bluuebunny/crossref_metadata_2025_split huggingface dataset:
Early diagenetic spherulitic siderites from Pennsylvanian palaeosols in the Boss Point Formation, Maritime Canada
Authors: BROWNE G. H. , KINGSTON D. M. 
Published: June 2006

ABSTRACTThe Boss Point Formation of Maritime Canada comprises alternating successions of braidplain sandstone, lacustrine mudstone, and lacustrine fluvio‐deltaic sandstone and mudstone. These rocks were deposited within an active strike‐slip basin during the early Pennsylvanian (Westphalian A), at a palaeolatitude of 8°S. Palaesols comprise a small but distinct proportion of the formation, and typically occur at the tops of fining upward sandstone‐siltstone cycles.Spherulitic siderites from the Boss Point Formation occur within sandy and silty palaeosols. They occur as ‘large’ (>200 μm) and ‘small’ (<200 μm) diameter spherulitic nodules within calcrete, and show either a radially arranged ferroan calcite and siderite spar morphology, or contain a core of ferroan calcite, surrounded by a later formed sheath of siderite. Analytical data indicate that with respect to Ca‐Mg‐Mn, wide compositional variation occurs within the siderites. The Boss Point Formation siderites are similar to, but contain less Ca for a given Mg/Mn ratio, than previously published siderite compositional data. Published data, together with the results from the Boss Point Formation, indicate that a continuum exists in freshwater siderites, between the relatively Mn‐depleted and the Mg‐enriched analytical fields that were previously reported.The relatively low Ca values determined in the Boss Point Formation samples reflect the general lack of calcium in the sedimentary basin during sedimentation. Both chlorite and smectite clays may have been important sources of iron. It is concluded that the spherulitic siderites are eogenetic, and formed within small anoxic ponds rich in organic matter, under reducing and low dissolved sulphate conditions. With time these pools dried up, ferroan calcite precipitating as calcrete nodules around the earlier formed siderite spherulites.
Sediment suspension under waves and currents: time scales and vertical structure
Authors: OSBORNE PHILIP D. , GREENWOOD BRIAN 
Published: June 2006

ABSTRACTField measurements of the vertical structure of near‐bed suspended sediment concentrations were obtained from arrays of fast response optical backscatter suspended solids sensors to examine the time‐dependent response of sediment resuspension to waves and currents and the constraints imposed by bedforms. Data were recorded from both a nonbarred, marine shoreface and a barred lacustrine shoreface, under both shoaling and breaking waves (significant heights of 0·25–1·50m; peak periods of 3 and 8 s) and in water depths of 0·5–5·0 m. Sediment concentrations are positively correlated with increasing elevation above the bed, but lagged in time. The time lag varies directly with separation distance between measurement locations and inversely with the horizontal component of the near‐bed oscillatory velocity.Both the presence of wave groups and the settling velocities of the sediment particules in suspension influence the temporal changes in concentration at a given elevation. Sediment concentrations appear to respond more slowly to the incident wind‐wave forcing with distance away from the bed as a result of two factors: (1) the sequential increase in concentration induced by a succession of large waves in a group; and (ii) the relative increase in finer sediments with smaller settling velocities. Bedforms interact with the near‐bed horizontal currents to impose a distinct constraint upon the timing of suspension events relative to the phase of the fluid motion, and, therefore, the vertical structure of the suspended sediment concentration at a range of time scales. The near‐bed concentrations appear to be strongly dependent upon the vertical convection of sediment associated with the ejection from the wave boundary layer of separation vortices generated in the lee of ripple crests. Concentration gradients in the presence of vortex ripples are large, as are the correlation between concentrations measured at different elevations within the fluid.
Pleistocene glaciolacustrine sedimentation in a tectonically active zone, Kleszczów Graben, central Poland
Authors: KRZYSZKOWSKI DARIUSZ 
Published: June 2006

ABSTRACTThe Kleszczów Graben in central Poland was formed by late Oligocene to Middle Pleistocene extensional tectonics. During the Pleistocene it was infilled with a 200 m thick sequence of predominantly glacial sediments. Four distinct formations of Elsterian and Saalian age are identified, each containing 15–40 m of glaciolacustrine strata. The boundaries between formations are marked by erosional surfaces and, in part, by angular discordances caused by tectonism. Glaciolacustrine sedimentation was tectonically controlled: the thickness of the sequences in the graben are three to five times greater than outside the area of fault‐controlled subsidence. Deposition in the proglacial lakes was controlled by differential subsidence rates within the basin: deep‐lake facies (varved clays) were deposited in sub‐basins with high subsidence rates and deltaic to shallow‐water facies accumulated in areas of moderate subsidence or occasional uplift. These variations led to the development of a very complex, ‘mosaic’ of lateral facies relationships, suggesting that several sub‐basins with differing subsidence rates were present. The Vertical successions show proximal‐distal sequences typical of glacier‐fed lakes that have limited contact with the ice sheet. However, gravity flow facies are very common, and occur both in the shallow‐ and deep‐water deposits. These deposits are interpreted to have been formed adjacent to active fault scarps which bordered the lake basin. Although several distinct phases of glaciolacustrine sedimentation occurred during the history of trough infilling, the location of the areas of high subsidence varied through time.
The effects of fluctuating base level on the structure of alluvial fan and associated fan delta deposits: an example from the Tertiary of the Betic Cordillera, Spain
Authors: FERNÁNDEZ JUAN , BLUCK BRIAN JOHN , VISERAS CÉSAR 
Published: June 2006

ABSTRACTThe Villanueva Complex is a lacustrine alluvial fan ‐ fan delta system which accumulated on the northern margin of the Guadix Basin during the Pliocene. Five transitional zones can be distinguished from proximal to distal areas: proximal alluvial fan, mid‐fan, fan fringe (transition zone), proximal fan delta and distal fan delta (lacustrine).This paper focuses on sedimentation in the fan fringe and the proximal fan delta areas, where the effects of fluctuations in the base level (lacustrine level) are more easily observed. The stratigraphical succession is here characterized by an alternation of fine lacustrine sediments (mudstones and siltstones) and gravels. The gravels appear as isolated channels, stacked channels, lenses and sheets.The isolated channels, which have a V‐shaped profile and better developed wings towards the top, appear in the fan fringe zone and in the fan delta. The stacked channels originate in the fan fringe zone and evolve laterally and distally to isolated channels. The lenticular gravel bodies (lenses) are well represented throughout the fan delta and present small channels at the base, indicating a radial flow pattern. Finally, the sheets are characteristic of the fan fringe zone. The first episodes of channel incision occurred at lowstand lake level. The channels and lenses developed in rising lake level conditions, and sheet deposit took place at highstand lake level. Although the final form of the lithosome was heavily controlled by the fluctuations in lake level, it depended on the relative proportions of gravel and silt sedimentation. The gravel‐siltstone interface therefore represents an equilibrium surface between the proportions of sedimentation of these lithologies.The bodies mentioned above are organized in coarsening and thickening upwards sequences tens of metres thick, in which a distal to proximal evolution can be observed from isolated channels to lenses or from stacked channels to sheets. The building and thickness of these sequences were controlled by fluctuations in the lake level. An initial fall in base level caused lengthening of the channels and entrenchment from distal to proximal areas, and a continuous increase in supply due to erosion in the drainage basin installed on the subaerial fan. When the lake level rose, lobes were formed at the channel endings and overbank processes were made possible, thus generating radial channels, whose levees were formed by amalgamation with the levees of the main lens channels. At the same time, sheets were formed in proximal areas, where the available amount of sediment was greater.
Development of cusp‐related, gravel size and shape facies at Malin Head, Ireland
Authors: SHERMAN DOUGLAS J. , ORFORD JULIAN D. , CARTER R. W. G. 
Published: June 2006

ABSTRACTSamples of beach gravels were obtained from foreshore cusp deposits at Portmore Beach, near Malin Head, Republic of Ireland. Axial dimensions (A, B and C) were measured, and the maximum projection sphericity was derived, for each of 4360 clasts. Each sample was also categorized according to depositional subenvironment. Principal components analysis and cluster analysis were used to identify potential facies zonation. Results indicate that reworking of the foreshore by incident and edge waves resulted in clast size and shape segregation both parallel and perpendicular to the beach. Patterns of zonation were distinctly different from those described in earlier facies descriptions, showing a complex set of foreshore facies. The distribution of these facies was controlled primarily by location within beach cusp systems. Primary and secondary facies demonstrate alongshore variability of a magnitude comparable to across shore differences. The results have important implications for palaeoenvironmental reconstruction, morphosedimentary description and research sampling design, and provide the basis for a conceptual model of gravel beach cusp facies.
Porosity evolution of the Cambrian Bonneterre Dolomite, south‐eastern Missouri, USA
Authors: GREGG JAY M. , LAUDON PETER R. , WOODY ROBERT E. , SHELTON KEVIN L. 
Published: June 2006

ABSTRACTThe Cambrian Bonneterre Dolomite of south‐eastern Missouri, USA, hosts the large Mississippi Valley type (MVT) lead‐zinc‐copper ore deposits of the region. The Bonneterre Dolomite consists of dolomitized algal bioherms, oolitic grainstone and associated lithologies that were deposited on a carbonate platform surrounding the Precambrian age St Francois Mountains. Porosity was determined by point counting thin sections from cores and mines in the Bonneterre Dolomite and by gas porosimetry. Volumes of epigenetic cements were estimated by point counting cement filling micro‐ and mesoporosity using cathodoluminescence. Cement volumes were added to present porosity to estimate porosities during various stages of mineralization. Prior to the onset of mineralization, micro‐ and mesoporosity in the Bonneterre Dolomite averaged approximately 19%. Precipitation of early dolomite cement (roughly concurrent with the main period of sulphide deposition) reduced average porosity to approximately 7% and closed off much of the intercrystalline pore space. Later cementation by dolomite (prior to late stage sulphides) reduced porosity to approximately 5%, and late cementation by quartz further reduced porosity to the present average value of <4%. Periods of carbonate dissolution during MVT mineralization enhanced large scale megaporosity associated with fractures and breccias but did not significantly increase smaller scale porosity. Dolomite cementation associated with MVT mineralization, porosity and permeability were facies controlled. Today, as a result of mineralization, large scale fractures and breccias control porosity and permeability. This study indicates that dolomite porosity may undergo significant change during basinal brine migrations associated with MVT mineralization.
Rip currents as a geological tool
Authors: GRUSZCZYŃSKI MICHAŁ , RUDOWSKI STANISŁAW , SEMIL JULIA , SŁOMIŃSKI JAN , ZROBEK JERZY 
Published: June 2006

ABSTRACTThis paper considers the nature and sedimentary significance of rip currents. Rip currents are the main factor responsible for the transport of coarse sediments from the littoral zone to greater depths. Such sediments, deposited outside the zone of wave deformation, may be identified as storm rip current increments within sediments deposited during fair weather. Composite beds deposited during a given wave cycle by storm rip currents are closely similar to ‘turbidites’ and many so called ‘fluxo‐turbidites’ described from flysch deposits.Using data gathered in studies conducted on the modern Baltic coast, supplemented by experimental work and theoretical considerations, a sedimentary model is proposed. The model may be used to interpret possible rip current deposits among shallow water ‘turbidites’, and both modern storm sediments and ancient ‘tempestites’.
Zeolitic diagenesis of late Quaternary fluviolacustrine sediments and associated calcrete formation in the Lake Bogoria Basin, Kenya Rift Valley
Authors: RENAUT R. W. 
Published: June 2006

ABSTRACTLate Quaternary fluviolacustrine siltstones, mudstones and claystones (Loboi Silts) on the northern margins of the saline, alkaline Lake Bogoria in the Kenya Rift Valley contain up to c. 40% authigenic analcime and minor natrolite. The zeolitic sediments are reddish brown and up to 1 m thick. The amount of analcime increases upward in the profile, but decreases with distance from the lake. The altered sediments show many pedogenic features including zeolitic root mats, rootmarks, concretions and carbonate rhizoliths. Residual patches of calcrete locally cap the zeolitic rocks. The profile is interpreted as an exhumed palaeosol and land surface on the former margins of the lake.The analcime occurs as submicroscopic (0–5–2–5 μ.m) subhedral and euhedral crystals, which have an average Si/A 1 ratio of 2–33 (as determined by X‐ray microanalysis) or 2–18 (d‐value of 639 analcime peak). The analcime formed in lake marginal sediments (soils) by reaction of silicate detritus with Na2CO3 rich pore waters concentrated close to the land surface by evaporative pumping and evapotranspiration. Poorly ordered clay minerals were probably the main reactants. Authigenic illite may have been a by‐product of the reactions. Chemical analyses suggest that pore waters supplied some of Na+, and possibly K+ and SiO2. The associated calcrete and rhizoliths were formed during or shortly after the main period of zeolitic alteration. The Ca2+ may have originated from infiltrating dilute runoff and groundwater. Authigenic smectite was precipitated in open porosity following analcime formation. The zeolitic alteration at Lake Bogoria provides a relatively recent analogue for lake marginal zeolites found in many ancient saline, alkaline lake sediments.
Stable isotopic compositions of Recent freshwater cyanobacterial carbonates from the British Isles: local and regional environmental controls
Authors: ANDREWS J. E. , RIDING R. , DENNIS P. F. 
Published: June 2006

ABSTRACTRecent (<50 years old) freshwater cyanobacterial carbonates from diverse environments (streams, lakes, waterfalls) throughout Britain and Ireland were analysed for their stable carbon and oxygen isotope compositions. The mean δ18O value of −5–9‰ PDB for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central Britain (−7–5‰SMOW) assuming a mean water temperature of 9°C. The mean δ18O of lake data, −4–5‰ PDB, is statistically different, reflecting the effects of residence time and/or variations in the oxygen isotopic composition of rainfall. Carbon isotopes have wide variations in both fluviatile and lake data sets (+ 3 to −12‰ PDB). These variations are principally controlled in the fluviatile samples by contribution of isotopically light ‘soil zone’ carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution. Lake samples have the heaviest carbon isotope values, reflecting a trend toward isotopic equilibrium between atmospheric CO2 and aqueous HCO−3.We infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information, although the effects of stabilization and diagenesis on primary δ18O values will need careful consideration. Primary carbon isotope compositions should be well preserved, although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate.
Facies and depositional processes in an Upper Jurassic to Lower Cretaceous pelagic sedimentary sequence, Antarctica
Authors: WHITHAM A. G. 
Published: June 2006

ABSTRACTThe Nordenskjöld Formation (?Oxfordian‐Berriasian age) is exposed on the east coast of the Antarctic Peninsula, where it consists of interbedded ash layers and biosiliceous mudstones which accumulated under anaerobic to dysaerobic bottom waters. The mudstones were deposited by pelagic settling and the ash layers by pelagic settling from suspension or as fallout from subaerial eruption columns. The lower part of the succession accumulated in a basinal setting under anaerobic bottom waters and is characterized by parallel bedding. Mudstones deposited in this setting preserve abundant zooplankton faecel pellets. Compaction of these pellets has given rise to a bedding parallel fissility. The upper part of the succession accumulated under dysaerobic bottom waters in a slope setting. The sequence is wavy bedded and contains abundant evidence of post‐depositional sediment instability and resedimentation, much of which was caused by tectonic activity. Discrete slide masses are absent from the slope sequence and it appears that slope processes were dominated by creep. Examination of the mudstones shows that as levels of dissolved oxygen in bottom waters increase, pelleted mudstones give way to structureless mudstones before visible bioturbation is noted.
The origin of massive diamicton facies by iceberg rafting and scouring, Scoresby Sund, East Greenland
Authors: DOWDESWELL JULIAN A. , WHITTINGTON ROBERT J. , MARIENFELD PETER 
Published: June 2006

ABSTRACTAlmost 90% of 39 m of core material recovered from Scoresby Sund and the adjacent East Greenland shelf is massive diamicton, interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring. There is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources. Model calculations suggest that the 14C derived Holocene sedimentation rate of 0.1‐0.3 m 1000 yr−1 in Scoresby Sund can be accounted for mainly by iceberg rafting of debris. A further 4% of core material is of gravel or coarse sand lenses, interpreted to reflect iceberg dumping of debris. Intensive iceberg scouring, which reworks sea floor sediments, is observed on acoustic records from over 30 000 km2 of the Scoresby Sund fiord system and the adjacent East Greenland shelf (69‐72°N and 75°N). The rate of iceberg production from Greenland Ice Sheet outlet glaciers, and iceberg drift tracks on the shelf, suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break. The relatively extensive modern occurrence of massive diamicton, formed by iceberg rafting and scouring, together with suspension settling of fines, suggests that it may also be a significant facies in the glacier‐influenced geological record. The recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers.
Transgression of an estuarine channel and tidal flat complex: the Lower Triassic of Barles, Alpes de Haute Provence, France
Authors: RICHARDS MARCUS T. 
Published: June 2006

ABSTRACTThe Lower Triassic succession of Barles, Alpes de Haute Provence, France, comprises an unconformable quartz arenite sand body of 90m thickness. The succession may be informally divided into (i) lower channellized cross‐bedded member overlain by (ii) an upper fining upward member. The lower member comprises vertically stacked, subtidal channel units separated into five major sand bodies by thin developments of fine grained channel margin and shoal deposits. Subtidal channel fill deposits are dominated by varying scales of cross bedding. These scales vary systematically from the base to the top of the member, with large scale planar sets dominating the lowest channel sand body (sand body 1), medium scale planar and trough cross bedding characterizing sand bodies 2‐4, the largest scale planar sets in the highest sand body (sand body 5). This upward change in cross bedding scale is concomitant with a decrease in both the relief of major channel sand body erosion surfaces, and the proportion of preserved interchannel shoal deposits. The succeeding fining upward member comprises small scale tidal channel units overlain by channel shoal and tidal flat deposits. Tidal flat sequences are characterized by parallel laminated, wave and current rippled sandstones separated by bioturbated, fine grained siltstones and mudstones.The vertical variation in facies of the Lower Triassic succession suggests two main periods of deposition. The lower member is considered to preserve successively more seaward components of a transgressive estuarine complex. The overlying upper member records the seaward progradation of tidal channel, shoal and tidal flat environments.The unconformity bounded nature of the lower member, combined with its systematic variation in facies, suggests it may represent an incised valley‐estuarine fill developed in response to an early Triassic relative sea level fall and subsequent rise. Succeeding tidal channel and tidal flat deposits forming the upper fining upward member reflect a change in sediment supply and/or rate of relative sea level rise comparable with a progradational shoreline. It is unclear whether this final depositional episode represents a period of highstand progradation or a later lowstand shoreline system developed following a further period of relative sea level fall and rise.