Common Traces Research Articles

Biogenic structures of organics‐poor siliciclastic sediments: Examples from Paleogene variegated shales, Polish Carpathians

The chiefly red and green (variegated), muddy to clayey sediments of the Polish Carpathian flysch display low diversity assemblages of macroscopic biogenic sedimentary structures (trace fossils). Plano‐lites and Chondrites are the most common distinctive traces in these sediments. A restricted food supply for tracemakers and low shear strength of sediments inhabited by them are suggested as the chief factors responsible for the low diversity of biogenic structures. Because of temporal fluctuations in rates of sediment accretion and/or changes in food supply some bioturbation occurred cyclically in what we are now the variegated shales.

Androecium and floral nectaries ofHarungana madagascariensis (Clusiaceae)

The mature flower ofHarungana madagascariensis (Choisy)Poir. has an androecium of five antipetalous fascicles, consisting of four stamens each. The stamen fascicles alternate with five indented nectary scales. A SEM-study of the floral development, as well as a study of the floral anatomy was carried out to understand whether the nectariferous scales represent staminodia or are receptacular in nature and consequently whether or not the androecium ofHarungana, and theClusiaceae in general, is originally diplostemonous. The five petals originate by the splitting of petal-stamen complexes. Next the upper part of each complex differentiates basipetally in four stamens. The stamens remain fascicled and are lifted on a long stalk at maturity. Five carpel primordia are initiated united in a low ringwall. The five nectary scales appear after carpel inception and develop an external morphology reminiscent of anthers. The floral anatomy reveals an independent origin of sepal median traces and common sepal lateral traces, free petal traces, stamen fascicle traces and alternating vascular tissue which supplies the nectaries. The petal-stamen complexes are the result of a retardation in petal inception, linked with the absorption of petal tissue into the stamen primordia. The development of the stamen fascicles is discussed; it is suggested that they are of a secondary nature and do not appear as a reduction from a multistaminate androecium. The external morphology and vascular anatomy of the scales speaks in favour of a staminodial nature. The comparison with some other species of theClusiaceae gives evidence of a diplostemonous ancestry of the androecium.

A diverse ichnofauna from silurian flysch of the aberystwyth grits formation, Wales

AbstractThe most extensive ichnofauna yet recorded from a deep water Lower Palaeozoic sequence occurs within the distal turbidites of the Lower Silurian Aberystwyth Grits Formation of Central Wales.The strata contain an abundant assemblage comprising 25 ichnogenera: Asteriacites, Bergaueria, Chondrites, Cochlichnus, Cosmorhaphe, Glockerichnus, Gordia, Helicolithus, Helminthopsis, Helminthoida, Hormosiroidea, Lorenzinia, Megagrapton, Monomorphichnus, Neonereites, Nereites, Palaeophycus, Paleodictyon, Planolites, Protopaleodictyon, Spirorhaphe, Spirophycus, Squamodictyon, Subphyllochorda, Taphrhelminthopsis; 36 ichnospecies are described, three of which (Asteriacites aberensis, Helminthopsis regularis, Cosmorhaphe elongata) are new.The inorganic sedimentary structures and trace fossils of some 418 sandstone beds were examined in detail; 16 per cent of the beds commence with Divisions A or B and 84 per cent with Division C of the turbidite sequence. This indicates a relatively distal environment, mainly receiving low velocity turbidity currents, and favouring trace fossil preservation. The most common traces were Helminthopsis, Paleodictyon, and Squamodictyon which were found on 46 per cent, 34 per cent, and 19 per cent of the beds examined.Data from this, and other recently described sequences, confirms that there was a gradual increase in trace fossil diversity in the deep oceans throughout the Lower Palaeozoic, in contrast to the situation in shallow water shelf seas where a peak was reached as early as the Lower Cambrian.

A case history of a cost effective 3D seismic survey over the Perth Basin, Western Australia

As part of an industry funded research project into the application of the technique of LOFOLD3D land seismic surveying, a four fold three dimensional seismic survey was performed in the Perth Basin at Moora, Western Australia in July 1987. The volume covered an area of four kilometres by just under two kilometres, producing a total of 23,000 common midpoint traces. The objective was to collect and process the data in such a manner that a three dimensional structural interpretation would result, which would be the same as that resulting from a conventional three dimensional survey. A cost comparison indicates that a commercial LOFOLD3D survey would reduce the cost of performing a land 3D survey to an estimated 20% of the full fold equivalent, and the technique therefore offers potential for substantial savings if it is adopted on a commercial basis.

Case Study of Stratigraphic Interpretation Using Shear and Compressional Seismic Data: ABSTRACT

Compressional and horizontal shear wave data recorded at the surface are used to detect lateral changes in the physical properties of a clastic unit. Shear and compressional wave transit times across the formation were measured from CDP-stacked sections derived from data collected along collocated shear and compressional seismic lines. At each surface position, the ratio of the shear to compressional transit times is formed from common CDP traces. It is shown how lateral changes in the transit time ratio primarily correlate with variations in the sand-shale ratio in the zone of interest. The horizon selected for this case study was the Morrow Formation, which produces gas from sand-channel bodies in the Empire-Abo field, New Mexico. As this field has been extensively drilled, a detailed cross section of the producing horizon was mapped along a seismic line which crossed two wells. In well A, the nonproductive Morrow cycles 1, 2, and 3 are principally shale and nonpermeable shaly sand facies. In well B, this same interval contains as much as 160 ft (49 m) of permeable gas-productive sand which has a calculated absolute open flow of 61 MMCFGD. Shear wave and compressional wave Vibroseis surveys were conducted along this seismic profile using data acquisition parameters designed to produce comparable signal-to-noise ratios and resolution in the field data. Similar ca e was taken during data processing to insure that the differences and similarities observed in the final CDP sections were due to variations in geology and not simply artifacts of the particular set of processing parameters that were employed. Along the seismic profile both compressional and shear wave interval transit times across the Morrow Formation showed a statistically significant decrease in going from the nonproductive to productive thicknesses of sand. There is, however, a proportionately greater decrease in the shear wave transit time than in the compressional transit time which results in an overall decrease in the shear-to-compressional transit time ratio. There are two changes in the physical properties of the Morrow which could account for the observed transit time ratio variations. First, the replacement of pore fluid in the sand by a small amount of gas would cause a decrease in the transit time ratio in going from well to well B. However, the compressional wave transit time should increase drastically in this case, while the shear wave transit time would decrease slightly. This behavior was not observed. A second possible explanation is that the decrease in transit time ratio was due to an increase in the sand-shale ratio between the two wells. Because of the marked differences in the shear-to-compressional transit times for pure shale (2.4) and pure sandstone (1.7), any increase in the sand-shale ratio should be accompanied by a decrease in the formation transit time ratio. Furthermore, it would be anticipated that a change in the sand-shale ratio would influence the shear wave transit time more significantly End_Page 510------------------------------ than the compressional transit time--a fact which is consistent with the observations. We thus conclude that shear-to-compressional transit time ratio measurements provide a method for estimating variations in the sand-shale ratio of a formation. End_of_Article - Last_Page 511------------

COMMON OFFSET PLANE MIGRATION (COPMIG)*

AbstractThe quality of results of migration before stack is sensitive to inaccuracies in the velocity field applied. This does not hold if only traces of similar sources‐receiver distances (common offset traces) enter the migration process. In this case, velocity deviations generate minor shifts in travel times of migrated interfaces but no deterioration in quality. These time shifts are proportional to both the velocity error and the square of the source‐receiver distance.The above observations suggest the following migration scheme: migrate separately the traces of the various common offset planes or groups of neighbouring common offset planes; for every common midpoint plane and as a function of travel‐time perform a residual NMO search to find trajectories t) =t)o+px)2 of maximum coherency along which migrated events are aligned; correct for residual NMO and stack the migration results obtained in the various common offset planes to obtain the final migration result.This process not only takes care of inaccurate migration velocities but also corrects partly for effects of refraction.It is shown by means of an example that good migration results are generated even with a considerably deviating velocity field.

Studies in the Floral Anatomy of Claytonia (Portulacaceae)

Claytonia virginica has a regular flower with two sepals, five petals with an equal number of stamens in positions opposite the petals and a many-seeded tricarpellate gynoecium with basal placentation. The flower has been interpreted as uniseriate, the putative sepals as bracts and the corolla as modified calyx lobes. Anatomical and developmental studies were undertaken to find evidence for the existence of vestigial or rudimentary parts whose existence would illuminate the true nature of the flower. Vascular and epidermal anatomy of sepals are both similar to that of leaves. Corolla and androecium develop basipetally and petals and stamens share common vascular traces in the lower part of the receptacle. Thus, in terms of both anatomy and development, evidence supports the conclusion that the perianth is essentially biseriate. Vestigial or rudimentary parts are not present which would alter the manifest design of the mature flower.

STUDIES IN THE FLORAL ANATOMY OF CLAYTONIA (PORTULACACEAE)

Claytonia virginica has a regular flower with two sepals, five petals with an equal number of stamens in positions opposite the petals and a many‐seeded tricarpellate gynoecium with basal placentation. The flower has been interpreted as uniseriate, the putative sepals as bracts and the corolla as modified calyx lobes. Anatomical and developmental studies were undertaken to find evidence for the existence of vestigial or rudimentary parts whose existence would illuminate the true nature of the flower. Vascular and epidermal anatomy of sepals are both similar to that of leaves. Corolla and androecium develop basipetally and petals and stamens share common vascular traces in the lower part of the receptacle. Thus, in terms of both anatomy and development, evidence supports the conclusion that the perianth is essentially biseriate. Vestigial or rudimentary parts are not present which would alter the manifest design of the mature flower.

Storm-generated graded beds and debris flow deposits withOphiomorphain a shallow offshore Oligocene sequence at Nelson, South Island, New Zealand

Abstract An Oligocene (Whaingaroan) succession of sandstones with rare perigenic breccias and fossiliferous detrital conglomerates is well exposed for 1 km along strike and for a stratigraphic thickness of 140 m on a wave-cut platform at Magazine Point, Nelson. Regional tectonic and stratigraphic relationships are uncertain. All lithologies are lensoidal; virtually no bed extends for more than 200 m. Planar-laminated to hummocky cross-stratified, normally graded, mud-free sandstones 10-80 cm thick alternate with bioturbated muddy finer sandstones and sandy mudstones 10-35 cm thick. Ophiomorpha nodosa is the only common trace within the clean sandstones; it is locally abundant in the lower 60 m of the succession and exceedingly rare in the upper 80 m. Thallassinoides, formed by the same progenitor as Ophiomorpha, occurs with more common other indeterminate traces within the muddy units. Benthic microfauna from the muddy intervals indicate “shelf” settings ranging from inner, at the base of the sequence, to...

Les effets des liaisons associatives sur le temps de dénomination verbale

Summary In the experiments reported, Ss were asked to name as quickly as possible a series of objects presented on slides. There were 50 different objects chosen so that their names allowed the constitution of 25 pairs of highly associated words. The Ss of Group I had to retrieve the second word of each pair immediately after the first one, whilst in Group II (control condition) the objects were randomly presented. Pattern of responses indicates that retrieval time for a particular word is strongly shortened when it is associated with the word named at the preceding item. To the Ss of Group III the slides were randomly presented as for Group II, except for 5 pairs which were kept togelher and inserted at carions positions in the series. As regards to the names of objects occurring in the 2d positions of these 5 pairs, time reduction is very significant for 3 of them, although smaller than in Group I. Thus, retrieval time is shortened even when the cooccurrence of the associated items is unexpected. This suggests that the effect may not be entirely attributable to response anticipation, but at leasl partially to the intersection between successive retrieval processes, made possible by the recall of some common memory traces.

Imagens periféricas: os Estudos Culturais e o Terceiro Cinema

Este artigo pretende apresentar algumas notas sobre as possibilidades de conexão entre o campo dos Estudos Culturais e o Cinema contemporâneo. A intenção é tanto verificar como a própria configuração do cinema (especialmente aqueles filmes produzidos na periferia mundial ou aquilo que ainda pode ser chamado de Terceiro Cinema) demanda o olhar interdisciplinar que caracteriza a empresa metodológica dos Estudos Culturais, como também encontrar em alguns traços comuns que definem o cinema periférico novos desafios e inquietações para a teoria da cultura contemporânea. Para efetivar essa dupla operação, começaremos por apresentar muito panorâmica e resumidamente o surgimento dos Estudos Culturais e as transformações ocorridas ao longo dos últimos cinqüenta anos na área, associando posteriormente essa trajetória à consolidação progressiva do circuito cinematográfico das margens do capitalismo

AUTOMATED STATIC CORRECTIONS*

AbstractThe widespread use of common depth point techniques has emphasized the need for accurate static corrections. Manual interpretation methods can give excellent results, but a computer technique is desirable because of the great volumn of data recorded in common depth point shooting. The redundancy inherent in common depth point data may be used to compute a statistical estimate of the static corrections. The corrections are assumed to be time‐invarient, surface‐consistent, and independent of frequency. Surface consistency implies that all traces from a particular shot will receive the same shot static correction and all traces from a particular receiver position will receive the same receiver correction.Time shifts are computed for all input traces using crosscorrelation functions between common depth point traces. The time shift for each trace is composed of a shot static, a receiver static, residual normal moveout if present, and noise. Estimates of the shot and receiver static corrections are obtained by averaging different sets of the measured time shifts. Time shifts which are greatly in error are detected and removed from the computations.The method is useful for data which has a moderate to good signal to noise ratio. Residual normal moveout should be corrected before estimating the statics. The program estimates the statics for correctly stacking common depth point traces but it is not sensitive to constant or very slowly changing static errors.

A NEW DATA‐PROCESSING TECHNIQUE FOR MULTIPLE ATTENUATION EXPLOITING DIFFERENTIAL NORMAL MOVEOUT

A new data‐processing technique is presented which utilizes optimum multichannel digital filtering in conjunction with common subsurface horizontal stacking for the efficient rejection of multiple reflections. The method exploits the differential normal moveout between primary and multiple reflections that results from an increase in average velocity with depth. Triple subsurface coverage is obtained in the field; the common subsurface traces are individually prefiltered with different filters and stacked. The digital filters are designed on the least‐mean‐square‐error criteria to preserve primaries (signal) in the presence of multiples (noise) of predictable normal moveout, and random noise. The method achieves wide‐band separation of primary and multiple energy with only a three‐point stack; it can work effectively with small normal moveout differences eliminating the need for long offsets and the attendant signal degradation due to wide‐angle reflections; it does not require equal multiple moveout on the triplet of traces stacked; and finally the method is not sensitive to small errors in statics or predicted normal moveout. The technique is illustrated in terms of synthetic examples selected to encompass realistic field situations, and the parameter specification necessary for the multichannel filter design.