bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reconstructing random topography from preserved stratification
Authors: PAOLA CHRIS , BORGMAN LEON 
Published: June 2006

ABSTRACTOne of the fundamental problems of interpreting the sedimentary record is reconstructing the original heights of palaeotopographical features such as bedforms or river channels. This requires an understanding of the relationship between topography and set thickness, but at present an exact theory exists only for periodic topography of uniform height. The applicability of this simple theory is severely limited by the random variability characteristic of many sedimentary systems. In this paper, we develop an exact theory for the probability‐density function (PDF) of sets generated from topography of random height. We focus on the limiting case of zero net deposition in order to provide a lower bound for the set thickness, and derive an analytical set‐thickness PDF that is determined by one parameter of the PDF for topographical height. This parameter, β, measures the breadth of the tail of the topographical PDF. The mean set thickness is 0.8225 β for bedforms and 1.645 β for river channels. If the topographical height is gamma distributed, the preservation ratio, defined as (mean thickness of preserved sets)/(mean topographical height), is 0.8225 r2 for bedforms and 1.645 r2 for river channels, where r is the coefficient of variation (standard deviation/mean) of the generating topography.In a comparison with data from laboratory current ripples, our analytical predictions compare well with observations of both mean set thickness and thickness distribution. The preservation ratio for the ripples is about 0.5, whilst measured dune heights give a preservation ratio of about 0.12. Depth data from two modern braided streams yield preservation ratios ranging from 0.4 to 0.75. As more data on the distributions of topographical height in modern environments become available, calculations such as these should help provide reliable error bounds for quantitative topographical reconstruction.
Dolomite‐rock textures and secondary porosity development in Ellenburger Group carbonates (Lower Ordovician), west Texas and southeastern New Mexico
Authors: AMTHOR JOACHIM E. , FRIEDMAN GERALD M. 
Published: June 2006

ABSTRACTPervasive early‐ to late‐stage dolomitization of Lower Ordovician Ellenburger Group carbonates in the deep Permian Basin of west Texas and southeastern New Mexico is recorded in core samples having present‐day burial depths of 1.5–7.0 km. Seven dolomite‐rock textures are recognized and classified according to crystal‐size distribution and crystal‐boundary shape. Unimodal and polymodal planar‐s (subhedral) mosaic dolomite is the most widespread type, and it replaced allochems and matrix or occurs as void‐filling cement. Planar‐e (euhedral) dolomite crystals line pore spaces and/or fractures, or form mosaics of medium to coarse euhedral crystals. This kind of occurrence relates to significant intercrystalline porosity. Non‐planar‐a (anhedral) dolomite replaced a precursor limestone/dolostone only in zones that are characterized by original high porosity and permeability. Non‐planar dolomite cement (saddle dolomite) is the latest generation and is responsible for occlusion of fractures and pore space.Dolomitization is closely associated with the development of secondary porosity; dolomitization pre‐and post‐dates dissolution and corrosion and no secondary porosity generation is present in the associated limestones. The most common porosity types are non‐fabric selective moldic and vuggy porosity and intercrystalline porosity. Up to 12% effective porosity is recorded in the deep (6477 m) Delaware basin. These porous zones are characterized by late‐diagenetic coarse‐crystalline dolomite, whereas the non‐porous intervals are composed of dense mosaics of early‐diagenetic dolomites. The distribution of dolomite rock textures indicates that porous zones were preserved as limestone until late in the diagenetic history, and were then subjected to late‐stage dolomitization in a deep burial environment, resulting in coarse‐crystalline porous dolomites. In addition to karst horizons at the top of the Ellenburger Group, exploration for Ellenburger Group reservoirs should consider the presence of such porous zones within other Ellenburger Group dolomites.
Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover
Authors: SQUYRES STEVEN W. , ANDERSEN DAVID W. , NEDELL SUSAN S. , WHARTON ROBERT A. 
Published: June 2006

ABSTRACTLake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross‐sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 × 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice‐covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach ∼ 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization and stabilization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.
Origin of manganese carbonates in Jurassic red shale, central Japan
Authors: MINOURA KOJI , NAKAYA SHU , TAKEMURA ATSUSHI 
Published: June 2006

ABSTRACTManganese carbonate deposits in Japanese Jurassic sedimentary rocks were studied petrogeochemically. The deposits are characteristically composed of spheroidal micronodules, up to 1 mm in diameter, and always contain well‐preserved radiolarian shells. Chemical elemental composition and mineralogical characteristics indicate that the micronodules contain rhodochrosite in a mixed carbonate phase composition (Mn86.7−92.2Ca2.2−2.9Mg2.6−6.7Fe2.6−5.6)CO3 Carbon and oxygen isotope values, which range from −7.99 to −4.78‰ and −4.05 to 0.28‰ relative to PDB, respectively, suggest that the manganese carbonate was precipitated in a suboxic zone. The micronodules closely resemble agglutinated benthic foraminifera in shape. We suggest that agglutinated foraminiferal tests composed of radiolarian shells accumulated selectively on the sediment surface during redeposition of bottom sediments and were replaced by manganese carbonate in suboxic diagenetic conditions of manganese reduction.
Diagenesis and reservoir quality of the Aldebaran Sandstone, Denison Trough, east‐central Queensland, Australia
Authors: BAKER JULIAN C. 
Published: June 2006

ABSTRACTThe Lower Permian Aldebaran Sandstone is the principal hydrocarbon reservoir in the Denison Trough (Bowen Basin), east‐central Queensland, Australia. It accumulated in a wide range of fluvio‐deltaic and nearshore marine environments. Detailed petrological study of the unit by thin section, X‐ray diffraction, scanning electron microscopy, electron microprobe and isotopic analysis reveals a complex diagenetic history which can be directly related to depositional environment, initial composition and burial‐temperature history. Early diagenetic effects included the precipitation of pyrite, siderite and illite‐smectite rims (δ18O (SMOW) =+8.9 to + 11.3‰). Deep burial effects included physico‐chemical compaction and the formation of quartz overgrowths, siderite (δ13C(PDB) =−34.0 to + 11.5‰, δ18O =−0.7 to +22.7‰), illite/illite‐smectite and ankerite (δ13C=−9.3 to −4.9‰) δ18O=+ 7.6 to + 14.4‰). Involved fluids were in part ‘connate meteoric’ water derived from compaction of the underlying freshwater Reids Dome beds. Important post‐maximum burial effects, controlled by deep meteoric influx from the surface, were ankerite and labile grain dissolution and formation of kaolinite (δ18O=+7.8 to +8.9‰, δD=−115 to −99‰), calcite (δ13C=−9.5 to +0.9‰, δ18O=+9.0 to +20.0‰) and dawsonite (δ13C=−4.0 to +2.3‰, δ18O=+9.8 to +19.8‰), the formation of dawsonite reflecting eventual stagnation of the aquifer. Entrapment of contained hydrocarbons was a relatively recent event which may be continuing today. Reservoir quality varies from marginal to good in the west to poor in the east, with predictable trends being directly linked to depositional environment and diagenesis.
Microbial micritic carbonates in uppermost Permian reefs, Sichuan Basin, southern China: some similarities with Recent travertines
Authors: GUO LI , RIDING ROBERT 
Published: June 2006

ABSTRACTThe uppermost Permian Chuenmuping reef formed on the western side of a carbonate platform situated in the eastern Sichuan Basin, southern China. Contrasts exist between this western patch reef and the better known Jiantianba barrier reef complex on the eastern platform margin in western Hubei Province, 250 km to the east. Microbial micritic carbonates form significant components of the Chuenmuping reef limestones. Three types of fabric can be identified: irregular, clotted and scalloped‐laminated. An additional, cuneiform fabric has been found only in fore‐reef facies at Jiantianba.Irregular fabric is comparable with the surface of presently forming travertines at Rapolano Terme, central Italy, which are produced by calcification of cyanobacteria. Clotted fabric shows indistinct peloids which tend to lack rims, and are amalgamated into irregular masses, some of which exhibit bush‐like arrangements where traces of filaments can be seen. Traces of filaments are observed in both dark and light layers in the scalloped‐laminated fabric, again suggesting a microbial origin. Cuneiform fabric consists of peloids and filaments, and closely resembles deposits in Quaternary travertines which may have been caused by bacterial action.Chuenmuping reef shows a shallowing sequence in normal marine conditions. The micritic fabrics interpreted here as microbial occur more commonly in the upper part of the reef. This indicates that microbial micrites, with a cementing role, formed coevally with reef growth within the upper part of the photic zone.
Depositional controls on Lower Carboniferous microbial buildups, eastern Midland Valley of Scotland
Authors: PICKARD NEIL A. H. 
Published: June 2006

ABSTRACTIn the eastern Midland Valley of Scotland non‐skeletal carbonate buildup complexes are present in the Charlestown Main Limestone (Brigantian), a thin marine carbonate unit within a lower Carboniferous basin fill otherwise dominated by fluvio‐deltaic sediments and volcanics. The buildups are restricted geographically to West Lothian and Central Fife and correspond to an area of reduced subsidence, the Burntisland High. Buildup geometry and local facies mosaics reflect the relative water depth and position on the Burntisland High that, because of its slight topographical relief and more distal position with respect to the location of fluvio‐deltaic systems, became an area of increased carbonate productivity and hence a locus for buildup development. Away from the Burntisland High, in the Fife‐Midlothian Low, more monotonous argillaceous limestone facies, of low energy and somewhat deeper water aspect, accumulated.Buildup facies contain a diverse marine fauna and are characterized by peloidal, clotted and homogeneous micrites interpreted as predominantly microbial in origin. Two types of buildup complex occur. At Charlestown, vertically stacked, tabular banks (up to 2 m thick and 100 m wide) form the western margin of an asymmetric buildup accumulation. East of this margin a complex mosaic of isolated low relief buildups and inter‐buildup sediments was deposited. Skeletal sand shoals present within these inter‐buildup sediments indicate that high energy conditions prevailed during buildup growth. In contrast, at Roscobie, inter‐buildup sediments are of low energy aspect and buildup geometry is domical rather than tabular. Initiated in slightly deeper and calmer water on the flank of the Burntisland High, the Roscobie buildups (up to 15 m thick and 46 m wide) accreted vertically, rather than laterally as at Charlestown, and coalesced to form an elongate ridge‐shaped buildup complex.
Subaqueous sediment gravity flow deposits: practical criteria for their field description and classification
Authors: GHIBAUDO GUIDO 
Published: June 2006

ABSTRACTA new method for the description and classification of subaqueous sediment gravity flow deposits is proposed. The classification scheme employs a convenient letter code and divides deposits (individual beds) into descriptive categories of two hierarchical levels: facies and subfacies. Facies, as the higher rank categories, are distinguished chiefly on the basis of sediment type (i.e. bed grain size/texture). A total of 13 facies have been distinguished: G= gravel; GS = gravel‐sand couplet; GyS = gravelly sand; S = sand; SM = sand—mud couplet; MS = mud—sand couplet; TM = silt—mud couplet; MT = mud—silt couplet; M = mud; MyS = muddy sand; SyM = sandy mud; MyG = muddy gravel; GyM = gravelly mud. Subfacies, as the lower rank categories, are distinguished within the individual facies on the basis of the bed's internal structures. The number of subfacies is unlimited, and their labelling code includes particular facies symbols (see above) preceded by lower—case letters denoting specific sedimentary structures and their vertical arrangement. Subfacies thus refer to the bed's intervals, or divisions, which are labelled as follows: m = massive (unstratified and ungraded); g = graded (unstratified and graded); s = plane‐stratified; x=cross‐stratified; 1 = parallel– and/or cross‐laminated; q = liquefied. For example, subfacies gsG (graded to plane‐stratified gravel) are gravel beds that have a lower graded interval and an upper plane‐stratified interval; subfacies xG (cross‐stratified gravel) are gravel beds that are cross‐stratified throughout; subfacies slS (plane‐stratified to laminated sand) are sand beds that have a lower plane‐stratified interval and an upper laminated (parallel‐ and/or cross‐laminated) interval.
Alluvial response to differential subsidence: sedimentological analysis aided by remote sensing, Willwood Formation (Eocene), Bighorn Basin, Wyoming, USA
Authors: KRAUS MARY J. 
Published: June 2006

ABSTRACTA colour Landsat Thematic Mapper image was used to identify and to map on a regional scale alluvial facies in the lower Eocene Willwood Formation. Each facies covers a distinct geographical area of several hundred square kilometres in the Bighorn Basin of Wyoming, USA. Comparison of the image with laboratory spectra from Willwood Formation rocks and field exposures shows that the image provides information regarding the colour of mudstones, their relative abundances, and the relative abundance of sandstones. Facies were further characterized from field study and published descriptions on the basis of sandbody geometry, the types of nodules present in the mudstones, and the abundance and geometry of carbonaceous mudstones. This information helps to interpret the fluvial environments represented and types of alluvial palaeosols found in the Willwood Formation.Four facies have been distinguished. The first facies is dominated by sheet sandbodies associated with immature palaeosols. The sheets mark the locations of major channels, which tend to occur in topographic lows. The second facies is characterized by more mature, moderately drained soils that required relatively lengthy periods of non‐deposition. Facies three and four dominantly consist of drab mudstones and abundant carbonaceous units, both formed in poorly drained areas. Although minor red mudstones demonstrate that drainage conditions periodically improved in facies three, facies four underwent prolonged saturation.The geographical facies distribution suggests that east‐west faults previously mapped in the Bighorn Mountains, extend westward into the Bighorn Basin and were active during early Eocene time. The lithological heterogeneity of the Willwood Formation rocks is attributed to warping associated with movement along these basement‐controlled faults. Fault activity created topographic gradients which influenced the position of major channel systems and helped produce variable drainage conditions that affected Eocene soil development.
Fusain in Carboniferous shallow marine sediments, Donegal, Ireland: the sedimentological effects of wildfire
Authors: NICHOLS GARY , JONES TIM 
Published: June 2006

ABSTRACTEvidence from fusain deposits in Lower Carboniferous rocks of western Ireland indicates that a catastrophic wildfire destroyed thousands of square kilometres of Carboniferous ‘forest’. In addition to yielding large quantities of charcoal, this wildfire event resulted in increased surface water runoff which affected sedimentation in an adjacent estuarine environment where the fusain is now preserved. This is the oldest documented evidence for a catastrophic palaeowildfire and a clear example of the sedimentological effects of large‐scale fires.The Lower Carboniferous (Visean) rocks in the Largymore Syncline of western Donegal, Ireland, are shallow marine sandstones, mudstones and limestones. The Upper Shalwy Beds are mudstones and cross‐bedded sandstones which show bi‐polar cross‐stratification and mud drapes on cross‐bed foresets indicating deposition in a tidal environment, probably a large estuary. In three coastal exposures a bed containing up to 20% fusain is found at the same stratigraphic horizon. The fusain is interpreted as fossil charcoal produced by palaeowildfire in a land area to the north‐west. The volume of fusain present in the unit can be estimated and by comparison with charcoal production in modern wildfires it has been calculated that around 95 000 km2 (more than the present land area of Ireland) was burnt.Along with the fusain, other effects of the wildfire can be seen in the deposits, which are poorly sorted compared to the rest of the Upper Shalwy Beds and are characterized by inclined heterolithic stratification produced by the draping of underlying bedforms. These features are considered to be due to a considerably increased sediment load in the estuary, resulting from enhanced surface runoff and soil erosion due to the wildfire.
Modern carbonate and terrigenous clastic sediments on a cool water, high energy, mid‐latitude shelf: Lacepede, southern Australia
Authors: JAMES NOEL P. , BONE YVONNE , VON DER BORCH CHRISTOPHER C. , GOSTIN VICTOR A. 
Published: June 2006

ABSTRACTThe wide Lacepede Shelf and narrow Bonney Shelf are contiguous parts of the south‐eastern passive continental margin of Australia. The shelves are open, generally deeper than 40 m, covered by waters cooler than 18°C and swept by oceanic swells that move sediments to depths of 140 m. The Lacepede Shelf is proximal to the ‘delta’of the River Murray and the Coorong Lagoon. Shelf and upper slope sediments are a variable mixture of Holocene and late Pleistocene quartzose terrigenous clastic and bryozoa‐dominated carbonate particles.Bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m. They can be grouped into four depth‐related assemblages. Coralline algae, the only calcareous phototrophs, are important sediment producers to depths of 70 m. Active benthic carbonate sediment production occurs to depths of 350 m, but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions.The shelf is separated into five zones. The strandline is typified by accretionary sequences of steep shoreface, beach and dune carbonate/siliciclastic sediments. Similar shoreline facies of relict bivalve/limestone cobble ridges are stranded on the open shelf. The shallow shelf, c.40–70 m deep, is a wide, extremely flat plain with only subtle local relief. It is a mosaic of grainy, quartzose, palimpsest facies which reflect the complex interaction of modern bioclastic sediment production (dominated by bryozoa and molluscs), numerous highstands of sea level over the last 80 000 years, modern mixing of sediments from relatively recent highstands and local introduction of quartz‐rich sediments during lowstands. The middle shelf, c.70–140 m deep, is a gentle incline with subtle relief where Holocene carbonates veneer seaward‐dipping bedrock clinoforms and local lowstand beach complexes. Carbonates are mostly modern, uniform, clean, coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes. The deep shelf edge, c. 140–250 m deep, is a site of diverse and active bryozoa growth. Resulting accumulations are characteristically muddy and distinguished by large numbers of delicate, branching bryozoa. The upper slope, between 250 and 350 m depth, contains the deepest platform‐related sediments, which are very muddy and contain a low diversity suite of delicate, branching cyclostome bryozoa.This study provides fundamental environmental information critical for the interpretation of Cenozoic cool water carbonates and the region is a good model for older mixed carbonate‐terrigenous clastic successions which were deposited on unrimmed shelves.
Morphology, internal structure and mechanics of small longitudinal (seif) dunes in an aeolian horizon of the Proterozoic Dhandraul Quartzite, India
Authors: CHAKRABORTY CHANDAN 
Published: June 2006

ABSTRACTThe excellently preserved metre‐scale, linear bedforms in an aeolian horizon of the Proterozoic Dhandraul Quartzite, India, show oppositely dipping strata arranged in a zigzag pattern. The strata are dominantly of translatent type, deposited by along‐crest migrating ripples preserved on the flanks of dunes. The bedforms thus may be interpreted in a morphodynamic sense as longitudinal (seif) dunes.In order to determine the regional palaeoflow pattern, the migration directions of ripples preserved at the top of sheet sandstones that are associated with the dune cross‐strata and internally show subhorizontal translatent strata were measured. A directionally varying flow with a mean direction nearly parallel to the mean axial trend of the dunes is indicated. The kinematics of the dunes were thus largely the result of alternate operation of two oblique flow components, each of which was deflected at a dune crest into an along‐crest flow on the downwind flank of the dune. The deflected flow formed along‐crest migrating ripples, which in turn deposited climbing ripple strata. Alternate deposition on the two opposite flanks resulted in near vertical accretion of the dunes, as is indicated by the zigzag pattern of stratal arrangement.