bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deep‐sea avulsion and morphosedimentary evolution of the Rhône Fan Valley and Neofan during the Late Quaternary (north‐western Mediterranean Sea)
Authors: TORRES J. , DROZ L. , SAVOYE B. , TERENTIEVA E. , COCHONAT P. , KENYON N. H. , CANALS M. 
Published: November 2003

ABSTRACTThe Petit‐Rhône Fan Valley (north‐western Mediterranean) is a broad, sinuous, filled valley that is deeply incised by a narrow, sinuous thalweg. The valley fill is differentiated into three seismic subunits on high‐resolution seismic‐reflection profiles. The lower chaotic subunit probably consists of channel lag deposits that seem to be in lateral continuity with high‐amplitude reflections representing levee facies. The intermediate transparent subunit, which has an erosional base and clearly truncates levee deposits, is interpreted to be mass‐flow deposits resulting from the disintegration of the fan‐valley flanks. The upper bedded subunit shows an overall lens‐shaped geometry and the seismic reflections onlap either onto the top of the underlying transparent subunit or onto the Rhône levees. Piston core data show that the upper few meters of this upper subunit consist of thin turbidites, probably deposited by overflow processes. The few available 14C ages suggest that the upper stratified subunit filled the Petit‐Rhône Fan Valley between 21 and 11 kyr BP.The upper bedded subunit is deposited within the Petit‐Rhône Fan Valley downslope of a major decrease in slope gradient. This upper subunit and the thalweg are genetically related and represent a small channel/levee system confined within the fan valley. Previous studies interpreted this thalweg to be an erosional feature resulting from a recent avulsion of the major channel course. Our interpretation implies that the thalweg is not a purely erosional feature but a depositional/erosional channel. This small channel/levee system is superimposed on a large muddy channel/levee system after the sediment supply changed from thick muddy flows during the main phase of aggradation of the Rhône Fan levees, to thin, mixed (sand and mud) flows at the end of Isotope Stage 2 (∼16–18 ka BP). The pre‐existing morphology of the Petit‐Rhône Fan Valley played a determinant role in the sediment dispersal leading to the creation of this small and confined channel/levee system. These mixed flows have undergone flow stripping resulting from the changes in the slope gradient along the thalweg course. The finer sediment overflowed from the thalweg and were deposited in the Petit‐Rhône Fan Valley. Coarser channelled sediment remaining in the thalweg were deposited as a ‘sandy’lobe (Neofan). As indicated by 14C dating, sedimentation on this lobe continued until very recently, suggesting a further evolution of the turbidity flows from small mixed flows to small sandy flows. the deposition of this study lobe and the sedimentary fill of the Petit‐Rhône Fan Valley may be related to widespread shelf edge and canyon wall failures with a resulting downslope evolution of failed sediment into turbidity currents.
A method for the disaggregation of mudstones
Authors: YANG YUNLAI , APLIN ANDREW C. 
Published: November 2003

ABSTRACTWe describe a method which effectively and gently disaggregates muds and mudstones by combining a saturation‐freeze‐thaw technique with treatment by ultrasonic probe. The method works well for samples containing <5% TOC and which have been buried to depths less than about 3500 m. It does not work for samples strongly cemented with carbonates or silicates. Scanning electron micrographs of size fractions and the strong mineralogical segregation between size fractions are offered as evidence of complete disaggregation.
Comparison of laser grain size analysis with pipette and sieve analysis: a solution for the underestimation of the clay fraction
Authors: KONERT MARTIN , VANDENBERGHE JEF 
Published: November 2003

ABSTRACTClassically, the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the ‘Stokes’ sedimentation rates, for the fine fractions. Results from the two methods are compared with results from laser diffraction size analysis, which is based on the forward scattering of monochromatic coherent light. From a point of view of laboratory efficiency, the laser sizing technique is far superior. Accuracy and reproducibility are shown by measurements on certified materials. It appears that laser grain size measurements of certified materials correspond very well with the certificated measurements. Tests were also done on a set of randomly selected sediments of fluvial, aeolian and lacustrine origin. Except for the (<2 μm) clay fraction, there is a coarsening of the mean diameter of one to two size classes (0.25 ɛ), caused by the non‐sphericity of the particles. The platy form of the clay particles induces considerable differences (eight size classes) between pipette and laser measurements: the <2 μm grain size, defined by the pipette method corresponds with a grain size of 8 μm defined by the Laser Particle Sizer for the studied sediments. Using a higher grain size level for the clay fraction, when laser analysis is applied, enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique.
The effects of source lithology, transport, deposition and sampling scale on the composition of southern California sand
Authors: CRITELLI SALVATORE , LE PERA EMILIA , INGERSOLL RAYMOND V. 
Published: November 2003

ABSTRACTThe Transverse Ranges of southern California represent an uplifted and variably dissected Mesozoic magmatic arc, and Mesozoic to Holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings. Modern sand within part of the Western Transverse Ranges represents: first‐order sampling scale of the Santa Monica and the San Gabriel Mountains; second‐order sampling scale of the Santa Clara River draining both mountain ranges; and third‐order sampling scale of the beach system between the mouth of the Santa Clara River and the eastern Santa Monica Mountains, and turbidite sand of the Hueneme‐Mugu submarine fan.Source lithology includes plutonic and metamorphic rocks of the San Gabriel Mountains, and sedimentary and volcanic rocks of the Santa Monica Mountains. First‐order sands have large compositional variability. Sand from local coastal drainage of the Santa Monica Mountains ranges from basaltic feldspatholithic to quartzofeldspathic. Sand of the San Gabriel Mountains local drainages has three distinct petrofacies, ranging from metamorphiclastic feldspatholithic to mixed metamorphi/plutoniclastic and plutoniclastic quartzofeldspathic. Second‐order sand is represented by the main channel of the Santa Clara River; the sand has an abrupt downstream compositional change, from feldspathic to quartzofeldspathic. Third‐order sand (beaches and deep‐sea turbidite samples) of the Santa Monica Basin is quartzofeldspathic. Beach sand is more quartz‐rich than is Santa Clara river sand, whereas turbidite sand is more feldspar‐rich than is beach sand. Deep‐sea sand has intermediate composition with respect to second‐order samples of the Santa Clara River and third‐order samples of the beach system, suggesting that (1) the Santa Clara River is the main source of sediments to the marine environment; and (2) local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions. Petrologic data of modern sand of the study area are highly variable at first‐ and second‐order scale, whereas third‐order sand is homogenized. The homogenized composition of deep‐marine sand is similar to the composition of most ancient sandstone derived primarily from the Mesozoic dissected magmatic arc of southern California. This study of the Western Transverse Ranges illustrates the effects of source lithology, transport, depositional environment, and sampling scale on sand composition of a complex system, which provides insights regarding actualistic petrofacies models.
Lower Jurassic epicontinental carbonates and mudstones from England and Wales: chemostratigraphic signals and the early Toarcian anoxic event
Authors: JENKYNS HUGH C. , CLAYTON CHRISTOPHER J. 
Published: November 2003

ABSTRACTSections through Lower Jurassic epicontinental carbonates from Southern Britain (Junction Bed and equivalent) show a positive carbon‐isotope excursion (δ13Ccarbonate), detectable in bulk rock, in the falciferum Zone of the lower Toarcian. Isotopic data from organic matter in more clay‐rich sections from Wales and north‐east England, together with determinations on belemnite calcite, indicate that highest δ13C values are localized in the upper exaratum Subzone of the falciferum Zone. Levels of particular enrichment in organic carbon were developed in the early to mid‐exaratum Subzone and hence pre‐date this δ13C maximum. These phenomena reflect the impact of the early Toarcian oceanic anoxic event in the British area. Similar isotopic trends have been recorded in other Toarcian sections from Tethyan Europe and are interpreted as reflecting the chemistry of sea water. On the assumption of isotopic correlation between the English and Tethyan sections, the δ13C maximum would be everywhere dated as latest exaratum Subzone in terms of the north European ammonite scheme.Absolute oxygen‐isotope values in carbonates probably reflect both early diagenetic cementation and later temperature‐related burial diagenesis, although a palaeotemperature maximum is tentatively identified as characterizing the early falciferum Zone. Subsequent climatic deterioration may have been triggered by drawdown of CO2, related to regional excess carbon burial during the oceanic anoxic event. Using the positive δ13C excursion as a correlative level in sections from different faunal provinces (Britain, Italy and Spain) implies that lower Toarcian zonal stratigraphy is diachronous between northern and southern Europe. There is evidence for partitioning of water masses between the north European shelf and the Tethyan continental margin during the Early Jurassic.
Oxfordian (Upper Jurassic) coral reefs in Western Europe: reef types and conceptual depositional model
Authors: INSALACO E. , HALLAM A. , ROSEN B. 
Published: November 2003

ABSTRACTComparative sedimentology and palaeoecology of Oxfordian (Upper Jurassic) coral‐dominated reefs of England, France, Italy and Switzerland has been used to: (1) identify and characterize different types of Late Jurassic coral reefs with regard to their litho‐ and biofacies; and (2) develop a depositional model for these reefs relating different reef types to each other within a palaeoenvironmental framework. Eight generic reef types and one associated reef facies are recognized. These are: (I) biostromal units dominated by platy microsolenids developed within clean limestone facies; (II) biostromal units dominated by platy microsolenids developed within marly facies; (III) reefal thickets dominated by tall dense phaceloid colonies developed within pure carbonate muds; (IV) microbial‐coral reefs dominated by massive, branching ramose and phaceloid colonies; (V) large high diversity reefal units associated with large volumes of bioclastic material; (VI) small species‐poor reefs developed within mixed carbonate/siliciclastic facies; (VII) microbial‐coral reefs dominated by massive colonies; (VIII) reefal thickets dominated by branching ramose colonies with widely spaced branches developed amongst sand shoals and coral debris channels; and (IX) conglomerates rich in rounded coral fragments (the reef associated facies).The development of these different constructional and compositional reef types is interpreted as being primarily a function of light intensity, hydrodynamic energy levels and sediment balance. A conceptual depositional model based on these parameters can be used to predict the spatial and temporal distribution of different reefal carbonates and highlight sedimentological and palaeoecological trends in reef development.
Physical compaction of vertic palaeosols: implications for burial diagenesis and palaeo‐precipitation estimates
Authors: CAUDILL MICHAEL R. , DRIESE STEVEN G. , MORA CLAUDIA I. 
Published: November 2003

ABSTRACTBurial compaction is one of several major obstacles to estimating palaeoprecipitation from depth to pedogenic carbonate in favourably preserved palaeosols. Palaeosols must be decompacted and the preburial depth to the pedogenic carbonate obtained. Vertic palaeosols may be particularly good candidates for palaeoprecipitation estimates, because of their increased likelihood of preserving clastic dykes, one of the best features for estimating burial compaction. Compaction estimates from clastic dykes and literature‐based depth of burial estimates suggest vertic palaeosols undergo significantly less burial compaction than may be commonly assumed. Late Carboniferous vertic palaeosols, buried to 2·5–3·0 km, compacted to 93% of their original thickness. In contrast, clastic dykes in a nonpedogenic shale directly underlying one of the Late Carboniferous palaeosols records compaction to 70% of original thickness. Similarly obtained burial compaction and burial depth estimates for Early Carboniferous, Ordovician, and Proterozoic vertic palaeosols were used to test a burial compaction curve and equation specific to vertic palaeosols. Results suggest this ‘vertic‐calibrated’curve and equation can be used to estimate burial compaction for vertic palaeosols lacking clastic dykes, but additional testing is needed. Naturally high bulk densities may have limited the compactibility of vertic palaeosols. Likewise, high initial bulk density and an abundance of swelling clays may have severely limited the transmissivity of some vertic palaeosols as they passed from pedogenic to burial environments. Upon burial these vertic palaeosols may have behaved as closed systems, which has implications for understanding their diagenetic modification. Additional efforts to understand burial compaction of vertic palaeosols also promises to improve our understanding of aquifer/aquiclude and hydrocarbon reservoir/seal relationships in sedimentary basins containing intercalated palaeosols.
Architecture of fluvial‐dominated valley‐fill deposits in the Cretaceous Fall River Formation
Authors: WILLIS BRIAN J. 
Published: November 2003

ABSTRACTThe Fall River Formation is a 45 m thick layer of fluvial‐dominated valley‐fills and shore‐zone strata deposited on the stable cratonic margin of the Cretaceous Western Interior Seaway. Fall River deposits in Red Canyon, in the south‐west corner of South Dakota (USA), expose a cross‐section of a 3.5 km wide valley‐fill sandstone and laterally adjacent marine deposits. The marine deposits comprise three 10 m thick upward‐shoaling sequences; each composed of multiple metres‐thick upward‐coarsening successions. The lower two of these sequences are laterally cut by the valley‐fill sandstone, and are capped by metres‐thick muddy palaeosols. The upper sequence spans the top of the valley‐fill sandstone, and is overlain by the Skull Creek Shale. The 30 m thick valley sandstone is partitioned into four distinct fills by major erosion surfaces, and each of these fills contain many metres‐thick channel‐form bodies. Deposits in the lower parts of these fills are sheet‐like, top‐truncated channel bodies, whereas deposits in the upper parts of fills are upward‐concave, laterally amalgamated channel bodies, more completely preserved heterolithic channel bodies, or wave‐deposited sheets. Each valley‐fill basal erosion surface records an episode of valley incision and relative sea‐level fall, and the gradual progression from fluvial to more estuarine deposits upwards within each fill records relative sea‐level rise. All fills are dominantly channel deposits and are capped by marine flooding surfaces. The dominance of channel deposits, the gradual change to more estuarine facies in the upper parts of fills, and the location of flooding surfaces at valley‐fill tops all suggest that sediment supply initially kept pace with relative sea‐level rise and valleys filled during late marine lowstand and transgression, not during subsequent highstands. Recently proposed facies models have focused on variations in the relative strength of tide, wave and river currents as controls on valley‐fill deposits. However, relative rates of sediment supply and basin accommodation change, and the shift in this ratio along the depositional profile during multiple‐scale cycles in relative sea‐level, are equally important controls on the style of valley‐fill deposits.
Mid‐cycle condensed shellbeds from mid‐Pleistocene cyclothems, New Zealand: implications for sequence architecture
Authors: ABBOTT STEPHEN T. 
Published: November 2003

ABSTRACTRichly fossiliferous and disconformity‐bounded facies successions, termed Mid‐Cycle Condensed Shellbeds (MCS), occupy a mid‐cycle position within depositional sequences in the Castlecliff section (mid‐Pleistocene, Wanganui Basin, New Zealand). These shell‐rich intervals (0.1–4.5 m thick) comprise the upper of two loci of shell accumulation in Castlecliff sequences. The lower disconformable contacts are sharp and variably burrowed, and are interpreted as submarine transgressive surfaces formed by storm or tidal current erosion at the feather‐edge of contemporary transgressive systems tracts. Above (i.e. seaward) of this erosion surface, macrofossil remains (mainly bivalves and gastropods) accumulated, with little reworking, on the inner‐shelf under conditions of reduced terrigenous sediment supply. The upper contacts are sharp transitions from shell‐rich to relatively shell‐poor lithofacies; parautochthonous shell accumulation was ‘quenched’by downlapping highstand systems tract shelf siltstones and muddy fine sandstones. Castlecliff MCS, together with the basal shell‐rich part of overlying highstand systems tracts, occupy a stratigraphic position which corresponds to the condensed section that forms at the transgressive/highstand systems tract boundary in the sequence model of Haq et al. (1987). Palaeoenvironmental analysis indicates that Castlecliff MCS are substantially, if not entirely, transgressive deposits. This study therefore shows that the ‘condensation maximum’within a depositional sequence does not necessarily bracket the transgressive systems tract/highstand systems tract boundary.
Lithofacies and sequence development on an Upper Devonian mixed carbonate‐siliciclastic fore‐reef slope, Canning Basin, Western Australia
Authors: GEORGE ANNETTE D. , PLAYFORD PHILLIP E. , POWELL C. McA. , TORNATORA P. M. 
Published: November 2003

ABSTRACTDetailed sedimentological and stratigraphical analysis coupled with conodont biostratigraphy of a fore‐reef slope succession in the Napier Range (Napier Formation) is used to develop a depositional model and relative sea‐level history for late Frasnian to late Famennian reef evolution in the Canning Basin of north‐western Australia. Changes in sedimentary style on the slope, reflecting differing rates of carbonate production on the platform, are linked to third‐ and higher order relative sea‐level fluctuations.Overlapping slope aprons accumulated along the base of a steep‐walled platform margin. Coarse carbonate debris was deposited adjacent to the margin as talus breccias (via rockfall) and debris‐flow breccias. Depositional slopes up to 45°, and locally steeper, are demonstrated using rotated geopetal cavity fills. The predominance of channel‐filling lithofacies throughout the slope succession indicates the highly channelized nature of the aprons. The middle slope is dominated by sandy oolitic‐peloidal turbiditic grainstones interpreted as sediment exported from an active platform. The turbidites and associated debris‐flow breccias contrast with condensed carbonate intervals and deep‐water, non‐fenestral stromatolites that record times of very low platform production. Lower slope turbidites and associated intraclastic breccias indicate widespread redeposition of sediment eroded from lithified and semi‐lithified limestones higher up the slope.Several third‐order sequences are recognized in the fore‐reef succession and these are composed primarily of transgressive and highstand deposits. Carbonate production was severely restricted in the early Famennian coinciding with development of onlapping siliciclastic aprons during a relative sea‐level lowstand. Evidence for a subaerial exposure event is also preserved within the siliciclastic strata. Controls on sequence development are difficult to constrain. Although two sequence boundaries can be correlated with falls on the global sea‐level curve, the reef complexes evolved in an active extensional regime and it is highly likely that tectonism, in conjunction with eustasy, controlled accommodation on the platform and therefore carbonate productivity.
Impact‐related clastic injections in the marine Ordovician Lockne impact structure, Central Sweden
Authors: STURKELL ERIK F. F. , ORMÖ JENS 
Published: November 2003

ABSTRACTClastic injections generated in connection with the formation of impact craters show many similarities to injections created by other geological processes. However, circumstances such as their position relative to the impact structure and the evidence of forceful processes indicate an impact origin. The Ordovician Lockne impact structure was formed in a marine environment with both sedimentary (Cambrian and Ordovician) and underlying crystalline (Proterozoic) target rocks. Sea water played a substantial part in the cratering process, especially in the modification of the newly formed crater as the water surged back into the structure.In the Lockne area clastic dykes and sills have long been known and have earlier been interpreted as neptunian dykes and conglomerates. So far seven cases of dykes and sills are known in the area. In this work these are interpreted as clastic injections formed in connection with the Lockne impact. The clastic injections occur in the crystalline basement and the sedimentary sequence. The material in the injections comes from all local lithologies (both sedimentary and crystalline) but the sedimentary sequence dominates as a source. The dykes and sills were injected simultaneously with the fracturing and dilation of the host rock in the cratering process, and occur at different stratigraphic levels. In some dykes, clasts from the host rock wall can be fitted back to their original position; the clasts are slightly rotated and surrounded by exotic material. Quartz grains with planar deformation features were observed in the injected material. Most of the sills within the bedded Ordovician limestone are restricted to marly beds, except for the feeder dykes which cut through the overlying beds. This circumstance demonstrates how the decompression has opened the strata along weaker layers and that the underpressure created subsequently sucked the material down. Laminar flow is a conspicuous internal structure in the dykes and sills and indicates viscous flow of injected material. The lamination in the injected material is parallel to the walls in each case. The material was lithified prior to the event and was crushed, mobilized in a water/sediment slurry and injected as dykes and sills.