bluuebunny/crossref_metadata_2025_split huggingface dataset:
In situ acoustic measurements of marine gravel threshold and transport
Authors: THORNE PETER D. , WILLIAMS JON J. , HEATHERSHAW ANTHONY D. 
Published: June 2006

ABSTRACTMeasurements of the nearbed turbulent current flow and the bedload transport of marine gravel have been made over three tidal cycles. The turbulence in the bottom boundary layer was measured using two electromagnetic current meters, and the gravel transport was measured using a passive acoustic system which monitored the interparticle collision noise of locally mobile material. Visual estimates of bedload were also obtained with an underwater TV camera. The acoustic technique, unlike a conventional bedload sampler, has allowed estimates of transport to be obtained with a temporal resolution comparable with the turbulence data collected. This has enabled a detailed comparison to be made between the turbulent flow and the sediment response to the instantaneous flow conditions. The results of the study show that of the turbulent bursting events which contribute towards the Reynolds stress, only the sweeps and outward interactions play a significant role in the transport of coarse sedimentary material. The measurements show that it is the instantaneous increases in the horizontal turbulent velocity fluctuations that generate excess shear stresses which drive the transport process.
Travertines in the northern Hula Valley, Israel
Authors: HEIMANN ARIEL , SASS EYTAN 
Published: June 2006

ABSTRACTThis study describes the field and petrographic relationships of a widespread deposit of Pleistocene travertines in the northern Hula Valley, northern Israel. The travertines interfinger with conglomerate deposits and basaltic lava flows. Field relationships and radiometric dating indicate that the travertines accumulated intermittently over the past million years, and their formation virtually stopped 25 000 years ago.The travertines are characteristically highly porous. Some of the pores, as well as some spar‐filled voids, preserve the shapes of stalks and leaves. The abundance of plant material suggests that photosynthesis, rather than bacterial or abiogenic processes, was the main mechanism which induced carbonate precipitation.The reasons for travertine accumulation in the past and for the cessation of its formation today are ascribed to differences in the palaeogeographic setting. In the past, water flow is viewed as having been mostly sluggish, and a widespread and shallow sheet of water was formed. The lush vegetation, combined with the relatively long residence time of the water in the area, led to increased efficiency of the calcium carbonate precipitation. Today, by contrast, water flows rapidly in gorges, precipitating only a small fraction of its load of dissolved calcium carbonate. The conjectured change in hydrological conditions is ascribed to rejuvenation of faulting activity in the Late Quaternary.
Comparisons between acoustic measurements and predictions of the bedload transport of marine gravels
Authors: WILLIAMS JON J. , THORNE PETER D. , HEATHERSHAW ANTHONY D. 
Published: June 2006

ABSTRACTContinuous, detailed records of marine gravel transport have been obtained acoustically and compared with bedload transport rates (qb) predicted by five bedload transport equations using measurements of the near‐bed turbulent current flow. When mean flow data are used in these equations, total qb estimates are similar to those measured. However, when instantaneous flow data are used, total qb is over‐estimated by approximately one order‐of‐magnitude. Based on the acoustic measurements, an empirical equation has been obtained that gives accurate estimates of total qb over a tidal cycle and simulates well the intermittent characteristics of marine bedload transport.
Fluvial‐aeolian interactions: Part I, modern systems
Authors: LANGFORD R. P. 
Published: June 2006

ABSTRACTTwo modern fluvial‐aeolian depositional systems (Great Sand Dunes National Monument, Colorado and the Mojave River Wash, California) are remarkably similar in spite of different climates, sizes, fluvial sediment textures, and relative directions of aeolian and fluvial transport. Dune growth and migration, and deflation of blowouts create 8–10 m of local relief in unflooded aeolian landscapes.There are six prominent fluvial‐aeolian interactions. (1) Fluvial flow extends into the aeolian system until it is dammed by aeolian landforms; (2) interdune areas (overbank‐interdunes) upstream of aeolian dams, and alongside channels are flooded; (3) water erodes dunes alongside channels and interdunes; (4) flood waters deposit sediment in interdune areas; (5) fluvially derived groundwater floods interdunes (interdune‐playas); (6) wind erodes fluvial sediment and redeposits it in the aeolian system.Unique and characteristic sediments are deposited in overbank‐interdunes and in interdune‐playas, reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions. These fluvial‐aeolian interdune deposits are characterized by irregular, concave‐up bases and flat upper surfaces containing mudcracks or evaporite cement.Characteristic low‐relief surfaces form in aeolian systems as an effect of flooding. Fluvial deposits are resistant to aeolian deflation. Aeolian sand is preserved when flood sediments are deposited around the bases of the dunes. Thus repetitive fluvial and aeolian aggradation tends to be ‘stepwise’ as interdune floors are suddenly raised during floods. The effects of flooding should be easy to recognize in ancient aeolianites, even beyond the area covered with overbank muds.
Detrital modes and provenance of the Stilo‐Capo d'Orlando Formation (Miocene), southern Italy
Authors: CAVAZZA WILLIAM 
Published: June 2006

ABSTRACTThe Stilo‐Capo d'Orlando Formation (SCO Fm) is a Miocene clastic unit nonconformably covering the basement of the southern portion of the Calabria‐Peloritani Arc (CPA), a small‐scale terrane which was accreted onto the Apennines‐Maghrebides orogenic system during Neogene time. The SCO Fm is composed of conglomerate, sandstone and mudrock deposited in a marine environment through the action of gravity currents.Detrital modes of sandstones and conglomerates of the SCO Fm indicate a local provenance. In fact, petrological parameters can be matched directly with nearby basement lithologies. Two petrofacies with distinctive parameters are present. A northern petrofacies is predominantly composed of plutonic and low‐grade metamorphic detritus, and was derived from the Serre massif, which is mostly made of late Hercynian plutons intruded into metasedimentary rocks. A southern petrofacies is mostly composed of metamorphic detritus and was derived from the Aspromonte and the Peloritani Mountains, which are predominantly composed of middle‐to high‐grade metamorphic rocks.Petrological results place important constraints on the geodynamic evolution of the CPA. According to several authors, the arc is composed of two sectors (microterranes) with different geological histories and partly composed of contrasting rock types, whose timing of juxtaposition is debated (Early Cretaceous against middle‐late Miocene; that is, much before or soon after deposition of the SCO Fin). The SCO Fm crops out only in the southern sector of the CPA and does not contain any detritus derived from the northern sector, in spite of a favourable sediment palaeodispersal system. This fact indicates that the amalgamation of the two sectors probably took place after deposition of the SCO Fm.
Near‐surface shrinkage and carbonate replacement processes, Arran Cornstone Formation, Scotland
Authors: TANDON S. K. , FRIEND PETER F. 
Published: June 2006

ABSTRACTA 47 m thick succession of conglomerates, sandstones and mudstones, of Late Devonian or Early Carboniferous age, outcrops at Fallen Rocks in northeast Arran (western Scotland). It is defined here as the type section of the Arran Cornstone Formation. At numerous levels in the succession, varieties of fissures and carbonate concretions formed during the accumulation of the Formation. The fissures opened as a result of drying‐shrinkage, and were closed again either by filling with different sediment, or by wetting and expansion of the fissure wall sediment. Carbonate concretions form complete beds, discontinuous, bedding‐concordant sheets, or bedding‐discordant nodules or rods (the rod cornstones). These concretions formed close enough to the surface to be incorporated, after erosion and redeposition, as clasts into overlying beds. The concretions were formed by growth of micrite, mainly by replacement, but shrinkage displacement played an important role in subsequently fracturing and reworking the micrite. The micrite was also locally replaced by microspar and spar, and this involved dissolution and precipitation. No independent evidence of biological influence in any of these processes has been found.
Palaeochannel reconstructions from point bar deposits: a three‐dimensional perspective
Authors: WILLIS BRIAN J. 
Published: June 2006

ABSTRACTQuantitative determination of palaeochannel geometry and hydraulics from point bar deposits requires an understanding of the interaction between channel‐bend migration, temporal and spatial variation of point bar geometry and facies, and outcrop orientation. This interaction is modelled with the aid of a computer program which predicts three‐dimensional (3‐D) geometry and grain size variation of point bars. Synthetic deposits are produced for the cases of down‐valley bend migration and/or increase in channel‐bend sinuosity. Two‐dimensional (2‐D) cross‐sections in varying orientations across these simulated deposits display lateral‐accretion bedset surface geometry, and variation in mean bedset grain size and local palaeocurrent orientation.Most cross‐sections show point bar deposits thickening away from the meander‐belt axis due to a lateral progression from thinner bend‐exit deposits to thicker bend‐apex deposits (caused by down‐valley channel translation), and/or due to a progression from thinner low sinuosity deposits to thicker high sinuosity deposits caused by channel bend expansion. In association with this lateral thickening, bedset surfaces become steeper and more convex upwards while the variation in mean grain size up bedsets commonly increases. Down‐valley point bar translation allows preservation only of deposits formed downstream of the band apex, and produces characteristic fining upwards sequences. Marked lateral and vertical variations in palaeocurrent directions due to varying channel orientation relative to a given cross‐section are also predicted. These results indicate a need in palaeochannel reconstructions, for a more detailed examination of 3‐D variations in bedset surface geometry, palaeocurrent orientation and grain size distribution within and between bedsets of laterally accreted sediment.
Petrography and provenance of silicified early Archaean volcaniclastic sandstones, eastern Pilbara Block, Western Australia
Authors: DiMARCO MICHAEL J. , LOWE DONALD R. 
Published: June 2006

ABSTRACTIntense post‐depositional alteration has profoundly affected sandstones in the volcanic portions of Early Archaean (3·5–3·3 Ga) greenstone belts. The mineralogy and bulk compositions of most grains have been completely destroyed by pervasive metasomatism, but grain textures are commonly well preserved. Consequently, microtextural information coupled with present alteration compositions as determined petrographically can be used to estimate original framework modes.Silicified Early Archaean volcaniclastic sandstones assigned to the Panorama Formation and Duffer Formation, Warrawoona Group, eastern Pilbara Block, Western Australia, were originally composed of volcanic (VRF) and sedimentary (SRF) rock fragments, volcanic quartz, feldspar, traces of ferromagnesian minerals and pumice. Only volcanic megaquartz remained stable during alteration. All other primary components were replaced by granular microcrystalline quartz (GMC) and sericite. In most areas, the sandstones were composed of dacitic to rhyolitic VRFs, now totally replaced by sericite‐poor GMC and recognized by preserved microporphyritic textures. In a few areas, quartz‐poor dacitic to andesitic(?) VRFs dominated the detrital assemblage. Minor SRFs and mafic VRFs, now replaced by GMC, are recognized on the basis of colour, internal structures, and internal textures, including skeletal, possible spinifex textures. Detrital feldspar is represented by blocky, sericite‐rich grain pseudomorphs.A semi‐quantitative point‐count scheme, developed for the analysis of heavily altered sandstones, indicates the following primary detrital‐mode ranges for Panorama arenites: quartz, 0–28%; feldspar, 0–28%, VRFs, 58–86%, and SRFs 0–25%. In about half the point‐counted samples, feldspar could not be distinguished from rock fragments. In such cases, both were counted as one grain type, Lv', which makes up from 84 to 100% of the framework modes of these rocks.These sands were derived from a terrane composed largely of fresh felsic volcanic rocks and sediments, but locally including minor mafic, ultramafic, and sedimentary rocks. Much, but not all, of the felsic volcaniclastic sand represents reworked pyroclastic debris. There is no evidence for contributions from plutonic or metamorphic sources. The Panorama modal assemblage represents a provenance that is lithologically more restricted than that of Archaean greywackes and other siliciclastic units common in the sedimentary portions of these same Early Archaean greenstone belts and younger greenstone belts (3·0–2·7 Ga).
Analcime in lake and lake‐margin sediments of the Carboniferous Rocky Brook Formation, Western Newfoundland, Canada
Authors: GALL Q. , HYDE R. 
Published: June 2006

ABSTRACTIn the Deer Lake Basin of western Newfoundland, Canada, analcime has been found within fine‐grained, siliciclastic and carbonate, lake and lake‐margin sediments of the Carboniferous Rocky Brook Formation. Analcime is the only zeolite observed in these unmetamorphosed and non‐volcanogenic rocks. Microscopic analcime occurs as vug‐filling, limpid, isotropic to anisotropic crystals. Microprobe analyses show this type of analcime to be lower in silica than most analcime in sedimentary rocks. A second textural type of finer‐grained submicroscopic analcime can be detected from X‐ray diffraction spectra of Rocky Brook Formation mudstones, where it is associated with phyllosilicates (illite, interstratified chlorite/smectite, smectite, chlorite), other silicates (quartz, feldspar) and carbonates (dolomite, calcite). Results of this study suggest that the analcime in the Rocky Brook Formation formed either by direct lakewater/porewater precipitation or by reaction of these waters with one or more clay mineral types or plagioclase.
Nodular silcretes of the Cypress Hills Formation (upper Eocene to middle Miocene) of southern Saskatchewan, Canada
Authors: LECKIE D. A. , CHEEL R. J. 
Published: June 2006

ABSTRACTSiliceous nodules in the upper Eocene to middle Miocene Cypress Hills Formation in southern Saskatchewan formed on the distal portions of an extensive braidplain. The nodules are similar to silcretes described elsewhere in the literature but their morphology and occurrence suggests that they are of a rare variety. The silcretes are discrete equant to disc‐shaped nodules, 1–3 cm thick, and up to 15 cm long. The silicretes form horizontal, discontinous layers parallel to bedding within an unweathered profile. Void spaces and fractures within the nodules are lined or filled with drusy quartz. The silcretes contain less than 0.07% TiO2. The TiO2/SiO2/Al2O3 and TiO2/SiO2/Fe2O3 ratios are similar to values obtained from nodules formed in an arid to semi‐arid environment based on comparison with modern silcretes. This interpretation is confirmed by independent sedimentological and palaeontological climatic evidence for an arid to semi‐arid climate throughout Oligocene time in the western Canadian plains.
Lower Cambrian shelf and shelf margin buildups, Flinders Ranges, South Australia1
Authors: JAMES NOEL P. , GRAVESTOCK DAVID I. 
Published: June 2006

ABSTRACTCarbonate buildups in the Flinders Ranges of mid‐Early Cambrian age grew during a period of high archaeocyath diversity and are of two types: (1) low‐energy, archaeocyath‐sponge‐spicule mud mounds, and (2) high‐energy, archaeocyath‐calcimicrobe (calcified microbial microfossil) bioherms. Mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone, have a fenestral fabric, display distinct stromatactis, contain abundant sponge spicules and form structures up to 150m wide and 80 m thick. Bioherms are either red or dark grey limestone and occur as isolated small structures 2–20 m in size surrounded by cross‐bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across. Red bioherms comprise masses of white Epiphyton with scattered archaeocyaths and intervening areas of archaeocyath‐rich lime mudstone. Grey bioherms are complex intergrowths of archaeocyaths, encrusting dark grey Renalcis and thick rinds of fibrous calcite cement. The bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities, up to 1.5 m across, lined with fibrous calcite.The buildups are isolated or in contiguous vertical succession. Mud mounds occur alone in low‐energy, frequently nodular, limestone facies. Individual bioherms and bioherm complexes occur in high‐energy on‐shelf and shelf‐margin facies. The two types also form large‐scale, shallowing‐upward sequences composed of basal (deep water) mud mounds grading upward into archaeocyath‐calcimicrobe bioherm complexes and bioherms in cross‐bedded carbonate sands. The uppermost sequence is capped by ooid grainstone and/ or fenestral to stromatolitic mudstone.The calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent Phanerozoic time.
Large‐scale current‐induced erosion and deposition in the path of the 1929 Grand Banks turbidity current
Authors: CLARKE JOHN E. HUGHES , SHOR ALEXANDER N. , PIPER DAVID J. W. , MAYER LARRY A. 
Published: June 2006

ABSTRACTNew observations concerning the degree of current‐induced erosion and deposition in the path of the 1929 Grand Banks turbidity current are presented. Most of the observations are available from Eastern Valley, Laurentian Fan. Seabeam and SeaMARC I data reveal widespread current erosion along the valley over a distance of 200 km from the shelfbreak. Erosional valley‐floor channels are preferentially developed adjacent to the valley margins and the flanks of intravalley highs. Asymmetric transverse bedforms (herein termed gravel waves) are moulded in a deflationary pebble and cobble lag that overlies the eroded valley floor. In contrast, at the distal limit of Eastern Valley, thick deposits of massive granule gravel indicate deposition beneath a decelerating turbidity current. Symmetrical transverse bedforms (herein termed macrodunes) are developed within these granule gravel sediments.The spatial distribution of both bedforms and the areas of erosive excavation suggest that the turbidity current in 1929 was accelerating over the first 100 km from the shelfbreak and was eroding and entraining sediment from the valley floor over a distance of at least 200 km. With the loss of lateral constraint at the distal limit of Eastern Valley the turbidity current spread laterally and started depositing sediment as it decelerated. Current‐induced erosion of the valley floor represented a potential source of between 50 and 100 km3 of sediment for incorporation into the resulting turbidite.
Flume experiments on the alignment of transverse, oblique, and longitudinal dunes in directionally varying flows
Authors: RUBIN DAVID M. , IKEDA HIROSHI 
Published: June 2006

ABSTRACTFor more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow, whereas others are parallel or oblique to flow. This problem of bedform alignment was studied experimentally using subaqueous dunes on a 3–6‐m‐diameter sand‐covered turntable on the floor of a 4‐m‐wide flume.In each experiment, two flow directions (relative to the bed) were produced by alternating the turntable between two orientations. The turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms; the resulting bedforms were in equilibrium with the time‐averaged conditions of the bimodal flows. Dune alignment was studied for five divergence angles (the angle between the two flow directions): 45°, 67–5°, 90°, 112–5° and 135°. The flow depth during all experiments was approximately 30 cm; mean velocity was approximately 50 cm s‐1 and mean grain diameter was 0–6 mm. Each experiment continued for 30–75 min, during which time the flume flow was steady and the turntable position changed every 2 min. At the end of each experiment, water was slowly drained from the flume and dune alignment was measured. Transverse dunes (defined relative to the resultant transport direction) were created when the divergence angle was 45° and 67–5°, and longitudinal dunes were created when the divergence angle was 135°. At intermediate divergence angles, dunes with both orientations were produced, but transverse dunes were dominant at 90°, and longitudinal dunes were dominant at 112–5°.One experiment was conducted with a divergence angle of 135° and with unequal amounts of transport in the two flow directions. This was achieved by changing the orientation of the turntable at unequal time intervals, thereby causing the amount of transport to be unequal in the two directions. The dunes formed during this experiment were oblique to the resultant transport direction.These experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments. In both sets of experiments, the bedforms developed with the orientation having the maximum gross bedform‐normal transport (the orientation at which the sum of the bedform‐normal components of the two transport vectors reaches its maximum value). In other words, the bedforms develop with an orientation that is as transverse as possible to the two flows. In those cases where the two flows diverge by more than 90° and transport equal amounts of sand, bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors. Although such bedforms have been defined by previous work as longitudinal bedforms, they are intrinsically the same kind of bedform as transverse bedforms.