bluuebunny/crossref_metadata_2025_split huggingface dataset:
A coarse grained turbidite system with morphotectonic control (Middle Albian, Ondarroa, northern Iberia)
Authors: AGIRREZABALA L. M. , GARCIA‐MONDÉJAR J 
Published: June 2006

ABSTRACTThe Middle Albian Ondarroa turbidite system is a coarse grained, deep water unit which outcrops in the north‐eastern part of the Basque‐Cantabrian region, west of the Pyrenees. It is about 18 km long and 7 km wide, and shows an unusual ‘L’shape resulting from both a direct morphotectonic confinement and the presence of nearby shallow water carbonate buildups.Eight main facies have been distinguished within this turbidite system: (1) clast‐supported conglomerates; (2) mud‐supported conglomerates; (3) slump deposits; (4) normally graded pebbly sandstones; (5) cross stratified sandstones; (6) interbedded graded sandstones and mudstones; (7) interbedded non‐graded sandstones and mudstones: and (8) mudstones. Inner system, middle system, outer system and basin plain divisions have been distinguished. The inner turbidite system is characterized by stacked channel fill conglomerates and lesser sandy turbidites and mudstones. The middle system consists of sandy and conglomeratic fining upwards sequences, normally several metres thick. The outer system has alternating non‐channellized sandstones and mudstones, without any predictable vertical arrangement. The basin plain is characterized by mudstone‐siltstone laminations and lesser, randomly occurring thin bedded sandy turbidites.Three main channel fills make up the inner turbidite system. Although all of them can be compared with the valley channel fills of the modern Mississippi Fan, and thus their bases can be interpreted as sequence boundaries, only the lowermost and the uppermost channel bases are documented as allocyclic boundaries. The Ondarroa turbidite system was deposited in an immature passive margin subjected to transtensional movements. It filled a composite pull apart depression with coarse clastics derived from a narrow platform to the north of the present outcrops which was invaded by fan deltas. A major pattern of sinistral strike‐slip faulting linked to the opening of the Bay of Biscay is invoked to explain the Ondarroa turbidite system appearance and its tectonic confinement.
Origin and diagenesis of Quaternary travertine shrub fabrics, Rapolano Terme, central Italy
Authors: GUO LI , RIDING ROBERT 
Published: June 2006

ABSTRACTMillimetre to centimetre sized arborescent shrub‐like calcite precipitates are common constituents of hot water travertine shallow pool deposits of Quaternary age at Rapolano Terme, Tuscany, Italy. In the presently forming travertines, the shrubs consist of apparently random associations of (i) micrite aggregates and (ii) subhedral to euhedral rhombic spar crystal aggregates. In thin section, the micrite aggregates appear dark and the spar‐rhomb aggregates light, giving the shrubs a mottled appearance.Travertines are basically produced by CaCO3 precipitation due to degassing and evaporation of the spring waters, although biological influence may also stimulate precipitation. The formation of masses of erect shrubs, rather than dense crystal crusts that form on slopes, is probably due to limited water flow in the pool environments.Microbes, including bacteria and diatoms, are important influences on shrub microfabric and external shape. The micrite aggregates are associated with bacteriform bodies, seen as tiny rods and spheres. The micrite precipitates around these bodies and in adjacent biofilm. Spar‐rhomb precipitation appears to be external to the biofilm, and may be related to the presence of diatoms which are locally closely associated with the spar‐rhombs, although an essentially inorganic origin, particularly for the more euhedral rhombs, cannot be ruled out.In the older Quaternary travertines, the original microfabric of the shrubs has been diagenetically altered. The original mottled appearance of the shrubs has become uniformly dark and micritic, and the evidence for the dual micritic and spar‐rhomb origin of the shrubs is obscured or destroyed. Spar‐micritization of the shrubs is probably due to abiotic, and locally biotic, dissolution. Previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity.
Magnesite diagenesis in redbeds: a case study from the Permian of the Northern Calcareous Alps (Tyrol, Austria)
Authors: SPÖTL CHRISTOPH , BURNS STEPHEN J. 
Published: June 2006

ABSTRACTThe Upper Permian Gröden Formation of the Northern Calcareous Alps (Austria) is composed of alluvial fan and playa lake sediments that were deposited in intramontane basins. A conspicuous feature of these redbeds is the abundance of magnesite in the form of nodules and discrete layers in mudstones as well as intergranular cement in sandstones. Sedimentological observations indicate that the bulk of these carbonates formed during early diagenesis and were probably syndepositional. Petrographically, most magnesites consist of micrite or, less commonly, microspar. An early non‐ferroan magnesite is post‐dated by later stage ferroan magnesites. Nodules consisting of recrystallized, sparry magnesite were observed only at one location. The general absence of relics of a non‐magnesite precursor mineral and the occurrence of shrinkage features suggest that the fine grained magnesites formed by transformation of a hydrated magnesium carbonate mineral, e.g. hydromagnesite. Carbon, oxygen, sulphur and strontium isotope ratios in conjunction with sedimentological criteria support a model of (hydro)magnesite precipitation in an inland playa lake system, which was fed by run‐off from the surrounding hinterland. The scarcity of evaporites and the dominance of magnesite over calcite and dolomite suggest that the playa lake brines were low in sulphate and had high Mg/Ca ratios. The source for the high magnesium concentrations is thought to be the weathering of Devonian dolostones and associated massive magnesite deposits in the catchment area.
Multiple‐step recrystallization within massive ancient dolomite units: an example from the Dinantian of Belgium
Authors: NIELSEN P. , SWENNEN R. , KEPPENS E. 
Published: June 2006

ABSTRACTSouth of the Caledonian Brabant‐Wales Massif a more than 200 m thick Tournaisian to Lower Visean replacive dolomite unit can be followed for several hundred kilometres from the Boulonnais (France) to Aachen (Germany). Field observations, of features such as karst cavities occurring at the top of the Lower Visean dolomite which are filled by Lower Visean crinoidal limestone, indicate that dolomitization and karstification took place during the Early Visean. This early development of the dolomite is in agreement with the presence of stylolites cutting the dolomite fabric. The minor element composition of the majority of the dolomites remains almost uniform throughout the entire studied area. Values for Fe, Mn, Na and Sr are normally in the range 700–4700 ppm, 15–400 ppm, 80–300 ppm and 50–200 ppm, respectively. The δ13C values (range‐0.72 to +5.31%o) mainly reflect the carbon isotopic composition of the precursor limestones. The δ18O values, in contrast, are highly variable: ranging from‐19.15 to +0.85%o. This rather large range of δ18O values is explained by multiple‐step re‐equilibration/recrystallization during progressive burial and subsequent uplift of the dolomites. These processes are also responsible for the high 87Sr/86Sr values of the dolomites which range from about 0.7088 to 0.7098. They are distinctly more radiogenic than Lower Visean marine carbonates (0.7076–0.7078). Correlation, however, of δ18O values or 87Sr/86Sr ratios with dolomite and/or cathodoluminescenec (CL) textures has not been very successful. This suggests that recrystallization may remain unrecognized if only petrographic techniques are used. Nevertheless, certain CL textures can be related to specific interactions with the ambient recrystallizing fluids.
Hydrothermal origin of Late Proterozoic bedded chert at Gusui, Guangdong, China: petrological and geochemical evidence
Authors: ZHOU YONGZHANG , CHOWN E. H. , GUHA JAYANTA , LU HUANGZHANG , TU GUANGZHI 
Published: June 2006

ABSTRACTThe Late Proterozoic bedded chert from Gusui in Guangdong Province, southern China, is characterized by bedded, laminated, massive and pseudobrecciated structures. The chert is depleted in TiO2, Al2O3 and most trace elements. However, it is enriched in Ba, As, Sb, Hg, and Se. In Al‐Fe‐Mn ternary diagrams, it falls into the ‘hydrothermal field’. Factor analysis shows that many elements show up in the principal trace element factor suggesting their enrichment results from leaching of the country rock by hydrothermal solutions. The chert has low REE concentrations and displays an REE pattern consistent with a hydrothermal origin. It may have formed in a Late Proterozoic rift or extension zone developed within the Yunkai continental margin back‐arc basin, with a fault system linking it to an unknown heat source at depth.
Field experiments of aeolian dust accumulation on rock fragment substrata
Authors: GOOSSENS DIRK 
Published: June 2006

ABSTRACTThe effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long‐term field experiment in the Negev desert of Israel. Four parameters were studied: pebble eccentricity, pebble size, pebble flattening and cover density. The effect of these parameters on the accumulation of dust on the pebbles, on the accumulation of dust between and underneath the pebbles, and on total dust accumulation (pebbles+interpebble space) was measured separately. Accumulation on the pebbles increased as the pebbles became larger, less flattened and more elongated, and as cover density increased. Accumulation between and underneath the pebbles increased as the pebbles became smaller, more flattened and more elongated, and as cover density increased (although the accumulation area available became smaller). Total dust accumulation increased as the pebbles became smaller, more flattened and more elongated, and as cover density increased.Rock fragments act as a dust trap as dust accumulation on pebble‐covered surfaces is several tens of times larger than dust accumulation on similar but pebble‐free surfaces. However, less than 20% of the initially settled dust is protected from further erosion.In the Negev desert, dust erosion by wind is of the order of 10 times larger than dust erosion by water. The rate of long‐term dust accumulation in the Negev is of the order of 15–30 g.m−2.yr−1. This is considerably lower than the rates proposed elsewhere in the literature, which are based upon over optimistic dust retainment percentages.
Sedimentary dynamics and evolutionary history of a Late Carboniferous Gondwanic lake in north‐western Argentina
Authors: BUATOIS LUIS ALBERTO , MANGANO MARIA GABRIELA 
Published: June 2006

ABSTRACTLacustrine deposits are well represented in the lower part of the Late Carboniferous Agua Colorada Formation in the north‐west Sierra de Narváez, Catamarca Province, Argentina. Lake Narváez was one of the several water bodies formed in the region immediately after the Gondwana glaciation.The lacustrine transport system has been divided into three distinct zones: delta, shallow lake and deep lake. Delta progradation proceeded from the ESE. Coarse‐grained delta plain and turbidite delta front deposits suggest that the delta was formed close to the headwaters (‘short‐headed stream delta’type). During periods of high discharge, river mouths acted as bypass zones and fine and very fine sands were transported further into the lake by underflow currents. The clastic material supplied by the deltaic system was partially reworked by wave action. Sands accumulated in unstable conditions at the upper delta front as a consequence of delta progradation. As a result of the addition of clastics in the steep delta front, turbidity currents were formed, spreading their load along the lower delta slope. Deep lacustrine deposits are typically stacked, forming two different kinds of progradational turbidite lobe sequences. Type I lobes were formed in a basinal setting and were probably detached from their feeder systems as a result of sediment‐bypassing in a shallow lake during periods of low lake level. These turbidite lobes are replaced upwards by type II lobes, which were formed on the delta slope during periods of lake level rise that allowed the onset of delta progradation. The presence of highly deformed sandstone bodies suggests rapid depositional rates in a high slope setting, whereas the occurrence of hummocky cross‐stratified sandstones indicates wave reworking of the sands initially emplaced by turbidity currents. Therefore, the inner part of type II lobes was formed above storm wave base. The depositional history of Lake Narváez can be traced through four evolutionary stages: lake transgression, formation of type I lobes, formation of type II lobes and delta progradation. Tectonic activity was probably important at the early stage of lake evolution, but the subsequent depositional history was mainly controlled by fluctuations of lake level.
Carbonate pond deposits related to semi‐arid alluvial systems: examples from the Tertiary Madrid Basin, Spain
Authors: SANZ M. E. , ZARZA A. M. ALONSO , CALVO J. P. 
Published: June 2006

ABSTRACTCarbonate pond deposits occur associated with alluvial sediments in Miocene sequences of the Madrid Basin, central Spain. The ponds developed near the basin margins, either in floodplain environments (north) or mud‐flat settings (south). Three main facies assemblages are recognized: (1) floodplain/mud‐flat, (2) palaeosols and (3) pond deposits.In the northern part of the basin, ponds developed on the floodplain of terminal fluvial systems. The floodplain facies are typically red mudstones with interbedded sandstones and siltstones. Palaeosols associated with the ponds show a pedofacies relationship, the maturity of soils increasing with distance from the main channel. Carbonate pond deposits consist mainly of limestones, which display typical ‘palustrine’features. The formation and further accumulation of carbonate in the ponds took place in periods of reduced clastic sediment input and it is suggested that recharge into the pond areas was mainly from groundwater.In the south, ponds developed on mud‐flats located between sheet‐flood‐dominated alluvial fans and evaporite lakes. Mud‐flat facies consist of red mudstone that exhibits evidence of progressive soil development near both edges and beneath the carbonate pond lenses. Carbonate in the ponds is mainly dolomite and comprises two subfacies, mottled and laminated dolomicrites. This mineralogy, together with the presence of gypsum crusts below and in the lower part of the carbonate body, suggests higher evaporation rates and/or more saline waters filling the ponds in this part of the basin.In spite of differences in depositional setting and, to some extent, climatic conditions between the two areas of the basin, both facies associations and the sequential arrangement of the ponds show strong similarities that allow the proposal of a facies model for carbonate pond deposits related to semi‐arid alluvial systems. The sequences recognized from the pond deposits record a set of facies clearly different to those forming in swampy lakes associated with many permanent fluvial systems developed in more humid climates.
Two hundred million years of karst history, Dachstein Limestone, Hungary
Authors: JUHÁSZ E. , KORPÁS L. , BALOG A. 
Published: June 2006

ABSTRACTPlatform carbonates of the Upper Triassic Dachstein Limestone in Naszály Hill have been karstified extensively over the past 200 million years. They provide an excellent example of polyphase karstic diagenesis that is probably typical of many subaerially exposed carbonate sequences.Seven karstic phases are recognized in the area, each of which include polyphase karstic events. The first karst phase was associated with the Löfer cycles. Meteoric waters caused dissolution; enlarged fractures and cavities, were filled by marine and/or vadose silts and cement.The second karst phase was caused by local tectonic movements. Bedding‐plane‐controlled phreatic caves were formed, and filled by silts.The third karst phase lasted from the end of the Triassic to the Eocene. This was a regional, multiphase karstic event related to younger composite unconformities. Bauxitic fill is the most characteristic product of this phase. The karst terrain reached its mature or senile stage with very little porosity.Narrow veins and floating rafts of white calcite marks karst phase 4, which resulted from hydrothermal activity associated with Palaeogene magmatism. The early Rupelian phase of Alpine uplift caused large‐scale rejuvenation of the former karst terrain (karst phase 5). Subsequently Naszály Hill was buried as an area of juvenile karst with significant porosity. A second period of hydrothermal activity in the area (karst phase 6) was induced by Miocene volcanism, which resulted in wide, pale green calcite veins. Finally karst phase 7 was of tectonic origin. Following the most recent, Miocene uplift of the Naszály Hill, the carbonates have again become the site of vadose karst development.
Facies architecture and sequentiality of nearshore and ‘shelf’sandbodies; Haystack Mountains Formation, Wyoming, USA
Authors: MELLERE DONATELLA , STEEL RONALD J. 
Published: June 2006

ABSTRACTThe Haystack Mountains Formation (Campanian, Mesaverde Group, US Western Interior Basin, Wyoming) contains a series of shallow‐marine sandbodies, extending tens of kilometres out from a basin margin. The study succession (around 200 m thick) is composed of eight major sandstone tongues (Bolten Ranch, O'Brien Spring, Seminoe 1–2–3–4, Hatfield 1 and 2 members), each partially encased within marine shale intervals. The Formation is ‘sequential’at several scales. At the largest scale, the whole succession presents an aggradational to basinward‐stepping stacking pattern of the sandstone tongues. At a lower level, each tongue (member) is characterized internally by two different types of lithosome: the first represents shoreface progradation with hummocky cross‐strata passing up to swaley and trough cross‐stratified sandstones. This lithosome is erosively truncated at its top in most cases, and has a general sheet‐like geometry along strike, whereas down dip it displays a series of sharp‐bounded clinothems. The latter sometimes indicate a downward as well as a basinward shift through time, as suggested by the occurrence of coarser and/or shallower facies at a lower level in the shoreface profile. The second type of lithosome is sheet‐ or wedge‐like and sharply overlies the shoreface deposits. The lithosome consists of laterally widespread units of planar tabular to trough cross‐bedded medium sandstones passing laterally (in a dip direction) into bioturbated sandstones. The lower part of this lithosome is progradational, becoming retrogradational into the overlying shales. The facies within the cross‐bedded lithosome suggest a tidally dominated delta front to estuarine depositional setting.The two types of lithosome are not related genetically. The erosion surface separating the two lithosomes is a sequence boundary separating forced‐regressive (relative sea‐level fall) shoreface deposits from lowstand to transgressive (early relative sea‐level rise), cross‐bedded deposits. The uppermost part of the cross‐stratified lithosome shows a landward‐stepping of component parasequences and is abruptly blanketed by open‐marine shales.The most widespread cross‐bedded lithosomes are apparently best developed in the lowermost members of the Haystack Mountains Formation, i.e. in the aggradational part of the large‐scale progradational succession. In the uppermost, highly progradational sandstone tongues, the shoaling‐upward shoreface lithosome dominates, whereas the cross‐bedded lithosome occurs in narrow, lensoid belts, or is absent. The middle portion of the succession shows intermediate characteristics. The vertical variation in geometry, thickness and progradational extent of successive cross‐bedded lithosomes results from greater confinement of the incised nearshore systems both in space (landward direction) and in time (from the aggradation to the progradation architecture). The latter is a consequence of a decreasing rate of accommodation creation through time.
Sedimentary structures and sediment transport across the continental slope of Israel from piston core studies
Authors: ALMAGOR GIDEON , SCHILMAN BETTINA 
Published: June 2006

ABSTRACTThe continental terrace of Israel consists of Nile‐derived sediments. They are classified into three major groups, according to their structures: (1) irregularly to wavy laminated, coarse‐grained sediments (quartz and skeletal debris) of the flat outer shelf and upper bend of the slope (10–20% of the bulk) which are influenced by currents. These sediments are bioturbated to various degrees. Smectitic silty clays (80–90%) form two structural groups: (2) laminated, turbiditic sediments which accumulate on the slope, particularly in the canyons of the northern slope. Irregular, wavy, thickly laminated, coarse‐grained sediments of the upper slope and canyon heads merge downslope with parallel, thinly laminated, fine‐grained sediments. Toward the foot of the slope and on the adjacent deep‐sea floor lamination becomes indistinct and the sediment is visually homogeneous. (3) Slump‐generated mud lumps of various size which accumulate on the lower slope and along the transport axes of the canyons. These are the most visible evidence for large‐scale slumping mass movement.Transportational and depositional processes are far more intensive over the steep northern continental slope of Israel, and especially in its canyons than over the gentle southern slope.Very stiff overconsolidated sediments unconformably overlain by the ubiquitous recent silty‐clayey sediment were cored on steep sections of the middle continental slope and along the canyon walls. Their preconsolidation stress values suggest that these sections were formerly overlain by more than 40 m of sediment and now are exposed by slumping. The downsliding slabs usually disintegrated into small fragments although several huge fragments could be identified along the canyon axes.
Megaripple dynamics and sediment transport in a mesotidal mangrove creek: implications for palaeoflow reconstructions
Authors: LARCOMBE P. , RIDD P. V. 
Published: June 2006

ABSTRACTAn experiment was conducted to study megaripple morpho dynamics on a sandy intertidal shoal in a mesotidal mangrove creek (Gordon Creek, Townsville, Australia). Tidal current velocity and depth were recorded with S4 current meters over a period of 35 tides. The tidal megaripples were 0.06–0.2 m in height and 1–2 m in wavelength, and their movement was monitored by (1) electromagnetic bed‐elevation probes (which automatically recorded bed level every 2 min at three positions along the survey transect) and (2) daily surveying for 8 days around spring tidals.The tidal currents in Gordon Creek are ebb‐dominated, with maximum depth‐mean current velocities for the flood and ebb tides of 0.62 and 0.98 m s−1respectively. Significant bedload transport occurs only during spring tides, and only on the larger of the unequal semi‐diurnal tides. Bedload transport is overwhelmingly in the ebb direction. Megaripple migration rates reach 5.6 m per tide in the ebb direction and up to 0.1 m min−1within individual tides. Within‐tide ‘bedform transport rates’are up to 0.29 kg m−1s−1.The results suggest that for reconstruction of palaeoflows from deposits of preserved fine‐ to medium‐grained sandy tidal megaripples, it is valid to use a depth‐averaged velocity of 0.5–0.6 m s−1as the migration threshold. Velocity thresholds associated with partial or complete reversal of megaripple asymmetry are invalid.