east and west around the embryonic Shinghar Range and overbank and lacustrine deposition occurred, represented by the middle member. When the Shinghar Range achieved significant topography, the upper member was deposited by streams transporting gravel and sand that flowed north and west out of the range and into a piggyback basin that formed on the hangingwall of the Salt Range thrust. New and previously published palaeomagnetic stratigraphy and fission‐track ages from volcaniclastic deposits within the Upper Siwalik Group provide tight constraints on the chronology of sedimentary‐facies transitions and timing of uplift of the Shinghar Range. The integration of sedimentological and geochronological data indicates that motion on the Salt Range thrust and repositioning of the Indus River began at ∼1·0 Ma.
Thermokarst‐lake‐basin sediments, Tuktoyaktuk Coastlands, western arctic Canada
Authors: MURTON JULIAN B. 
Published: June 2006

ABSTRACTThree stages of deposition are distinguished in thermokarst‐lake‐basin sequences in ice‐rich permafrost of the Tuktoyaktuk Coastlands, western arctic Canada: (1) widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes, forming a distinctive basal unit of impure sand and/or diamicton; (2) a reduction or cessation of slumping‐because of the pinching out of adjacent ground ice, slump stabilization or climatic cooling, that reduces the input of clastic sediment, permitting reworking of sediment around lake margins and suspension settling, principally in basin centres; (3) lakes drain and deposition may continue by gelifluction and accumulation ofin situpeat or aeolian sand.Radiocarbon dating of detrital peat and wood from a progradational sequence (basal unit) defines a lateral younging trend in the direction of progradation. A progradation rate is calculated to be ∼ 4 cm yr−1, consistent with rapid deposition during stage (1) above. The nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents.In comparison with thermokarst‐lake‐basin sequences previously described in Alaska, Canada and Siberia, the middle unit of those in the Tuktoyaktuk Coastlands is similar, whereas the basal unit is generally thicker and, by contrast, often contains diamicton. These differences are attributed, respectively, to larger‐scale resedimentation of upland sediments by retrogressive thaw slumping and debris‐flow deposition in thermokarst lakes in the Tuktoyaktuk Coastlands. Compared with the sediments within supraglacial lakes in areas of moderate to high relief, the middle unit of thermokarst‐lake‐basin sequences in the Tuktoyaktuk Coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable. These differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes, which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the Tuktoyaktuk Coastlands.It may be impossible to distinguish glacial and periglacial thermokarst‐lake‐basin sediments in permafrost areas of incomplete deglaciation. Not only is it often difficult to distinguish intrasedimental and buried glacier ice, but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar.
Internal architecture and sedimentary evolution of coarse‐grained, turbidite channel‐levee complexes, Early Eocene Regência Canyon, Espírito Santo Basin, Brazil
Authors: BRUHN CARLOS H. L. , WALKER ROGER G. 
Published: June 2006

ABSTRACTSuccessions of Early Eocene coarse‐grained turbidites up to 400 m thick fill fault‐controlled canyons along the eastern Brazilian continental margin. They form part of a Late Albian to Early Eocene transgressive succession characterized by onlapping, deepening‐upward sedimentation. In the Lagoa Parda oil field (Regência Canyon, Espírito Santo Basin) the turbidite facies consist mostly of unstratified conglomerate and sandstone, with interbedded bioturbated mudstone and thin‐bedded, stratified sandstone. Within the main Regência Canyon, the coarser grained facies occur within 38 deeply incised channels. The fills are 9 to >50 m thick, 210 to >1050 m wide and >1 km long. The finer grained facies build asymmetrical levees that are higher and thicker on the left side (looking downstream) of their channels, probably as an effect of the Coriolis force (to the left in the Southern Hemisphere). Nine levee successions up to 50 m thick are associated with the 20 youngest channels. The deposits filling the low‐sinuosity Lagoa Parda channels record successive channel abandonment through relatively rapid avulsions. Avulsions of unleveed channels took place randomly, but channels with well‐developed levees show preferential avulsion to the right (looking downstream), opposite to the direction of preferential levee growth.Lagoa Parda channels can be grouped into three complexes 20–100 m thick. These complexes have an estimated duration of about 140 000 years. It is suggested that control of the development of individual channel complexes was related to variation in sediment supply, in turn probably related to climatic changes. The deposition of each channel complex would have followed an increase in sediment supply into the Regência Canyon through delta/fan‐delta and littoral drift systems, which in turn would have responded to phases of higher denudation rates in the high‐relief, ancestral coastal ranges of south‐eastern Brazil.Overall, the three Lagoa Parda channel complexes form a turbidite succession characterized by channel fills that become narrower, thinner and finer grained upward. These trends were induced mostly by a longer term (>400 000 years) decrease in sediment supply, which in turn resulted from the combined effects of a long‐term (second‐order) trend of sea‐level rise, and the decreasing fault activity at the basin margin and source area.
Marine‐derived dolomite in the shallowly buried temperate Port Campbell Limestone (Miocene), Otway Basin, Australia
Authors: NICOLAIDES STELIOS 
Published: June 2006

ABSTRACTThe Miocene Port Campbell Limestone in the Otway Basin (Port Campbell Embayment), south‐eastern Australia, is a shallowly buried (<350 m), temperate carbonate grainstone which consists primarily of benthonic foraminifera, bryozoans, brachiopods, echinoids and planktonic foraminifera. Volumetrically insignificant calcite cements include scalenohedral, blocky and syntaxial overgrowths. Dolomite is present in variable amounts (1–25%), scattered throughout the unit as euhedral rhombs, usually comprising <2% of the whole rock volume. The dolomite post‐dates the calcite cements and is mainly an interparticle cement with crystal size varying between 10 and 150 μm (mean 50 μm). Under cathodoluminescence the dolomite rhombs have a dull core and a nonluminescent outer rim.The dolomite is nonstoichiometric, Ca‐rich (Ca54–62Mg38–46), with high trace element concentrations. The Mn concentrations range from 0 to 310 p.p.m. in the crystal cores (mean 140 p.p.m.) and 80–240 p.p.m. in the crystal rims (mean 140 p.p.m.). The Fe concentrations increase from the crystal cores (range 640–5690 p.p.m.; mean 2030 p.p.m.) to the crystal rims (range 2840–9440 p.p.m.; mean 6040 p.p.m.), whereas the Sr concentrations decrease from the crystal cores (range 690–1510 p.p.m.; mean 1280 p.p.m.) to the crystal rims (620–1240 p.p.m.; mean 930 p.p.m.). The δ13CPDB values of the dolomite range between +2.5 and +2.6%, whereas the δ18OPDB values range from +0.3% to+0.6%.This dolomite occurrence supports the idea that marine or near‐marine dolomite can form not only syndepositionally, but also in the shallow subsurface of temperate units, soon after sediment deposition, under reducing conditions. The fine‐grained, low‐permeability nature of the Port Campbell Limestone contributed to the reducing conditions at shallow depth, the high trace element concentrations of the dolomite (especially in Fe) and the near marine composition of the dolomitizing fluids, as large volumes of meteoric water were inhibited.
Anatomy and evolution of a Lower Cretaceous alluvial plain: sedimentology and palaeosols in the upper Blairmore Group, south‐western Alberta, Canada
Authors: MCCARTHY PAUL J. , MARTINI I. PETER , LECKIE DALE A. 
Published: June 2006

ABSTRACTThe Lower Cretaceous (Albian) upper Blairmore Group is part of a thick clastic wedge that formed adjacent to the rising Cordillera in south‐western Alberta. Regional transgressive intervals are superimposed on the overall regressive succession. Alluvial conglomerates, sandstones and mudstones were deposited in east‐north‐eastward draining fluvial systems, orientated transverse to the basin axis. Five facies associations have been identified: igneous pebble conglomerate, thick sandstone, interbedded lenticular sandstone and mudstone, thick mudstone with thin sandstone interlayers, and fossiliferous sandstone and mudstone. The facies associations are interpreted as gravelly fluvial channels, sandy fluvial channels, sand‐dominated floodplains, mud‐dominated floodplains, and marine shoreline deposits, respectively.Five types of palaeosols are recognized in the upper Blairmore Group based on lithology, the presence of pedogenic features (clay coatings, root traces, ferruginous nodules, slickensides, carbonate nodules) and degree of horizonization. The regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution. In source‐proximal areas, palaeosol development was inhibited by high rates of sedimentation. In source‐distal locations, poor drainage resulting from high watertables, low topography and lower rates of sedimentation also inhibited palaeosol development. The best‐developed palaeosols (containing Bt horizons) occur in intermediate alluvial plain positions (tectonic hinge zone) where the floodplains were most stable due to a balance between sedimentation, erosion and subsidence rates. Extrapolating from the upper Blairmore Group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis. At the hinge zone, soil development is controlled primarily by climate and tectonics and their effect on sediment supply, whereas closer to the palaeoshoreline, relative sea level fluctuations, resulting in poor drainage, may have a more significant influence.
Formation of silica oncoids around geysers and hot springs at El Tatio, northern Chile
Authors: Jones Brian , Renaut Robin W. 
Published: June 2006

ABSTRACTSiliceous oncoids, up to 4 cm in diameter, are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at El Tatio in northern Chile. Many of these complex oncoids developed close to geyser and spring vents that discharge boiling water. Internally the oncoids, which are composed of precipitated amorphous silica, are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains. Spicular growth is dominant in most examples. The formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes, mucus, and possibly bacteria. The microbes and mucus were silicified by replacement and encrustation. In some laminae the filamentous microbes lay parallel to the growth surface; in other laminae most filaments forming the thin mats were suberect. Amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric.The oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools. Most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and/or periodic shallow flooding of the discharge aprons. Unlike silica oncoids at other geothermal sites, vertical growth of oncoids that formed in some rimstone pools was not limited by water depth.
THE EFFECT OF THE PLANT HORMONE ABSCISIC ACID ON LIPID BILAYER MEMBRANES
Authors: LEA E. J. A. , COLLINS J. C. 
Published: June 2006

SummaryIn the presence of the plant hormone 2‐cis,4‐transabscisic acid, bimolecular lipid membranes exhibited conductance fluctuations of the type associated with channels. Under a voltage clamp of 100 mV, channels were observed of mean conductance 0‐4 × 10−10S and mean lifetime 0·2 msec.Membrane conductance was measured as a function of concentration of abscisic acid and a log‐log plot of the data revealed a linear relationship. The slope of the regression line was 0·52 ± 0·08 with Pearson's product moment 0·85.An analysis of current fluctuations is presented.The results are discussed in terms of a process in which multimeric channels are generated from abscisic acid monomers and in which channels are destroyed by collision.
PHOTOSYNTHESIS, RESPIRATION AND WATER CONTENT IN BRYOPHYTES
Authors: DILKS T. J. K. , PROCTOR M. C. F. 
Published: June 2006

SummaryResponse curves of photosynthesis to water content of bryophytes of dry habitats (e.g. Tortula intermedia, Camptothecium lutescens) show an optimum, with photosynthesis declining again at high water contents. Respiration may be stimulated by water stress, but is unaffected by high water contents. The steep portions of the photosynthesis and respiration curves lie within a similar range at low water contents. Some species of constantly moist habitats (e.g. Pellia epiphylla, Hookeria lucens) show photosynthesis increasing progressively to water contents of 500 to 1000 % of dry weight, and affected at much lower water deficits than respiration as the plant dries out. The response of photosynthesis and respiration to water potential is broadly similar in the two groups. In the species investigated there was generally measurable photosynthesis at –60 to – 100 bar, but little or none at – 150 to –200 bar. Respiration continues to somewhat lower water potentials of which the limits were not determined.Field measurements of the water content of shoots of five species over a period of 12 months showed much greater variation in Tortula muralis than in the woodland species. Maximum water contents in the field generally lay close to the optima of the photosynthesis response curves. The lower water contents recorded in these and in published data are considered in relation to sorption isotherms for bryophytes and other plant materials.The water associated with bryophyte shoots can be divided into (1) water within the cell walls (apoplast water), (2) water within the cytoplasm (symplast water), and (3) external capillary water. Changes in water content below about –200 bar take place chiefly within (1), between c.– 200 and c. ‐ 2 bar within (2), and at higher water potentials chiefly within (3). Water movement within the shoots is physiologically important; the distribution and movement of water are mediated by the geometry of the capillary spaces of the cell walls and the plant surface. In species with papillose leaves, rates of capillary conduction in the interstices between the papillae are more than sufficient to balance evaporation. Conduction within the cell walls is likely to be important in species with non‐papillose leaves, hut other pathways may also be involved, and water movement in these species requires further investigation.