bluuebunny/crossref_metadata_2025 huggingface dataset:
Hot‐spring travertine facies and sequences, Late Pleistocene, Rapolano Terme, Italy
Authors: Guo Li , Riding Robert
Published: March 2003

Late Pleistocene travertines up to 40 m thick near Rapolano Terme in Tuscany, central Italy, were precipitated by hot water issuing from springs on hillsides and flowing into adjacent depressions to mix with rainwater. Proximal light‐coloured slope and terrace travertines pass distally into darker reed mound and depression‐fill travertines. Lithotypes include crystalline crust, shrub, pisoid, paper‐thin raft, coated bubble, reed, and lithoclast‐breccia. High precipitation rates resulted in rapid slope aggradation and progradation. Dilution by rainwater likely lowered precipitation rates in depressions, but deposition was augmented by allochthonous material eroded from upslope travertines.

Slope Depositional Systems consist of Smooth and Terrace Slope facies characterized by white crystalline crusts, with diverse additional lithotypes in terrace pools. Depression Depositional Systems have mixed light and dark travertines with horizontal to gently concave stratification. Extensive light‐coloured Shrub Flat travertine is dominant; darker Marsh‐Pool Facies composed of fine lithoclast and reed travertine is localized. Reed Mounds composed of mixed light and dark travertines localized by abundant reed growth, formed where spring water emerged near the bases of low angle slopes.

Distal reduction in accretion rate was the major influence on sequence development. Light‐coloured slope travertines interdigitate with darker depression deposits. Vertical aggradation of slope deposits, mound progradation, and filling of topographic depressions is expressed by advance and retreat of facies. Evolution from depression to slope or mound sequences is termed ‘steepening up’. Up‐sequence change from slope or mound to depression facies is termed ‘levelling up’. Exposure surfaces associated with palaeosols are common in all facies and often constitute sequence boundaries. They are more closely spaced in depression sequences, reflecting slower and possibly also more discontinuous accumulation at sites furthest from hot springs.
Radar facies of paraglacial barrier systems: coastal New England, USA
Authors: Heteren Sytze Van , Fitzgerald Duncan M. , Mckinlay Paul A. , Buynevich Ilya V.
Published: March 2003

Analysis of a large data base of ground‐penetrating‐radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid‐ to high‐latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment‐source areas are characterized by chaotic, parallel, and tangential‐oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection‐free, and bounding‐surface configurations. Back‐barrier sediments may yield basin‐fill configurations, but generally include abundant signal‐attenuating units.

The GPR data, calibrated with information from cores, were collected across swash‐aligned and drift‐aligned barriers in a variety of wave‐ and tidal‐energy settings. Application of a 120‐MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0·2 m and 0·7 m.

The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt‐marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.
Geochemistry and provenance of the Middle Ordovician Austin Glen Member (Normanskill Formation) and the Taconian Orogeny in New England
Authors: BOCK BARBARA , MCLENNAN S. M. , HANSON G. N.
Published: March 2003

The Austin Glen Member of the upper Middle Ordovician Normanskill Formation is a sandstone‐shale flysch succession deposited in the foreland of the Taconian Orogen. Petrographic, major and trace element, and Nd–Pb isotopic data provide substantial constraints on its provenance. Lack of K‐feldspar and paucity of plagioclase, in addition to the dominance of sedimentary rock fragments, indicate that the source was dominated by recycled, sedimentary components. Major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same. No evidence of an ophiolitic or volcanic component was observed. Interpretation of Nd isotopic characteristics are complicated by a partial resetting of the Nd isotope system at about the time of sedimentation but indicate that the provenance of the Austin Glen Member had a long‐term history of light rare earth element (LREE) enrichment (average TDM = 1·8 Ga). Furthermore, Nd isotopic compositions are extremely homogeneous (ɛNd = –8·1 ± 0·6; 1 s.d.; n = 23) at 450 Ma, the approximate depositional age, indicating either a single source or very well‐mixed sources. 207Pb/204Pb ratios are variable but within the range of Pb isotopic compositions typically described as Grenvillian. The range of 207Pb/204Pb is greater than expected for the range of 206Pb/204Pb and suggests an additional component of Pb, possibly introduced during diagenesis. The immediate source of the Austin Glen Member may have been the accretionary prism that developed as older sediments of the Laurentian margin were scraped off the basin floor, incorporated within the accretionary prism and shed into the basin. No evidence indicating the arrival of an undifferentiated island arc or continental fragment during the Taconian Orogeny has been found. The data acquired during this study can be explained almost exclusively by Grenville Province source components but with possible additional contributions from older Laurentian terranes and Late Proterozoic rift volcanics that are not readily quantified but likely to have been minor. Accordingly, we conclude that the Taconian Orogeny in New England involved either: (1) a continental arc that involved exclusively Laurentia; (2) collision of a continental block with identical geochemical characteristics as Laurentia; or (3) essentially no detritus from any exotic colliding block (island arc or continental fragment) reached the foreland basin at the time of Austin Glen deposition.
Chemical and mechanical processes during burial diagenesis of chalk: an interpretation based on specific surface data of deep‐sea sediments
Authors: BORRE MAI , FABRICIUS (LIND) IDA L.
Published: March 2003

Burial diagenesis of chalk is a combination of mechanical compaction and chemical recrystallization as well as cementation. We have predicted the characteristic trends in specific surface resulting from these processes. The specific surface is normally measured by nitrogen adsorption but is here measured by image analysis of scanning electron micrographs. This method concentrates on the micritic matrix alone. Deep‐sea sediments are ideally suited to the study of burial diagenesis because they accumulate in a relatively conservative tectonic setting. We used material from the Ontong Java Plateau in the Pacific, where a > 1 km thick package of chalk facies sediments accumulated from the Cretaceous to the present. In the upper 200–300 m the sediment is unconsolidated carbonate ooze, throughout this depth interval compaction is the principal porosity reducing agent, but recrystallization has an equal or larger influence on the textural development. In the chalk interval below, compaction is not the only porosity reducing agent but it has a larger influence on texture than concurrent recrystallization. Below 850 m grain‐bridging cementation becomes important resulting in a lithified limestone below 1100 m. This interpretation is based on specific surface data alone, and modifies current diagenetic models.
Archean cherts derived from chemical, biogenic and clastic sedimentation in a shallow restricted basin: examples from the Gorge Creek Group in the Pilbara Block
Authors: SUGITANI K. , YAMAMOTO K. , ADACHI M. , KAWABE I. , SUGISAKI R.
Published: March 2003

The >3·0 Ga chert sequence of the Gorge Creek Group is exposed at Ord Ranges about 50 km east of Port Hedland in the Pilbara Block. The chert sequence examined in this study is 15 m thick and consists of oxide‐rich laminated chert, grey chert (silicified clastic rock), carbonaceous black chert and carbonate‐rich laminated chert. Although the cherts have undergone postdepositional silica enrichment, such as cementation and metasomatic silicification, primary precipitation of silica at the site of deposition is indicated by abundant microstructures (mosaic and spherulitic structures). Other primary to early diagenetic components were carbonates, sulphates (gypsum and anhydrite) and organic matter. Although these mineral associations, on the whole, correspond to those of modern marine evaporites, they are different from modern equivalents with respect to abundant precipitation of amorphous silica and presumed primary precipitation of iron‐carbonate (siderite). This feature is a possible manifestation of peculiar physicochemical conditions in the water mass from which the chemical sediments were precipitated; compared with modern ocean waters, the concentrations of Fe and Si were significantly higher and the pH value might have been lower. These conditions could be obtained by contributions of Fe‐ and Si‐enriched hydrothermal solutions and continental run‐off to the site of deposition.

Grey cherts contain detrital quartz and altered Fe–Ti oxides and were formed in a period of input of terrigenous detrital materials. They are characterized by higher concentrations of TiO2, Al2O3, Cr, Ni, Zn, Rb and Zr compared with the other types of chert and by very low (< 4) Al2O3/TiO2 values. These features are attributed to the supply of terrigenous detrital materials that contain abundant Fe–Ti oxides (ilmenite and titanomagnetite) and fine TiO2 particles. Such detrital materials might have been formed by extensive chemical alteration of source rocks and residual enrichment of Ti relative to Al.
Dynamics of the turbidity maximum zone in a micro‐tidal estuary: Hawkesbury River, Australia
Authors: Hughes  , Harris  , Hubble
Published: March 2003

Bed sediment, velocity and turbidity data are presented from a large (145 km long), generally well‐mixed, micro‐tidal estuary in south‐eastern Australia. The percentage of mud in the bed sediments reaches a maximum in a relatively narrow zone centred ≈30–40 km from the estuary mouth. Regular tidal resuspension of these bed sediments produces a turbidity maximum (TM) zone in the same location. The maximum recorded depth‐averaged turbidity was 90 FTU and the maximum near‐bed turbidity was 228 FTU. These values correspond to suspended particulate matter (SPM) concentrations of roughly 86 and 219 mg l−1, respectively.

Neither of the two existing theories that describe the development and location of the TM zone in the extensively studied meso‐ and macro‐tidal estuaries of northern Europe (namely, gravitational circulation and tidal asymmetry) provide a complete explanation for the location of the TM zone in the Hawkesbury River. Two important factors distinguish the Hawkesbury from these other estuaries: (1) the fresh water discharge rate and supply of sediment to the estuary head is very low for most of the time, and (2) suspension concentrations derived from tidal stirring of the bed sediments are comparatively low. The first factor means that sediment delivery to the estuary is largely restricted to short‐lived, large‐magnitude, fluvial flood events. During these events the estuary becomes partially mixed and it is hypothesized that the resulting gravitational circulation focuses mud deposition at the flood‐determined salt intrusion limit (some 35 km seaward of the typical salt intrusion limit). The second factor means that easily entrained high concentration suspensions (or fluid muds), typical of meso‐ and macro‐tidal estuaries, are absent. Maintenance of the TM zone during low‐flow periods is due to an erosion‐lag process, together with a local divergence in tidal velocity residuals, which prevent the TM zone from becoming diffused along the estuary axis.
Intertidal clay‐drape couplets (Gironde estuary, France)
Authors: Fenies Hugues , Resseguier Amaury De , Tastet Jean‐Pierre
Published: March 2003

Clay‐drape couplets on subaqueous dunes have been regarded as a diagnostic feature of the subtidal environment since Visser’s seminal paper (1980). The new observation of clay‐drape couplets in the intertidal zone on a present day tidal bar of the Gironde estuary shows that they are not restricted to the subtidal zone.

In the intertidal zone, low‐tide slack‐water clay drapes are deposited in the bottomsets of the dominant current dunes when the muddy water retained in the troughs is absorbed into the sand during the emergence of the intertidal bar. They drape emergence run‐off ripples generated by the drainage currents in the bottomsets. High‐tide slack‐water clay drapes are deposited over the entire dune surface and are preserved on the lee side of the dunes and in the bottomsets. They drape the subordinate current ripples. Low‐tide and high‐tide slack‐water clay drapes enclose one thin rippled sand layer (the subordinate current bundle) and are isolated from other adjacent clay‐drape couplets by the dominant current bundle.

The clay‐drape couplets deposited in the intertidal zone can be distinguished from their subtidal counterparts on the basis of two morphological differences:

1. In the intertidal zone, the low‐tide clay drape is only present in the bottomsets of the dunes, whereas in the subtidal zone equivalent clay drapes are also present on the lower part of the lee side of the dunes.

2. In the intertidal zone, low‐tide clay drapes are deposited in the bottomsets of the dunes over emergence run‐off ripples oriented in the direction of the drainage currents (i.e. in a direction normal to the tidal currents). Conversely, in the subtidal zone, the equivalent clay drapes are typically deposited over ripples oriented in the tidal‐current direction (ebb or flood). There is a difference of polarity of 90° between the intertidal and subtidal small‐scale bedforms draped by the low‐tide slack‐water drapes.
Sedimentary response to Late Quaternary sea‐level changes in the Romagna coastal plain (northern Italy)
Authors: Amorosi  , Colalongo  , Pasini  , Preti
Published: March 2003

Data from 17 continuously cored boreholes, 40–170 m deep, reveal the subsurface stratigraphy of the Romagna coastal plain. Sedimentological and microfaunal data allow the distinction of eight facies associations of Late Pleistocene–Holocene age, including 18 lithofacies and 16 faunal associations. Ten14C dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky BP of the last glacio‐eustatic cycle. The eight facies associations can be grouped into lowstand, transgressive and highstand systems tracts. The upper part of the lowstand systems tract consists of alluvial plain deposits. These accumulated during the Late Pleistocene when the shoreline was ≈250 km south of its present‐day position. A pronounced stratigraphic hiatus (between 25 and 8·8 ky BP) is invariably recorded at the upper boundary (transgressive surface) of these Pleistocene, indurated and locally pedogenized alluvial deposits. The succeeding postglacial history is represented by a well developed transgressive–regressive cycle. Transgressive deposits, interpreted to reflect the rapid landward migration of a barrier–lagoon system, include two wedge‐shaped, paralic and marine units. These thicken in opposite directions and are separated by a ravinement surface. Above the transgressive deposits, the maximum flooding surface (MFS) marks the change from a transgressive barrier–lagoon complex to a prograding, wave‐dominated delta system (early Po delta). The MFS can be traced landwards, where it constitutes the base of lagoonal deposits. An aggradational to progradational stacking pattern of upper delta plain (marsh), lower delta plain (lagoon/bay), and delta front (beach ridge) deposits reflects the progressive increase in the sediment supply/accommodation ratio during the following highstand. The alluvial deposits capping the sequence accumulated by the 13th century AD, in response to an avulsion event that caused abandonment of the former Po delta lobe and the northward migration of the Po River towards its present position.
An empirical model for the development and equilibrium morphology of current ripples in fine sand
Authors: Baas Jaco H.
Published: March 2003

A flume study on the development and equilibrium morphology of current ripples in fine sand (D50 = 0·238 mm) was performed to extend an empirical model for current ripple stability in 0·095 mm sand to larger grain sizes. The results of the flume experiments agree with the very fine sand model that current ripple development from a flat bed is largely independent of flow velocity. At all flow velocities, ripples evolve from incipient, through straight, sinuous and non‐equilibrium linguoid, to equilibrium linguoid plan morphology. The time needed to achieve an equilibrium linguoid plan form is related to an inverse power of flow velocity and ranges from several minutes to more than hundreds of hours. Average equilibrium height and length are 17·0 mm and 141·1 mm respectively. These values are about 20% larger than in very fine sand. Equilibrium ripple height and length are proportional to flow velocity near the stability field of dunes. In the same velocity range, a characteristic grouping of ripples with smaller ripples migrating on the upstream face of larger ripples was observed.

Bed‐form development shows a conspicuous two‐phase behaviour at flow velocities < 0·49 m s−1. In the first phase of development, ripple height and length increase along an exponential path, similar to that at higher flow velocities, thus reaching intermediate equilibrium values of 14·8 mm and 124·5 mm respectively. After some time, however, a second phase commences, that involves a rapid increase in bed‐form size to the typical equilibrium values for 0·238 mm sand.

A comparison with literature data shows that the results obtained for 0·238 mm sand agree reasonably well with other flume studies at similar grain size. Yet considerable variability in the relationships between ripple dimensions and flow strength ensues from, among others, underestimation of equilibrium time, shallow flow depths and differences in sediment texture.
Test of sediment initial‐motion theories using irregular‐wave field data
Authors: Green Malcolm O.
Published: March 2003

Sediment initial‐motion theories predict the flow conditions that coincide with onset of sediment motion, but usually the most that can be determined from burst‐sampled field data is whether or not sediment was in motion. Furthermore, initial‐motion theories are usually based on regular‐wave laboratory data, with little or no guidance given on how such theories are to be transferred to the real world of irregular waves. A field dataset obtained from the zone of wave shoaling beyond the surfzone is used to compare the performance of three initial‐motion theories in a way that takes explicit account of wave irregularity and the limitations of burst sampling. The dataset comprises video images of the seabed and measurements of waves, currents and suspended sediment. The initial‐motion theories tested wereKomar & Miller’s (1975,J. Sedim. Petrol.,45,362–367) ‘wave‐orbital‐speed’ theory, a ‘wave‐stress’ theory, and a ‘wave‐plus‐current‐stress’ theory. Fourteen transitions from no sediment motion to sediment motion were observed, but not all of those represented a challenging test of theory. Using the criterion that the best theory is the one that minimizes errors in classifying bursts as ‘no sediment motion’ or ‘sediment in motion’,Komar & Miller’s (1975) theory was found to perform the best when waves were characterized by significant wave height and mean spectral period, both of which can be estimated directly from pressure data alone. Komar and Miller’s theory was better at predicting the onset of extended transport events, which occurred during confused seas, rather than the transition back to moribund seabed under clean swell at the end of such events. The conclusion regarding best theory is dependent on the choice of scales used to characterize wave motion. The way forward therefore is to standardize and define terms precisely.
Authigenic albite in carbonate rocks – a tracer for deep‐burial brine migration?
Authors: Spötl Christoph , Longstaffe Fred J. , Ramseyer Karl , Rüdinger Bernd
Published: March 2003

Euhedral, post‐depositional albite from the Eastern and Western Alps, the western Carpathians and some Greek islands was examined petrographically and geochemically to gain insights into the nature of feldspar reactions in carbonate rocks. This study focuses on coarsely crystalline, homogeneously nucleated albite in order to avoid problems related to the presence of inseparable detrital material in fine‐grained albite varieties. All albite samples show a very restricted compositional variability and are typically ≥ 99 mol% Ab component. Unit‐cell parameters determined by Rietveld analysis are slightly more variable than previously accepted, but confirm high Al–Si ordering characteristic of low albite. The oxygen isotopic composition of albite ranges from + 19·4‰ to + 28·3‰ VSMOW. There is no direct relationship between the δ18O value and the inferred temperature of albite formation, nor is there one with stoichiometry. The coarse crystal size (up to several millimetres in diameter), petrographic evidence showing albite cross‐cutting stylolites, greater abundance of albite in carbonate rocks subject to high‐grade diagenetic or weak metamorphic overprinting and available fluid inclusion data suggest that albite precipitation is favoured at higher temperatures in carbonates than in sandstones. Pore fluids were invariably brines, as suggested by the inferred high positive δ18Ofluid values, the common association of albite‐bearing carbonates and evaporites and reports of saline fluid inclusions in albite. The presence of authigenic albite may thus be a useful tracer of palaeobrine–carbonate reactions, particularly in deep‐burial and incipient metamorphic settings.
Sediment resuspension and transport in Lake Michigan during the unstratified period
Authors: Hawley Nathan , Lee Chang‐Hee
Published: March 2003

Instrumented moorings were deployed during the winter of 1994–95 at three depths (28, 58 and 101 m) in southern Lake Michigan. Storms during the observation period were not unusually severe, so the processes observed are typical of those that occur during an average winter. Time series observations of water temperature, beam attenuation coefficient (a measure of water transparency) and current velocity show that local resuspension of bottom sediment occurred frequently after the breakdown of the thermocline. Resuspension was most frequent close to the shore but was also observed at the 58 m station. Local resuspension did not occur at the 101 m station, but advection to the site of material resuspended at shallower sites was observed. These observations do not support the hypothesis proposed by previous investigators that local resuspension at depths of 100 m or greater occurs during the unstratified period. It is more likely that fine‐grained material resuspended by storm action in intermediate water depths (≈ 30–60 m) is transported into the deeper parts of the lake by the general lake circulation.
Facies architecture of an isolated carbonate platform: tracing the cycles of the Latemàr (Middle Triassic, northern Italy)
Authors: Egenhoff Sven O. , Peterhänsel Arndt , Bechstädt Thilo , Zühlke Rainer , Grötsch Jürgen
Published: March 2003

The 720‐m‐thick succession of the Middle Triassic Latemàr Massif (Dolomites, Italy) was used to reconstruct the lagoonal facies architecture of a small atoll‐like carbonate platform. Facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations, which reflect a syndepositional palaeorelief. Based on tracing of lagoonal flooding surfaces, the metre‐scale shallowing‐upward cycles are interpreted to be of allocyclic origin. Short‐term sea‐level changes led to subaerial exposure of wide parts of the marginal zone, resulting in the development of a tepee belt of varying width. Occasional emergence of the entire lagoon produced lagoon‐wide decimetre‐thick red exposure horizons. The supratidal tepee belt in the backreef area represented the zone of maximum elevation, which circumscribed the sub‐ to peritidal lagoonal interior during most of the platform’s development. This tepee rim, the subtidal reef and a sub‐ to peritidal transition zone in between stabilized the platform margin. The asymmetric width of facies belts within individual metre‐scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present‐day south and west. The overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit, overlain by three tepee‐rich intervals, separated by tepee‐poor units composed of subtidal to peritidal facies. This stacking pattern reflects two third‐order sequences during the late Anisian to early middle Ladinian.
Cause of dominance by sheetflood vs. debris‐flow processes on two adjoining alluvial fans, Death Valley, California
Authors: Blair Terence C.
Published: March 2003

Two large, adjoining alluvial fans of the Panamint Range piedmont, Death Valley, California, are composed of different facies assemblages deposited by contrasting sedimentary processes. The Anvil Spring fan was built solely by water‐flow processes (incised‐channel floods and sheetfloods), whereas the neighbouring Warm Spring fan has been constructed principally by debris flows. The boundary between these fans delineates a sharp provincial piedmont contact between sheetflood‐dominated fans to the south and debris‐flow‐dominated fans to the north. Factors such as climate, catchment area, fan area, catchment relief, aspect, vegetation types and density, and neotectonic setting are essentially identical for these two fans. The key difference between them is that their catchments are underlain by dissimilar bedrock types, which weather to yield distinctive sediment suites. Weathering of the granite and andesite of the Anvil fan catchment produces significant volumes of medium to very coarse sand, granules, pebbles, cobbles and boulders, but minimal silt and clay. In contrast, the shale, quartzite and dolomite that dominate bedrock in the Warm Spring catchment weather to yield a wide suite of sedimentary particles spanning from clay to boulders. The abundance of mud, and the unsorted character of the yielded sediment, cause precipitation‐induced slope failures in the Warm Spring catchment to transform readily into debris flows. This propensity is due to the low permeability of the colluvial sediment, which causes added water to become trapped quickly and pore pressure to rise rapidly, promoting transformations to debris flows. In contrast, the limited volume of sediment finer than medium sand yielded from the Anvil fan catchment causes the colluvium to have high permeability. This factor prevents the transformation of wet colluvium to a debris flow during hydrologically triggered slope failures, instead maintaining sediment transport as entrained bed load or suspended load in a water flow.
Tertiary syntectonic carbonate platform development in Indonesia
Authors: Wilson Moyra E. J. , Bosence Dan W. J. , Limbong Alexander
Published: March 2003

Cenozoic tropical carbonate sedimentation was strongly influenced by local and regional tectonics in SE Asia. This paper outlines the evolution of the syntectonic Eocene to middle Miocene Tonasa Formation of South Sulawesi, evaluating controls on sedimentation, facies distribution and sequence development. Development of a facies model for this Cenozoic tropical carbonate platform provides a meaningful analogue for similar, less well‐studied SE Asian carbonates, which commonly comprise targets for hydrocarbon exploration. This study also has considerable implications for the study of syntectonic carbonates, controls on carbonate sedimentation, carbonate platform development in backarc areas and SE Asian tectonics. Detailed facies mapping, logging, petrographic and biostratigraphic analyses indicate that the Tonasa Formation was deposited initially as part of a transgressive sequence in a backarc setting. By late Eocene times, shallow‐water carbonates were being deposited over much of South Sulawesi forming a widespread (100‐km long) platform area. Shallow‐water sedimentation continued unabated in some areas of the platform until the middle Miocene. Elsewhere, active normal faulting resulted in fault‐block platforms, with local subaerial exposure of footwall blocks and the formation of basinal graben in adjacent hangingwall areas. Platform‐top facies were aggradational and dominated by larger benthic foraminifera. Low‐angle slopes, particularly hangingwall dip slopes, were characterized by the development of ramps. Faults, controlled in part by pre‐existing structures, were periodically active and formed steep escarpment margins. Variable regional subsidence strongly influenced the development of the Tonasa Carbonate Platform, whereas platform‐wide effects caused by regional eustacy have not been identified. Computer modelling of the Tonasa Platform confirms that the accommodation space and sedimentary geometries observed can be produced by block faulting and regional subsidence alone. Modelling also reveals that regional subsidence and extension, oblique to the main stretching direction, were low on the margins of the backarc basin. Shallow‐water accumulation rates for this foraminifera‐dominated tropical carbonate platform were an order of magnitude lower than those for modern warm‐water platforms dominated by corals or ooids.
The Maesan fan delta, Miocene Pohang Basin, SE Korea: architecture and depositional processes of a high‐gradient fan‐delta‐fed slope system
Authors: Hwang I. G. , Chough S. K.
Published: March 2003

The Maesan fan‐delta‐fed slope system in the Miocene Pohang Basin occurs between two Gilbert‐type fan deltas. Detailed analysis of sedimentary facies and bed geometry reveals that the sequence is represented by 13 sedimentary facies. These facies can be organized into three facies associations, representing distinct depositional environments: alluvial fan (facies association I), steep‐faced slope (facies association II), and basin plain (facies association III). Subaerial debris flows and dense, inertia‐dominated currents were transformed into subaqueous sediment gravity flows in steep‐faced slope environments. Further downslope, these flows were channelized and formed lobate conglomerate and sandstone bodies at the terminal edge of the channels (or chutes). Interchannel and interlobe areas were dominated by homogeneous mudstone and muddy sandstone, deposited by suspension settling of fine‐grained materials. Part of the steep‐faced slope deposits experienced large‐scale slides and slumps. The chutes/channels, lobes and splays on the steep‐faced slope of the Maesan system are similar to those in modern subaqueous coarse‐grained fan‐delta systems.
Submarine lobes and feeder channels of redeposited, temperate carbonate and mixed siliciclastic‐carbonate platform deposits (Vera Basin, Almería, southern Spain)
Authors: Braga Juan C. , Martin Jose M. , Wood Jason L.
Published: March 2003

Temperate carbonates and mixed siliciclastics‐carbonates of Upper Tortonian age were deposited on a narrow platform along the southeastern margin of the Sierra de los Filabres on the western side of the Vera Basin. The temperate carbonates were unlithified or were only weakly lithified on the seafloor and so were easily prone to synsedimentary removal. Part of the shelf sediments were eroded, reworked and redeposited in submarine lobes, up to 40 m thick and 1 km wide. The lobes consist of turbiditic carbonates (calcarenites and calcirudites) and mixed siliciclastics‐carbonates, which contain up to 30% siliciclasts, derived from the Sierra de los Filabres to the northwest, and abundant bioclasts of coralline algae, bivalves and bryozoans. In the inner platform, the feeder channels of the lobes cross‐cut beach and shoal deposits, and are filled by strings of debris flow conglomerates (up to 3 m thick and a few metres wide). These channels presumably developed as the continuation of river courses entering the sea. Further towards the outer platform, they pass into large channels (up to several hundred metres wide and 20 m deep) steeply cutting into the horizontally bedded strata of the platform. Significant quantities of platform sediment were removed by erosion during their excavation. Once abandoned, they were filled by new platform sediments. Further towards the basin, the channels associated with the lobes exhibit lateral accretion and internal cut‐and‐fill structures, and are intercalated between hemipelagic deposits. The channel‐filling sediments are in this latter case coarse‐grained carbonates and mixed siliciclastics‐carbonates. Lobe development concentrated first at Cortijo Grande on the western side of the study area, and then to the east at Mojácar. This migration may relate to the uplift of the Sierra Cabrera, a major high occurring immediately to the south of the channel and lobe outcrops.
The emission and vertical flux of particulate matter <10 μm from a disturbed clay‐crusted surface
Authors: Houser Christopher A. , Nickling William G.
Published: March 2003

Arid and semi‐arid environments are important sources for the atmospheric loading of PM10 (particulate matter <10 μm), although the emission of this material is often limited by surface crusts. This study investigates the emission and vertical flux of PM10 from a clay‐crusted playa, with and without saltating grains to abrade the surface. Using a portable field wind tunnel, it was found that, despite disturbance to the surface, the emission of PM10 decays rapidly without abrasion. Only in the presence of saltating grains was PM10 continuously liberated from the surface, such that the emission rate (the total amount of PM10 emitted from the surface expressed as a horizontal flux) varied linearly with the saltation transport rate. Although the emission of PM10 was found to depend on saltation abrasion, past studies have tended to focus on the relationship between the vertical flux of PM10 (the amount of PM10 being transported vertically through the boundary layer) and the shear velocity. In this study, the vertical flux of PM10 was found to vary with the shear velocity to the power of 2·14. Although the vertical PM10 flux is a proportion of the emission rate (the horizontal flux), no statistically significant relationship was observed between the emission rate and the shear velocity. The disparity of these results is explained by the lack of a consistent relationship between the shear velocity and the saltation transport rate in this supply‐limited environment. This suggests that the observed relationship between the vertical PM10 flux and the shear velocity is a spurious correlation, resulting from the use of shear velocity to calculate the vertical dust flux. It is thus concluded that shear velocity is not an appropriate variable for emission modelling in supply‐limited environments and that improvements in dust emission modelling will only be realized if the abrasion process is the focus of a concerted research effort.
The formation of large mudwaves by turbidity currents on the levees of the Toyama deep‐sea channel, Japan Sea
Authors: Nakajima Takeshi , Satoh Mikio
Published: March 2003

The development of mudwaves on the levees of the modern Toyama deep‐sea channel has been studied using gravity core samples combined with 3·5‐kHz echosounder data and airgun seismic reflection profiles. The mudwaves have developed on the overbank flanks of a clockwise bend of the channel in the Yamato Basin, Japan Sea, and the mudwave field covers an area of 4000 km2. Mudwave lengths range from 0·2 to 3·6 km and heights vary from 2 to 44 m, and the pattern of mudwave aggradation indicates an upslope migration direction. Sediment cores show that the mudwaves consist of an alternation of fine‐grained turbidites and hemipelagites whereas contourites are absent. Core samples demonstrate that the sedimentation rate ranged from 10 to 14 cm ka−1 on the lee sides to 17–40 cm ka−1 on the stoss sides. A layer‐by‐layer correlation of the deposits across the mudwaves shows that the individual turbidite beds are up to 20 times thicker on the stoss side than on the lee side, whereas hemipelagite thicknesses are uniform. This differential accretion of turbidites is thought to have resulted in the pattern of upcurrent climbing mudwave crests, which supports the notion that the mudwaves have been formed by spillover turbidity currents. The mudwaves are interpreted to have been instigated by pre‐existing large sand dunes that are up to 30 m thick and were created by high‐velocity (10°ms−1), thick (c. 500 m) turbidity currents spilling over the channel banks at the time of the maximum uplift of the Northern Japan Alps during the latest Pliocene to Early Pleistocene. Draping of the dunes by the subsequent, lower‐velocity (10−1ms−1), mud‐laden turbidity currents is thought to have resulted in the formation of the accretionary mudwaves and the pattern of upflow climbing. The dune stoss slopes are argued to have acted as obstacles to the flow, causing localized loss of flow strength and leading to differential draping by the muddy turbidites, with greater accretion occurring on the stoss side than on the lee slope. The two overbank flanks of the clockwise channel bend show some interesting differences in mudwave development. The mudwaves have a mean height of 9·8 m on the outer‐bank levee and 6·2 m on the inner bank. The turbidites accreted on the stoss sides of the mudwaves are 4–6 times thicker on the outer‐bank levee than their counterparts on the inner‐bank levee. These differences are attributed to the greater flow volume (thickness) and sediment flux of the outer‐bank spillover flow due to the more intense stripping of the turbidity currents at the outer bank of the channel bend. Differential development of mudwave fields may therefore be a useful indicator in the reconstruction of deep‐sea channels and their flow hydraulics.
Hyperpycnal plume formation from riverine outflows with small sediment concentrations
Authors: Parsons Jeffrey D. , Bush John W. M. , Syvitski James P. M.
Published: March 2003

A series of laboratory experiments has been conducted in order to elucidate the sediment‐induced mixing processes accompanying riverine outflows; specifically, the discharge of a warm, fresh, particle‐laden fluid over a relatively dense, cool brine. In a parameter regime analogous to recently acquired field measurements, hypopycnal (surface) plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm, fresh, sediment‐laden plume and particle settling within it. Convection was robust in the presence or absence of intense turbulence, at sediment concentrations as low as 1 kg m−3, and took the form of millimetre‐scale, sediment‐laden fingers descending from the base of the surface plume. A consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal (bottom‐riding) flow. The experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient. The resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond.
Cryptic sequence boundaries in braided fluvial successions
Authors: Miall Andrew D. , Arush Mohamud
Published: March 2003

In braided fluvial deposits, consisting of monotonous successions of sandstone or conglomerate, it may be difficult to distinguish regionally significant bounding surfaces (sequence boundaries) from autogenic channel‐scour surfaces. Major surfaces may be characterized by erosional relief and draped by lag deposits, but not all sequence boundaries show these characteristics. Other clues to the presence of a major surface are sharp changes in detrital composition, shifts in regional palaeocurrent trends and evidence of early diagenesis of the sandstones immediately below the sequence boundary. Examples of these attributes of cryptic sequence boundaries are illustrated from three Mesozoic units in the Colorado Plateau area of the United States. In the Chinle Formation (Triassic), near Moab, Utah, angular intraformational unconformities overlie sandstones showing evidence of early diagenesis. In the Castlegate Sandstone (Upper Cretaceous) of east‐central Utah, a cryptic sequence boundary can be discriminated from other erosion surfaces by the evidence of detrital petrography and early diagenesis. Palaeocurrent data indicate changes in regional palaeoslope at two sequence boundaries within this unit. Evidence of early diagenesis is also present at a sequence boundary in the Kayenta Formation (Jurassic) of westernmost Colorado.
Depth–transport functions and erosion–deposition diagrams as indicators of slope inclination and time‐averaged traction forces: applications in tropical reef environments
Authors: Hohenegger Johann , Yordanova Elza
Published: March 2003

The trigonometric relationship between slope inclination, the horizontally acting time‐averaged traction force and the vertical depth of transport allows the estimation of one factor, when both others are known. Depth–transport functions can be deduced by comparing the depth distributions of living organisms and their skeletal remains, and this paper simplifies this comparison using foraminifera in which a single test represents an individual. Differences in distribution parameters between living individuals and empty tests allow depth–transport functions to be determined; these functions differ between species at a single transect according to the varying buoyancies of the tests. Within a single species, differences in depth–transport functions between locations are based on either slope inclination or traction intensities. After establishing a mean depth–transport function by averaging species‐characteristic functions, the time‐averaged traction force acting on the studied transect can be calculated. Transport intensities are also estimated using an erosion–deposition diagram that combines the relative frequency distributions of living individuals and empty tests. The proportion of ‘eroded’, ‘parautochthonous’ and ‘allochthonous’ tests mirrors the influence of both slope inclination and traction force for the deposition of empty tests. To test the model, six species of symbiont‐bearing benthic foraminifers were investigated at two transects in front of a NW Pacific coral reef. One transect is distinguished by a strong slope flattening below the steep reef slope (30 m), whereas further steepening characterizes the equivalent part in the other transect. These differences are mirrored in the depth–transport functions as well as in the erosion–deposition diagrams of all species. The time‐averaged traction forces differ in intensities between transects, because of the position of the reef front with respect to the predominant wind direction. However, the form of the functions is identical and distinguished by an increase from the surface to 35 m depth, followed by a decrease down to 105 m. This can be explained by successive onshore and offshore forces acting on the shallow slope, such as the tropical cyclones that cross the region every summer.
Significance of pot and gutter casts in a Middle Triassic carbonate platform, Betic Cordillera, southern Spain
Authors: Pérez‐López A.
Published: March 2003

Pot casts and gutter casts are described for the first time in the lower part of the Majanillos Formation, a Middle Triassic carbonate unit located in the External Zones of the Betic Cordillera (southern Spain). Their identification, as well as their relation to tempestites, enables the better interpretation of the depositional environments and the shoreline‐to‐offshore facies transition on the Anisian muddy carbonate ramp of the southern Iberian Massif. The Majanillos Formation contains three members, which become progressively more marly towards the top. Well‐preserved pot and gutter casts and thin intercalations of calcarenite, which are interpreted as tempestites, are abundant in the lowest member. Above the pot and gutter casts, thicker calcarenite beds, which locally contain hummocky cross‐stratification, predominate. Bioturbated nodular limestones are prevalent at the top of the member. The remaining succession, which records a long‐term Triassic transgressive cycle, consists mostly of fine‐grained limestones deposited in very shallow‐marine environments. Calcarenitic sediments only accumulated within potholes and gutters in the nearshore. They developed during storms when strong currents transported sediment to the outer shelf, where it was deposited as tempestite beds. Pot and gutter casts characterize sedimentation in the bypass zone. It is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry; it is proposed that gutter casts display a trend of increasing width/thickness ratios towards the outer shelf. The identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments.