bluuebunny/crossref_metadata_2025_split huggingface dataset:
A reconnaissance of the Recent sediments of the Ranns of Kutch, India
Authors: GLENNIE K. W. , EVANS G. 
Published: June 2006

ABSTRACTThe Ranns of Kutch are flat salt‐covered desert areas (sabkhas) which are just above the normal tidal range and may be regarded as supratidal flats. They are flooded annually by the storm tides of the Southwest Monsoon. As the waters recede and evaporate they leave behind a crust of halite, and gypsum crystals grow within the clays and sands. The increase in salinity of the interstitial waters as they are traced inland is reflected in the higher boron content of the clays. The Mg2+/Ca2+ratio of these waters increases from 3 on the coast, to 240 in the evaporite environment of the shoreline of Pachham Island.Much of the sediment of the Ranns was probably once derived from the Indus and Nara rivers which used to flow into the western end of the Great Rann. Clay is now probably carried in by the monsoon storm tides after being transported along shore from the Indus, and also from the rivers of Kutch and Kathiawar. Coarser siliciclastic sediment is carried into the eastern inland portion of the area by the Luni and other intermittently flowing rivers and streams. Some sand and silt is blown into the Ranns from the surrounding hilly areas. Foraminifera are found concentrated in the sandier fractions of the sediments, having been transported there primarily by tidal currents and also by the wind. One species ofAmmoniais almost the only fauna found in the sediments of the very saline environment around Pachham Island.
Rollers and ripples in sand, streams and sky: rhythmic alteration of transverse and longitudinal vortices in three orders
Authors: FOLK ROBERT L. 
Published: June 2006

ABSTRACTSediment ripples are caused by systematically‐spaced transverse roller vortex systems in a moving fluid undergoing shear. With greater shear, these transverse rollers change over into longitudinal (helicoidal) vortices. This is the basic cause for the change from so‐called ‘lower flow regime’ conditions to ‘upper flow regime’ conditions. All characteristics of these two regimes (sediment transport rate, bed form, sedimentary structures) are logically explained by attributing them to change in type of vortex system. For currents depositing sediments, there are three orders of magnitude of vortices, each order beginning with transverse rollers, passing through festoon to longitudinal rollers. A chaos zone (antidunes) ensues, followed by resumption of transverse rollers that are five to ten times as large as those in the previous order. Features of river sediments, marine sands, turbidites, desert sand dunes, sky, and stars are satisfactorily explained by this model.
Depositional environments of Upper Miocene (Messinian) evaporite deposits of the Sicilian Basin*
Authors: SCHREIBER B. CHARLOTTE , FRIEDMAN GERALD M. , DECIMA ARVEDO , SCHREIBER EDWARD 
Published: June 2006

ABSTRACTIn Sicily, Messinian evaporitic sedimentary deposits are developed under a wide variety of hypersaline conditions and in environments ranging from continental margin (subaerial), to basin‐margin supratidal, to intertidal, to subtidal and out into the hypersaline basin proper. The actual water depth at the time of deposition is indeterminate; however, relative terms such as ‘wave base’ and ‘photic zone’ are utilized. The inter‐fingering relationships of specific evaporitic facies having clear and recognizable physical characteristics are presented. These include sub‐aerial deposits of nodular calcium sulphate formed displacively within clastic sediments; gypsiferous rudites, arenites and arenitic marls, all of which are reworked sediments and are mixed in varying degrees with other clastic materials (subaerial, supratidal, and intertidal to deep basinal deposits). Laminated calcium sulphate alternating with very thin carbonate interlaminae and having two different aspects; one being even and continuous and the other of a wavy, irregular appearance (subtidal, intertidal, and supratidal deposits). Nodular calcium sulphate beds, usually associated with wavy, irregular laminated beds (supratidal, sabkha deposits); very coarsely crystalline gypsum beds (selenite), associated with more even, laminated beds (subaqueous, intertidal to subtidal deposits); wavy anastomozing gypsum beds, composed of very fine, often broken crystals (subaqueous, current‐swept deposits); halite having hopper and chevron structures (supratidal to intertidal); and halite, potash salts, etc. having continuous laminated structure (subaqueous, possibly basinal).Evidence for diagenetic changes is observed in the calcium sulphate deposits which apparently formed by tectonic stress and also by migrating hypersaline waters. These observations suggest that the common, massive form of alabastrine gypsum (or anhydrite, in the subsurface) may not always be ascribed to original depositional features, to syndiagenesis or to early diagenesis but may be the result of late diagenesis.
Energy relations of density‐current flows: an experimental investigation*
Authors: KERSEY DAVID G. , HSÜ KENNETH J. 
Published: June 2006

ABSTRACTThree series of density‐current experiments were performed in a 5.76 m flume. In the first series, the flume was horizontal, and in the second and third, it was inclined with a positive slope and negative slope, respectively. Energy relations during successive stages of density‐current movement were computed from observed data, which showed an appreciable frictional energy dissipation. The computed friction factors of our experimental density‐flows were compared to the friction factors for pipe flows (Moody diagram), and while the calculated friction factor increases with increasing Reynold's number within the range of our experiments (Re 2 × 103−2 × 104), it is concluded that with increasing Reynold's number above about 5 × 104 the friction factor decreases. For natural turbidity currents, the Moody diagram gives a reasonable estimate of the friction factor between the current and sediment bed. The value of the friction factor for the interface between the current and overlying water was found to be about 0.2 times the friction factor for the current and flume. However, due to errors inherent in measuring the depth of the current, a value of 0.4 would be more reasonable for density‐currents in our range of Reynold's number. Friction tends to decrease the value of the dimensionless coefficient in Keulegan's law of saline front and to decrease the thickness of the flow. In contrast, the presence of a slope in the direction of flow tends to compensate the effect of friction. The angle θc that provides the potential energy to exactly offset the energy losses incurred during movement by the density‐currents in our experiments has a calculated value of 31′. An empirical formula φ= 0.935θ—0·57 relating friction, in terms of the hydraulic gradient φ, to the slope angle θ was obtained. Since the thickness of the current can be computed from the relationship between φ and θ, we estimated the thickness of naturally occurring density‐currents in Swiss lakes. The results suggest the applicability of our experimental results to small turbidity currents in nature. Our analysis further indicates that large turbidity currents have a small φ and can be expected to flow very long distances on a flat abyssal plain.
An automated rapid sediment analyser (ARSA)
Authors: NELSEN TERRY A. 
Published: June 2006

ABSTRACTThe automated rapid sediment analyser (ARSA) is a pressure‐transducer grain‐size analysis system. This basic Woods Hole‐type fall tube was automated by the addition of a digital voltmeter, Hewlett‐Packard 9810A calculator, and an x‐y plotter. Eight min after sample introduction, the system automatically produces size distribution data in 0·25‐φ intervals, distribution statistics, and a plotted frequency histogram.
The origin of horizontal laminae in ephemeral stream channel‐fill
Authors: FROSTICK LYNNE E. , REID IAN 
Published: June 2006

ABSTRACTThe number of paired horizontal laminae in an ephemeral channel‐fill increases systematically down‐catchment from stream headwaters, and is shown to be functionally related to tributary confluence. Under moving storm conditions, each tributary sub‐catchment delivers a sediment‐laden discharge pulse that finds sedimentary expression in paired laminae of light and heavy minerals. Lamina differentiation is attributed to a congregational sorting mechanism. The direct relationship (r, = 0.903) between paired laminae and confluencing tributaries permits palaeoenvironmental inference of drainage‐net character, and palaeoclimatic variability.
The plan shape of current ripples in relation to flow conditions
Authors: ALLEN J. R. L. 
Published: June 2006

ABSTRACTTwo sets of empirical data on the relationship of the plan shape of current ripples to flow conditions previously thought incompatible are reconciled by taking explicit and necessary account of the effects of flow width relative to flow depth. The aspects of plan shape considered are the mean streamwise ripple wavelength and the wavelength, measured across the flow, of longitudinal features due to centrifugal instability formed on the backs of the ripples. A regression analysis connecting these attributes with flow conditions including the width‐effect shows that the amount of unexplained variability is of the same order as the accumulated experimental errors, and suggests that the two sets of data are in excellent agreement. The relationship of the plan geometry to flow conditions is less simple than has sometimes been supposed, but ways are suggested in which the experimental results can be used to establish the hydraulics of past environments.
Structural state of detrital alkali feldspars
Authors: SUTTNER LEE J. , BASU ABHIJIT 
Published: June 2006

ABSTRACTThe structural state of an alkali feldspar is determined by the nature of the distribution of Al and Si in the tetrahedral sites of the feldspar structure. This state is a function of a number of genetic controls including temperature, cooling rate, deformation, crystal size, and several chemical factors. Together these controls constitute a genetic regime. Identification of the structures of detrital feldspars may enable recognition of genetic regimes and be useful in provenance interpretation and mineral province definition.A 2‐peak method of X‐ray diffraction (XRD) determination as a variant of an earlier proposed 3‐peak method of structural state determination is used in this study. Total analytical time for each determination is about 50–55 min per grain. Results of structural state identification of 126 detrital feldspars from Holocene stream sands derived from volcanic, plutonic and metamorphic rocks are presented in order to illustrate the application and potential of the technique. Detrital feldspars from the metamorphic rocks are all maximum microcline; those from the plutons range from orthoclase to microcline depending on the age of the pluton, whereas those from the volcanic rocks are sanidines.
Flow regimes in debris flow
Authors: ENOS PAUL 
Published: June 2006

ABSTRACTThe Bingham model has been suggested for the rheological behaviour of debris flow. Velocity plotted against yield strength uniquely defines turbulent and laminar flow in published experimental data on flow of Bingham materials. These regimes are not defined by a unique value of the Bingham number even though it includes both of the critical parameters, yield strength and velocity. Laminar flow in at least the final stages natural debris flows is suggested by sediments with parallel‐to‐flow or inclined clast fabric, preservation of delicate clasts, blocks projecting from the top of the deposit(?), and an absence of flutes.
The origin of bounding surfaces in ancient aeolian sandstones
Authors: BROOKFIELD M. E. 
Published: June 2006

ABSTRACTThree orders of aeolian bounding surface are arranged in a hierarchy based on their extent and regularity.First order surfaces are the most extensive. They are flat‐lying bedding planes cutting across all other aeolian structures and are attributed to the passage of the largest aeolian bedforms—draas—across an area. First order surfaces cut across second order surfaces, which are gentle to moderately dipping surfaces bounding sets of cross‐strata. Second order surfaces are attributed to the passage of dunes across draas, or to longitudinal dunes migrating across the lower ice slopes of draas. Third order surfaces bound bundles of laminae within coscts of cross laminae and are due either to local fluctuations in wind direction and velocity or to changes in airflow patterns caused by configurational changes in dune patterns. All these bounding surfaces could be explained by wind variations and dune migration, but the rates of dune migration relative to probable sediment deposition rates are incompatible with this general explanation of the form and spacing of the bounding surfaces. The concept of climbing bedforms of different hierarchical order together with subsidence provides a better explanation. Analogous bounding surfaces in aqueous bedforms have already been attributed to climbing bedforms of differing hierarchical order.
Origin of subaerial Holocene calcareous crusts: role of algae, fungi and sparmicritisation
Authors: KAHLE CHARLES F. 
Published: June 2006

ABSTRACTThe Pleistocene Miami Limestone that crops out on the lower Florida Keys is overlain by thin (16 cm or less), discontinuous, Holocene calcareous crusts (caliche) that are usually laminated, composed dominantly of calcite micrite and may or may not incorporate part of the underlying limestone. Both allochems and sparry calcite cement in the former unit contain endolithic algae and fungi, borings and unicellular algae. Biogenic structures identical to those in the Miami Limestone also occur in the calcareous crusts but are somewhat less abundant in the latter unit versus the former unit.The calcareous crusts were formed in the vadose diagenetic environment. Some of the CaCO3 necessary for the micrite that comprises the bulk of the crusts was probably derived from solution of carbonate from a soil cover and some from wind blown salt spray. Most of the micrite, however, was formed by replacement of the uppermost portions of the Miami Limestone. Replacement involved micritisation of allochems and a previously unreported process, sparmicritisation, the degrading recrystallization of sparry calcite to micrite. Minor sparmicritisation was caused by micrite calcification of endolithic fungi or algae within sparry calcite cement or by micrite precipitation in empty borings within such cement. Most sparmicritisation took place by dissolution of sparry calcite and concomitant precipitation of micrite in the space occupied previously by the dissolved spar. Such sparmicritisation is interpreted to be caused by chemical reactions involving the crystals, pore water which is moving slowly but steadily and organic compounds released during bacterial decomposition of fungi, algae or both.It is recognized that sparmicritisation occurs in the marine diagenetic environment and is not, therefore, necessarily indicative of vadose diagenesis. Incomplete sparmicritisation is responsible for some of the clotted textures typically found within calcareous crusts and may explain such textures in many other carbonate rock types. A combination of sparmicritisation and micritisation has probably greatly influenced the porosity of many reefs and, in some cases, led to the formation of ‘micritic reefs’.
Nature, origin and classification of peritidal tepee structures and related breccias
Authors: ASSERETO RICCARDO L. A. M. , ST C. KENDALL CHRISTOPHER G. 
Published: June 2006

ABSTRACTDistinctive peritidal tepee antiform structures, buckled margins of saucer‐like megapolygons are common in marine vadose fenestral and pisolitic limestones and/or dolomites of carbonate platform sequences and occur in intertidal and supratidal carbonates ranging in age from Silurian to Holocene. These megapolygons commonly form and are sometimes truncated before the deposition of the next sedimentary layer. The megapolygons result from the expansion of surface sediments by as much as 15%. The expansion is caused by the following continuously repeated sequence of processes: (1) Desiccation and thermal contraction causing small fractures; (2) phases of wetting causing enlargement of fractures; (3) phases of crystallization of calcium carbonate and other minerals causing the enlargement, fill and cementation of the fractures. Precipitation is from brines and meteoric waters; (4) hydration of minerals, thermal expansion, breaking waves and faulting may add to this disruption.The development of the tepee fabric can be traced from an initially cemented subaerial fenestral crust, exhibiting expansion and compressional structures, to a completely disrupted and brecciated sediment riddled by a labyrinth of fractures and solution cavities. These spaces are filled by numerous phases of internal marine and fresh‐water cement and sediment, the latter containing penecontemporaneous or younger marine faunas.Peritidal tepees are useful tools for geologic reconstruction and provide evidence of subaerial exposure; a tropical to subtropical climate; and back‐beach or back‐barrier deposition. Proper identification of tepees is of economic importance, because they provide good early porosity and permeability for petroleum entrapment and a site for mineralization. Aesthetically, tepee rocks are a fine kaleidoscopic decorative stone.
Algal crusts, autochthonous and clastic gypsum in a cannibalistic evaporite basin: a case history from the Messinian of Northern Apennines
Authors: VAI GIAN BATTISTA , LUCCHI FRANCO RICCI 
Published: June 2006

ABSTRACTThe Messinian Vena del Gesso Basin in the Northern Apennines is filled by very thick (up to 35 m) beds of coarse crystalline gypsum (selenite) associated with thinner carbonate and shaly (euxinic) intercalations. The conventional Usiglio model of salt fractionation does not apply to this evaporitic sequence for the following reasons: carbonate which underlies gypsum is not evaporitic but algal in origin; most gypsum did not precipitate from surface brines but at and below a sediment‐water interface occupied by algal mats; a significant portion (10–80%) of gypsum beds is composed of redeposited selenite which was removed from the margins and transported toward the centre of the basin by slope‐controlled currents and gravity flows (debris flows).We call this process cannibalistic because of its intraformational character (connected with evaporative fall of water level) and volumetric importance.A recurrent vertical pattern of six main facies (euxinic to gypsum fanglo‐merates) is interpreted as a bathymetric, regressive cycle controlled by both sedi‐mentological and tectonic‐eustatic factors. The inferred environmental setting is a residual turbidite trough (Marnoso‐arenacea) evolving abruptly toward lagoonal conditions and filled up to sea level by evaporitic and mechanical (mostly fluvial) processes. Repeated inundations of restricted‐marine water started the depositional cycle thirteen or fourteen times.
Gravelly flood deposits of Irvine Creek, Ontario, Canada
Authors: MARTINI I. P. 
Published: June 2006

ABSTRACTIn May 1974 a powerful flood flushed the Grand River basin, Ontario. The effects on the bedload were drastic in a narrow (30 m) and deep (40 m) rock walled and floored gorge near Elora, Ontario. Along Irvine Creek, the tributary occupying the gorge, the gravel cover was reworked in several types of bars, predominantly transverse and point bars. The bars formed very rapidly in response to essentially steady, non‐uniform flow that developed during a brief period of high flood.Superimposed on major bars are several minor sedimentary features such as coarse transverse ribs, chute channels and bars, longitudinal ribs, imbrication clusters, backsets with well developed imbrication, that were formed under very high stream discharge. Structures like imbrication clusters, transverse ribs and small riffle bars require a ‘live bed’ situation to form, and they develop when stones come to a stop either because they cluster during transport, or because keystone effects occur along shallow channels. In Irvine Creek, very few sedimentary features were formed during waning and low flood stages: only some shadow deposits and a few Ostler lenses. The few fines that were available were lost downstream or filled in lower parts of gravel beds.This study confirms that in streams that experience strong seasonal fluctuations in discharge, bedforms that develop during high floods have a high probability of preservation. In gravelly deposits, foreset structures and plane beds are most commonly preserved, although they may be difficult to recognize in old deposits, which may appear massive, particularly if the gravel has been infilled with finer pebbles and sand. In the case of Irvine Creek, all deposits are organized, and lateral and vertical variations in textures, particularly imbrication and packing, are very useful in the recognition of sedimentary structures.
Range, velocity, and material flux of compaction flow in growing sedimentary sequences
Authors: EINSELE GERHARD 
Published: June 2006

ABSTRACTIn growing sedimentary sequences range and velocity of vertically ascending pore water (advection) can be determined quantitatively by using a simple graphical method. During continuing deposition and maintenance of compaction equilibrium, the pore water from deeper layers cannot reach the sediment‐water interface. Range and velocity of advective flow decrease from top to bottom of a sequence and depend on the thickness affected by compaction. The velocity of pore water flow as well as the transport of solutes by advective flux are proportional to the sedimentation rate. Compaction flow can also result from under‐con‐solidation and diagenetic reduction of pore space. At the sediment‐water interface, a direct contact between the ascending pore water and the overlying water body is feasible only under special conditions (interrupted sedimentation over under‐consolidated material, erosion). These results are demonstrated on geometric models of sedimentary sequences, on experimentally deposited clay, and on selected examples of the Deep Sea Drilling Project.
Significance of CM diagrams of sediments deposited by suspensions
Authors: PASSEGA R. 
Published: June 2006

ABSTRACTCM grain‐size diagrams of clastic deposits were introduced in 1957. Since that time a large number of diagrams representing most environments were constructed. Discussions of parameters C and M by the writer and by others showed that these parameters are indicators of hydraulic conditions under which sediments were deposited. In a 1975 paper Vandenberghe discussed the CM diagram of the Boom Clay, Belgium, and excluded that CM diagrams gave indications on the mechanism of sediment deposition.In order to answer Vandenberghe's assertions, the writer systematically compared the numerous CM diagrams representing suspension deposits with the characteristics of the environments. Result of this comparison is that CM diagrams give coherent indications on deposition which agree with the known environment characteristics. The Boom Clay diagram is no exception.Another result of the present study is that, in environments as a whole, two types of currents can be recognized, distinguished by the relation between bottom turbulence and grain‐size of sediment in suspension. Deposits of these two current types and distribution of bottom turbulence are indicated by CM diagrams. Characteristics of these currents vary with the environment and help the reconstruction of ancient environments.Information given by CM diagrams has limits and should be integrated with other evidence on the environment. However, contrarily to the information given by ecology or sedimentary structures, the evidence provided by grain‐size has the advantage of being universal, as it can be obtained in all clastic deposits. This evidence therefore is a means for comparing and classifying clastic deposits as a whole.