bluuebunny/crossref_metadata_2025_split huggingface dataset:
Subaqueous liquefied and fluidized sediment flows and their deposits
Authors: LOWE DONALD R. 
Published: June 2006

ABSTRACTA clear distinction must be made between liquefied and fluidized systems. In liquefied beds and flows, the solids settle downward through the fluid, displacing it upward, whereas, in fluidized beds, the fluid moves upward through the solids, which are temporarily suspended without net downward movement. Many recent references to fluidized sediment gravity flows refer, in fact, to flows of liquefied debris.Most uniformly liquefied beds of well‐sorted sand‐ or gravel‐sized sediment will resediment as simple two‐layer systems. Liquefied flows can originate either by liquefaction followed by failure, as in many retrogressive flow slides, or by failure followed by liquefaction, as in the case of some slumps. Empirical and theoretical estimates of flow velocity, thickness, and travel distance suggest that natural laminar liquefied flows of fine‐grained sand will generally resediment after moving a kilometre or less. Laminar flows of coarse‐grained sand will resediment after moving only a few metres. Grain dispersive pressure is thought to be of little significance in the development or maintenance of liquefied flows.Many surficial submarine sand beds are apparently susceptible to liquefaction, including submarine canyon and continental rise deposits. Within submarine canyons and narrow fjords, steep slopes and channels promote the evolution of liquefied flows from slumps by liquefaction after failure and of high density turbidity currents from liquefied flows by the development of turbulence. Upon moving into the lower parts of submarine canyons or into proximal fan channels, liquefied flows will resediment and high density turbidity currents will tend to decline to flows transitional between liquefied flows and turbidity currents. The liquefied, coarser detritus within such transitional flows will be deposited while finer‐grained debris will remain in suspension and continue downslope as dilute turbidity currents. Resedimentation of the liquefied portions of such flows may be responsible for the deposition of the A‐subdivision of many turbidites and many thick, structureless ‘proximal turbidites’ or ‘fluxoturbidites’. Similar units can originate by liquefaction of the traction deposits of normal turbidity currents.Fluidized flows are probably uncommon, thin, and, where formed, originate through fluidization of the fine‐grained tops of liquefied graded beds.
Authigenic pyrite and gypsum in South West African continental slope sediments
Authors: SIESSER WILLIAM G. , ROGERS JOHN 
Published: June 2006

ABSTRACTAn unusual association of authigenic pyrite and authigenic gypsum has been found in silty clays recovered from the South West African continental slope. Nannofossil content suggests that the sediments are Upper Miocene‐Lower Pliocene in age.Pyrite occurs as (1) granular masses, (2) ‘worm’tubes, (3) foraminiferal infillings, and (4) framboids. Gypsum occurs as euhedral single or twinned crystals of selenite. ‘Worm’tubes and foraminiferal infillings of pyrite are partially or completely enclosed in some gypsum crystals. Electron microprobe analyses show a relatively high concentration of manganese in both the granular masses and tubes.Present‐day waters off this coast are dominated by the upwelling of cold, nutrient‐enriched waters (the Benguela Current). These rich waters support an enormous population of plankton. Death and decomposition of these plankton consume oxygen, thereby creating a belt of anaerobic sediments close to shore. An Upper Miocene‐Lower Pliocene regression (Dingle & Scrutton, 1974) lowered sea level and shifted an older analogue of this upwelling zone seaward, eventually establishing an anaerobic environment in places on the present continental slope.Anaerobic bacteria thrived in these conditions. They reduced SO4 dissolved in sea water, initiating the formation of H2S. The H2S reacted with iron minerals present in the sediment to form FeS. Addition of elemental sulphur produced pyrite. This strongly reducing, low pH, environment became saturated with calcium obtained by the dissolution of planktonic calcareous organisms. Gypsum was precipitated once the product of the concentrations of dissolved calcium and SO4 exceeded the gypsum solubility product.
Relationships between sand input from rivers and the composition of sands from the beaches of Southern California*
Authors: RICE ROBERT M. , GORSLINE DONN S. , OSBORNE ROBERT H. 
Published: June 2006

ABSTRACTDuring the period from 1967 through 1972, a sampling programme was completed to determine the economic potential of heavy metals in the beach and river sands of the southern California coastal zone. These samples were employed to test the hypothesis that sand composition in a given beach cell is dominantly controlled by the provenance draining into that cell and is not strongly influenced by longshore leakage from upcurrent cells. Sample sets obtained before and after the exceptional flood of 1969 made it possible to compare the sediment supplied by normal river flow with that supplied by a major flood. Multivariate statistical analysis of the heavy mineral distribution of southern California beaches and rivers indicate that the sand composition of the two northern cells is controlled by the dominantly sedimentary Transverse Range provenance, whereas the composition of the three southern cells is controlled by the dioritic Peninsular Ranges. Some leakage occurs between the two northern cells around the Point Dume‐Hueneme‐Mugu Canyon Zone, whereas no important southward mixing occurs between cells around the Palos Verdes‐Redondo Canyon Zone. Even though the Santa Clara River flows mostly through sedimentary terrains, samples from this river strongly reflect the granodioritic source present in its headlands. Although the basic sand composition within each cell persists during major flooding, leakage between cells may increase following flooding and the compositional packages present may show evidence of greater mixing.
The fissility of some Carboniferous shales
Authors: SPEARS D. A. 
Published: June 2006

ABSTRACTLaminations control the fissility of a sequence of shales and mudstones from the Upper Carboniferous Coal Measures in Britain. This was established by measuring the thickness of pairs of laminations in unweathered borehole material and comparing with the thickness of shale fragments at the outcrop of the same sequence. The parallel orientation of the clay minerals is not responsible for the fissility and it could be that its importance has been overestimated. The processes responsible for the formation and preservation of the laminations will also produce a well orientated clay fabric and hence fissility and clay orientation may be indirectly related.
The influence of palaeosalinity, grain size distribution and clay minerals on the content of B, Li and Rb in Quaternary sediments from Eastern Jutland, Denmark
Authors: VILLUMSEN ARNE , NIELSEN OLE BJØRSLEV 
Published: June 2006

ABSTRACTBulk sample analysis of Late‐ and Postglacial sediments from the Randers fjord area, Eastern Jutland, seem to indicate a relationship between palaeosalinity and B, Li and Rb contents determined on weak acid extracts of the sediment. Investigations of different size fractions, grain size distribution, and of clay minerals show, however, that variations in palaeosalinity as determined by palaeontological methods in this case have no direct influence on the chemistry.The variation of Li and Rb is related to variation in grain size, while the B variation seems to be related to the content of montmorillonite in the clay fraction.
Chertification in the Mississippian Lake Valley Formation, Sacramento Mountains, New Mexico
Authors: MEYERS WILLIAM J. 
Published: June 2006

ABSTRACTChert distribution in the Lake Valley rocks is selective to mud‐supported facies; it is not related to proximity to unconformities. The facies selectivity of the chertification is believed to be a function of the depositional distribution of indigenous silica as sponge spicules, an interpretation that is supported by high positive qualitative correlation of chert with spiculitic rocks. Petrography indicates that the spicules were all originally siliceous, and that they all went through a moldic stage during which many molds were compactively destroyed and distorted. Remaining molds were subsequently cemented by calcite or chalcedony. Chert distribution and spicule petrography argue for an intraformational source for much of the silica.Chert micro‐fabrics are dominated by microquartz, a replacement of grains and lime mud; length‐fast chalcedony, a pore‐filling cement; and megaquartz, a post‐chalcedony pore‐filling cement.Petrography of compaction features within chert masses indicates that chertification occurred after some burial. Based on stratigraphic reconstruction this burial depth was a maximum of about 215 m. and was most likely a few metres to a few tens of metres.Petrography of chert‐calcite cement relationships indicates that chertification occurred before and during first generation, pre‐Pennsylvanian non‐ferroan calcite cementation, and was completed before late‐stage, post‐Mississippian ferroan calcite precipitation. Petrography of chert clasts in basal Rancheria (Meramecian) and basal Pennsylvanian conglomerates proves these clasts derived from the Lake Valley Formation and were chertified before redeposition. Thus, some cherts in the Lake Valley are pre‐Meramecian in age, but all are pre‐Pennsylvanian in age. Furthermore, association of the cherts with the non‐ferroan cements indicates the cherts were probably precipitated in meteoric phreatic lens established beneath the pre‐Meramecian and pre‐Pennsylvanian subaerial unconformities.
Distinctive thin‐bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South‐central Pyrenees, Spain)
Authors: MUTTI EMILIANO 
Published: June 2006

ABSTRACTThe vertical and lateral stratigraphic relations of facies and facies associations, palaeocurrent directions, and geometry and internal organization of associated thick‐bedded and coarse‐grained bodies of sandstone provide the framework for distinguishing five thin‐bedded turbidite facies in the Eocene Hecho Group, south‐central Pyrenees, Spain. Each facies is characterized by a number of primary features which are palaeoenvironmental indicators by themselves. These features and their palaeoenvironmental significance are summarized below.

The impressive regularity and lateral persistence of bedding and depositional structures, combined with the association of thin hemipelagic intercalations are typical characteristics of the basin plain thin‐bedded turbidites. Lateral variations in bed thickness, internal structures, grain size, sand: shale ratio, and amounts of hemipelagic intercalations are present in these sediments, but take place so gradually that they cannot generally be recognized at the scale of even very large exposures. The basin plain facies has a remarkable character of uniformity over great distances and considerable stratigraphic thicknesses.
Thickening‐upward and/or symmetric cycles with individual thicknesses ranging from a few metres to a few tens of metres are typical of lobe‐fringe thin‐bedded turbidites. The sediments that comprise the cycles contain small but recognizable variations in bed thickness and sand: shale ratio. The diagnostic cyclic pattern can be detected in relatively small exposures. It should be noted that in absence of coarse‐grained and thick‐bedded sandstone of the depositional lobes the above cyclic pattern is diagnostic of fan‐fringe areas.
An extremely irregular bedding pattern with lensing, wedding, and amalgamation of individual beds over very short distances, sharp rippled tops of many beds, and internal depositional structures indicative of mainly tractional processes without substantial fallout, are typical and exclusive characteristics of channelmouth thin‐bedded turbidites.
Bundles of interbedded thin‐bedded sandstone and mudstone as thick as a few metres that are separated in vertical sequences by mudstone units of roughly similar or greater thickness are typical of interchannel thin‐bedded turbidites. The most diagnostic feature of this depositional environment is the presence of beds of sandstone filling broad shallow channels as probable crevasse‐splays.
Thin, thoroughly rippled sandstone beds with marked divergence of the bedding attitude characterize the channel‐margin facies. The divergence or expansion in thickness, is consistently toward the channel axis. Small and shallow channels filled with thin‐bedded deposits, interpreted here as crevasses cut into channel edges or levees during period of severe overbanking are also characteristic.
Chalk deformation and large‐scale migration of calcium carbonate
Authors: MIMRAN Y. 
Published: June 2006

ABSTRACTSixty Upper Cretaceous chalk exposures were examined and sampled in Dorset, the Isle of Wight and Guildford, South England, in order to investigate the effects of tectonic deformation on the chalk fabric. Light and scanning‐electron microscopes were used extensively, and chemical, mineralogical and isotopic analyses ware carried out.Two types of fabric modification were distinguished. The first type involves more than 90% volume loss by mechanical compaction at the early stages of deformation followed by dissolution and removal of calcium carbonate in the advanced stages of deformation. Chalks which have undergone this type of fabric modification are dense and consist of well rounded 0.5–3 μ calcite crystals with well developed pressure‐solution contacts. These chalks contain a high proportion of calcispheres (many of which are plastically deformed) but very few well preserved planktonic foraminifera and coccoliths. They are relatively enriched in insoluble constituents and depleted in strontium.The second type of fabric modification involves introduction of calcium carbonate into the pore spaces. Chalks which have undergone this type of modification are dense and contain a high proportion of 3–5 μ polygonal interlocking calcite crystals. Fossils are virtually never deformed, and delicate foraminifera and coccoliths are well preserved. Insoluble constituents similar to those found in the unmodified chalks occur in low concentrations.Removal of calcium carbonate at crystal contacts has taken place in chalks which have been subjected to high effective tectonic stresses and at crystal peripheries in chalks which have been subjected to high pore fluid pressure. Dissolution at crystal peripheries is responsible for the extensive calcium carbonate losses, and it is termed herein ‘confining pressure solution’.Introduction of calcium carbonate occurs in rocks which were under low tectonic stresses. During deformation calcium carbonate migrates from chalks under high stresses towards those under tow stresses, while some goes into solution in sea water. Well developed joints and high pore fluid pressure might increase the rate of calcium carbonate removal by three orders of magnitude. Petrographic and isotopic data suggest‐that all fabric modifications studied took place in meteoric water.
Sedimentation and water escape structures in some late Precambrian shallow marine sandstones from Finnmark, North Norway
Authors: JOHNSON HOWARD D. 
Published: June 2006

ABSTRACTWater escape structures are abundant in the Grønnes Formation, a tectonically undeformed, late Precambrian shallow marine sandstone deposit in North Norway.Trough cross‐bedded sandstones of the current‐dominated shallow marine environment were frequently liquefied, presumably due to recurring seismic shocks. Subsequent dewatering resulted in deformation of the cross‐bedding and the formation of convolute lamination. A three‐fold upward vertical sequence developed where liquefaction occurred below the sediment‐water interface: convoluted bed → passively deformed bed → undeformed bed. The passively deformed bed resulted from differential subsidence of a relatively plastic bed above a liquefied bed. It is characterized by anticlinal ridges and sand volcanoes at the sites of vertical sediment extrusion, and synclinal troughs at the sites of lateral sediment movement.Liquefaction may have been induced by either tectonic (earthquake shocks) or non‐tectonic (storm‐induced microseisms) trigger mechanisms, or a combination of both. The restriction of such a high frequency of water escape structures to deposits immediately above a gentle regional unconformity lends support for a tectonic trigger mechanism.
Shallow marine sand bar sequences: an example from the late Precambrian of North Norway
Authors: JOHNSON HOWARD D. 
Published: June 2006

ABSTRACTFive coarsening upward shallow marine sandstone sequences (2–10 m thick), are described from the late Precambrian of North Norway, where they occur in a laterally continuous and tectonically undeformed outcrop.The sequences consist of five facies with distinct assemblages of sedimentary structures and palaeocurrent patterns. Each facies is the product of alternate phases of sedimentation during relatively high‐ and low‐energy periods. Facies 1 to 4 are interpreted as representing prograding, subtidal sand bars. Sand bar progradation occurred during the highest energy periods when unidirectional currents flowed to the northwest, depositing trough cross‐bedded sandstones (facies 3 and 4) on the bar crests and flanks, and sheet sandstone beds (facies 1 and 2) in the offshore environments. Weaker northwesterly flowing currents continued during moderate energy fair weather periods. Low energy fair weather periods were dominated by wave processes, which formed largescale, low‐angle, westerly inclined surfaces on the bar flanks (facies 4) and wave rippled sandstone beds (facies 2) and flat laminated siltstone layers (facies 1) in the offshore environments.One sand bar was dissected by channels and infilled by tabular cross‐bedded sandstones (facies 5). Bipolar palaeocurrent evidence, with two modes separated into two laterally equivalent channel systems, suggests deposition by tidal currents in mutually evasive ebb and flood channels.The inferred processes of these sand bars are compared with those associated with modern storm‐generated and tidal current generated linear sand ridges. Both are influenced by the interaction of relatively low and high energy conditions. The presence of the tidal channel facies, however, combined with the inferred strong bottom current regime, is more analogous to a tidal current hydraulic regime.
Uranium oxidation and probable subaerial weathering of phosphatized limestone from the Pourtales Terrace*
Authors: BURNETT WILLIAM C. , GOMBERG DAVID N. 
Published: June 2006

ABSTRACTPhosphatized limestones from the Pourtales Terrace, Straits of Florida, have undergone fresh‐water diagenesis, as shown by several selective petrologic features such as dissolution of aragonitic skeletal material and preservation and recrystallization of Mg‐calcite. This interpretation is supported by the fact that greater than 94% of the uranium in these samples is in the U(VI) oxidation state.On the deeper Pourtales Escarpment, phosphatized limestones show no alteration features indicative of fresh‐water diagenesis. The uranium in these samples is a mixture of U(IV) and U(VI) with oxidation‐state ratios similar to other sea‐floor phosphorites.Our interpretation of these data is that uranium in the terrace samples was oxidized when that area was emergent. The karsted surface of the terrace, therefore, is a result of subaerial exposure of this portion of the Floridan platform. The escarpment samples were never above sea level, and so more closely retain their original uranium oxidation‐state ratios.
Clay minerals as an index of the degree of metamorphism of the carbonate and terrigenous rocks in the South Wales coalfield
Authors: GILL W. D. , KHALAF F. I. , MASSOUD M. S. 
Published: June 2006

ABSTRACTIllite, illite‐montmorillonite (I‐M) mixed layer, kaolinite and chlorite are the principal clay minerals identified in the carbonate and terrigenous carboniferous rocks in the South Wales coalfield. Mineralogic changes and illite crystallinity are the main modifications in the studied rocks. Progressive illitization of I‐M mixed layers (decrease in their expandabilities) towards the western part of the coalfield (i.e. in the direction of increase in coal‐rank and grade of metamorphism), and the development of vermicular kaolinite, dickite, allevardite and pyrophyllite in the anthracite area are the main mineralogic changes. Illite crystallinity was determined by Weaver's sharpness ratio (S.R.) and isosharpness ratio maps of illite in the carbonate and terrigenous rocks are produced showing a gradual increase in illite crystallinity towards the west. Illites in the terrigenous rocks tend to be aluminous (evidenced by the increase in their intensity ratios, ‘I.R.’) with increase in coal‐rank and grade of metamorphism towards the west. These changes are controlled to some extent by lithology. Correlation of illite S.R. with either its I.R. or expandability of I‐M mixed layer, has outlined two diagenetic zones in the coalfield: zone I, the Diagenetic zone, in the eastern and southern regions; and zone II, the Metadi‐agenetic zone, covering the central and northern parts of the central region. The Anchimetamorphic zone (zone III), which corresponds to the anthracite area in the northwestern region, was differentiated by correlating the illite S.R. with coal‐rank. The occurrence of the above mentioned diagenetic zones and modifications of the clay minerals in the carboniferous rocks of the South Wales coalfield are mainly lateral without variation with increase in depth.