bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbonate turbidite sequences deposited in rift‐basins of the Jurassic Tethys Ocean (eastern Alps, Switzerland)
Authors: EBERLI GREGOR P. 
Published: June 2006

ABSTRACTSyn‐rift sediments in basins formed along the future southern continental margin of the Jurassic Tethys ocean, comprise, in the eastern Alps of Switzerland, up to 500 m thick carbonate turbidite sequences interbedded with bioturbated marls and limestones. In the fault‐bounded troughs no submarine fans developed; in contrast, the fault scarps acted as a line source and the asymmetric geometry as well as the evolution of the basin determined the distribution of redeposited carbonates.The most abundant redeposits are bio‐ and lithoclastic grainstones and packstones, with sedimentary structures indicating a wide range of transport mechanisms from grain flow to high‐ and low‐density turbidity currents. Huge chaotic megabreccias record catastrophic depositional events. Their main detrital components are Upper Triassic shallow‐water carbonates and skeletal debris from nearby submarine highs.After an event of extensional tectonism, sedimentary prisms accumulated in the basins along the faults. Each prism is wedge‐shaped with a horizontal upper boundary and consists of a thinning‐ and fining‐upward megacycle. Within each megacycle six facies associations are distinguished. At the base of the fault scarp, an association of breccias was first deposited by submarine rockfall and rockfall avalanches. A narrow, approximately 4000 m wide depression along the fault was subsequently filled by the megabreccia association, in which huge megabreccias interfinger with thin‐bedded turbidites and hemipelagic limestones. The thick‐bedded turbidite association covered the megabreccias or formed, farther basinward, the base of the sedimentary column. Within the thick‐bedded turbidites, thinning‐ and fining‐upward cycles are common. The overlying thin‐bedded turbidite association shows nearly no cyclicity and the monotonous sequence of fine‐grained calciturbidites covers most of the basin area. With continuous filling and diminishing sediment supply, a basin‐plain association developed comprising fine‐grained and thin‐bedded turbidites intercalated with bioturbated marls and limestones. On the gentle slopes opposite the fault escarpment, redeposited beds are scarce and marl/limestone alternations as well as weakly nodular limestones prevail.
Selective and reversible carbonate—silica replacements in Lower Cretaceous carbonate‐bearing turbidites of the Eastern Alps
Authors: HESSE REINHARD 
Published: June 2006

ABSTRACTIn the diagenetic history of calcareous sandstones, silicacementation and silicification may be followed by carbonatecementation and replacement and vice versa, and the change‐over from one to the other may occur more than once. This is well illustrated by calcareous and siliciclastic turbidites of the Gault Formation (Aptian to Albian) of the Eastern Alps which have been interpreted as deep‐sea trench plain and deep‐sea fan deposits.In these turbidites silicification selectively affects ooids and a few other biogenic carbonate fragments rich in organic matter (algae and bryozoans) which form a small fraction of the bulk sediment. The type and sequence of diagenetic changes are largely controlled by host‐rock composition and may vary vertically within individual beds as a result of compositional grading. In the carbonate turbidites, silicification follows widespread calcite cementation. The process is slow, resulting in relatively coarsely crystalline replacement quartz. In ooids with quartz nuclei, rim‐quartz forms mostly monocrystalline ‘overgrowths’ by outward replacement of the concentrically laminated carbonate cortex. This type of silicification is often incomplete leaving parts of the ooid cortices unaffected. In quartz arenites and sublitharenites silicification precedes calcite cementation. There the process is rapid, forming microcrystalline quartz. Even if the ooid nucleus consists of quartz, a syntaxial ‘overgrowth’ does not normally form. The replacement quartz is almost always polycrystalline. Late‐stage diagenetic calcite and dolomite which develop euhedral crystal shapes and cut across grain boundaries may replace the earlier secondary rim‐quartz of the ooids as well as other minerals.Possible sources of the silica are pressure‐solution of quartz, dissolution of opaline silica of radiolarian tests and of sponge spicules, and feldspar in the host bed. In a number of examples an increase in the degree of silicification can be observed towards the lower bedding planes of individual turbidites requiring an additional external source of silica which seems to necessitate cross‐formational flow of pore solutions. Silicification in both the carbonate and the siliciclastic turbidites probably took place at about the same time; in the carbonate turbidites it was preceded, however, by calcite cementation, which significantly reduced porosity and permeability before silicification took place.The greater degree of alteration experienced by the Gault turbidites of the Falknis and Tasna Nappes, which are more internal structural units of the Alps (compared to the Flysch Zone of the Eastern Alps), is reflected by the growth of quartz ‘beards’ and spikes from the ooids in the direction perpendicular to maximum stress. This is the only case observed where the rim quartz of the ooids grows beyond the original grain boundaries.
Mass transport in European Cretaceous chalk; fabric criteria for its recognition
Authors: BROMLEY RICHARD G. , EKDALE A. A. 
Published: June 2006

ABSTRACTAlthough it is a pelagic sediment, fine‐grained calcareous ooze may be mobilized prior to general lithification and redeposited as allochthonous units. Numerous occurrences of allochthonous chalk have been reported in recent years, having been recognized by large‐scale bedding features seen in outcrop. Smaller‐scale internal features, such as contorted laminae, and larger features, such as smeared burrows and imbricated flint nodules, attest to a significant amount of soft‐sediment deformation and synsedimentary slumping in European chalk sections of Late Cretaceous age.Truly autochthonous chalks contain complex, tiered ichnofabrics and in some cases exhibit a diagenetic nodular fabric that is undisturbed by transport. In some situations, such as stagnant water conditions, autochthonous chalks may exhibit primary lamination, although this is very uncommon in European chalk sequences.Different types of redepositional processes produce an array of varied allochthonous fabrics. Glide and slump units, for example, contain internal deformational features produced during sliding. Ooze flow causes plastic deformation of chalk units, internally as well as externally. Resuspension and fluid flow of chalk sediment produces a deposit having a totally new fabric, such as a conglomerate composed of detrital chalk clasts.In this paper, typical macroscopic, sedimentary fabric types are illustrated, and the means of identifying them are discussed in terms of bioturbation features, in situ diagenetic nodules versus detrital clasts, physical deformation structures and development of flints.
Channel formation and migration by mass‐flow processes in the Lower Carboniferous fluviatile Fell Sandstone Group, northeast England
Authors: TURNER BRIAN R. , MONRO MARY 
Published: June 2006

ABSTRACTSmall, steep‐sided narrow channels, locally developed within the braided fluviatile Lower Carboniferous Fell Sandstone of northeast England, are attributed to mass‐flow processes initiated by channel‐bank slumping. The channels have sharp undisturbed margins and are filled with moderately well‐sorted medium to coarse sandstone identical to the sandstone which they cut. Most channel‐fills are structureless, but a few show diffuse concentric marginal laminations. Laminations also occur towards the top of channel fills, but they are less regular and show low‐amplitude trough‐like undulations. Channel margin inclinations range from 13° to 55°, and channel depths vary between 1·7 m and 2·5 m. The channels, which are only seen in profile, are orientated perpendicular to the local and regional palaeocurrent trend, and cut through structureless sandstone and planar cross‐stratified sandstone characterized by compound and compound‐complex bar bedforms. Only one channel has both margins preserved; and of the remainder (seven) only one has its northern margin preserved.Undercutting and retrogressive slumping of the sandy channel bank is thought to have initiated a subaqueous sediment gravity flow, which moved across the main channel along a transverse scour at the base of the slip face of a large composite bar bedform. Such scours have strong asymmetric profiles with the steeper slope along the base of the active slip face (northern side) and the lower slope on the downstream (southern) side of the scour. Thus, the northern channel margin was steeper, less stable and more prone to collapse than the southern margin, and is almost never preserved. Flow reconstruction indicates that on entering the channel a hydraulic jump developed at the change in slope, and the flow became more turbulent and erosive. Scoured sand incorporated into the flow increased concentration and shearing along the boundaries. Reverse shear was also exerted by the overlying current, on top of the flow, but the central part remained relatively unaffected. The presence or absence of marginal laminations is probably related to marginal shearing and flow dilution. Deposition occurred in response to deceleration and frictional freezing of the sand flow.
Longitudinal petrographic variations in a Middle Ordovician trench deposit, Central Appalachian orogen
Authors: LASH GARY G. 
Published: June 2006

ABSTRACTPetrographic analysis of Middle Ordovician turbidite sandstones of the Greenwich slice of the Hamburg klippe (eastern Pennsylvania), inferred to be part of a fossil subduction complex, define three coeval petrofacies. The Jonestown petrofacies was derived from felsic plutonic and less abundant metasedimentary rocks, whereas the Windsor Township, the most extensive petrofacies, and Werleys Corner petrofacies were derived from sources characterized by various proportions of sedimentary/metasedimentary, plutonic, and volcanic rocks. The presence of minor but conspicuous extrabasinal carbonate and microlitic volcanic lithic fragments together with higher percentages of polycrystalline quartz, serve to distinguish the Werleys Corner from the Windsor Township petrofacies. It is conceivable that sandstones of the Greenwich slice were derived from microplates inferred to have existed to the southeast of the proto‐North American plate in Early Palaeozoic time.The variations in sandstone composition along the length of the Greenwich slice may be explained by post‐accretion tectonic juxtaposition of petrofacies derived from various sources. An equally plausible explanation involves transverse infilling of a channelized longitudinal transport system (Windsor Township petrofacies) by sediment derived from compositionally diverse source terranes orthogonal to the trench (Jonestown and Werleys Corner petrofacies).
Evolution and stratigraphy of a regressive barrier/backbarrier complex: Kiawah Island, South Carolina
Authors: DUC AILEEN WOJTAL , TYE ROBERT S. 
Published: June 2006

ABSTRACTAnalysis of 75 vibracores from the backbarrier region of Kiawah Island, South Carolina reveals a complex association of three distinct stratigraphic sequences. Beach ridge progradation and orientation‐controlled backbarrier development during the evolution of Kiawah Island, and resulted in deposition of: (1) a mud‐rich central backbarrier sequence consisting of low marsh overlying fine‐grained, tidal flat/lagoonal mud; (2) a sandy beach‐ridge swale sequence consisting of high and low marsh overlying tidal creek channel and point bar sand, and foreshore/shoreface; and (3) a regressive sequence of sandy, mixed, and muddy tidal flats capped by salt marsh that occurs on the updrift end of the island.Central backbarrier deposits formed as a result of the development of the initial beach ridge on Kiawah Island. Formation of this beach ridge created a backbarrier lagoon in which fine‐grained estuarine and tidal flat mud accumulated. Washovers, oyster mounds, and tidal creek deposits form isolated sand and/or shell‐rich lenses in the lagoon. Spartina alterniflora low marsh prograded into the lagoon as the tidal flats aggraded.Barrier progradation and sediment bar‐bypassing at Stono Inlet created digitate beach ridges on the northeast end of Kiawah Island. Within the beach‐ridge swales, tidal flats were disconformably deposited on shoreface and foreshore sand of the older beach ridges. Tidal creek drainage systems evolved to drain the swales. These rapidly migrating creeks reworked the tidal flat, foreshore, and shoreface sediments while redepositing a fining‐upward sequence of channel lag and point bar deposits, which served as a substrate for salt marsh colonization.This resultant regressive sedimentary package marks the culmination of barrier island development and estuary infilling. Given enough time and sedimentation, the backbarrier sequence will ultimately prograde over the barrier island, reworking dune, beach, and foreshore sediments to form the upper sand‐rich bounding surface of the barrier lithosome. Preservation of the regressive sequence is dependent upon sediment supply and the relative rate of sea‐level rise, but the reworking of barrier islands by tidal inlets and migrating tidal creeks greatly alter and complicate the stratigraphic sequence.
Fringing reef growth on a terrigenous mud foundation, Fantome Island, central Great Barrier reef, Australia
Authors: JOHNSON D. P. , RISK M. J. 
Published: June 2006

ABSTRACTThe leeward fringing reef at Fantome Island (central Great Barrier Reef province) is a carbonate body which has developed under the influence of terrigenous sedimentation. The reef flat is up to 1000 m wide and is surfaced by mobile sand and gravel, with almost all live corals restricted to the seaward rim. The reef slope has coral columns and heads on the upper part, but below 5 m water depth it is a muddy substrate with scattered mounds of branching corals.Three high recovery cores show the reef is up to 10 m thick and developed over a gently sloping terrace of weathered Pleistocene alluvium. Three post‐glacial stratigraphic units are recognised: (1) carbonate reef top unit of coral rudstone and framestone including Sinularia spiculite; (2) lower slope unit of coral floatstone in a terrigenous muddy matrix; and (3) transgressive basal unit of skeletal arkosic sand. The acid insoluble content of matrix and of individual corals increases downwards. Coral growth rates decrease downwards, reflecting slower growth in muddier environments.Radiocarbon dating shows that the reef prograded seaward at almost stable sea level. An average vertical accumulation rate of 6.7 mm yr‐1 is indicated. Two age reversals are interpreted as material transported by storms or by erosion in response to a late Holocene sea‐level fall.The carbonate reef top unit has developed adjacent to, and is environmentally compatible with a muddy terrigenous, lower slope unit. Terrigenous influx has not changed during the Holocene, and terrigenous content of sediments is controlled by deposition on the reef slope of fine sediment winnowed from the reef flat and concentration of coarse sediment in the transgressive basal sheet.
Steady state saltation in air
Authors: UNGAR J. E. , HAFF P. K. 
Published: June 2006

ABSTRACTCoupled equations of motion for steady state saltation over an infinite plane are derived and solved for a simplified model of the grain‐surface impact process. Experimentally observed features of the wind velocity profile in saltation are qualitatively reproduced, including a diminution of the sub‐saltation layer mean wind speed, as the friction speed increases. In this model the surface impact velocity of the saltating grains remains relatively constant over a wide range of free‐stream shear stresses, and the grain mass flux increases with friction speed uf* less rapidly than uf3.
Bedform migration and bed‐load transport in some rivers and tidal environments
Authors: VAN DEN BERG JAN H. 
Published: June 2006

ABSTRACTReliable field data obtained by directly measuring bed‐load transport of fine‐ to coarse‐grained bed material are extremely scarce, mainly because of the difficulty of sampling accurately. Therefore, the verification of bed‐load transport formulae is largely based on flume experiments, which refer to unrealistic shallow‐water conditions. In this study, some bed‐load transport formulae were tested against data from natural environments. As an alternative to ascertaining the bed‐load transport rate by sampling the bed‐load, the transport rate was deduced from data on bedform height and bedform celerity. For this purpose, 43 sets of data from rivers, representing a wide range of bed material, bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings. Two formulae were used for the prediction of the bed‐load transport: the formula of Van Rijn (1981) and the Kalinske (1947) formula as approximated by Elzerman & Frijlink (1951) (and, in the present study, slightly modified for application to tidal waters). Both the bed‐load function of Van Rijn and the modified formula of Kalinske‐Frijlink require data which are easily obtained and that can be measured accurately.At those stages of the flow when bed‐load transport was high the Van Rijn function tended to overestimate that transport. For flow stages when bed‐load transport was low the opposite was true. The modified Kalinske‐Frijlink function gave consistently good results: 86% of the transport rates predicted using the river data were within 0·5–2·0 times the values actually measured.
Authigenic natroalunite in middle Miocene evaporites from the Gulf of Suez (Gemsa, Egypt)
Authors: ROUCHY JEAN‐MARIE , PIERRE CATHERINE 
Published: June 2006

ABSTRACTThis paper deals with a new occurrence of sedimentary natroalunite (Na, K) Al3, (SO4)2 (OH)6, in the caprock of a diapir of middle Miocene evaporites from the Gemsa peninsula, located on the southwestern coast of the Gulf of Suez. Field observations, petrographic examinations and stable isotope (18O, 34S) measurements on the associated authigenic phases of anhydrite and native sulphur argue for the genesis of natroalunite at a rather high temperature (i.e. higher than 75°C) by the reaction of clay minerals with sulphuric acid. The sulphuric acid was produced by the concatenation of the following reactions which are thought to increase the diagenetic temperature: bacterial reduction of sulphate evaporites, and oxidation of hydrogen sulphide to native sulphur and sulphate where aerated conditions prevailed in the pore fluids. These changes through time from reducing to oxidizing diagenetic conditions were controlled by the progressive uplift of the diapiric system toward the land surface so that the draining ground waters became progressively oxygenated.
Deep marine arc apron deposits and syndepositional magmatism in the Alisitos group at Punta Cono, Baja California, Mexico
Authors: WHITE JAMES D. L. , BUSBY‐SPERA CATHY J. 
Published: June 2006

ABSTRACTRocks exposed at Punta Cono include very fine‐grained to coarse‐grained tuffs, lapilli tuffs, and tuff breccias deposited in a deep marine environment. Syndepositional basaltic intrusive activity was common. In one locality a hyaloclastite‐peperite complex formed. Slumped sections with fluidal basalt ‘clasts’, derived from intrusions that entered the sediment pile from below, are present elsewhere. Abundant soft‐sediment folds in fine‐grained laminated subaqueous fall‐out tuff suggest steep gradients; these are cut by shallow channels filled with coarse‐grained tuff, lapilli tuff, and rare tuff breccia. The combination of marine fossils, extreme textural immaturity, abundant slump features, and syndepositional magmatism indicates deposition upon the submarine flanks of an active volcano.Recognition of magma‐wet sediment interaction is hampered in volcaniclastic rocks because of the similarity between host and intrusive fragments. Products of magma‐water‐sediment interactions at Punta Maria include: (1) jigsaw‐puzzle hyaloclastite, formed by non‐explosive hydroclastic fragmentation of magma upon contact with water and water‐bearing sediment; (2) peperites, produced by mixing of magma with sediment; and (3) an unusual tuff breccia unit, the result of non‐explosive mixing of ‘wisps’of lava with sediment during remobilization of an unconsolidated section. Low‐explosivity magma‐water‐sediment interactions are favoured by relatively high hydrostatic pressures in sub‐wave base settings.
A computer‐interfaced sedigraph for modal size analysis of fine‐grained sediment
Authors: JONES K. P. N. , McCAVE I. N. , PATEL D. 
Published: June 2006

ABSTRACT A system has been developed allowing the direct storage on disc of size data from the X‐ray scanning settling tube SediGraph 5000ET. Processing of the cumulative percentage data output to produce smooth frequency curves is described. This allows rapid (15 min) and precise (±M 0.1ø) discrimination of size modes, peak heights, median and silt and clay percentages of fine‐grained sediments. An example of a mud turbidite is given showing systematic changes in bulk and modal properties, not visible by eye. Lack of size segregation in the > 1 m thickness of this turbidite shows that it may have been deposited from a highly concentrated flow, rather than from a dilute, waning turbidity current. Such flows may explain ungraded/poorly graded, muddy sediments also known as homogenites, unifites or megaturbidites by other authors.
The Hunghae Formation, SE Korea: Miocene debris aprons in a back‐arc intraslope basin
Authors: CHOE MOON YOUNG , CHOUGH SUNG KWUN 
Published: June 2006

ABSTRACT During early to middle Miocene times a sudden opening of the Ulleung (Tsushima) back‐arc basin in the East Sea (Sea of Japan) led to the development of intraslope basins along the rifted southwestern margin (southeast Korea). Abrupt subsidence resulted in the deposition of the 200 m thick Hunghae Formation (middle Miocene), a sand/mudstone sequence that can be divided into five facies. Facies I (sand and mudstone couplet) and II (coarse sand) are turbiditic in origin, as evidenced by massive, graded, crudely‐layered and parallel‐laminated sand beds. Facies III (homogeneous mudstone) is characterized by various lignite and plant fragments, clastic and biogenic grains that are randomly oriented, suggestive of hemipelagic deposition. Facies IV (chaotic deposit) is characterized by the disruption of beds, the presence of isolated siltstone blocks (or balls) and large clasts in the muddy matrix, indicative of retrogressive rockfall and slide/slump. Facies V (conglomerate) is of debris flow origin, as evidenced by clast‐ and matrix‐supported features, floating large clasts and absence of traction structures.Individual facies are organized into two types of facies association: (1) homogeneous mudstone (facies III) associated randomly with the rest (facies I, II, IV and V), indicative of hemipelagic and episodic sediment‐gravity flow processes, respectively; (2) conglomerate (facies V), coarse sand (facies II) and sand/mudstone couplet (facies I), representing the flow transformation from debris flow to high‐ and low‐concentration turbidity currents. These facies associations are similar in many respects to modern and ancient debris (or slope) aprons found elsewhere. Numerous isolated slide/slump blocks, wedged conglomerates with armoured mudstone balls, discontinuous lignite‐containing sand/mudstone beds, chaotic structure and growth faults suggest that the deposition occurred on a steep slope (intraslope basin) off coalescing fan‐deltas, mainly by unchannellized sediment‐gravity flows. Ancient deposits with irregular facies sequences can be viewed as debris‐apron systems, which provide alternatives to submarine‐fan models in many clastic basins with a line rather than point source.