bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Quaternary sequence stratigraphy of Lake Malawi (Nyasa), Africa
Authors: SCHOLZ CHRISTOPHER A. , FINNEY BRUCE P.
Published: June 2006

High resolution seismic data, multichannel seismic data and sediment cores were used to examine the Songwe Sequence, the uppermost of four depositional sequences identifiable on multichannel seismic data from Lake Malawi (Nyasa). The sequence has a maximum thickness of about 115 m in two areas of the lake, but is typically less than 70 m thick over most of the basin. The sequence is distributed along the entire length of the 560 km long lake, and is concentrated in three main depocentres. 14C age dates from sediment piston cores are extrapolated to provide an age estimate of about 78 000 yr bp for the oldest sediments within the Songwe Sequence. In the North and Central bathymetric basins of the lake, high resolution seismic data indicate a dynamic depositional environment, dominated by turbidity and mass flow deposits. Seismic data from the southern basin show acoustically transparent sediments with relatively low amplitude internal reflections, indicative of pelagic and hemipelagic sedimentation. In many areas the Songwe Sequence is underlain by a pronounced angular unconformity, suggestive of a significant, prolonged, low lake stage prior to deposition of the sequence. Seismic reflectors within the Songwe Sequence can be correlated to younger low lake stages identified from sediment core data. Major late Quaternary low lake level stages in Lake Malawi, interpreted from features identified in the seismic data and sediment core analyses, are tentatively interpreted at 6000 to 10 000 yr bp, 28 000 to >40 000 yr bp, and prior to 78 000 yr bp. Budget calculations indicate mean sediment concentrations from catchment runoff during the period of deposition of the Songwe Sequence to be about 190 mg 1−1, comparable to estimates of modern rainy season discharges from the major river systems. Erosion rates within the drainage basin are estimated to be higher than the African average by a factor of three or more, probably due to the high relief within the Lake Malawi catchment.
Current crescents from the Herreria Formation (Lower Cambrian) of northern Spain
Authors: OWEN GERAINT
Published: June 2006

Current crescents are well preserved on the upper surfaces of quartzite beds in the Lower Cambrian Herreria Formation of the Cantabrian Mountains in northern Spain. Within a sequence of nearshore deposits, the current crescents are interpreted as having formed by flow separation of wave backwash around obstacles on a beach. The obstacles are not preserved and are inferred to have been perishable organic material, such as stranded algae or jellyfish, which subsequently decayed.
Diagenetic alteration of early marine cements of Upper Silurian stromatactis
Authors: BOURQUE PIERRE‐ANDRÉ , RAYMOND LYNDA
Published: June 2006

Stromatactis is a spar network whose elements in cross section have flat to undulose lower surfaces and digitate upper surfaces. The network is composed principally of isopachous crusts of centripetal cement and commonly occurs embedded in finely crystalline limestone. It is the cement filling of interconnected cavities. Stromatactis of Upper Silurian red stromatactis limestone from Gaspé Peninsula, Québec Appalachians, exhibits two types of cements: (1) an isopachous cement that lined the walls of the conduits and is interpreted as early marine; and (2) a later blocky cement that occupies the centres of cavities. The first cement is composed exclusively of non‐ferroan calcite, whereas the second cement is mixed non‐ferroan and ferroan calcite. The early isopachous cement is white on polished slabs and has a turbid aspect under transmitted light. In a few samples, the relative homogeneity of this early cement is broken by the presence of distinctive grey clear calcite. Under cathodoluminscence, the grey clear calcite is non‐luminescent and exhibits well defined bladed crystal shapes, whereas the white turbid cement has a dull orange luminescence and indistinct crystal shapes. The relationships between the two cements indicate that the dull luminescent cement is a secondary form of the non‐luminescent cement, and it is concluded that the dull cement is the product of alteration of the non‐luminescent cement by burial or meteoric fluids. The later blocky cement has the same dull luminescence as the white turbid cement and is thought to have been precipitated from the same fluids as those responsible for the alteration of the early marine cements. Oxygen isotopic values of the dull cement of the early isopachous crusts (mean δ18O= ‐6.8%o are intermediate between those of the non‐luminescent early marine cement (mean δ18O= ‐5.3%o) and the dull luminescent blocky cement (mean δ18O= ‐11.8%o), while carbon isotopic values do not differ significantly (δ13C=+2.9, +2.4 and +2.6%o, respectively). The alteration also has affected the distribution of some trace elements, particularly Mg. Both unaltered and altered cements contain less than 1% microdolomite inclusions, but the Mg content of the background calcite of unaltered cement is three times that of altered cement (14171 vs. 5502 ppm). Precursor early marine cement is thought to have been low‐Mg calcite. The mean δ18O value (− 5.3%o) of unaltered early marine cement is higher than values for the oxygen isotopic signature of Silurian oceans provided by brachiopod shells.
Diachronous evolution of systems tracts in a depositional sequence from the middle Pleistocene palaeo‐Tokyo Bay, Japan
Authors: ITO MAKOTO , O'HARA SAKAE
Published: June 2006

Palaeo‐Tokyo Bay is a relic of the Plio‐Pleistocene Kazusa forearc basin in the Boso Peninsula of Japan. The sedimentary infill of palaeo‐Tokyo Bay is characterized by shallow marine to paralic sediments of the middle to upper Pleistocene Shimosa Group. Sequence stratigraphical analysis has been used to describe spatial and temporal variations in the depositional systems of the lowest units of the Shimosa Group, deposited during the early stage of development of palaeo‐Tokyo Bay.

Three different type of depositional systems were recognized: sand ridge to shelf (SRS), shelf to delta (SDL) and shelf to non‐deltaic nearshore (SNS) systems. They overlie early transgressive estuarine deposits infilling lowstand valleys incised in the south‐eastern margin of palaeo‐Tokyo Bay. These systems were developed during late transgressive through highstand stages of a relative sea level cycle, which may have been controlled by a glacio‐eustatic sea level change at about 0·4 Ma. Spatial variation in depositional systems is largely identical to that in modern Tokyo Bay; environmental conditions similar to those prevailing at the present day probably characterized the early history of palaeo‐Tokyo Bay.

The timing of highstand systems tracts within a high frequency depositional sequence was analysed in terms of the effect of sedimentation rate, based on the mapping of a chronostratigraphical surface marked by the Hy4 volcanic ash layer. From spatial variations in sedimentation rate, it was possible to identify the diachronous evolution of highstand systems tracts from the SDL system, through the SNS system, to the SRS system. Time lag is indicated by major bounding surfaces, such as maximum flooding or downlap surfaces associated with a condensed section, which developed immediately above or below the Hy4 volcanic ash layer. The lag may be of the order of a few thousands to tens of thousands of years within a depositional sequence with a total of duration of about 100 000 years.
Discrimination of accreted and eroded coasts using heavy mineral compositions of the Nile Delta beach sands, Egypt
Authors: FRIHY OMRAN E.
Published: June 2006

Coastal erosion has occurred on the beaches of the three major promontories of the Nile Delta of Egypt. The eroded sand is generally carried alongshore to the east, or locally to the west, from these promontories and is deposited in areas of beach accretion between promontories. In this study the heavy minerals of 150 samples have been investigated with the aim of differentiating between eroded and accreted beaches. Discrimination was achieved by using bivariate plots of the raw weight percentage data and Q‐mode factor analysis. Factor analysis yielded two ‘mineral assemblages’: Factor 1 is dominated by augite, hornblende and epidote, while Factor 2 consists of opaque minerals, garnet, zircon, rutile and monazite. These two mineral factors are produced by the selective sorting of heavy minerals by natural processes of waves and currents. Minerals of Factor 2 are associated with high density opaques which tend to concentrate as a lag in areas of erosion. Conversely, the lower density minerals of Factor 1 are preferentially transported away from areas of erosion and carried to the accreted shorelines.
Origin of anhedral Sr‐rich calcite in deep‐water mixed sediment, north‐east Australia
Authors: DIX GEORGE R.
Published: June 2006

At burial depths of 800‐1000 m, within the epicontinental Queensland Trough of north‐east Australia (ODP Site 823), microcrystalline inter‐ and intraskeletal mosaics of anhedral (loaf‐shaped, rounded) calcite have Sr2+ values ranging from below microprobe detection limits (<150 ppm) to 8100 ppm. Host rocks are well lithified, fine‐grained mixed sediment to clayey wackestone and packstone of Middle and Late Miocene age. Petrography demonstrates that calcite precipitation has spanned shallow to deep burial, overlapping formation of framboidal pyrite in the upper 50 m; shallow‐burial dolomitization (<300 m); and dedolomitization during sediment consolidation and incipient chemical compaction at greater (>400–500 m) depths. Petrographic observations illustrate that the calcite microfabric formed through coalescing crystal growth resulting from one or a combination of displacive growth in clay, porphyroid neomorphism of aragonite/vaterite, and clay replacement by calcite. Sr2+ mean concentrations in calcite between depths of 800 and 1000 m are similar to an expected equilibrium pore‐water concentration, using a Dsr of 0.06, and may indicate active calcite precipitation. However, Sr2+ variation (2000–5000 ppm) within and among crystals, and concentrations that range well above predicted equilibrium values for a given depth, illustrate either variable Sr2+ retention during recrystallization of shelf‐derived aragonite (and authigenic local vaterite) or relative uptake of Sr2+ during calcite precipitation with burial. Within the context of calcite formation during burial to 1 km, diagenetic attributes that affect the latter process include increased concentrations of pore‐water Sr2+ with depth associated with aragonite recrystallization/dissolution; upward migration of Sr‐rich pore water; and increased DSr related to local variation in precipitation/recrystallization rates, differential crystal sector growth rates and/or microvariation in aragonite distribution.
Theory of the sedimentation of suspended particles from fluvial plumes
Authors: BURSIK M. I.
Published: June 2006

A two‐layer model for the flow and sedimentation within a salt wedge or highly stratified hypopycnal fluvial plume emptying into a fiord is developed from basic principles. From this model, it is found that the amount of suspended sediment of a particular grain size decreases as an exponential function of distance, and that the velocity and depth of the plume converge to constant values. The model is consistent with measurements from the plume of the Homathko River in Bute Inlet, British Columbia, Canada, and suggests that certain aspects of current empirical models of plume sedimentation are based upon sound principles.
Sand supply to the Algodones dunefield, south‐eastern California, USA
Authors: WINSPEAR N. R. , PYE K.
Published: June 2006

In an effort to gain a better understanding of the relationship between climate, sand supply and aeolian sand deposition, an investigation was undertaken in the Algodones dunefield of south‐eastern California to determine: (1) the source of the sand and (2) the mode of sand supply to the Algodones dunefield. Textural, geochemical and mineralogical analyses show that the dune sands were mainly derived from Colorado River sands during episodes when the Colorado River drained west to the Salton Basin instead of south to the Gulf of California. A model is presented which relates episodic aeolian deposition in the Algodones dunefield to the growth of the resulting lake under a persistent, intense north‐westerly wind regime and to subsequent desiccation of the lake following diversion of the Colorado River to the Gulf of California. Late Holocene radiocarbon ages for relict lake shoreline deposits correlate with documented episodes of extreme flooding and increased winter storminess across the south‐western United States. These conditions are likely to have been the cause of intensified north‐westerly winds which coincided with high stands of Lake Cahuilla. Although diversion of the Colorado River to the Salton Basin occurred at least three times during the late Holocene, it is evident that the river did not change its course in response to the majority of the floods. It appears that the critical control on diversion of the river was the difference in gradient between courses leading to the Salton Basin and Gulf of California, which in turn was influenced by fluvial deposition and tectonic activity. Flooding was able to cause diversion of the Colorado River to the Salton Basin only when the difference in gradient between the two courses was relatively small.
Phosphate stromatolites from condensed cephalopod limestones, Upper Jurassic, Southern Spain
Authors: MARTÍN‐ALGARRA AGUSTÍN , SÁNCHEZ‐NAVAS ANTONIO
Published: June 2006

Upper Jurassic phosphate stromatolites of the Almola Sierra (Southern Spain) encrust macrofossils and hardgrounds, and form oncoids included within pelagic, condensed fossiliferous limestones. Their accretion was determined by bacterially mediated precipitation of phosphate, by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera. Phosphorous, trace elements and rare‐earth elements were concentrated from degraded organic matter and seawater by stromatolite‐building communities, which mediated the formation of phosphate‐rich and Fe‐Al‐Si‐rich organic gels under oxic conditions, favouring the precipitation of amorphous mineral precursors (ACP and Fe‐Al‐Si oxyhydroxides). The observed Ce‐enrichment for some stromatolites is explained by oxidative scavenging of Ce4+ from seawater by Fe—Mn oxyhydroxides. The bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure, and later changed to carbonate‐fluorapatite, haematite and poorly crystalline Fe‐rich clays under postoxic conditions. Phosphatization of trapped carbonate particles also occurred. The phosphate stromatolites formed on a sediment‐starved pelagic swell, during periods of no carbonate sedimentation and hardground development. Stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis, sedimentation and erosion, suggesting episodic changes in the sedimentary environment. Although some of the parameters that controlled phosphate precipitation associated with the stromatolites (local high organic productivity, sediment starvation, moderate depth of deposition and physicochemical conditions) were similar to those found in modern and ancient phosphogenic settings, the palaeogeographical framework and the intensity of sedimentary processes were different to those of the World's major phosphorite deposits.
Origin and modification of Cambrian dolomites (Red Heart Dolomite and Arthur Creek Formation), Georgina Basin, central Australia
Authors: NICOLAIDES STELIOS
Published: June 2006

The Early to Middle Cambrian Red Heart Dolomite and lower Arthur Creek Formation of the southern portion of the Georgina Basin, Australia, is an entirely dolomitized succession of shallow‐water evaporitic mudflat and deeper‐water subtidal lithologies. Three types of dolomite have been identified and are interpreted as: (1) syndepositional dolomite; (2) regional replacement dolomite; and (3) void‐filling dolomite (cement). Syndepositional dolomite, derived from saline pore fluids developed in a sabkha environment, is a minor dolomite type with very fine crystal mosaics and has a mottled, non‐zoned cathodoluminescence. The widespread regional replacement dolomite ranges from fine‐ to medium‐crystalline forming mainly planar‐s and non‐planar‐a crystal mosaics, and displays blotchy, mottled, non‐zoned cathodoluminescence. Void‐filling dolomite commonly forms planar‐s to planar‐e, medium to very coarse crystal mosaics. Rare non‐planar‐c, very coarsely crystalline saddle dolomite also exists. Void‐filling dolomite has a successively zoned cathodoluminescence pattern from non‐, to brightly, to dully luminescent.

Geochemically, the syndepositional dolomite has δ18O (PDB) values ranging between − 5.3 and − 8.6%o. Regional replacement dolomites exhibit a wide range of δ18O values from − 3.3 to − 10.9%o whereas void‐filling dolomite has δ18O values ranging from − 10.8 to − 14.3%o. All three dolomite types have similar δ13C (PDB) values, in the range between +1.7 and −1.7%o.

Three initial dolomitization episodes are interpreted: (1) a sabkha stage, forming the syndepositional dolomite and dolomitizing the evaporitic mudflat lithologies; (2) a brine‐reflux stage, replacing the subtidal lithologies; and (3) a burial stage, forming the void‐filling dolomite type. Final dolomite stabilization occurred during burial, at elevated temperatures, in the presence of basinal fluids, resulting in progressive recrystallization and stabilization of the earlier‐formed syndepositional and replacement dolomites. Both textural and geochemical evolution should be taken into account when studying the origin of dolomites, based on their present geochemical composition.

Sulphates are represented by very fine‐crystalline syndepositional anhydrite in association with the syndepositional dolomite, and coarse to very coarse anhydrite cement. Evaportic mudflat (sabkha) and burial environments are inferred for the origin of the former and the latter anhydrite types, respectively. Evaporite dissolution breccias, indicative of the former presence of evaporites, are common throughout the succession.
The Cretaceous Uhangri Formation, SW Korea: lacustrine margin facies
Authors: CHUN S. S. , CHOUGH S. K.
Published: June 2006

The Uhangri Formation forms part of the Cretaceous sedimentary sequence deposited in a series of inland basins in the south‐western Korean Peninsula. It comprises an approximately 400‐m‐thick epiclastic sequence of conglomerate, (gravelly) sandstone, cherty mudstone and black shale. The entire sequence can be represented by 16 distinctive sedimentary facies organized into four facies associations.

Facies association I is characterized by thick homogeneous brownish siltstone, wedge‐shaped disorganized conglomerate and thinly interlayered gravelly sandstone units. The siltstone units were formed by large floods submerging the alluvial fan fringe (floodplain), whereas the conglomerate and gravelly sandstone units were deposited by sheetfloods and debris flows. Facies association II consists of stratified conglomerate — gravelly sandstone, laminated sandstone and sandstone/siltstone couplets which form fining‐upward cycles. Some facies units are low‐angle trough cross‐bedded and show broad channel geometries. This association represents subaqueous delta lobes fed by high‐ and low‐concentration turbidity currents in the distal delta realm. Facies association III is characterized, by wedged conglomerate and gravelly sandstone facies with interfingered massive sandstone bounded by scoured bases. It represents a delta front where distributary channels and mouth bars are dominant. Facies association IV consists of laterally continuous sequence of laminated black shale, crudely stratified sandstone and convoluted sandstone/cherty mudstone. This facies association is suggestive of depositional processes controlled by chemical equilibrium resulting from an interaction between density inflows and lake water. The cherty mudstone resulted from inorganic precipitation from siliceous solution provided by acidic volcanism.

The Uhangri sequence generally shows a fining‐upward trend with a transition from alluvial fan fringe, coarse‐grained subaqueous delta, to shallow lake. The retrogradation was probably due to continuous subsidence related to continental rifting in the oblique‐slip mobile zone.
Experiments on the entrainment threshold of well‐sorted and poorly sorted carbonate sands
Authors: PRAGER ELLEN J. , SOUTHARD JOHN B. , VIVONI‐GALLART ENRIQUE R.
Published: June 2006

Few studies have examined the hydrodynamic behaviour of carbonate sediments. The data presented here are the result of preliminary research on entrainment in well‐ and poorly sorted carbonate sands. Experiments were performed using naturally occurring sediments in a tilting, recirculating freshwater flume. Results indicate that when of similar size, shape and density, the transport threshold of carbonate sands is similar to that of quartz. However, owing to their lower density and often platy or irregular shape, skeletal sands require a lower shear stress to initiate transport. Because the density of carbonate particles may increasingly vary with grain size, the threshold of motion in coarse carbonate grains may differ more markedly from that of quartz. In poorly sorted samples, results show that the coarse‐grained constituents move before the finer‐grained components. Grain properties and boundary‐layer dynamics are believed to explain this phenomenon. Rollability of the larger grains combined with physical trapping and immersion within a low velocity sublayer are believed to prevent finer particles from moving. Given the appropriate sediments and flow conditions, it may therefore be possible to deposit and preserve fine‐grained sediments in a flow regime typically thought to transport such materials.
Deconvolution of pyroclastic grain‐size spectra for interpretation of transport mechanisms: an application to the AD 79 Vesuvio deposits
Authors: LIRER LUCIO , SHERIDAN MIKE , VINCI ANNA
Published: June 2006

A computer code using sequential fragmentation/transport theory was used to deconvolute and characterize a large grain‐size data set taken from the AD 79 Vesuvio deposits. The results allow us to interpret transport and deposition processes. Four principal morphological classes of grain‐size spectra were recognized in the AD 79 deposits:

1 unimodal distributions with coarse modes and very good sorting;

2 polymodal distributions in which relative fractions of each subpopulation are considerably variable;

3 polymodal distributions, but with one mode greatly prevailing over the other ones;

4 flat spectra in which a large number of size classes show the same loading.

Because different eruptive, transport and deposition conditions may have operated on pyroclasts which occur in the same bed, we have assigned grain‐size subpopulations, with different modes to specific mechanisms of particle movement and sedimentation depending on the size range of the particles and the textures of the beds. The fragmentation/transport processes considered here occur either within dilute flows (as fall, traction, saltation and suspension loads) or in high‐concentration flows (as a fluidized system or one with an extremely high sedimentation rate).

Variation in strength and position of modes throughout the entire vertical section of AD 79 products illustrates changes in transport and deposition processes with time. Size spectra from Vesuvio quantitatively demonstrate contemporaneous deposition from fall and surge mechanisms as well as contributions from different levels of hydrovolcanic products. In contrast, vertical variations in size spectra within individual pyroclastic flow deposits suggest variation from high particle concentration near the base of the bed to more dilute depositional conditions towards the top. Lateral variations in size spectra for one marker horizon show how a local pyroclastic flow in a channel grades into a surge on the margins. This study supports the model of continuous modification in loadings of several discrete subpopulations during deposition from a single explosive cloud.
Extensive carbonate algal bioherms in upper Pleistocene saline lakes of the central Altiplano of Bolivia
Authors: ROUCHY JEAN MARIE , SERVANT MICHEL , FOURNIER MARC , CAUSSE CHRISTIANE
Published: June 2006

During the upper Pleistocene the Central Altiplano of Bolivia was repeatedly flooded by deep and extensive saline lakes in response to climatic fluctuations. Development of carbonate algal bioherms took place during at least three major periods of lacustrine highstands, discontinuously covering the 300‐km‐long and 100‐km‐wide lacustrine slopes and terraces up to an elevation of 100 m above the surface of the modern halite crust of Uyuni. Distribution, size and shape of the bioherms are diverse due to various factors, e.g. the nature and morphology of the substrate and the hydrodynamic conditions that prevailed during growth. On larger palaeoterraces, the build‐ups coalesced to form platform‐like carbonate accumulations. Although the morphologies closely resemble those induced by cyanobacteria, they were predominantly constructed by other plant communities, probably dominated by filamentous green algae. Cyanobacterial communities flourished in association with these plants, but they did not contribute significantly to the architecture of the bioherms; they participated to encrust the plant stems and algal bushes or to form thin laminated layers covering the build‐ups. A prominent feature of some bioherms is their composite structure due to repeated algal growth during successive lacustrine episodes that were separated by subaerial exposures with moderate erosional effects. The build‐ups located between 3660 and 3680 m elevation display up to three major parts: (1) a massive inner core formed during an early Minchin highstand, before 40 ka; (2) a large peripheral envelope deposited at about 40 ka (late Minchin) and (3) a thinner outermost crust formed during a late glacial event. Lake level dropped during interlacustrine stages, sometimes leading to desiccation and deposition of salt layers in the deepest parts of the system, i.e. the present‐day salar of Uyuni.
On the modelling of two‐dimensional aeolian dunes
Authors: STAM J. M. T.
Published: June 2006

In this study the modelling of aeolian dunes is treated from the background of the physical processes that form them. The paper concentrates on two‐dimensional modelling, which can be applied to transverse and barchan dunes. The basic assumptions and equations are discussed and three models are presented: (a) a kinematic model which is based on a linear variation of the sediment transport with the topographic height; (b) an analytical model based on a boundary‐layer model of the wind velocity and Bagnold's linearized sediment transport formula; (c) a generalization of this analytical model in a computer program which includes a simple routine for simulating the redistribution of sediment through avalanching. The relative importance of the simplifications is considered and indications are given for the practical applications of these three models in field studies.
Fluvial and lacustrine palaeoenvironments of the Miocene Siwalik Group, Khaur area, northern Pakistan
Authors: ZALEHA MICHAEL J.
Published: June 2006

The Miocene Siwalik Group (upsection, the Chinji, Nagri, and Dhok Pathan Formations) in northern Pakistan records fluvial and lacustrine environments within the Himalayan foreland basin. Thick (5 m to tens of metres) sandstones are composed of channel bar and fill deposits of low‐sinuousity (1·08–1·19), single‐channel meandering and braided rivers which formed large, low‐gradient sediment fans (or ‘megafans’). River flow was dominantly toward the south‐east and likely perennial. Palaeohydraulic reconstructions indicate that Chinji and Dhok Pathan rivers were small relative to Nagri rivers. Bankfull channel depths of Chinji and Dhok Pathan rivers were generally ≤ 15 m, and up to 33 m for Nagri rivers. Widths of channel segments (including single channels of meandering rivers and individual channels around braid bars) were 320–710 m for Chinji rivers, 320–1050 m for Nagri rivers, and 270–340 m for Dhok Pathan rivers. Mean channel bed slopes were on the order of 0·000056–0·00011. Bankfull discharges of channel segments for Chinji and Dhok Pathan rivers were generally 700–800 m3s−1, with full river discharges possibly up to 2400 m3s−1. Bankfull discharges of channel segments for Nagri rivers were generally 1800–3500 m3s−1, with discharges of some larger channel segments possibly on the order of 9000–32 000 m3s−1. Full river discharges of some of the largest Nagri braided rivers may have been twice these values.

Thin (decimetres to a few metres) sandstones represent deposits of levees, crevasse channels and splays, floodplain channels, and large sheet floods. Laminated mudstones represent floodplain and lacustrine deposits. Lakes were both perennial and short‐lived, and likely less than 10 m deep with maximum fetches on the order of a few tens of kilometres. Trace fossils and body fossils within all facies indicate the former existence of terrestrial vertebrates, molluscs (bivalves and gastropods), arthropods (including insects), worms, aquatic fauna (e.g. fish, turtles, crocodiles), trees, bushes, grasses, and aquatic flora. Palaeoenvironmental reconstructions are consistent with previous palaeoclimatic interpretations of monsoonal conditions.
CYTOKININS AND APICAL DOMINANCE IN SOLANUM ANDIGENA: LATERAL SHOOT GROWTH AND ENDOGENOUS CYTOKININ LEVELS IN THE ABSENCE OF ROOTS*
Authors: WANG T. L. , WAREING P. F.
Published: June 2006

Summary

Outgrowth of lateral buds following decapitation of the main apex occurs in shoots of Solanum andigena which have been without roots for periods of up to 30 days prior to decapitation. Axillary shoots of one‐node potato cuttings have been found, similarly, to be capable of growth in the absence of roots. The cytokinin content of de‐rooted shoots has been measured using both the soybean and tobacco callus assays and was found to be maintained after at least 40 days of growth without roots. The results indicate that shoots may be capable of synthesizing cytokinin in the absence of roots. The implications for the involvement of cytokinins in apical dominance are discussed.
HYPOCOTYL SWELLING IN MARROW SEEDLINGS IN RESPONSE TO 2,4‐D TREATMENT
Authors: YOUSIF O. A. F. , FIELDER N. A. , PINFIELD N. J.
Published: June 2006

Summary

Swelling of the hypocotyl base was induced in marrow seedlings by incubation in 2,4‐D concentrations in the range 0·001 to 1·0 p.p.m. This swelling resulted partly from cell enlargement and partly from increased cell division. The radial enlargement of cells was not achieved at the expense of longitudinal cell extension, unlike many instances where swelling has been induced by ethylene. Increased cell division was most pronounced in the interfascicular region of the hypocotyl, indicating increased cambial activity in this area.
ENZYME ACTIVITY AND ELECTROPHORETIC PATTERN OF ISOENZYMES OF AMYLASE, CATALASE AND PEROXIDASE IN PHOTO‐ AND GIBBERELLIN‐INDUCED PLANTS OF IMPATIENS BALSAMINA L. VAR. ROSE
Authors: SAWHNEY S. , SAWHNEY N. , KUMAR S. , Nanda K. K.
Published: June 2006

Summary

Floral buds were induced either by 8 h photoperiods or by the application of GA3 and GA13 in Impatiens balsamina. Total enzyme activity was not directly related to floral morphogenesis although some interesting qualitative correlations existed. Thus, the presence of a new isoenzyme of amylase (RF 0·05) may be related to flower formation since it was present only in the induced plants and not in the vegetative ones, regardless of whether the flowering was caused by inductive photoperiods or by gibberellin treatment. Catalase activity, as well as its isoenzyme forms, could not be detected in the stem and the isoenzyme profile in leaves did not alter with photoperiodic or gibberellin treatment. Treatment with gibberellins induced the synthesis of new isoenzymes of peroxidase but inductive photoperiods did not. The enzyme profiles in relation to photoperiod and gibberellin application are discussed.
Chronic Steroid‐Eluting Lead Performance: A Comparison of Atrial and Ventricular Pacing
Authors: HUA WEI , MOND HARRY G. , STRATHMORE NEIL
Published: June 2006

It is generally believed that atrial pacing leads have higher stimulation thresholds and long‐term complication rates than ventricular leads, and this is one of the factors limiting the use of dual chamber pacing. A study was undertaken to compare atrial and ventricular bipolar tined steroid‐eluting leads in two designs: the Medtronic CapSure SP and the Telectronics Encor Dec. There were 123 pairs of leads: 81 CapSure SP and 42 Encor Dec. Bipolar atrial and ventricular stimulation thresholds, electrograms. and pacing impedance were measured using the Telectronics META DDDR pulse generator immediately postimplantation, and at 1, 3, and 6 months for all leads and at 12, 18, and 24 months for the CapSure SP. The only major lead complication was a 2% atrial lead dislodgment rate. All leads demonstrated low stimulation thresholds, with the CapSure SP leads having lower values than comparable Encor Dec leads. All leads had a mean range of 0.53–0.89 V at all testing periods with P < 0.05 for atrial leads only. There were no differences in electrogram size between manufacturers and no instances of atrial and ventricular undersensing. Pacing impedance was about 100 Ω higher for the Encor Dec leads (P < 0.05, atrial leads only), suggesting that these leads will result in lower pacing energy losses provided the pulse generators are at identical settings. More than 90% of patients could be paced chronically in the atrium and ventricle at 2.5 V, but for chronic 1.6‐V pacing, the CapSure SP leads were superior. In conclusion, atrial and ventricular steroid‐eluting leads of both manufacturers gave excellent stimulation threshold results allowing low energy dual chamber pacing.
Noninvasive Beat‐to‐Beat Arterial Blood Pressure Measurement During VVI and DDD Pacing: Relationship to Symptomatic Benefit from DDD Pacing
Authors: CHANNON K.M. , HARGREAVES M.R. , GARDNER M. , ORMEROD O.J.M.
Published: June 2006

To noninvasively assess the hemodynamic effects of VVI and DDD pacing modes we measured beat‐to‐beat arterial blood pressure during VVI and DDD pacing in 30 patients with complete heart block (CHB), using fingertip photoplethysmography. Of these patients, 15 undertook a double‐blind cross‐over comparison of the symptomatic effects of VVI versus DDD pacing to determine the relationship between blood pressure changes and the occurrence of symptoms suggestive of the pacemaker syndrome during ventricular pacing. Mean (SD) systolic blood pressure was 11.7 (15.4) mmHg lower during VVI pacing compared to DDD pacing (P < 0.0005). The mean (SD) beat‐to‐beat variability of systolic blood pressure was 5.20 (2.87%) in VVI mode versus 2.12 (1.07%) in DDD mode (P < 0.0000005). In comparison with DDD pacing, the excess of symptoms experienced by patients during VVI pacing did not correlate with the change in mean systolic blood pressure, but was significantly correlated with the increase in beat‐to‐beat systolic blood pressure variation during VVI pacing (r = 0.58, P = 0.024). We conclude that noninvasive measurement of fingertip arterial beat‐to‐beat blood pressure is a rapid and simple method of assessing the hemodynamic effect of VVI pacing. Beat‐to‐beat blood pressure variability was related to symptomatic intolerance of VVI pacing and may have potential utility as an aid to diagnosis or as a predictor of pacemaker syndrome.
Band‐Limited Morphometric Analysis of the Intracardiac Signal: Implications for Antitachycardia Devices
Authors: MORRIS MILTON M. , JENKINS JANICE M. , di CARLO LORENZO A.
Published: June 2006

Inappropriate electrical therapy and power efficiency play a major role in algorithm implementation for antitachycardia devices (ATD) that capture, store, and analyze the patient electrogram as an adjunct to rate determination. Morphologically based algorithms have been demonstrated to improve specificity, thereby decreasing occurrences of inappropriate electrical therapy. However, morphologically based algorithms are power demanding. Optimization of power efficiency can be achieved by eliminating unnecessary algorithmic computation, but must not compromise the effectiveness of algorithms, which perform direct analysis on raw signals. Significant reductions can be achieved by reduced sampling rates, which allow for increased overall ATD efficiency via concomitant decreases in computation and data storage. This investigation determined the upper and lower bounds for filter cutoff frequency beyond which detection precision by an established morphometric method for arrhythmia classification, correlation waveform analysis (CWA), was unfavorable. Four measurement statistics were used. In ten patients with inducible VT and VF, all bipolar intraventricular electrograms were classified correctly with a minimum passband of 10–50 Hz using any of the four measurement statistics. There was ± 80% correct classification using all four measurement statistics with passbands having low frequency cutoffs ± 15 Hz and high frequency cutoffs ± 50 Hz. Correct classification of ± 90% of unipolar electrograms during NSR, VT, and VF occurred using all four measurement statistics with a passband of 1–50 Hz. There was ± 80% correct classification with passbands 1, 10, 15, or 20–500 Hz and 10–50 Hz. The classification of NSR, VT, and VF was most accurate on an intrapatient basis. Accuracy decreased using an interpatient rhythm classification. Optimum filter settings of 1–50 Hz and 10–50 Hz were determined for unipolar and bipolar electrograms, respectively. Sampling data at 120 Hz was found to be sufficient. Bipolar electrode configuration statistically outperfomed unipolar data. In conclusion, morphometric analysis of bipolar and unipolar intraventricular electrograms appears to be achievable using band limited data and reduced sampling rates.
Influence of Duration of Rapid Ventricular Pacing on Ventricular Refractoriness in the Presence of Propafenone and Lidocaine
Authors: STARK ULRIKE , STARK GERHARD , KASPER KARIN , SCHWARZL INGRID , DECRINIS MARTIN , PILGER ERNST , TRITTHART HELMUT A.
Published: June 2006

Propafenone and lidocaine have a rate dependent negative dromotropic effect on intraventricular conduction. We investigated the use dependent actions of propafenone and lidocaine on intraventricular conduction in isolated guinea pig hearts perfused by the method of Langendorff. Of primary interest was how the number of stimuli of the conditioning train (S1) might influence the ventricular effective refractory period (VERP) when refractoriness is assessed at a high pacing rate. Propafenone (0.3 μM) and lidocaine (50 μM) caused a comparable prolongation of the intraventricular conduction time during sinus rhythm. During ventricular pacing in the presence of propafenone an abrupt decrease of the pacing cycle length (220 to 120 ms) resulted in an initial peak of rate dependent prolongation of the QRS interval that subsequently decreased to a stable steady‐state level. Lidocaine also induced a rate dependent increase of the intraventricular conduction time up to a steadystate level. The time constant, characterizing the changes of the intraventricular conduction time after shortening the ventricular pacing cycle length from 220 to 120 ms was significantly (P < 0.01) longer in the presence of propafenone (τ= 31 ± 4 beats; mean ± SEM; n = 11) than for lidocaine (τ= 3 ± 1; n = 10). Both drugs caused the greatest increase of tbe VERP when the number of conditioning stimuli (S1, interstimulus interval = 120 ms) was in the range of their respective time constant. However, when the number of conditioning stimuli was further increased, VERP progressively diminished. These effects may be explained by a shortening of the action potential during high rates that results in a decreased binding of propafenone to Na+ channels and by the direct shortening of repolarization period by lidocaine (Class IB drug).
Determinants of Nonthoracotomy Biphasic Defihrillation
Authors: HORTON RODNEY P. , CANBY ROBERT C. , ROMÁN CARLOS A. , HULL MICHAEL L. , KAYE SUSAN A. , JESSEN MICHAEL E. , PAGE RICHARD L.
Published: June 2006

The clinical variables affecting DFT for ICD systems are not completely determined, especially with regard to biphasic shocking devices. To distinguish which factors correlate with DFT, we examined data from patients who were enrolled in the Ventak P2/Endotak protocol. A total of 284 patients were enrolled in the study. Two patients had a DFT > 25 J and did not receive the device; 154 did not undergo stepdown to failure DFT testing. The remaining 128 patients had formal DFT testing and were suitable for analysis. Variables available for analysis included age, body surface area (BSA), LVEF, gender, lead configuration, primary arrhythmia, primary cardiac disease, and use of cardioactive medication. Data were evaluated using regression analysis, fitting DFT (range, 1–25 J, mean 11 ± 5 J) as a function of each variable. As a univariate predictor, BSA was found to be significant in predicting DFT, but accounted for only 9% of the total variation on the DFT (P < 0.01, r = 0.3). This study suggests that DFT using a biphasic shocking waveform is modestly influenced by the BSA of the patient. Other specific factors, including LVEF, do not predict DFT.
Mechanisms in Adrenergic Dependent Onset of Torsades de Pointes
Authors: ABILDSKOV J.A. , LUX ROBERT L.
Published: June 2006

Pause dependent onset of torsades de pointes is characteristic in acquired long QT syndromes, and the probable mechanism is reentry facilitated by increased disparity of refractoriness following a long cycle. Adrenergic dependent onset is usual in familial long QT syndromes, and the mechanism is uncertain. In this study with a computer simulation of torsades de pointes, possible mechanisms of adrenergic dependent onset have been identified. Decreased refractory periods facilitated the initiation of torsades de pointes by permitting earlier premature excitation and allowing reentry in the presence of the shorter refractory period that had been further shortened by the earlier excitation. In addition, accelerating rate resulted in responses occurring in the presence of refractory periods set by the prior response so each response was premature with respect to the preceding one. The difference between cycle lengths and refractory period decreased with increasing rate leading to the functional block required for initiation of simulated torsades de pointes. Findings define possible mechanisms in which the adrenergic effects of reduced refractory period duration and increased rate may lead to the initiation of torsades de pointes.
Spurious Detection of Ventricular Fibrillation By a Transvenous Implantable Cardioverter Defibrillator During Percutaneous Transluminal Coronary Angioplasty
Authors: RIZK ANTOINE B. , CHANDLER JOHN P. , SCHOENFELD MARK H. , MARIEB MARK A.
Published: June 2006

This case describes another example of inappropriate implantable defibrillator shock. We also show that this phenomenon resulted from electromagnetic current traveling down a coronary wire during coronary angioplasty.
Effect of Shock Timing on Defibrillation Success
Authors: HSU WILLIAM , LIN YAYUN , HEIL JOHN E. , JONES JANICE , LANG DOUGLAS J.
Published: June 2006

The goal of this study was to determine whether delivering transvenous defibrillation shocks, coordinated with the up/down‐slope VF waveform patterns in the shocking lead, would improve the probability of successful defibrillation. Anesthetized swine (32–38 kg, n = 8) were implanted with an RV → SVC + SQArray transvenous system to measure VF waveform patterns and to deliver shocks. The shocks were generated by a Cardiac Pacemakers Inc. biphasic waveform generator. Energy required for 50% success probability (E50) was determined using the multishock up‐down protocol. VF was repeatedly induced and defibrillation shocks at E50 were given after 10 seconds. The defibrillation outcome, delivered energy (Ed), peak voltage (V), peak current (I), system impedance (Z) and VF waveform pattern at the time of shock were recorded and measured. Out of a total of 685 shocks, 324 (47%) succeeded and 361 (53%) failed. The Ed, V, I, and Z were similar for the two defibrillation outcome groups (success or failure). VF patterns were classified as high or low amplitude at the time of the shock based on the peak‐to‐peak amplitude of signals recorded between shocking electrodes. Shocks that coincided with high amplitude VF patterns were further divided into shocks that occurred on the up‐slope or on the down‐slope. The probability of success when the E50 shocks were coincident with high or low amplitude fibrillation did not differ significantly (Student's t‐test: 46% vs 48%, P = NS). However, during high amplitude fibrillation, shocks delivered on the up‐slope were significantly more successful than those delivered on the down‐slope (Chi‐square: 67% vs 39%; P < 0.001). These results suggest that delivering defibrillation shocks during the up‐slope of the high amplitude signal in the shocking lead may improve the probability of successful defibrillation of ICDs.
Temporary Transvenous Cardioversion and Defibrillation: A New Method for Practical Tachyarrhythmia Management
Authors: LUCERI RICHARD M. , ACCORTI PETER R.
Published: June 2006

The use of transvenous ICD systems and the recent advances in atrial defibrillation techniques have heightened interest in internal defibrillation. However, most shocks for induced or spontaneous arrhythmias in patients without devices are still delivered transthoracically using high energy. We describe the history of temporary internal defibrillation techniques and report the initial clinical results with a custom built disposable catheter for internal cardioversion and defibrillation. This prototype successfully converted more than 95% of 109 episodes of VT or VF in 28 patients, with biphasic energies ≤ 20 J. A newer disposable catheter, using 40‐wire Matrix technology as the defibrillating electrode, has design features that provide high surface area, low impedance, and low current density when compared to other leads used for similar purposes. Temporary internal cardioversion‐defibrillation of induced and spontaneous arrhythmias using such catheter designs is likely to be widely applicable to patients undergoing electrophysiology procedures and to those in critical care units prone to tachyarrhythmias.