bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sedimentology of 40 000 year Milankovitch‐controlled cyclothems from central Hawke's Bay, New Zealand
Authors: HAYWICK DOUGLAS W. , CARTER ROBERT M. , HENDERSON ROBERT A. 
Published: June 2006

ABSTRACTCyclothemic sedimentary rocks of the Plio‐Pleistocene Petane Group outcrop extensively in the Tangoio block of central Hawke's Bay, New Zealand. They are products of inner to mid‐shelf sedimentation and were deposited during glacio‐eustatic sea level fluctuations along the western margin of a shallow, pericontinental seaway located in a forearc setting. The succession consists of five laterally continuous cyclothems, each containing a fine grained interval of silt and a coarse grained interval of siliciclastic sand ± gravel or limestone. Five sedimentary facies assemblages comprising 20 separate facies have been recognized. Coarse grained intervals of cyclothems were deposited mostly during relative sea level lowstands and contain up to four facies assemblages: (1) a non‐marine assemblage (with three component facies, representing braided river and overbank environments); (2) an estuarine assemblage (with three component facies, representing tidal flat and mud‐dominated estuarine environments); (3) a siliciclastic shoreline assemblage (with six component facies, representing greywacke pebble beach, shoreface and inner shelf environments); and (4) a carbonate shelf assemblage (with four component facies, representing tide‐dominated, inshore and shallow marine environments). Fine grained intervals of cyclothems were deposited during sea level highstands when the Tangoio area was generally experiencing mid‐shelf sedimentation. This produced an offshore assemblage consisting of four component facies. The distribution of facies assemblages during relative sea level lowstands was dependent upon proximity to the shoreline, the type and rate of sediment supply to the basin, and shelf hydrodynamics. Carbonate shelf facies dominate coarse grained intervals in Cyclothems 3–5, but siliciclastic shoreline and non‐marine facies dominate in Cyclothems 1 and 2. The abrupt change from siliciclastic to carbonate sedimentation during relative sea level lowstand deposition is thought to have been induced by rapidly falling interglacial to glacial sea level accentuated by regional tectonic shoaling. This caused most of the terrigenous sediment supply to bypass the Tangoio area. Consequently, carbonate sediment accumulated in inshore and shallow marine settings. Facies assemblages rarely show lateral interdigitation, but are vertically stratified over the entire Tangoio block. Facies successions in each cyclothem preserve a record of relative sea level change during deposition of the Petane Group and are consistent with a Plio‐Pleistocene sea level change in eastern New Zealand of c. 75–150 m, i.e. approximately the magnitude suggested for Late Quaternary glacio‐eustatic sea level changes.
Pillow‐beds: a new type of seismites? An example from an Oligocene turbidite fan complex, Alicante, Spain
Authors: ROEP T. B. , EVERTS A. J. 
Published: June 2006

ABSTRACTA new type of soft sediment deformed beds, termed ‘pillow‐beds’, originally a packet of calcarenitic turbidites, show sand‐in‐sand loading with plane lower and upper surfaces. The pillow‐beds have some resemblance to ball and pillow structures and they are considered to have formed as a result of dewatering. The pillow‐beds are Oligocene in age and are part of turbidite lobes in a submarine fan system, which was fed through a canyon along the southern border of the ancient Iberian continent. Three hypotheses may explain their occurrence: overloading, sliding or seismic shock. A seismic origin is preferrred on the basis of the flat, undeformed lower surface of the pillow‐beds, excluding dewatering of—and loading into—the previously deposited beds. Furthermore, the pillow‐bed structures are related to grain size and may show repetitions, thus excluding sliding. The scale and nature of the pillow‐beds suggest they could be the result of an earthquake with a magnitude of 6–7 on the Richter scale.
Changes in velocity profiles at roughness transitions in coarse grained channels
Authors: ROBERT ANDRE , ROY ANDRE G. , DE SERRES BERNARD 
Published: June 2006

ABSTRACTHeterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness. Distinct spatial zones in terms of grain size have been reported, for example sand ribbons and bedload sheets. The transition from areas of finer to coarser grained surface sediment is often abrupt. However, the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels. This paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistancé on the structure of the turbulent boundary layer. Measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river. Immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface, boundary shear stress and roughness length increase considerably. Downstream from this transition, velocity profiles become concave upwards. Downstream and upstream sections show significant differences in terms of near bed velocities (deceleration downstream of the transition), velocity gradient and turbulence intensity of the streamwise velocity component. Comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity (or shear stress) associated with the pressure drag produced by large and isolated obstacles.
Void‐filling deposits in karst terrains of isolated oceanic islands: a case study from Tertiary carbonates of the Cayman Islands
Authors: JONES BRIAN 
Published: June 2006

ABSTRACTCaves, fossil mouldic cavities, sinkholes and solution‐widened joints are common in the Cayman and Pedro Castle members of the Bluff Formation (Oligocene‐Miocene) on Grand Cayman and Cayman Brac because they have been subjected to repeated periods of karst development over the last 30 million years. Many voids contain a diverse array of sediments and/or precipitates derived from marine or terrestrial environs, mineral aerosols, and groundwater. Exogenic sediment was transported to the cavities by oceanic storm waves, transgressive seas, runoff following tropical rain storms and/or in groundwater.At least three periods of deposition were responsible for the occlusion of voids in the Cayman and Pedro Castle members. Voids in the Cayman Member were initially filled or partly filled during the Late Oligocene and Early Miocene. This was terminated with the deposition of the Pedro Castle Member in the Middle Miocene. Subsequent exposure led to further karst development and void‐filling sedimentation in both the Cayman and Pedro Castle members. Speleothems are notably absent. The void‐filling deposits formed during these two periods, which were predominantly marine in origin, were pervasively dolomitized along with the host rock 2–5 million years ago. The third period of void‐filling deposition, after dolomitization of the Bluff Formation, produced limestone, various types of breccia, terra rossa, speleothemic calcite and terrestrial oncoids. Most of these deposits formed since the Sangamon highstand 125 000 years ago. Voids in the present day karst are commonly filled or partly filled with unconsolidated sediments.Study of the Bluff Formation of Grand Cayman and Cayman Brac shows that karst terrains on isolated oceanic islands are characterized by complex successions of void‐filling deposits that include speleothems and a variety of sediment types. The heterogenetic nature of these void‐filling deposits is related to changes in sea level and climatic conditions through time.
Glaciation and tectonics in an active intracratonic basin: the Late Palaeozoic Itararé Group, Paraná Basin, Brazil
Authors: EYLES C. H. , EYLES N. , FRANCA A. B. 
Published: June 2006

ABSTRACTThe Paraná Basin (1 600 000 km2) is the largest intracratonic basin in southern South America and contains a thick (1300 m) Permo‐Carboniferous glacial succession (the Itararé Group). This paper describes over 1700 m of drill core recovered during recent exploration for oil and gas. Itararé Group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones, and massive and laminated mudstones. Facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin.Three stratigraphic formations can be defined across the basin, each consisting of a lowermost sandstone‐rich member overlain by a diamictite‐rich member. Examination of Itararé Group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes. Primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the Itararé Group. Ice masses fringing the eastern (southern African) and western (Bolivian) basin margins supplied sediment to the basin in the form of fluvio‐glacial deltas, fans and floating ice tongues. This sediment was then resedimented downslope as debris flows and turbidites.Both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step‐wise expansion by outward faulting within Late Proterozoic mobile belts. The position of successive basin margins can be related to specific lineament structures in the underlying basement. Asymmetric expansion of the Paraná Basin occurred along the northern and southern basin margins during deposition of the Itararé Group; this expansion probably reflects shallow crustal adjustments activated by collisional movements along the Andean margin of South America during the Hercynian Orogeny.
Calcite cementation during bacterial manganese, iron and sulphate reduction in Jurassic shallow marine carbonates
Authors: HENDRY JAMES P. 
Published: June 2006

ABSTRACTFaunally restricted argillaceous wackestones from the Middle Jurassic of eastern England contain evidence of early diagenetic skeletal aragonite dissolution and stabilization of the carbonate matrix, closely followed by precipitation of zoned calcite cements, and precipitation of pyrite. Distinctive cathodoluminescence and trace element trends through the authigenic calcites, their negative δ13C compositions and the location of pyrite in the paragenetic sequence indicate that calcite precipitation took place during sequential bacterial Mn, Fe and sulphate reduction. Calcite δ18O values are compatible with cementation from essentially marine pore fluids, although compositions vary owing to minor contamination with 18O‐depleted ‘late’cements. Mg and Sr concentrations in the calcites are lower than those in recent marine calcite cements. This may be a result of kinetic factors associated with the shallow burial cementation microenvironments.Bicarbonate for sustained precipitation of the authigenic calcites was derived largely from aragonite remobilization, augmented by that produced through anaerobic organic matter oxidation in the metal and sulphate reduction environments. Aragonite dissolution is thought to have been induced by acidity generated during aerobic bacterial oxidation of organic matter. Distinction of post‐oxic metal reduction and anoxic sulphate reduction diagenetic environments in modern carbonate sediments is uncommon outside pelagic settings, and early bacterially mediated diagenesis in modern platform carbonates is associated with extensive carbonate dissolution. High detrital Fe contents of the Jurassic sediments, and their restricted depositional environment, were probably the critical factors promoting early cementation. These precipitates constitute a unique example of calcite authigenesis in shallow water limestones during bacterial Mn and Fe reduction.
The origin and fate of silt sized carbonate in subsurface Miocene—Oligocene mudstones, south Texas Gulf Coast
Authors: MILLIKEN K. L. , LAND L. S. 
Published: June 2006

ABSTRACTCombined petrographic and geochemical data document several kinds of detrital carbonate in subsurface Miocene‐Oligocene mudstones of the Texas Gulf Coast. In the extreme south of Texas, in muddy sediments deposited by ancient precursors to the modern Rio Grande, mudstone carbonate is dominated by extrabasinal detritus derived from Cretaceous limestones of the Edwards plateau. Further north, Oligocene mudstones contain carbonate that is mostly syndepositional skeletal material. Minor amounts of authigenic carbonate are found as replacements of silt sized feldspars in all the mudstones. Depth‐related shifts in δ18Ocalcite and δ13Ocalcite suggest that small amounts of authigenic carbonate also form by replacement of detrital carbonate (‘recrystallization’), although this cannot be demonstrated petrographically. Pervasive carbonate cementation in primary pores in mudstones is not generally observed. Textural evidence of carbonate loss through pressure dissolution is widespread, providing a mechanism for the depth‐related decline in carbonate content observed in many Gulf Coast wells. Carbonate dissolution in mudstones, and export of the CaCO3, implies a massive acid source, probably resulting from silicate reactions within the mudstones during burial diagenesis.
Geolimnology of Freefight Lake: an unusual hypersaline lake in the northern Great Plains of western Canada*
Authors: LAST WILLIAM M. 
Published: June 2006

ABSTRACTFreefight Lake, Canada's deepest salt lake, is a meromictic, hypersaline lake located in the most arid part of the northern Great Plains. The lake has a distinctive basin morphology, with a large expanse of seasonally flooded mud flats and sand flats adjacent to a deep, flat bottomed perennial waterbody. The mixolimnion, dominated by magnesium, sodium and sulphate ions, has an average salinity of 110 ppt and overlies a monimolimnion of 180 ppt total dissolved salts. The entire water column is strongly supersaturated with respect to a variety of calcium and magnesium carbonate minerals; the lower water mass is also saturated or supersaturated with respect to a number of very soluble sodium, magnesium and sodium + magnesium salts.The modern sedimentary processes operating in Freefight Lake give rise to six main sedimentary facies: (i) colluvium, (ii) mud flats and sand flats, (iii) algal flats, (iv) delta, (v) slope and debris apron, and (vi) deep basin. The colluvium, mud flats and sand flats, and delta facies are dominated by physical processes and consist mainly of detrital siliciclastic sediment. The algal flats, slope and debris apron, and deep basin facies are dominated by endogenic and authigenic sediments derived mainly by physicochemical and biologically mediated carbonate and evaporite mineral precipitation. As one of very few deep water lakes in the world in which soluble evaporite minerals are forming and being preserved, Freefight Lake occupies an important position within the realm of lacustrine sedimentology. Although many of the sedimentological and geochemical processes taking place in the basin today are unusual, the delineation and evaluation of these processes is essential in order to decipher properly the stratigraphic records of Quaternary lake sediments in this large area of North America, as well as lacustrine sequences from other arid and semi‐arid regions of the world.
Processes of late Quaternary turbidity current flow and deposition on the Var deep‐sea fan, north‐west Mediterranean Sea
Authors: PIPER DAVID J. W. , SAVOYE BRUNO 
Published: June 2006

ABSTRACTHigh‐resolution seismic boomer profiles, with a vertical resolution of less than 1 m, together with piston cores and previous side‐scan sonar data, are used to describe late Quaternary sedimentation on the Var deep‐sea fan. Chronological control is provided by foram biostratigraphy and radiocarbon dating in cores, and is extended over the fan by seismic correlation. Regional erosional events correspond to the oxygen isotopic stage 2 and 6 glacial maxima.Cores and seismic data define a widespread surface sand layer that is correlated with prodelta failure in 1979 and subsequent submarine cable breaks. Numerical modelling constrains the character of this 1979 turbidity current. It originated from a relatively small slide on the upper prodelta that put sufficient material in suspension to form an accelerating turbidity current which eroded sand from the Var Canyon. The turbidity current was only 30 m thick on the Upper Valley, but experienced significant flow expansion in the Middle Valley to thicknesses of more than 120 m, where it spilled over the eastern Var Sedimentary Ridge at a velocity of about 2·5 m s−1. Other Holocene turbidity currents (with a recurrence interval of 1000 years) were somewhat muddier and thicker, but also deposited sand on the levees of the Middle Valley, and are inferred to have had a similar slide‐related origin.Late Pleistocene turbidity currents deposited thick mud beds on the Var Sedimentary Ridge. The presence of sediment waves and the mean cross‐flow slope inferred from levee asymmetry indicates that some of these flows were many hundreds of metres thick and flowed at velocities of about 0·35 m s−1. This contrast with Holocene turbidites suggests that a slide origin is unlikely. Estimated times for deposition of thick mud beds on the levees are many days to weeks. The Late Pleistocene flows may therefore result from hyperpycnal flow of glacial outwash in the Var River. The variation in the Late Pleistocene to Holocene turbidite sedimentation is controlled more by variations in sediment supply than by sea‐level change.
Biostratigraphy, depositional environments, and diagenesis of the Tamana Formation, Trinidad: a tectonic marker horizon
Authors: ERLICH R. N. , FARFAN P. F. , HALLOCK P. 
Published: June 2006

ABSTRACTThe Tamana Formation of the Central Range of Trinidad was studied in order to determine its importance in the stratigraphical and structural development of north‐eastern South America. Biostratigraphical, petrological and mineralogical data, combined with field mapping show that the Tamana sediments are composed of five distinct lithofacies: inner to outer shelf, burrowed shaley mudstone; outer shelf, Fe‐rich sandy limestone; submarine channel, conglomeratic mudstone; middle shelf to nearshore, algal‐foram packstone/grainstone; and intertidal to nearshore, algal‐stromatolite‐coral boundstone with coral bioherms. Maximum thickness of the Tamana Formation is 244 m.Deposition of the Tamana limestones occurred between the Praeorbulina glomerosa (latest early Miocene) and Globorotalia fohsi robusta (middle part of the middle Miocene) planktonic foraminiferal zones, and in a more continuous trend than is seen in the current outcrop belt. Detailed biostratigraphy shows that the Tamana Formation is a facies equivalent of the shallow‐ and deep‐water shales of the Brasso Formation, and the deep water turbidites of the Herrera Member of the Cipero Formation.The early diagenetic history of the Tamana limestones was dominated by the precipitation of authigenic glauconitic smectite, and the dissolution of skeletal grains and carbonate matrix. Late burial diagenesis was dominated by the precipitation of illite and illite/smectite. Comparative mineralogy and textural analyses indicate a minimum range of burial depth for the Tamana Formation at 800–1500m, with a maximum of 2400 m. Alteration of Fe‐bearing minerals to geothite and late fracturing occurred during post‐Pliocene tectonic uplift and unroofing of the Central Range.The Tamana Formation sediments can be used as a structural and stratigraphical event marker within the Late Tertiary geological history of Trinidad. These units record a phase of the tectonic interaction between the Caribbean and South American plates in the south‐eastern Caribbean, and reflect the onset of contractile deformation in the Central Range.
Entrainment of planktonic foraminifera: effect of bulk density
Authors: OEHMIG REINHARD 
Published: June 2006

ABSTRACTDepositional hydrodynamics have been studied using settling rate distributions of Norwegian deep sea sediments (between Jan Mayen Island and the Vøring Plateau), together with Shields’ critical shear stress velocities. Planktonic foraminifera are the dominant sand sized component of these sediments. The bulk density of the foraminifera was calculated from their settling velocity, sieve size and shape. Density decreases from 2·39 g cm−3 at 0·05 mm diameter to 1·37 g cm−3 at 0·35 mm diameter. These density and size data were used to construct a threshold sediment movement curve. From the similarity in their Shield's critical shear‐stress velocities and the observed correlation of foraminifera size with decreasing percentage of fine fraction, it is concluded that the two components, the sand size foraminifera and the quartz and carbonate silt, are transport‐equivalent.
Obstacle marks produced by flow around stranded ice blocks during a glacier outburst flood (jökulhlaup) in west Greenland
Authors: RUSSELL ANDREW J. 
Published: June 2006

ABSTRACTThe effects of glacier ice block grounding on the morphology and sedimentology of proglacial fluvial outwash were examined during a glacier outburst flood or jökulhlaup, near Søndre Strømfjord, west Greenland. Observations made during and after the 1987 jökulhlaup both on the surface of an ice contact delta and within a confined valley sandur plain provided information about the formation of ice block obstacle marks and the significance of these bedforms for sandur morphology and sedimentology. Flow directions determined from obstacle mark morphology have been used successfully to chart flow direction changes on the falling limb of the jökulhlaup. Maximum flow depths for scour around stranded ice blocks may be given by 0·5–0·9 times the diameter of the ice block, as estimated from the depth of scour, the height of the obstacle shadow or the extent of ice block meltout sediments. Minimum flow depths can be represented by the height of the obstacle shadow above the mean bed level. The internal composition of the shadow indicates the ability of the flow to transport various sizes of material into the lee of obstacles. Ice block obstacle marks within the distal portion of the sandur initiated waning stage channel change. Proximal and lateral erosion around stranded ice blocks extended downstream from the ice block, forming chute channels which then captured waning stage flows, resulting in significant bar incision with associated deposition of lobate or deltaic deposits. It is suggested that ice block obstacle marks are important in terms of channel morphology, channel morphological change and their usefulness as palaeohydrological indicators.