bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quaternary sediments in the northwestern part of the Barents Sea and their relation to the underlying Mesozoic bedrock
Authors: BJØRLYKKE K. , BUE B. , ELVERHØT A. 
Published: June 2006

ABSTRACTA sedimentological study of Quaternary sediments from the northwestern part of the Barents Sea shows that their composition is controlled by the underlying Mesozoic bedrock and that very little sediment has been supplied from outside sources.The Quaternary sediments consist of Pleistocene glacial clays (moraines) and Holocene gravel, sand and mud, derived by erosion of the clay‐rich moraines, which again have been derived from underlying Mesozoic rocks.On the shallow Spitsbergen Bank (30‐100 m depth) we find a high energy facies of bioclastic carbonate sand and gravel and lag deposits of Mesozoic rock fragments from the underlying moraine. 14C‐datings of the bioclastic carbonates (Molluscs and Barnacles) suggest that soft bottom conditions with Mya truncata prevailed in early Holocene time, succeeded by a hard bottom high energy environment with Barnacles in the last 2000‐3000 years. This may be due to a southward movement of the oceanic polar front into the Spitsbergen Bank due to colder climate in Late Holocene (subatlantic) time, which at present day produces strong bottom currents down to 100 m depth.On the Spitsbergen Bank carbonate sedimentation has succeeded glacial sedimentation as a result of withdrawal of clastic sediment supply in Holocene time and high organic productivity because of upwelling. A similar mechanism may have been operating during earlier glaciations, i.e. in Late Precambrian time to produce an association of glacial and carbonate sediments although the biological precipitation was different at that time. In Late Precambrian time precipitation or carbonate by algaes may have occurred in colder water on the shelves due to higher saturation of carbonate in the sea water.
Concretions, isotopes, and the diagenetic history of the Oxford Clay (Jurassic) of central England
Authors: HUDSON J. D. 
Published: June 2006

ABSTRACTIn interpreting the results of a petrographic and isotopic study of concretions, a range of subjects is discussed including the original texture of the Oxford Clay sediment, Jurassic palaeotemperatures, the diagenetic history of pore‐waters and the palaeo‐hydrology of central England.The concretions are all composed predominantly of calcite. They include precompactional, pyrite‐rich concretions that later suffered an eposide of brecciation, and others that only commenced to form after compaction had crushed ammonite shells included in the bituminous clay sediment. Petrographic, chemical, and especially carbon isotope data demonstrate a dominantly organic source for the carbon in the early formed concretions. Oxygen isotopes indicate formation at the same temperatures (13‐16°C) at which benthic molluscs were living. Concretion growth in pelleted, anaerobic mud proceeded concurrently with bacterial sulphate reduction and pyrite precipitation. Cracking of the concretions started at this stage: in a few concretions, the cracks were also partially filled with brown calcite.During post‐compactional growth, δ13C increased and pyrite content decreased, showing waning organic influence; δ18O decreased. The brecciated concretions were intruded by clay in which baryte crystals grew; finally, most remaining voids were filled with strongly‐ferroan calcite of δ18O about—7 PDB and δ13C about O PDB. This must indicate strong depletion of the pore waters in 18O. Mechanisms that might lead to this are reviewed. It is concluded that the sequence of mineralogical and chemical changes is most readily explained if originally marine porewaters, first modified by bacterial activity, were flushed from the compacting clays by water of ultimately meteoric origin. This had its source in palaeo‐aquifers beneath the Oxford Clay. Speculative attempts are made to relate this history to the geology of the region.
Depositional and diagenetic history of Pleistocene and Holocene oolitic sediments and sabkhas in Kuwait, Persian Gulf
Authors: PICHA FRANTISEK 
Published: June 2006

ABSTRACTThe Pleistocene and Holocene oolitic sediments of southern Kuwait appear as parallel ridges—ancient and recent barrier beaches and coastal dunes. They are underlain by Tertiary clastic deposits and interfingered with sabkhas. Considering the superposition, primary composition and diagenetic alterations five lithostratigraphic units were distinguished within the oolitic complex. Their formation and preservation were related principally to eustatic oscillations of sea level during Quaternary times, although post‐Pliocene tectonics also played an important role both in physiographic and sedimentary developments of the region.The large accumulation of oolites in southern Kuwait might be related, at least partly, to the existence of two tidal channels, khors, discharging waters over‐saturated with respect to calcium carbonate over broad tidal flats. The formation of oolites culminated in late Pleistocene probably due to an extreme aridity of the climate.The subaerial diagenesis of the oolitic ridges led to gradual cementation and recrystallization of oolites. The four stages of progressive diagenesis distinguished in the area are compared with schemes suggested by Land, Mackenzie & Gould (1967) for Quaternary sediments in Bermuda and by Gavish & Friedman (1969) for aeolianite ridges in Israel.On the sea floor the cementation has produced widespread beach rocks and hard layers. Aragonite encrustations and dripstones occur within the intertidal zone of channels and lagoons. The shallow, occasionally flooded depresssions in sabkhas are occupied by algal mats.The amount of dolomite in sabkha sediments is rather low in comparison with similar environments of the southern Persian Gulf. This might be at least partly explained by the absence of dolomitic rocks in the Tertiary substratum in Kuwait.The complex of Quaternary sediments in southern Kuwait represents a petroleum setting in which the organic rich source sediments of lagoons and sabkhas are closely associated with highly porous reservoir rocks of the oolitic coastal ridges.
The survivability of labile light‐mineral grains in fluvial, aeolian and littoral marine environments: the Permian Cutler and Cedar Mesa Formations, Moab, Utah
Authors: MACK GREG H. 
Published: June 2006

ABSTRACTA greater than 50% decrease in the percentage of labile light minerals occurs between the non‐marine Cutler Formation (Permian) and its facies equivalent, the marine Cedar Mesa Sandstone, in the vicinity of Moab, Utah. Both the Cutler and Cedar Mesa Formations were derived from crystalline rocks of the Uncom‐pahgre Mountains under semi‐arid to arid climatic conditions. Furthermore, diagenesis had little effect on the light‐mineral fraction. Therefore, the significant change in mineralogy where the fluvial Cutler beds grade into the littoral marine Cedar Mesa deposits can be directly related to active reworking of detritus in the shallow marine environment.Less coarse perthitic alkali feldspar, twinned plagioclase, undulose mono‐crystalline quartz, and polycrystalline quartz in the Cedar Mesa with respect to the Cutler suggest that compositional maturation was produced by breakage of mechanically weaker grains during grain‐to‐grain collisions. Furthermore, the end products of compositional modification by shallow marine processes may be sufficiently different from those produced by weathering and dilution from sedimentary source rocks to allow evaluation of the relative effects of these processes on the origin of compositionally mature ancient sandstones.
The formation of ooids
Authors: DAVIES PETER J. , BUBELA B. , FERGUSON JAMES 
Published: June 2006

ABSTRACTField and laboratory studies suggest that different types of ooids form during quiet and agitated water conditions. Both types have been synthesized in the laboratory. Quiet water types exhibit a radial orientation of carbonate crystals, whereas in those formed in agitated conditions, a tangential orientation is prevalent.Successful laboratory formation of quiet water ooids was accomplished in supersaturated seawater solutions containing humic acids. Negative results were obtained from strictly inorganic solutions, and from those containing simple amino acids, single proteins, mixtures of proteins or mucopolysaccharides, soil and sediment extracts. Partly successful results were obtained using an organic extract from Bahamian ooids. The organic parameters most important in quiet water ooid formation are molecular weight, the presence of carboxyl groups and an ability to participate in hydrophobic/hydrophilic interactions, all of which are critical to membrane formation. Membranes form concentric shells which act as growth surfaces for carbonate and also induce the periodicity in carbonate precipitation.Ooids exhibiting a tangential orientation of batten‐like crystals have been synthesized under conditions of agitation, supersaturation and without the intervention of organic processes during the precipitation. Complete growth may be divided into agitation, resting and sleeping stages In the agitation stage, quartz nuclei induce an inorganic, heterogeneous nucleation from a supersaturated solution, which finally ceases as a result of Mg2+ and possibly H+ poisoning of the carbonate surfaces. No further precipitation occurs until the crystal surfaces are reactivated by removal of Mg2+ and H+ during the resting stage. Following a series of agitation and resting stages, precipitation is inhibited by a degree of poisoning which is not totally removed during the resting stage. For further growth, a new substrate is required and is provided by the development of organic membranes around the grains. This occurs when the grains are buried in the subsurface, the period of organic growth constituting the sleeping stage. Only 2% of an ooid's life is spent growing in the agitated environment, while 95% of its life is spent accreting organic membranes in the subsurface.Our experimental work indicates that ooids of Bahamian type are inorganic precipitates. The tangential arrangement of battens is the result of suspension in an environment where the degree of turbulence is sufficient to induce grain to grain contact of sufficient strength and frequency to inhibit any crystal growth other than tangential. The role of organics is to provide a substrate for further growth after precipitation has slowed to a point when no further accretion is occurring.
Ferroan calcite replacement indicates former magnesian calcite skeletons
Authors: RICHTER DETLEV K. , FÜCHTBAUER HANS 
Published: June 2006

ABSTRACTThe replacement by ferroan calcite with preservation of the original structures can be used as a new criterion for identifying skeletons originally composed of high‐magnesian calcite. This applies to bryozoa, rugose corals, echinoderms, many foraminifera, most ostracods, red algae, and serpulids. On the other hand, skeletons originally composed of low‐magnesian calcite were never replaced by ferroan calcite, as shown by belemnites, brachiopods, and most of the pelecypods.Using this criterion, an original low‐magnesian calcite composition is inferred for Tentaculites and some ostracods and foraminifera, whereas a previous high‐magnesian calcite composition is inferred for trilobites, oligostegina and certain ooids. Chemical instability of high‐magnesian calcite is suggested to be the driving force of the replacement by ferroan calcite. In most of the thirty‐seven samples investigated, of Oligocene to Devonian age, the ferrous iron concentration of the interstitial fluid increased during diagenesis, as shown by well established sequences of cement A and B and fissure fill. This offers a relative time scale for diagenetic processes.Ferroan calcites contain up to 6 mol % FeCO3 and up to 5 mol % MgCO3. In this range of concentration, the distribution coefficients for Fe and Mg between calcite and solution at about 25°C are about 1 to 0‐03, respectively, according to experiments. Possible sources of iron are iron oxides and hydroxides as well as clay minerals including glauconite.Though a submarine origin below the sediment surface is conceivable for ferroan calcite, there are serious limiting conditions such as low Eh and, at the same time, lack in sulphate‐reducing bacteria. On the other hand, ferroan ‘dedolomite’, compositional zonality in individual ferroan calcite overgrowths, low δ18C and δ18O values, and low Mg concentrations point more to a meteoric‐phreatic origin of many ferroan calcite occurrences.
Mesozoic carbonate rudites, megabreccias and associated deposits from central Greece
Authors: JOHNS D. RHODRI 
Published: June 2006

ABSTRACTIn the Kokkinovrakhos Formation of central Greece, poorly sorted, grain supported, lithoclastic carbonate rudites, megabreccias and olistoliths are associated with accumulations of fine‐grained laminated carbonates. The laminae frequently exhibit grading and are interpreted as turbidity current deposits. The coarser grained rudites and megabreccias were also redeposited but were probably transported downslope by sliding and rolling, i.e. they are rock‐fall deposits. Olistoliths were emplaced into deeper water by sliding. The fine‐grained sediments of the laminated facies appear to have accumulated in pockets on an uneven sea floor during episodes of minimal rock fall activity. The sedimentary association is similar to that described from some modern fore‐reef environments and is possibly characteristic of accumulations of sediment on, or near to, steep slopes adjacent to carbonate platforms, when episodes of tectonic activity lead to the shearing off and transport downslope of masses of well‐cemented shallow marine carbonates.
Address of the retiring President of the International Association of Sedimentologists: Differences in size distributions of populations of particles among sands of various origins
Authors: FRIEDMAN GERALD M. 
Published: June 2006

ABSTRACTThis address reminisces and reflects on a subject in which I have been involved for more than twenty years: the effect of depositional processes on various parameters of the size‐frequency distribution of sands. Movements of air and water generally separate particles by their sizes; the distribution of sizes relates to (1) the availability of different sizes of particles in a parent material, (2) processes operating where the sediments are deposited, particularly the competency of flow, and (3) concentrations of particles in suspension. Differences in size‐frequency distributions among sands correlate with various origins, that is with their terminal depositional environments. Reminiscences in this address express my personal experience, both its up and downs, in advocating the study of this relationship, particularly in applying the method of moments on the basis of the concept that one statistical function expresses the characteristics of the population of particles.This address re‐emphasizes some points made in previous studies (Friedman, 1961, 1962b, 1967) on the interrelationship between textural parameters and depositional processes for beach, dune, and river sands and then complements and supplements data which have not been presented before. These new data are grouped on scatter plots for sands of various origins. Finally, this address displays on maps regional trends of process‐induced changes in size distributions of populations of particles in sands of four different settings: (1) a beach‐dune setting, as exemplified by Padre Island, Texas, on the shores of the Gulf of Mexico; (2) a point‐bar setting in the Arkansas River of Oklahoma; (3) a continental shelf‐slope setting in the Gulf of Mexico off Louisiana, Mississippi, and Alabama; and (4) a continental shelf setting of the western Atlantic Ocean off New Jersey.This address concludes with the observation that the distribution of particles in sands will be influenced by the conditions that determine what happens in the depositional environment, hence statistical parameters that define the size‐frequency distribution may be related to formative process.
Initiation of ripple marks under oscillating water
Authors: KANEKO A. , HONJI H. 
Published: June 2006

ABSTRACTIt was observed that a monolayer of glass beads which were scattered sparsely on a rigid plane floor grew into regular waves of particles under oscillatory water flow. The relative displacement of two nearby particles due to viscous fluid forces seems to be responsible for the initiation of these particle waves. It was also observed that the similar particle waves were formed on the initially flat surface of a thick sand bed and subsequently developed into oscillatory sand ripples of a common type. On the basis of these observations, it is suggested that the particle waves may be the basic cause of the initiation of general ripple marks under oscillatory flow.
Microbial alteration of Bahamian deep‐sea carbonates
Authors: ZEFF MARJORIE L. , PERKINS RONALD D. 
Published: June 2006

ABSTRACTAn analysis of microborings within sediment and hardground samples collected from the Northwest Providence Channel and the western margin of the Little Bahama Bank was conducted to characterize the endolithic assemblage present, to examine the role of microboring organisms in the alteration of deep‐sea carbonates, and to evaluate the palaeoecologic potential of the aphotic microboring assemblage found. Samples examined in this study were collected at depths ranging from 210 to 1450 m. The microboring assemblage was found to contain: (a) filamentous fungal borings of five distinct types, (b) a 1.0 × 2.5 μm vermicular form of fungal or bacterial origin, (c) an 8‐12 μm tubular, branching form of probably fungal origin, (d) a subapically branched form considered to be fungal, (e) a spinate form of uncertain affinity and (f) sponge borings. Three of these forms are known only from the deep‐marine environment; the remainder are also known from shallow‐marine sediments found well within the photic zone.Both carbonate sediments and lithified hardgrounds are highly altered through the activity of endolithic organisms. Infestation of individual skeletal fragments by microborers may be so extensive as to produce heavily bored envelopes resembling those previously reported to occur only under shallow‐marine conditions. Although the geological ranges of these microborings remain to be established, the presence of such an aphotic assemblage, coupled with the absence of photosynthetic algal borings, could provide a valuable tool in palaeoecological studies. Other potential applications include the determination of turbidite sediment sources and the establishment of relative water depths for the formation of hardground surfaces.
Holocene pisoliths and encrustations associated with spring‐fed surface pools, Pastos Grandes, Bolivia
Authors: RISACHER FRANÇOIS , EUGSTER HANS P. 
Published: June 2006

ABSTRACTCalcite pisoliths, with diameters ranging from 1 to 200 mm, are forming now on the surface of a playa (salar) in the Andean Altiplano (4500 m above MSL) of Bolivia. They are associated with active or recently active hot springs (20‐75°C) which flow onto the playa surface. Encrustations of pieces of an older caliche‐type crust, of pisoliths, of indurated mud and of older concretions are also found as well as series of small (1‐3 cm high) sinter terraces (rimstone dams). Arborescent concretions and overgrowths are common and they are reminiscent of drip‐stone textures. Water analyses demonstrate that calcite supersaturation (about twenty times) occurs mainly through CO2 loss, with photosynthesis by algae and degassing the main removal mechanisms. The two available analyses indicate slight evaporation and a calcium loss between spring and pool of 2.3 mmol per litre of water. It is thought that the hot springs pick up much of their solute load from the playa sediments. The closest analogues to these deposits have been reported from caves (cave pearls and concretions). Although the depositional processes may be similar, the environment on an evaporitic playa surface is quite different. The geological implications for this newly observed pisolith environment may be considerable.
The isotopic composition of strontium in non‐marine carbonate rocks: the Flagstaff Formation of Utah*
Authors: NEAT PATRICK L. , FAURE GUNTER , PEGRAM WILLIAM J. 
Published: June 2006

ABSTRACTThe isotopic composition of strontium in surface water in continental basins is determined primarily by the geology of the basin and to a lesser extent by climatic conditions. Consequently, the 87Sr/86Sr ratios of brines in such basins can change only as a result of changes in the geology or climate. This principle of isotope geology was studied by analysis of a suite of non‐marine carbonate rocks from the Flagstaff Formation (Palaeocene‐Eocene) of Utah. The samples were collected from a section in Fairview Canyon of Sanpete County. They include both limestone and dolomite and were selected to have low non‐carbonate residues. The concentrations of strontium in calcites averages 383 ± 128 p.p.m., while those of dolomites increase from 354 ± 74 p.p.m. in the lower 43 m of section to a maximum of 2259 p.p.m. higher up. The increase in the strontium content of dolomite is interpreted as evidence for a change from steady‐state to progressively more evaporitic conditions. Two dolomites have isotopic compositions of oxygen expressed as δ18O = ‐2.75‰ (relative to the PDB standard) and are enriched in 18O relative to two calcites whose average δ18O value is ‐9.9‰. The 87Sr/86Sr ratios of the carbonate minerals range from 0.70890 to 0.71260. These values are clearly greater than the 87Sr/86Sr ratio of marine carbonates of Early Eocene age which is 0.70744. The variation of the 87Sr/86Sr ratio in this section of the Flagstaff Formation is real and reflects the occurrence of geological events which changed the isotopic composition of Sr entering Lake Flagstaff. The non‐carbonate fractions of six carbonate rocks and one sandstone fit a straight line on the strontium mixing diagram in co‐ordinates of initial 87Sr/86Sr and 1/Sr concentration. These results suggest that the isotopic composition of strontium in Lake Flagstaff may have been modulated by periodic input of volcanogenic detritus of felsic composition.