50-m Section Research Articles

Predation of the social wasp Polybia occidentalis (Hymenoptera:Vespidae) by the water scorpion Ranatra obscura (Hemiptera:Nepidae)

The genus Ranatra (Nepomorpha) is a formidable predator with significant importance in trophic webs, playing a crucial role in regulating aquatic and semi-aquatic communities through population control. However, studies on the diet of Ranatra species remain scarce, particularly in poorly understood Amazonian regions such as Marajó Island. This lack of data hampers our understanding of species behavior and the development of targeted conservation actions needed to maintain the ecological balance of complex networks, especially in areas under anthropogenic threat. Our study was conducted in the municipality of Salvaterra, within the Marajó Island archipelago, where we observed predation of the predatory species Polybia occidentalis (Olivier, 1791) by Ranatra obscura Montandon, 1907. We captured the insects using a sieve in the water column of a stream, which had been previously divided into three 50-m sections. Subsequently, we monitored Ranatra's behavior during the predation event, revealing its predatory aggressiveness and hunting ability—traits often underestimated due to its piercing-sucking mouthparts. This new record enhances our understanding of the diet and natural history of Nepomorpha and Ranatra, and highlights the importance of allochthonous material for predator species, revealing their role in terrestrial and semi-aquatic ecological networks.

Pacing Behavior Development in Adolescent Swimmers: A Large-Scale Longitudinal Data Analysis.

This study aimed to use a large-scale longitudinal design to investigate the development of the distribution of effort (e.g., pacing) in adolescent swimmers, specifically disentangling the effects of age and experience and differentiating between performance levels in adulthood. Season best times and 50-m split times of 100- and 200-m freestyle swimmers from five continents were gathered between 2000 and 2021. Included swimmers competed in a minimum of three seasons between 12 and 24 yr old (5.3 ± 1.9 seasons) and were categorized by performance level in adulthood (elite, sub-elite, high-competitive; 100-m: n = 3498 (47% female); 200-m: n = 2230 (56% female)). Multilevel models in which repeated measures (level 1) were nested within individual swimmers (level 2) were estimated to test the effects of age, race experience, and adult performance level on the percentage of total race time spent in each 50-m section ( P < 0.05). In the 100-m, male swimmers develop a relatively faster first 50-m when becoming older. This behavior also distinguishes elite from high-competitive swimmers. No such effects were found for female swimmers. Conversely, more experienced male and female swimmers exhibit a slower initial 50-m. With age and race experience, swimmers develop a more even velocity distribution in the 200-m. Adolescent swimmers reaching the elite level adopt a more even behavior compared with high-competitive. This differentiation occurs at a younger age in female (>13 yr) compared with male (>16 yr) swimmers. Pacing behavior development throughout adolescence is driven by age-related factors besides race experience. Swimmers attaining a higher performance level during adulthood exhibit a pacing behavior that better fits the task demands during adolescence. Monitoring and individually optimizing the pacing behavior of young swimmers is an important step toward elite performance.

Replicate analyses of OSPAR beach litter data.

Replicate surveys of beach litter have seldom been performed in the past. In this study, replicate surveys of beach litter were conducted on the beach north of Hörnum (Sylt, Germany), from 2015 to 2019, applying a slightly modified OSPAR protocol of beach litter monitoring. Descriptive statistics and power analyses were calculated on data resulting from these replicate surveys, to find out whether the scatter of replicate beach litter data decreases and the statistical power increases with increasing numbers of replicate surveys. From 2015 to 2019, mean total abundances, given as numbers of litter items, ranged from 19 to 185 litter items on a 50m section of beach. With increasing numbers of replicate surveys, the scatter given by the coefficient of variation (CV) significantly increased up to 113%. Statistical power considerably increased with increasing numbers of replicate beach sections, e.g. from 82% (two beach sections) to nearly 100% (five beach sections) for a given reduction of beach litter of 50%. Based on these results from a morphologically straight coastline, the use of replicate surveys would be sensible for the future monitoring of beach litter. However, there is high need for studies, which consider coastlines with varying morphology.

Geochemical characteristics of carbonaceous chalk near the Cretaceous/Paleogene transition, central Jordan: Strong metal enrichment of redox-sensitive and biophile elements from remineralized calcitic plankton

Carbonaceous calcitic chalk from a 50-m stratigraphic section of the Maastrichtian-Danian Muwaqqar Chalk Marl (MCM) Formation, Jordan, has elevated concentrations of biophile and/or redox-sensitive trace metals (Mo, Ni, V, U, Cr, Cd, Ag, Se, and P) which indicate enhanced paleo-bioproductivity, biodegradation and remineralization under reducing conditions. Very low concentrations in Mn and Ba suggest a relatively open system for components mobile under reducing conditions. The last 800,000 years to the K/Pg boundary are not exposed in Jordan, but the stratigraphic 20-m-interval below and above the hiatus of the K/Pg transition (n = 8) with 2.6 ± 1.8 wt% organic C is particularly metal-enriched with average bulk-rock contents of 132 ppm Mo, 177 ppm Ni, 363 ppm V, 576 ppm Zn, 39 ppm Se, 1.4 ppm Ag, 106 ppm Cd, 474 ppm Cr. These concentrations are dominantly of authigenous origin, when normalized to PAAS, i.e. 100 % Mo, 100% Ag, 100% Cd, 96% Cr, 95% Ni, 95% Zn, 80% V authigenous, and testify to ≥90% of biodegradation of planktonic debris by anaerobic bacterial activity at or near the seafloor. The depositional environment is euxinic, and Mo/TOC ratios from <10 to around 100 (as well as analogous trends for Ni/TOC and Cr/TOC) indicate an evolution from initially restricted hydrographic conditions to unrestricted open-sea conditions towards the K/Pg transition. The common paleoenvironmental proxies for black shale such as V, V/(V + Ni) and V/Cr ratios, indicate oxic depositional conditions for the studied chalk, which are misleading because the low illite content in the calcareous ooze does not allow sufficient retention of V in this chalk. REE patterns identify a seawater and a clastic component to about equal amounts on average, with authigenous ΣREE of 23 ± 19 ppm (n = 20). The negative Ce anomaly of the authigenous component is −0.6 ± 0.2 (log PAAS normalized), compared to recent seawater with −1.1. The geochemical composition of the carbonaceous calcitic chalk sequence is an expression of the general Cretaceous-Paleogene upwelling regime on the southern passive margin of the Neo-Tethys Ocean in the Cretaceous-Palaeogene (K-Pg) greenhouse environment.

Local and landscape drivers of butterfly richness and abundance in a human-dominated area

In Europe, butterflies have declined over the last decades mainly because of the increasing urbanization and the agricultural intensification occurred in lowlands areas. Drivers of butterfly decline were identified in changes of both local scale habitat characteristics and landscape-scale land-use coverage. Thus, to counteract the negative trend of butterfly populations, management actions that simultaneously have an effect on local and landscape scale environments are needed.The present research was performed in northern Italy, in a human-dominated area of about 170 km2. From April to September 2014 and 2015, we surveyed butterflies in 494 50-m sections, grouped into 44 line transects. First, using a multi-scale GAMM, we analysed the simultaneous effect of local (nectar index, crop type, presence of woodlands and hedgerows and degree of shelter) and landscape (fractional cover in 500-m buffer of arable lands, meadows, woodlands and artificial surfaces) variables on butterfly richness and abundance. We evaluated the contribution of local and landscape variables by a variation partitioning approach. Second, we performed a GAMM to investigate the effect of specific management practices adopted in meadows, hedgerows and field margins on butterfly communities. Our results showed that the evaluation of the effect of local scale characteristics on butterfly communities definitely cannot disregard the landscape context. We thus suggest maintaining urban and agricultural areas alternated by a mosaic of nectar-rich land-covers, such as meadows and alfalfa, forest patches and hedgerows.Our study also allowed to formulate management guidelines of specific habitats. Accordingly, meadows should be managed by reducing the number of cuts, while wide herbaceous margins, characterised by a high grass layer rich in dicots, should be maintained in arable lands. To avoid a barrier effect and to guarantee the presence of a well-developed shrub layer, which provides high nectar resources, it is also necessary to avoid an excessive growth in hedgerows height. Results evidence that the adoption of these management guidelines and of a proper landscape planning strategy, can lead to play an important role in butterfly conservation even within human dominated areas.

Multi-temporal assessment of ground cover restoration and soil erosion risks along petroleum and gas pipelines in Azerbaijan using GIS and remote sensing

The main goal of this research was to perform vegetation cover restoration and soil erosion risk assessment based on multi-temporal NDVI monitoring and deterministic USLE erosion prediction model along Baku–Tbilisi–Ceyhan Oil and South Caucasus Gas pipelines. The categorization of NDVI derived from IKONOS 2007 and PLEIADES 2012 high-resolution multispectral satellite images into the bare lands, sparse and dense vegetation revealed the positive vegetation cover restoration along oil and gas pipelines. The change detection analysis of NDVIs showed that the class of ‘Significant Increase in Vegetation’ was 5.40 km2 within the croplands. However, the classes of ‘Significant Decrease in Vegetation’ and ‘No Significant Change in Vegetation’ were observed to be 2.56 and 5.10 km2 within croplands, correspondingly. This decrease can be explained by the encumbrances applied for the partial restrictions of land-use activities along oil and gas pipelines to mitigate potential risks to pipelines and by the slow natural vegetation restoration. NDVI analysis for 50-m section polygons of pipeline corridor and contiguous areas showed that 7072 polygons had no significant NDVI difference in 2012, whereas in 2007 it was 4383. USLE model run with cover-management factor derived from PLEIADES NDVI 2012 showed higher number of polygons with predicted erosion class of ‘0–10 ton/ha’ which is acceptable and not critical to pipelines. For higher erosion classes more than ‘0–10 ton/ha’, USLE model run with IKONOS NDVI 2007 revealed higher number of polygons. USLE model run predicted 37 % of total number of erosion occurrences identified during 2005–2014.

Road Section Length Variability on Pavement Management Decision Making for Ontario, Canada, Highway Systems

In a pavement management system, the performance evaluation indexes and their prediction methods are important aspects for assessing the overall pavement condition. Therefore, an accurate location reference system is necessary for managing pavement evaluations and maintenance. In this regard, the length of the pavement section selected for evaluation may also have significant impact on the assessment, irrespective of the type of performance indexes. This study investigated the variability in pavement performance evaluation and maintenance decisions attributed to change in pavement section lengths. It considered rut depth, pavement condition index, and international roughness index as performance indexes. Data from 27 road segments of Ontario, Canada, with a total length of 172.5 km were selected for empirical investigation. The distributions of these indexes were compared by grouping various segment lengths ranging from 50, 500, 1,000, and 10,000 m. The variations of performance assessment attributable to changing section length were investigated on the basis of their impacts on maintenance decisions. A Monte Carlo simulation was carried out by varying section lengths to estimate probabilities of the necessity of maintenance works. Results of this empirical investigation revealed that most of the longer sections were evaluated with low rut depth and the shorter sections were evaluated with higher rut depth. Monte Carlo simulation also revealed that 50-m sections have a higher probability of maintenance requirement than 500-m sections. Although the results are related to the Ontario highway system, these methods can also be applied elsewhere with similar conditions.

강관압입후 슬롯 홀을 갖는 비개착 터널공법의 현장적용에 관한 연구

In the study, a new non-open cut tunnel steel pipe method using slot hole has been developed. As is overcomes shortcomings of conventional methods, it is applied to the field. The main concept of the new method is the steel pipe pumping system with slot holes which, by means of formation slot holes between each steel pipe, applied to the magnitude of the relaxed earth pressure caused by excavation to the ground to prevent ground displacement. The stability of the support members and effect of displacement control of the new method were verified through several ways as numerical analysis and site test. The new method was applied to the construction of a 11.5m wide, 7.4m high and 50m long section that passes side subway and large buildings in inner city. By applying the new method, tunnel construction was successfully completed in 6 months. It decreases the construction period to 30% compared to that of conventional methods, and ground was almost negligible.

Assessment of tsunami damage on the .coastal vegetation in five selected districts in the coastal zone of Sri Lanka, after one and half years of tsunami

Assessment of tsunami damage on the .coastal vegetation in five selected districts in the coastal zone of Sri Lanka, after one and half years of tsunami

Differences in 200-m Sprint Running Performance Between Outdoor and Indoor Venues

Athletes' times in 200-m indoor races are greater than in outdoor races. The purpose of this study was to determine which 50-m sections were slower indoors than outdoors in 200-m sprint events and by how much. Using 2-dimensional photogrammetric techniques, a 50-m split-time analysis was made of the performance of 17 men and 16 women, all well-trained athletes, at 4 national competitions held over 5 years. The time taken to run the 0- to 50-m section was longer indoors than outdoors in women (6.89 ± 0.12 vs. 6.75 ± 0.04 seconds; p < 0.05) and in men (6.18 ± 0.10 vs. 6.08 ± 0.09 seconds; p < 0.05). Similarly, both women and men took more time to run the 100- to 150-m section indoors (6.03 ± 0.15 vs. 5.84 ± 0.06 seconds; p < 0.01, respectively) than outdoors (5.26 ± 0.15 vs. 5.06 ± 0.07 seconds; p < 0.01, respectively). Both sections indoors were run mostly on the curve. However, significant differences were not found in the split times for 50-100 and 150-200 m in either sex. In both categories, the relative average velocity (RAV), percentage of average velocity relative to the maximum velocity reached in the fastest section (50-100 m), was about 3% lower indoors than outdoors in 100- to 150-m section. The athletes' lower capacity to develop speed indoors could be caused specifically, by the curved 0- to 50-m and 100- to 150-m sections of the indoor track. Coaches could use these data as reference values there being few published data from high-level competitions. The RAV could be used by coaches to compare results among athletes of different levels and sexes.

A systematic re-sampling approach to assess the probability of detecting otters Lutra lutra using spraint surveys on small lowland rivers

Assessing and monitoring populations of elusive species frequently rely on the identification of indirect signs such as faeces. The absence of signs does not necessarily denote the absence of a species, thus, the ability to determine the presence/absence is susceptible to false negative results. The probability of detection is central to the interpretation and utility of data from field sign surveys. A low probability of detection may introduce considerable error into distribution patterns, resulting in inaccurate ecological conclusions.We used a systematic resampling approach, based on sequential spatial replication of spraint surveys, to investigate the probability of detecting Eurasian otters (Lutra lutra L.) with different survey designs. This included the standard otter transect survey methodology, which is widely used in conservation and scientific studies. In particular, we focus on the impact of applying broad scale population assessment techniques at smaller spatial scales. Fortnightly catchment-level otter surveys were undertaken on four lowland rivers in South Wales, over a period of two years. GIS was used to construct binary vectors for each survey, denoting the presence (1) or absence (0) of otters at each 50m section of river. Vectors from all study rivers were pooled and resampled to test the different survey designs. The mean probability of detecting otters based on the standard protocol of a single 600m transect survey was very low (0.26±0.01 SE). The best way of obtaining a detection probability of 0.8 was to undertake three repeat surveys at two separate sites, using a transect of 800–1000m.We demonstrate how sequentially collected spatial data can be analysed to determine the reliability of field sign surveys. Increasing the number of visits and study sites was a more efficient means of improving detection power than increasing transect length alone. The study emphasises the importance of determining detection probabilities and designing field sign surveys according to study scale and objectives. Our findings question the value of survey designs that aim to provide an instantaneous assessment of species presence/absence.

Effects of Reduced‐Impact Logging on Fish Assemblages in Central Amazonia

In Amazonia reduced-impact logging, which is meant to reduce environmental disturbance by controlling stem-fall directions and minimizing construction of access roads, has been applied to large areas containing thousands of streams. We investigated the effects of reduced-impact logging on environmental variables and the composition of fish in forest streams in a commercial logging concession in central Amazonia, Amazonas State, Brazil. To evaluate short-term effects, we sampled 11 streams before and after logging in one harvest area. We evaluated medium-term effects by comparing streams in 11 harvest areas logged 1-8 years before the study with control streams in adjacent areas. Each sampling unit was a 50-m stream section. The tetras Pyrrhulina brevis and Hemigrammus cf. pretoensis had higher abundances in plots logged > or =3 years before compared with plots logged <3 years before. The South American darter (Microcharacidium eleotrioides) was less abundant in logged plots than in control plots. In the short term, the overall fish composition did not differ two months before and immediately after reduced-impact logging. Temperature and pH varied before and after logging, but those differences were compatible with normal seasonal variation. In the medium term, temperature and cover of logs were lower in logged plots. Differences in ordination scores on the basis of relative fish abundance between streams in control and logged areas changed with time since logging, mainly because some common species increased in abundance after logging. There was no evidence of species loss from the logging concession, but differences in log cover and ordination scores derived from relative abundance of fish species persisted even after 8 years. For Amazonian streams, reduced-impact logging appears to be a viable alternative to clear-cut practices, which severely affect aquatic communities. Nevertheless, detailed studies are necessary to evaluated subtle long-term effects.

Biodegradable roads

This project assessed whether mulching windrows of waste wood from right-of-way logging could produce an all-weather road surface for in-block roads. Three in-block spur roads in the Alex Fraser Research Forest at Williams Lake, B.C., were divided into three 50-m sections with: (1) waste wood collected from a 40 m right-of-way, (2) waste wood collected from a 20 m right-of-way, and (3) no waste wood. A gravel truck was loaded to produce drive axle loads similar to a loaded logging truck and was used in the cyclic loading of the test road. The mulched wood roads clearly out-performed the soil roads. Failure occurred in the mulched wood roads at points of localized rutting in weak spots within the mulched layer. In an operational setting, the weak spots could easily be filled by hand or with a skidder blade.

The Decline of Swimming Performance With Advancing Age: A Cross-Sectional Study

The aim of this cross-sectional study was to measure the swimming parameters-speed (V), stroke frequency (SF), and stroke length (SL)- in 162 male athletes aged 50-90 (divided into 7 age groups, from A to G) participating in the World Master Championships in the 200-m freestyle event, and to analyze the rates and magnitudes of their age-associated declines. The swimmers were video-recorded by 2 digital cameras during the competitions and the swimming parameters related to every 50-m section (lap) and to the entire race (average) subsequently measured or calculated. Lap V and SF decreased in the second and third quarter (11 and 4% on average) and increased (3% on average) in the fourth quarter of the race, whereas lap SL decreased from the first to the last 50-m section. Average V (m.s(-1)) decreased from 1.39 +/- 0.09 (group A) to 0.84 +/- 0.11 (group G); average SL (m) decreased from 2.10 +/- 0.20 (group A) to 1.78 +/- 0.19 (group G); and average SF (cycles.s(-1)) decreased from 0.67 +/- 0.06 (group A) to 0.47 +/- 0.04 (group G). One-way analysis of variance showed significant declines in average V, SL, and SF (p < 0.01) across the 7 groups. The swimming parameters were normalized to the highest values (set equal to 100); thereafter, a linear regression curve was fitted and the regression equations calculated. Decline of SF was about 2.5 times steeper than that of SL. It was highlighted that (a) among the swimming parameters, SL is less affected by the ageing process; (b) SL decreased from group A through group C and thereafter tended to keep steady, whereas the trend for SF was opposite. The results have the potential to give master swimmers and their coaches useful information for training program design.

Relationships between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia

Small streams with acidic, nutrient-poor waters form a dense hydrological system in Central Amazonia. However, little is known about the fish assemblages that occur in these systems. We investigated the relationships among stream size, substrate, and other physical-chemical factors and fish distributions. Fish assemblages and stream characteristics were sampled in 50-m long sections of streams at 38 sites distributed throughout the 100-km2 florestal reserve. Forty-nine species were encountered. The mean richness was similar among sites; however, community composition was correlated with physical and chemical characteristics of the streams. The mean number of species per site (X̄ = 9) was low in relation to the total number of species recorded from the reserve (49) and in relation to the ichthyofauna that has been recorded from small forest streams near the study area. This contrasts with studies in temperate zones where strong patterns of species addition along the river continuum were found, resulting in prominent species richness gradients. The high between-site turnover in species composition and the strong habitat specificity indicate that it will be necessary to create a network of reserves to efficiently conserve the fish fauna of small forest streams in Central Amazonia.Na Amazônia Central, pequenos riachos de águas ácidas e pobres em nutrientes constituem uma densa rede hidrica. Contudo, pouco é conhecido sobre a riqueza e abundância de sua ictiofauna. Para determinar a composição ictiofaunistica existente, bem como determinar a relação entre o tamanho dos igarapés, substratos presentes nos leitos, e fatores fisico-quimicos e a estrutura da comunidade, nós amostramos trechos de 50-m em 38 locais distribuidos em uma reserva de 100-km2. A riqueza média foi semelhante entre os sitios de amostragem. No entanto, a composição de espécies foi relacionada com caracteristicas fisicas e quimicas dos riachos. O número médio de espécies por local (X̄ = 9) foi pequeno em relação ao número total de espécies encontrado na reserva (49) e em relação à ictiofauna que foi encontrada em pequenos riachos próximos à área de estudo. Isto contrasta com estudos realizados em zonas temperadas, onde um padrão muito forte de adição de espécies ao longo das bacias foi encontrado, resultando em um gradiente acentuado de riqueza de espécies. A alta troca na composição de espécies entre locais, e a alta especificidade de hábitat, indica que seria necessário criar uma rede de reservas para conservar eficientemente a ictiofauna de pequenos riachos na região.

Energetic Cost and Preferred Speed of Walking in Obese vs. Normal Weight Women

We tested the hypotheses that walking is more expensive for obese women, and they prefer slower walking speeds that minimize the gross energy cost per distance despite a greater relative aerobic effort [percent of maximal oxygen uptake (Vo(2max))/kg]. Twenty adult women, 10 obese (BMI = 34.1 +/- 3.2 kg/m(2)) and 10 normal weight (BMI = 20.4 +/- 2.1 kg/m(2)) volunteered. To determine the metabolic rate and energy cost per distance vs. speed relationships, we measured Vo(2) and V(CO(2)) while subjects walked on a treadmill at six speeds (0.50, 0.75, 1.0, 1.25, 1.5, and 1.75 m/s; 5-minute trials, with a 5-minute rest period between trials). We measured preferred walking speed on a 50-m section of level sidewalk and Vo(2max) using a modified Balke treadmill protocol. Walking was 11% more expensive for the obese subjects, but they preferred to walk at similar speeds as normal weight subjects (1.40 vs. 1.47 m/s, p = 0.07). Both groups preferred walking speeds at which their gross energy cost per distance was almost minimized. Obese subjects had a smaller Vo(2max)/kg, so they required a greater relative aerobic effort at the preferred speed (51% vs. 36%, p = 0.001). Obese women preferred a walking speed that minimized energy cost per distance, even though this strategy required a greater relative aerobic effort than walking more slowly. Our results suggest that walking slower for a set distance may be an appropriate exercise recommendation for a weight management prescription in obese adults.

New insights into Archean sulfur cycle from mass-independent sulfur isotope records from the Hamersley Basin, Australia

We have measured multiple sulfur isotope ratios (34S/33S/32S) for sulfide sulfur in shale and carbonate lithofacies from the Hamersley Basin, Western Australia. The Δ33S values (Δ33S≈δ33S−0.515×δ34S) shift from −1.9 to +6.9‰ over a 22-m core section of the lower Mount McRae Shale (∼2.5 Ga). Likewise, sulfide sulfur analyses of the Jeerinah Formation (∼2.7 Ga) yield Δ33S values of −0.1 to +8.1‰ over a 50-m section of core. Despite wide variations in Δ33S and δ34S, these two shale units yield a similar positive correlation between Δ33S and δ34S. In contrast, pyrite sulfur analyses of the Carawine Dolomite (∼2.6 Ga) yield a broad range in δ34S (+3.2 to +16.2‰) but a relatively small variation and negative values in Δ33S (−2.5 to −1.1‰). The stratigraphic distribution of δ33S, δ34S, and Δ33S in Western Australia allows us to speculate on the sulfur isotopic composition of Archean sulfur reservoirs and to trace pathways in the Archean sulfur cycle. Our data are explained by a combination of mass-independent fractionation (MIF) in the atmosphere and biological mass-dependent fractionation in the ocean. In the Archean, volcanic, sulfur-bearing gas species were photolysed by solar ultraviolet (UV) radiation in an oxygen-free atmosphere, resulting in MIF of sulfur isotopes. Aerosols of S8 (with Δ33S>0) and sulfuric acid (with Δ33S<0) formed from the products of UV photolysis and carried mass-independently fractionated sulfur into the hydrosphere. The signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments. Pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass-dependent fractionation on mass-independent atmospheric effects. Multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur-metabolizing organisms.

Stratigraphy and megaflora of a K-T boundary section in the eastern Denver Basin, Colorado

A 50-m-thick section of the Denver Formation (D1 sequence of Raynolds) exposed at the West Bijou Site of the Plains Conservation Center, Arapahoe County, Colorado, contains the first complete Cretaceous-Tertiary (K-T) boundary section in the Denver Basin. The 3-cm-thick boundary claystone coincides with a 21 percent palynological extinction, contains iridium and shocked-mineral anomalies, and is immediately overlain by a 7-cm-thick, fern-spore anomaly interval. The entire 50-m section is of reversed magnetic polarity and is interpreted to be subchron C29r because of paleontological data, the presence of a tuff with an 40 Ar/39 Ar date of 65.73 ± 0.13 Ma, and by correlation to the Kiowa cored well. A diagnostic basal Puercan (Pu1) mammal jaw was found 12 m above the boundry clay, and ceratopsian and hadrosaurian dinosaur fragments occur 4 m below the boundary clay. Estimates of the basin sedimentation rate derived from the duration of C29r based on marine cyclostratigraphy suggest that the 28 m of basal Paleocene strata represent approximately 200,000 years. Abundant fossil leaves found within the Paleocene sedimentary rocks at the West Bijou Site K-T boundary section allow assessment of early Paleocene patterns of plant diversity. Nine leaf localities at eight stratigraphic levels in the basal 22 m of the Paleocene section were sampled and analyzed to better understand the flora that survived the global K-T catastrophe. The Paleocene flora of this site is taxonomically dominated by dicotyledonous angiosperms (74%), with lesser numbers of monocotyledons (10%), ferns and allies (11%), and conifers (5%). By number of specimens, angiosperms comprise greater than 95 percent of the flora. Within the sampled section, there were no recognizable directional trends in diversity or abundance, suggesting that earliest Paleocene vegetation was stable, although not particularly diverse. The West Bijou Megaflora is strikingly similar in composition and relative abundance to basal Paleocene floras from the northern Great Plains. This K-T boundary disaster-recovery flora, also known as the FUI flora, is shown to have been widespread, ranging from central Colorado to southern Canada, a distance of at least 1,100 km. The West Bijou Site megaflora is markedly different from coeval floras along the western margin of the Denver Basin, supporting the hypothesis that orography and elevation provided greater influence on basal Paleocene floral composition and diversity than did latitude.

Techniques Applied to Obtain Very High-Resolution 3-D Seismic Imaging at an Athabasca Tar Sands Thermal Pilot: ABSTRACT

A high-resolution 3-D seismic survey was conducted at an Athabasca tar sands thermal pilot for the ultimate purpose of locating in-situ heat fronts. In order to obtain the required seismic expression, it is imperative that the field data have an extremely good signal-to-noise (S/N) ratio over a broad frequency band. This paper addresses the specialized acquisition and processing techniques which were used to acquire and process the 3-D data. The geology of the pilot site is characterized by a 50-m thick section of discontinuous McMurray tar sands resting on a Devonian unconformity, approximately 240 m below the surface. Imaging of this erosional surface, so critical to the pilot, is demonstrated by various interactive displays. The seismic definition of a narrow channel emphasizes that exceptional spatial and temporal resolution can be achieved, which will be necessary for the future monitoring of the in-situ heat fronts.

Coarse-Grained Volcaniclastic Sediments and Associated Penecontemporaneous Volcanism, Alisitos Group, Baja California, Mexico: ABSTRACT

Volcaniclastic rocks of Cretaceous age make up the Alisitos group, which is exposed over large areas of northern Baja California, Mexico, and is inferred to have been deposited within an island arc. Intimately intermixed penecontemporaneous intrusive, extrusive, and fragmental volcanic rocks characterize many of the intra-arc deposits within the Alisitos. Peperites, formed by mixing of magma and wet sediment, are useful for demonstrating contemporaneity of volcanism and sedimentation. Peperites were recently discovered at the type locality of the Alisitos group at Punta China, only 25 km south of Ensenada, Mexico. These intrude a 50-m thick section, dominated by mafic lithic lapilli tuff breccias and lava flows, that accumulated in a nearshore to beach environment. Near Punta Maria (about 100 km north of Guerrero Negro), coarse-grained volcaniclastics interpreted to have been deposited on a north to northwest-facing submarine slope are exposed in sea cliffs. Ammonite (Pervinquieria.) and belemnite fossils suggest a Cretaceous age and marine deposition for the Punta Maria sequence. Horizontal burrows and lack of wave reworking indicate subwave-base depth for most of the section. The most common rock types in the sequence are andesitic lithic lapilli tuff and tuff breccia, deposited from nonturbulent high-concentration sediment gravity flows (density-modified grainmore » flow). Comparison of the Punta Maria and Punta China sections suggests that hydrostatic pressure and depositional slope play important roles in controlling the magma/sediment interaction. At Punta China, a shallow-water association was intruded by small sills, resulting in a highly dispersed peperite (explosive interaction). The Punta Maria section, comprising deeper water slope deposits, was intruded by a larger magma body that partly ingested a limestone and produced a thick carapace of hyaloclastite (nonexplosive interaction).« less