bluuebunny/crossref_metadata_2025_split huggingface dataset:
Halite saltern in the Canning Basin, Western Australia: a sedimentological analysis of drill core from the Ordovician‐Silurian Mallowa Salt
Authors: CATHRO DONNA L. , WARREN JOHN K. , WILLIAMS GEORGE E. 
Published: June 2006

ABSTRACTThe Late Ordovician‐Early Silurian Mallowa Salt of the Carribuddy Group, Canning Basin, north‐west Australia, is the largest halite deposit known in Australia, attaining thicknesses of 800 m or more within an area of approximately 200 000 km2. Study of 675 m of drill core from BHP‐Utah Minerals’ Brooke No. 1 well in the Willara Sub‐basin indicates that the Mallowa Salt accumulated within a saltern (dominantly subaqueous evaporite water body) that was subject to recurrent freshening, desiccation and exposure. Textures and bromine signatures imply a shallow water to ephemeral hypersaline environment typified by increasing salinity and shallowing into evaporitic mudflat conditions toward the top of halite‐mudstone cycles (Type 2) and the less common dolomite/anhydrite‐halite‐mudstone cycles (Type 1). The borate mineral priceite occurs in the capping mudstones of some cycles, reinforcing the idea of an increasing continental influence toward the top of mudstone‐capped halite cycles.The rock salt in both Type 1 and Type 2 cycles typically comprises a mosaic of large, randomly orientated, interlocking halite crystals that formed during early diagenesis. It only partially preserves a primary sedimentary fabric of vertically elongate crystals, some with remnant aligned chevrons. Intraformational hiati, halite karst tubes and solution pits attest to episodic dissolution. Stacked Type 2 cycles dominate; occasional major recharges of less saline, perhaps marine, waters in the same area produced Type I cycles.The envisaged saltern conditions were comparable in many ways to those prevailing during the deposition of halite cycles of the Permian Salado Formation in New Mexico and the Permian San Andres Formation of the Palo Duro Basin area in Texas. However, in the Canning Basin the cycles are characterized by a much lower proportion of anhydrite, implying perhaps a greater degree of continental restriction to the basin. The moderately high level of bromine in the Mallowa Salt (156·5 ± 43·5 ppm Br for primary halite, 146·1 ± 54·7 ppm Br for secondary halite) accords with evolved continental brines, although highly evaporative minerals such as polyhalite and magnesite are absent. The bromine levels suggest little or no dissolution/reprecipitation of primary halite and yet, paradoxically, there is little preservation of the primary depositional fabric. The preservation of early halite cements and replacement textures supports the idea of an early shutdown of brine flow paths, probably at burial depths of no more than a few metres, and the resultant preservation of primary bromine values in the secondary halite.
Theoretical and measured aeolian sand transport on a barrier island, Louisiana, USA
Authors: DINGLER JOHN R. , HSU S. A. , REISS THOMAS E. 
Published: June 2006

ABSTRACTOver the past 100 years, the Isles Dernieres, a low lying barrier island chain along the coast of central Louisiana, Usa, has undergone more than 1 km of northward beach face retreat with the loss of 70% of its surface area. The erosion results from a long term relative sea level rise coupled with day to day wind and wave action that ultimately favours erosion over deposition. At a site in the central Isles Dernieres, 8 days of wind and beach profile measurements during the passage of one winter cold front documented aeolian erosion and deposition patterns under both onshore and offshore winds. For offshore winds, the theoretical erosion rate, based on wind shear velocity, closely matched the measured erosion rate; for onshore winds, the theoretical rate matched the measured rate only after being corrected by a factor that accounted for beach face morphology.In late February 1989, a strong cold front moved into coastal Louisiana. That cold front stalled over the Gulf of Mexico, resulting in 4 days of strong northerly winds at a study site on the Isles Dernieres. During those 4 days, the wind moved sand from the backshore to the upper beach face. When the cold front finally moved out of the area, the wind shifted to the south and decreased in strength. The onshore wind then restored some of the upper beach face sand to the backshore while increased wave activity moved the rest into the nearshore.The theoretical estimate of 1·28 m3 m−1 for the rate of sand transport by the northerly wind compares well with the measured backshore erosion rate of 1·26 m3 m−1, which was determined by comparing beach profiles from the start and end of the period of northerly winds. The theoretical estimate of 0·04 m3 m−1 for the rate of sand transport by the southerly wind, however, is notably less than the measured rate of 0·45 m3 m−1. The large discrepancy between the two rates can be explained by a difference in the shear velocity of the wind between the beach face, where the erosion occurred, and the backshore, where the wind stress was measured. Using an empirical relationship for the wind shear drag coefficient as a function of coastal environment, the theoretical estimate for the rate of sand transport by the southerly wind becomes 0·44 m3 m−1
Computer simulation of reef growth
Authors: BOSSCHER HEMMO , SCHLAGER WOLFGANG 
Published: June 2006

ABSTRACTLight is one of the major controls on reef growth and carbonate production. The growth of present reef builders depends largely upon the amount of light available for photosynthesis. As light decreases with water depth, so does reef growth.The computer model presented extends this principle by combining two functions, one for photosynthesis and the other for the extinction of light in water. The model is used to simulate the growth of Alacran Reef, Mexico, two reefs of the Great Barrier Reef and the reefs of the windward platform of St Croix, US Virgin Islands. The model also gives an accurate simulation of the growth of fore‐reef walls in Belize, in agreement with the accretion hypothesis developed for this feature.
The Ilchulbong tuff cone, Cheju Island, South Korea
Authors: SOHN Y. K. , CHOUGH S. K. 
Published: June 2006

ABSTRACTThe Ilchulbong mount of Cheju Island, South Korea, is an emergent tuff cone of middle Pleistocene age formed by eruption of a vesiculating basaltic magma into shallow seawater. A sedimentological study reveals that the cone sequence can be represented by nine sedimentary facies that are grouped into four facies associations.Facies association I represents steep strata near the crater rim composed mostly of crudely and evenly bedded lapilli tuff and minor inversely graded lapilli tuff. These facies suggest fall‐out from tephra finger jets and occasional grain flows, respectively. Facies association II represents flank or base‐of‐slope deposits composed of lenticular and hummocky beds of massive or backset‐stacked deposits intercalated between crudely to thinly stratified lapilli tuffs. They suggest occasional resedimentation of tephra by debris flows and slides during the eruption. Facies association III comprises thin, gently dipping marginal strata, composed of thinly stratified lapilli tuff and tuff. This association results from pyroclastic surges and cosurge falls associated with occasional large‐scale jets. Facies association IV comprises a reworked sequence of massive, inversely graded and cross‐bedded (gravelly) sandstones. These facies represent post‐eruptive reworking of tephra by debris and stream flows.The facies associations suggest that the Ilchulbong tuff cone grew by an alternation of vertical and lateral accumulation. The vertical buildup was accomplished by plastering of wet tephra finger jets. This resulted in oversteepening and periodic failure of the deposits, in which resedimentation contributed to the lateral growth. After the eruption ceased, the cone underwent subaerial erosion and faulting of intracrater deposits. A volcaniclastic apron accumulated with erosion of the original tuff cone; the faulting was caused by subsidence of the subvolcanic basement within the crater.
Distal alluvial deposits in a foreland basin setting—the Lower Freshwater Miocene), Switzerland: sedimentology, architecture and palaeosols
Authors: PLATT NIGEL H. , KELLER BEAT 
Published: June 2006

ABSTRACTThe Lower Freshwater Molasse (Untere Susswasser Molasse) crops out over a wide area of the Swiss Molasse Basin. Coarse grained alluvial fan conglomerates dominate in proximal basin areas along the Alpine front. These conglomerates pass northwards into sandstones and mudstones of an extensive northeastward draining meandering river system which ran parallel to the basin axis. Sedimentological study of outcrops, quarry exposures and boreholes in the basal Miocene (‘Aquitanian‘) has permitted detailed facies analysis of this distal alluvial sequence. The distal Aquitanian is made up of distinct ‘architectural elements’characterized by their geometries and sedimentary structures. Each may be assigned to a particular depositional setting: meander belt, levees, crevasse channels and splays, overbank fines and palaeosols, and lacustrine.Meander belt sandstones were deposited in mixed load channels with a dominant bedload component. Sandstones commonly comprise amalgamated and locally stacked ribbon bodies 2–15 m thick and 150–1500 m wide. Interbedded rippled, laminated and mottled fine grained levee sandstones and siltstones form lenticular packages up to 3 m thick and 30–100 m across. Small scale crevasse channel sandstones 2–4 m thick and 5–10 m across pass laterally into metre scale, medium to fine grained crevasse sandstone sheets. Rare laminated lacustrine siltstones occur only in the north‐east part of the basin. Floodplain mudstones and marls make up the remainder of the succession. These display a variety of pedogenic features recording cyclical palaeosol development. Palaeosols show strong variations in morphology and maturity both laterally across the floodplain and downstream along the basin axis, reflecting local variation in aggradation rate associated with proximity to alluvial channel courses as well as regional variation in subsidence and floodplain drainage.Analysis of the organization and distribution of the various sediment bodies permits reconstruction of the fluvial system and allows development of a model for the sedimentary architecture of the Lower Freshwater Molasse in the study area. Integration of palaeosol studies into a well defined architectural framework assists recognition of areal facies belts and may aid location of sand‐prone sequences in the subsurface.
A sedimentological and stable isotopic study of travertines and associated sediments within Upper Triassic lacustrine limestones, South Wales, UK
Authors: LESLIE ALICK B. , TUCKER MAURICE E. , SPIRO BARUCH 
Published: June 2006

ABSTRACTThe Upper Triassic in South Wales is composed of up to 100 m of red, dolomitic mudstones of the Mercia Mudstone Group which overlie and are laterally equivalent to basin margin coarse clastic deposits. In the Sully Island and Dinas Powys areas, a series of carbonate deposits was laid down within small basins adjacent to the main Bristol Channel Basin. The rocks consist of dolomites containing replaced evaporites, overlain by perilittoral freshwater limestones. The limestones are fenestral intrasparites and contain abundant pedogenic and stromatolitic horizons, as well as locally developed travertines. Evidence for vadose diagenesis within the limestones is common. The travertines consist of sheets of fibrous calcite (flowstone) associated with pisoids and flöe calcite. Most of the travertines consist of single sheets several millimetres in thickness although ‘mounds’up to 1 m in height and 5 m in diameter are also present. The topmost metre of the limestones, which has been dolomitized, is deformed into tepee and megapolygonal structures.The carbon and oxygen stable isotopic composition of the limestones suggests that they were precipitated in low salinity waters. Successive samples from individual bands of flowstone show a covariance of δ18C and δ13C which is consistent with the mixing of resurgent groundwaters with pools of more evolved waters at the surface. The sedimentological and geochemical evidence suggests that the limestones were deposited in a small, enclosed basin fed by upwelling meteoric groundwaters in an environment distinct from that in which the laterally equivalent gypsiferous red mudstones were formed.
The morphology and dynamics of low amplitude bedwaves upon upper stage plane beds and the preservation of planar laminae
Authors: BEST JIM , BRIDGE JOHN 
Published: June 2006

ABSTRACTExperimental studies of subcritical, unidirectional flow over upper stage plane beds of medium grained sand reveal the ubiquitous presence of low amplitude bedwaves. Flow depth was 0·11 m, mean flow velocities were 0·86–1·0 m s−1, shear velocities were 0·058–0·71 m s−1 and dimensionless shear stresses were 0·56–0·87. Bedwaves are asymmetrical in profile and range from 0·75 to 11 mm in height (mainly 2–6 mm), from 0·7 to 1·3 m in wavelength and have mean celerities of 10 mm s−1. Flow records suggest that the bedwaves are associated with accelerating flow over the bedwave crests and flow which decelerates and diverges laterally over the troughs. High resolution bed profiling during aggradation of the bed combined with subsequent box coring illustrates that these bedwaves are responsible for the planar laminae characteristic of upper stage plane beds. Lamina preservation is dependent upon the mean aggradation rate and the sequence of bedwaves of different height crossing any point; individual laminae are more readily preserved at higher aggradation rates where the possibility of reworking by later bedwaves is reduced. Laminae are recognized by small changes in grain size and commonly a fining upwards at the top of laminae which is generated by fine grained material infiltrating a lower lamina in the leeside of a bedwave.
On the entrainment of sediment and initiation of bed defects: insights from recent developments within turbulent boundary layer research
Authors: BEST JIM 
Published: June 2006

ABSTRACTSediment entrainment and the initiation of bed defects has commonly been ascribed to the impact of high velocity sweeps upon mobile sand beds. Results of visualization experiments suggest that these sweep impacts are grouped and may define ‘patches’of entrainment upon a mobile bed that may be wider than an individual sweep impact. Additionally, the presence of longitudinal ribs of sediment generated by sweep impacts may stabilize the position of sweeps and low speed streaks. These observations are interpreted in the light of recent boundary layer research which suggests the formation of multiple hairpin shaped vortices within turbulent flows: these are postulated to generate multiple sweeps that manifest themselves as entrainment patches on a mobile bed. These features of the turbulent boundary layer and its modification by sweep generated sediment ridges can be used to propose a model for bed defect formation and the subsequent development of current ripples.
Diagenesis of Ordovician carbonates from the north‐east Michigan Basin, Manitoulin Island area, Ontario: evidence from petrography, stable isotopes and fluid inclusions
Authors: CONIGLIO M. , WILLIAMS‐JONES A. E. 
Published: June 2006

ABSTRACTMiddle to Late Ordovician subtidal carbonates in the Manitoulin Island area of Ontario are predominantly limestone in composition, but non‐ferroan and ferroan dolomite is a common cement as well as a selective or locally pervasive replacement phase. Integration of field, petrographic, geochemical (δ13C, δ18O) and fluid inclusion data indicates that lithification of these carbonates occurred during burial diagenesis, with much of the alteration controlled by regional fracturing and hydrothermal influences.Aqueous (type 1) fluid inclusions in early calcite (pre‐dolomite) and dolomite are saline (> 29 wt% NaCl eq.) solutions with Ca and/or Mg in excess of Na and display homogenization temperatures with modes of 95 and 101°C, respectively. These temperatures can be explained by significantly more burial than can be accounted for either by the available stratigraphic information or by an unusually high palaeogeothermal gradient, which also is not well supported. The fluid inclusion temperatures are interpreted to have resulted from hydrothermal fluids which circulated during the burial diagenesis of these strata. Type 1 inclusions in late (post‐dolomite) calcite are less saline (<19 wt% NaCl eq.) and have a bimodal distribution of homogenization temperatures with a relatively well defined low temperature peak similar to those in early calcite and dolomite and a broad higher temperature grouping with a mode at 183°C. A small proportion of methane and light hydrocarbon‐bearing fluid inclusions (type 2) are present in all stages of carbonate.Dolomitizing fluids were derived from burial compaction of argillaceous sediments in the more central parts of the Michigan Basin and the updip migration of these brines along fractures to the basin margin where the carbonates of the Manitoulin Island area were dolomitized. Alternatively, migration of dolomitizing brines downward from the overlying pervasively dolomitized Silurian sequence into fractures in the Ordovician carbonates may have occurred. Integration of the aqueous fluid inclusion data into the diagenetic history of these carbonates remains equivocal because most of the inclusions are secondary or indeterminate in origin. Nevertheless, high salinities resulting from interaction with evaporitic strata and hydrothermal effects are clearly implicated although the origin of the latter remains unclear. The alteration styles of the Ordovician carbonates in the Manitoulin area are similar to those of Ordovician hydrocarbon reservoirs described from other parts of the Michigan Basin. They indicate that fracture‐related diagenesis occurred on a basin‐wide scale and that hydrothermal effects were important.
Tidal influence in Cretaceous fluvial strata from Utah, USA: a key to sequence stratigraphic interpretation
Authors: SHANLEY KEITH W. , McCABE PETER J. , HETTINGER ROBERT D. 
Published: June 2006

ABSTRACTDetailed models already exist that outline physical and temporal relationships in marine and marginal marine strata. Such models are still in their infancy in alluvial deposits. Recognition of tidal and estuarine influence in fluvial strata is critical to the development of high resolution sequence stratigraphic correlations between marine and non‐marine strata. Strata that have previously been interpreted as low energy meandering river deposits contain sedimentary and biogenic structures that suggest a tidal influence. These structures include sigmoidal bedding, paired mud/silt drapes, wavy and lenticular bedding, shrinkage cracks, multiple reactivation surfaces, inclined heterolithic strata, complex compound cross‐beds, bidirectional cross‐beds, and trace fossils including Teredolites, Arenicolites and Skolithos. Although none of these structures is unique to tidal processes, the preponderance of data suggests that fluvial systems have been affected by tidal processes well inland of coeval shoreline deposits. These deposits rarely form a significant proportion of a depositional sequence; however, their occurrence allows time significant surfaces to be extended for tens or even hundreds of kilometres inland from coeval shoreline deposits.In Turonian through Campanian strata exposed in the Kaiparowits Plateau of southern Utah, tidally influenced facies are recognized within at least two distinct stratigraphic levels that were deposited during periods of relatively rapid base level rise. These strata form part of an alluvial transgressive systems tract. Landward of each of the marine transgressive maxima, tidal facies are present in fluvial channels that are completely encased in non‐marine strata at distances up to 65 km inland from a coeval palaeoshoreline. Our work suggests that such deposits may have gone unrecognized in the past, but they form a significant component of alluvial strata in many depositional sequences. Although these tidally influenced fluvial deposits may be difficult to recognize, they are temporally equivalent to marine maximum flooding surfaces and provide a chronostratigraphic correlation between alluvial and nearshore marine deposits.
Reef Fabrics, biotic crusts and syndepositional cements of the Latemar reef margin (Middle Triassic), northern Italy
Authors: HARRIS M. T. 
Published: June 2006

ABSTRACTThe Latemar reef buildup of the central Dolomites (northern Italy) provides a rare opportunity to examine an in‐place Middle Triassic (Upper Anisian to Lower Ladinian) platform margin that is not strongly deformed or dolomitized. The margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms. Across this transition, the depositional profile relates directly to a consistent lateral facies pattern: (1) restricted‐biota grainstone of the platform interior, (2) ‘Tubiphytes’‐rich boundstone and (3) diverse‐biota grainstone that grades into (4) foreslope breccia beds. The boundstone and diverse‐biota grainstone facies comprise the platform margin.The boundstone facies consists of a framework of small (< 10 cm) skeletal remains (< 10% by volume) with associated biotic crusts, internal sediments and syndepositional cements. Crusts and cements constitute most of the rock volume and created the boundstone fabric. Biotic crusts exhibit gravity‐defying geometries and range from a light grey, ‘structure grumeleuse’ rind to dark grey, micritic laminae. Both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits, indicating a syndepositional origin.The diverse‐biota grainstone facies primarily consists of skeletal‐peloidal grainstone with a diverse open marine biotic assemblage, in contrast to the restricted biota grainstones of the platform interior that have a low diversity, restricted marine biota. Metre scale hexacoral boundstone and centimetre‐scale sponge boundstone and microbial boundstone occur as isolated patches (tens to hundreds of metres apart) within the diverse‐biota grainstone facies.The depositional profile, facies zonation and biotic constituents all indicate that the Latemar buildup had a shallow water reef margin, in contrast to previous interpretations that these were upper slope reefs. The syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave‐resistant reef fabric.