bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sedimentology of very thick calcarenite‐marlstone beds in a flysch succession, southwestern Pyrenees
Authors: RUPKE N. A. 
Published: June 2006

ABSTRACTSingle beds of up to 41 m thick are exposed for 16 km along the strike in an Eocene flysch, Spanish Pyrenees. These mega‐beds consist of a lower calcarenite (up to 25 m) and an upper marlstone (up to 16 m). Their volume is minimally of the order of 1 km3. The mega‐beds are underlain by slump sheets which in places exceed 100 m in thickness.The calcarenites show erosional sole markings, no internal amalgamation, a graded texture expressed by matrix percent, coarsest quartz grains, and coarsest foram tests. The marlstones are burrowed from their top, they are graded as expressed by matrix percent, coarsest quartz grains, and carbonate percent. Their grading continues the upward size decline in the underlying calcarenites, and their thickness and carbonate percent vary with those of the underlying calcarenites.Single calcarenite‐marlstone beds are interpreted as deposited by turbidity currents. The great thickness and other uncommon features (e.g. consistent association with an underlying slump sheet, distal thickening, locally repetitive grading, compositional inhomogeneity) can be accounted for by (1) widespread slumping initiating voluminous turbidity currents, (2) concurrence of tributary turbidity currents to deposit a single mega‐bed, and (3) ponding of the turbidity currents behind what may have been a local, palaeobasin floor high. Slumping and simultaneous turbidity currents were probably triggered by earthquakes of great magnitude. The basin floor high may have formed by basement faulting.The mega‐beds do not occupy a particular niche in a facies sequence and their great thickness does not reflect a particular environment of deposition. Instead, they more likely reflect the seismic regime (periodic earthquakes of great magnitude) and tectonic style (block faulting) of the flysch basin.
The ability of debris, heavily freighted with coarse clastic materials, to flow on gentle slopes
Authors: RODINE JAMES D. , JOHNSON ARVID M. 
Published: June 2006

ABSTRACTObservations of many debris‐flow deposits on gently‐sloping alluvial fans have disclosed that debris commonly is heavily loaded with coarse clastic material and contains large isolated blocks. The paper describes how debris charged with coarse granular material can transport large blocks, yet flow on gentle slopes.Experimental results of mixing sand‐sized particles with a slurry of clay plus water indicate that 45–55 vol. % of a single size, and up to 64% of two selected sizes, can be added before interlocking occurs. Theoretical analysis of multi‐size classes suggest that 89 to more than 95 vol. % debris can be clastic materials without significant particle interlocking.The clay fraction, even if minor, plays a critical role in determining strength properties of debris. The mixture of clay plus water provides a cohesive slurry that supports fine‐grained particles within the debris, as well as reduces the effective normal stresses between the particles. The increased unit weight of the clay plus water plus fine‐grained particles allows the support of coarser grained particles. The pyramiding upon the clay‐water slurry continues until the entire debris mass is supported in a virtually frictionless position because of the reduced effective normal stress and the lack of particle interlocking.Thus, the ability of debris flows to support large blocks can be understood in terms of the high unit weight of the displaced debris plus the strength of the fluid phase; that is, the blocks float in the debris as a result of a small density difference between the blocks and the debris, plus the cohesive strength of the clay‐water slurry.Also, the ability of coarse clastic debris to flow on gentle slopes probably is a result of poor sorting of debris‐flow materials which contain minor amounts of clay. The poor sorting allows the debris to have a high density yet have essentially no interlocking of clasts. The high density of the debris reduces effective normal stresses between clasts, thereby reducing apparent friction of the mixture.
The Rio Dell Formation: a Plio‐Pleistocene basin slope deposit in Northern California
Authors: PIPER DAVID J. W. , NORMARK WILLIAM R. , INGLE JAMES C. 
Published: June 2006

ABSTRACTThe Rio Dell Formation (Pleistocene and Pliocene), exposed south of Eureka, California, is a prograded sequence of basinal turbidites overlain by basin slope and shelf deposits. The slope deposits studied in the Centerville Beach section accumulated in a steadily shallowing environment delineated by analysis of palaeobathymetrically significant benthonic foraminiferal biofacies in turn suggesting deposition at depths of 1000–100 m. Lower slope deposits interfinger with basinal turbidites derived from the Eel River delta to the north. Slumped blocks of silty mudstone, and associated silt and mud beds, are common. The middle slope deposits are mudstones; coarser sediments bypassed this zone. Mudstones and muddy siltstones alternate on the upper slope. Shallow depressions, probably slump scars, that have been rapidly filled by upper slope sediment are common. The transition to shelf deposits is marked by an increase in sediment grain size, in the degree of oxidation, and in the abundance of megafossils. High percentages of benthonic foraminifera displaced from shelf depths indicate that resedimentation processes are most important on the upper slope.
Rare‐earth elements in Lower Palaeozoic epicontinental and eugeosynclinal sediments from the Oslo and Trondheim regions
Authors: DYPVIK H. , BRUNFELT A. O. 
Published: June 2006

ABSTRACTEight rare‐earth elements (REE) have been determined in Cambro‐Silurian sediments and volcanics from nine stratigraphic units in the Trondheim Region and ten stratigraphic units in the Oslo Region by neutron‐activation analyses.In the eugeosynclinal sediments from the Trondheim Region the REE variations are related to variations in source material, which mainly are volcanic debris of local origin. In the foreland sediments from the Oslo Region significant development of clays has occurred and therefore the REE variations reflect the deposition environment.
A note on the significance of lamination in stromatolites
Authors: PARK ROBERT 
Published: June 2006

ABSTRACTThe lamination found in recent stromatolites, an intrinsic feature of many of them, comprises a number of sediment‐rich and organic‐rich couplets. The significance of this lamination has figured in at least two avenues of research. In one is its possible influential role upon geochemical and diagenetic trends, in the other its possible calendar role. Algal growth follows a diurnal pattern but sedimentation, which is largely marine, is far less regular or predictable. The monitoring of modern algal mat surfaces has yielded much useful and accurate information concerning rates of mat accretion. Millimetre‐scale lamination may be produced on a number of interacting processes but as yet no one has been able to determine with any great assurance whether it represents a daily, monthly, annual or some other regular periodic growth. The evidence from the Trucial Coast tends to show, rather, that burial, subsequent compaction, distortion and, in the case of sabkha‐type sections, destruction owing to evaporite mineral growth, all tend to obliterate or at best mask any regular patterns of growth. In conclusion, one is forced to acknowledge that any computations concerning the calendar role of stromatolites are to be regarded with the utmost suspicion.
Log‐normal interpolation in grain size analysis
Authors: BURGER HEINZ 
Published: June 2006

ABSTRACTA computer program is described for the display of grain size distributions by log‐probability plots. These plots are useful to recognize and interpret log‐normal subpopulations. Because log‐probability plots of the cumulative curves often show two or more straight line segments we suggest a method of ‘log‐normal’interpolation for use in computing statistical parameters. The method combines advantages of graphical methods with those of mathematical moments. Finally, the frequency curve is derived by approximating the log‐probability plot of the cumulative curve with spline functions.
Sedimentary model for intertidal mudflat channels, with examples from the Solway Firth, Scotland
Authors: BRIDGES PAUL H. , LEEDER MICHAEL R. 
Published: June 2006

ABSTRACTIntertidal mudflat channels (gullies) in the Solway Firth, Scotland possess width/depth ratios similar to meandering rivers. Most channels deeper than 1 m show cut‐bank slides, but narrow, deep channels also have rotational slides on the point‐bar slopes. The channels display two types of point‐bar. The first, associated with gently curved meanders, is sigmoidal in profile. The second, associated with tight meander bends, possesses a pronounced lower platform. The onset of flow separation in meander bends, a phenomenon which enhances cut‐bank erosion and point‐bar deposition, is a direct function of meander‐bend tightness and Froude number. The effects of flow separation are greatest on tight meander bends at times of high velocity during late spring ebb and also during rainfall run‐off at low tide. These events appear to be responsible for the growth of the point‐bar platforms. A model, predicting the type of point‐bar development to be expected in different channel meanders, is used to reconstruct the sedimentary history of active and fossil point‐bars.
Dissolution and transport of manganese by organic acids and their role in sedimentary Mn ore formation
Authors: BROCKAMP OLAF 
Published: June 2006

ABSTRACTDissolution experiments of Mn and Fe under natural conditions from fresh basalt, weathered basalt and Mn laterite by different organic acids show that Mn is highly enriched over Fe in solutions from the weathered rocks but that more Fe than Mn is dissolved from the fresh basalt. The enrichment of Mn is caused by sparingly soluble Fe‐oxides and hydroxides and more soluble Mn‐oxides. In addition from the weathered rocks the Mn concentration dissolved by the organic acids is up to 1000 times higher than in inorganic solutions. Mn enrichment is caused by acid attack, organic reduction of Mn4+ to Mn2+ and complexing by the organic acids. The complexed Mn is not attacked as easily by oxidation as free Mn ions. Higher concentrations of manganese in the organic dissolved stage can therefore be transported by rivers over greater distances.Organic complexed Mn, derived from lateritic weathered rocks may therefore contribute to the formation of low iron marine sedimentary Mn deposits.
Spherular modern dolomite from the Coorong area, South Australia
Authors: VON DER BORCH C. C. , JONES J. B. 
Published: June 2006

ABSTRACTScanning electron micrographs show that the youngest and apparently least altered of the Coorong dolomite is in the form of spherular bodies about 0.2–1.0 μm in size which themselves are composed of spherules about 100 nm in diameter. Older and more lithified sediments show sharply defined dolomite crystals suggesting an origin as primary dolomite spherules followed by aggregation and diagenetic alteration to well crystallized dolomites.
Largescale ripples of the lower Wabash River
Authors: JACKSON ROSCOE G. 
Published: June 2006

ABSTRACTLargescale ripples in the meandering lower Wabash River of Illinois and Indiana, U.S.A., include scroll bars and three dunelike bed forms (dunes, sand waves, and transverse bars). Scroll bars are lobate crested, asymmetrical in stream‐wise vertical profile, usually solitary, and oriented approximately normal to local channel strike. They form by passive flow expansion downchannel from locally emergent topographic highs, face and lie near inner banks of meander bends, enjoy a high preservation potential as leveelike ridges of ridge‐and‐swale topography, and migrate only during relatively low stream discharges, when water depth over bar crests is less than 0·5 m.Dunes correspond to dunes of the flow‐regime classification and rarely are solitary or superimposed. Sand waves may be symmetrical or asymmetrical, are always superimposed by dunes, occur in depths greater than 4 m and in bed material coarser than 1 mm mean size, and develop at bankfull and flood flows. Transverse bars migrate in depths less than 5 m in straight reaches and near inner banks of bends, display crestal dunes, and correspond to the bars of Costello (1974) and to the sand waves of Boothroyd (1969). Hydrodynamic regimes of scroll bars and transverse bars differ from that of dunes. The omnipresence of dunes upon stoss‐sides of sand waves confirms the existence of an equilibrium superimposition of dunelike largescale ripples.Depth‐velocity‐size diagrams appear to be a valid representation of empirical stability fields of dunelike largescale ripples in deep unsteady nonuniform aqueous flows. Stability fields of dunes and sand waves overlap greatly. Velocity profiles demonstrate an absence of leeside flow separation over dunes and an appearance (rare) over transverse bars only when the ratio of trough depth to crest depth exceeds two.Dune stratification displays (1) largescale trough cross‐strata, (2) thinning of sets as bed‐material size increases, and (3) an orientation within 20° of local channel strike. Transverse bars show avalanche sets up to 2 m thick, with reactivation surfaces. Scroll bars display thick avalanche sets separated by reactivation structures consisting of erratically oriented smallscale trough cross‐strata. Avalanche sets of scroll bars and of transverse bars are oriented 50–150° from and within 50° of, respectively, local channel strike.
A cine‐camera technique for process measurement on a ridge and runnel beach
Authors: WRIGHT PETER 
Published: June 2006

ABSTRACTPrevious attempts to quantify beach processes with techniques involving direct measurement have met with varying degrees of success. Problems encountered can be attributed to three main areas of difficulty: (1) the rapidity of change in both process operation and the subsequent production and development of bed forms; (2) the inclement nature of the weather conditions during which the most rapid beach changes take place; (3) interference with the flows being measured, by the equipment. A photographic method is described here, which to a great extent overcomes these problems, and can be operated cheaply by a solitary field investigator.
The production and recognition of aeolian features on sand grains by silt abrasion
Authors: NIETER WILLIAM M. , KRINSLEY DAVID H. 
Published: June 2006

ABSTRACTSeveral size fractions of natural loess from Long Island, New York including sand and ventifacts were studied with the scanning electron microscope to determine if distinguishing surface features could be found. Long Island loess compares very closely to descriptions of a number of European loess deposits except for the inclusion of carbonate not found on Long Island. Ventifact and sand grain surfaces were experimentally prepared using natural loess as an abrasive agent, and compared well with those surfaces found in the natural materials. Given favourable circumstances, it is possible via scanning electron microscopy to distinguish surface features created by aeolian action in loess deposits and associated materials.
Man‐made turbidity currents in Lake Superior
Authors: NORMARK WILLIAM R. , DICKSON FRANKLIN H. 
Published: June 2006

ABSTRACTThe discharge of taconite tailings into Lake Superior at Silver Bay, Minnesota, produces turbidity current flow. The silty fine‐sand tailings fraction transported to the deepest part of the lake has formed a small fan with valleys similar in gross morphology to a submarine fan. Current meters anchored 5 m above the lake floor over the wall and over the levee of a distributary valley on the fan recorded intermittent turbidity current flows during 30 weeks in 1972–73. At least twenty‐five discrete periods of observation of turbidity current flow were obtained; single episodes lasted 4−328+ h. Only flows thick enough to overflow the eastern levee of the valley could be observed, and this accounts for the intermittent nature of our observations, as flow within the valleys is expected to be continuous as long as tailings are discharged. Flow velocities were higher near the valley axis where the flow is thicker. Velocities measured over the valley wall averaged 10.8 cm/s for eleven episodes; velocities measured over the levee, more than 1/2 km from the valley axis, only 3.3 cm/s. The maximum velocity during 1300 h of observation did not exceed 31 cm/s. This agrees reasonably well with velocities calculated from channel properties, as commonly done for turbidity currents on deep‐sea fans. Current meters tethered above the bottom meters indicate that lake currents normally parallel the shore throughout the water column. With the onset of a turbidity current, currents higher in the water column remain unchanged but velocities near the bottom go to zero, currents then change azimuth by 90° to parallel the downslope (down‐valley) direction of the fan, then increase in velocity. During a turbidity current episode, the direction of bottom flow stays relatively constant (± 20° of the down‐valley trend) but the velocity oscillates (commonly with 10 cm/s amplitude), periods being of 1/2 h or less to several hours. Turbidity currents generated on Reserve Mining Company's delta are effective in carrying essentially all tailings discharged into the lake into deeper water, where they are deposited.
The origin and diagenesis of cherts from Cyprus
Authors: ROBERTSON A. H. F. 
Published: June 2006

ABSTRACTThe Troodos Massif of Cyprus is overlain by a variety of cherts in pelagic chalks, volcanogenic sediments, radiolarites and radiolarian mudstones, all of Campanian to Upper Eocene age.There are two chert types, granular chert and vitreous chert. X‐ray diffraction (XRD) reveals the silica polymorphs, disordered cristobalite and quartz.Silicification of the chalks varies from incipient, to bedded, granular cherts, all with disordered cristobalite as the main silica phase. Quartzitic cherts are restricted to the base of Upper Palaeocene and Lower Eocene calciturbidite beds. Disordered cristobalite predominates in the radiolarian mudstones at the foot of the sequence.The form of disordered cristobalite in cavities ranges from microspherules of radiating bladed crystals, the ‘lepispheres’ of the Deep Sea Drilling Project (DSDP) to bladed overgrowths, and fibrous silica. In contrast, within the fine grained matrix, the disordered cristobalite takes the form of partly coalescent crude microgranules and microspherules.Most of the chalcedonic quartz in Cyprus is derived by recrystallization of previously inorganically precipitated disordered cristobalite rather than by direct precipitation.According to the concept of impurity‐controlled maturation the composition of host sediment controls the incorporation of exchangeable cations and other impurities into inorganically precipitated disordered cristobalite. With time (up to 100 million years) internal solid state reorganization of the disordered cristobalite is accompanied by gradual expulsion of impurities, until the cristobalite dissolves followed by quartz precipitation. Complete conversion to quartz takes place first in porous calcareous sediments free of impurities, as in the Cyprus calciturbidites; in fine grained clay‐rich sediments, like Cyprus radiolarian mudstones, disordered cristobalite persists much longer. Impurity‐controlled maturation also helps explain the diagenesis of Cyprus chert nodules.
Grain‐size parameters of insoluble residues in mixed terrigenous‐skeletal carbonate sediments and sedimentary rocks: some New Zealand examples
Authors: NELSON CAMPBELL S. 
Published: June 2006

ABSTRACTGrain‐size parameters derived from the mechanical analysis of acid‐insoluble residues from mixed terrigenous‐shell beach sediments from Auckland, New Zealand, are more effective for interpreting the depositional processes, and for characterizing the beach environment on textural scatter plots, than are parameters based on the analysis of the total beach samples. This results mainly from the wide variations in size of hydraulically equivalent skeletal carbonate grains in the sediment, especially in the coarser size grades, but may also be accentuated by the local origin and susceptibility to alteration of the shell material. Compared with the total sediment grain‐size distribution, the insoluble residues from the beach deposits are characteristically finer‐grained, better sorted, and more consistently coarse‐skewed and leptokurtic.The grain‐size distribution characteristics of insoluble residues from several stratigraphic units in a sequence of Oligocene mixed terrigenous‐skeletal shelf sediments in the South Auckland region distinguish depositional mechanisms and environmental energy levels for each unit that are consistent with interpretations made on the basis of carbonate petrography and palaeontology. With regard to the bulk content of terrigenous mud in the insoluble residues, the grain‐size distribution of the fraction coarser than 4φ is alone diagnostic of the energy‐time trends in these sediments.The grain‐size parameters of the acid‐insoluble residues in modern and ancient mixed terrigenous‐skeletal carbonate sediments may provide more reliable criteria for distinguishing and characterizing the depositional environment of these deposits than do the parameters obtained from the size distribution of the total grain population.
Basic types of stratification in small eolian dunes
Authors: HUNTER RALPH E. 
Published: June 2006

ABSTRACTThe thinnest recognizable strata in modern eolian dune sands can be grouped into six classes. They are herein named planebed laminae, rippleform laminae, ripple‐foreset crosslaminae, climbing translatent strata, grainfall laminae, and sandflow cross‐strata.Planebed laminae are formed by tractional deposition on smooth surfaces at high wind velocities. They are very rare in the deposits studied. Grainfall laminae are also formed on smooth surfaces, largely by grainfall deposition in zones of flow separation. They are much more common than planebed laminae, which they closely resemble.Eolian climbing‐ripple structures are composed primarily of climbing trans‐latent strata, each of which is the depositional product of a single climbing ripple. Climbing translatent strata that formed at relatively high or supercritical angles of ripple climb are typically accompanied by rippleform laminae, which are wavy layers parallel to the rippled depositional surfaces. Ripple‐foreset crosslaminae, which are incomplete rippleform laminae produced when the angle of ripple climb is relatively low or subcritical, are rarely visible in eolian sands.Sandflow cross‐strata are formed by the avalanching of noncohesive sand on dune slipfaces. Their form varies with slipface height and with other factors.