Lacustrine carbonate deposition in Middle Pennsylvanian cyclothems — the Upper Freeport Formation,Appalachian Basin,USA

The Upper Freeport Formation (Upper Allegheny Group, Middle Pennsylvanian) is one of the earliest non-marine cyclothems in the Appalachian Basin and contains carbonates, siliciclastics, and coal. A detailed facies analyses of 25 cores from the Upper Freeport Limestone in western Pennsylvania (Armstrong and Indiana Counties) identified four facies associations containing thirteen separate facies: rudstone-limestone (Association A), rudstone-laminated limestone (Association B), laminated limestone (Association C), and coal — siliciclastics (Association D). We interpreted them, respectively, as shallow, high energy lacustrine margin (A); littoral to sublittoral lacustrine (B); offshore lake (C); and vegetated swamp and marsh (D). The depositional environment is envisaged as an anastomosed channel system surrounded by extensive wetlands containing adjacent densely vegetated swamp and marsh areas and freshwater, carbonate-producing lakes.Lakes developed in the topographic lows of the alluvial plain, protected and filtered from siliciclastic deposition by vegetated swamps. These lakes were small in size (several square km), shallow, and stratified, as indicated by the abundance of laminated facies. They were hydrologically open, and interconnected by surface and ground waters. Carbonate production in this lacustrine system was not triggered by evaporative concentration but by biogenic algal production. Carbonates were continually being recycled, both physicochemically and biologically, within the depositional system. Various early diagenetic processes, including brecciation, pedogenesis and recrystallization, masked original evidence for transport mode. The Upper Freeport Limestone contains numerous features of palustrine carbonates, and provides a case study for one end-member of freshwater carbonate models, characterized by a very short period of subaerial exposure. Small-scale climatic changes or autocyclic processes such as small topographic differences, changes in local drainage patterns, and fluvial dynamics may have controlled Upper Freeport lake level changes.Facies analysis does not support a climate forcing as a control for cyclothem development of non-marine sequences during the Pennsylvanian. Tectonic and autocyclic processes better explain the evolution of these wetland (lacustrine/alluvial) systems with its associated coal formation.This is the seventh paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.     

Charophyta: their use in paleolimnology

Charophyta are common algae in limnic waters from many regions and are an interesting group from an evolutionary point-of-view, as they are believed to be related to the Chlorophyceae and land plants. Paleontological-botanical systematics are discussed, taking into consideration some new advances. Charophytes live in all types of inland waters and are sensitive to ecological change, and so they are very useful paleolimnological markers. Gaps concerning gyrogonite morphology in extant taxa and their responses to different environmental conditions must be described. This paper discusses data concerning ecological factors affecting the distribution of Argentinian Charophyta (principally distributed between 30°S and 40°S), gyrogonite morphology related to different ecological conditions, and the way that Charophyta can modify the environment.This is the fifth in a series of papers published in this issue on Paleolimnology in Southern South America. Dr C. A. Fernández served as guest editor for these papers.     

Optimizing Results from Automatic Objective-Prism Surveys

One of the most important results in observational cosmology is the galaxy star formation rate distribution, or its equivalent observable, the Hα luminosity function. The UCM-CIDA project has grown to address the problem of the poorly-known faint star forming galaxy population using the objective-prism technique along with a CCD mosaic in a Schmidt telescope. However, one tough problem when computing statistical properties of a selected sample are the selection effects. Here we present tools developed by us to undertake the analysis of objective-prism (OP) selected samples in an unbiased way and quantify the sensitivity of the survey to every object. The main tools for this purpose are simulations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geomorphological and sedimentological analysis of a catastrophic flash flood in the Arás drainage basin (Central Pyrenees, Spain)

On August 7th, 1996, an intense and short-duration convective storm occurred over the 18.6-km² Arás drainage basin (Central Pyrenees, Spain). This high relief basin is composed of three subbasins, Aso, Betés and La Selva, and feeds the Arás alluvial fan, in the Gállego river valley. This alluvial fan had been drained by an artificial channel (about 125 m³/s at bank-full capacity). More than 30 check dams in its feeder channel, the Arás barranco, had been previously filled by earlier sediments. The heaviest rain was over the Betés subbasin (total rainfall 178.4 mm; maximum rainfall intensity of 153 mm/h for a 10-min time interval was estimated). Most of the rainfall fell in a 70-min period. This storm resulted in high runoff, causing catastrophic damage and significant geomorphic changes in the drainage basin, especially in the Betés subbasin. The high discharge, concentrated in the Arás barranco, destroyed most of the check dams, flushing out a great amount of debris. Major channel trenching and widening occurred in this barranco. When the confined sediment-laden flash flood reached the basin mouth, it sheet-flooded the southern sector of the Arás fan depositing a massive amount of debris. On this fan 87 people lost their lives and the direct physical damage has been estimated at 55 million dollars. Two stages in the development of the flood have been differentiated from the sedimentological and morphological analysis of the flooded fan lobe. A first stage (peak discharge) of sheet-flooding deposited a coarse boulder lobe, burying the artificial channel at the fan head and causing a darnming effect on the water flood. During the second stage (discharge decline) the flood made its way through the fan head, incising the previous debris accumulation and splitting into two main flow paths.     

Optical Classification of IRAS Post-AGB Candidates

We present the first results of a survey carried out on a sample of optically bright post-AGB candidates selected from the IRAS Point Source Catalogue, many of them previously unidentified in the literature. The selection criteria are based on their characteristic far infrared colours. Low resolution spectroscopy of more than 150 sources has been obtained during 6 years. Our preliminary analysis confirms that most of the candidates observed are true post-AGB stars, some of them still strongly reddened. Some young planetary nebulae, a few young stellar objects and active galactic nuclei are also present in the sample. The distribution of post-AGB stars with different spectral types in the IRAS two-colour diagram and its evolutionary implications are briefly discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Climate Warming, Wildfire Hazard, and Wildfire Occurrence in Coastal Eastern Spain

A climatic series (1941 to 1994) from a Mediterranean locality of NE Spain was used to calculate two wildfire hazard indices based on daily meteorological data. Both fire hazard indices increased over this period, as a consequence of increasing mean daily maximum temperature and decreasing minimum daily relative humidity. These trends were observed in both mean values of the indices and in the number of very high risk days. Annual data on the number of wildfires and burned area also show an increase from 1968 to 1994, and are significantly correlated with both fire hazard indices. Although other non-meteorological causes (e.g., human activities, fuel accumulation) have likely contributed to the observed increase of wildfires, an effect of climatic warming on wildfire occurrence is supported by this relationship.     

Mesoscale Convective Complexes over the Western Mediterranean area during 1990–1994

Summary Mesoscale Convective Systems (MCSs) data registers from June to December during 1990–94 were obtained from the Spanish National Meteorological Institute (INM). Fifteen Mesoscale Convective Complexes (MCCs) were identified through this database. Most of the MCCs developed during the last week of September. The dominant synoptic patterns related to the mesoscale systems were cold fronts at the surface with warm and moist low-level cores, and cut-off low or deep trough throughout the middle and upper levels. These synoptic patterns were found in all the fifteen cases studied.The hourly centroid location of each MCC was used to trace their tracks, which followed a general direction towards the E or NE in almost all cases. These trajectories are clearly related to the synoptic patterns found. Finally, two MCCs chosen as representative of their evolution are described and the related physical processes are discussed.With 14 Figures     

Oscillatory behaviour in sunspot umbrae

Using a set of series of spectra of high spectral resoltion corresponding to the same umbra on several days, we have studied the oscillations related to evolution of the two main dark cores of it.We have detected differences in the behaviour of each core and an evolution in the power spectra not related with the external appearance of the spot. A quite constant value of the ratio of power at five minutes over three minutes has been found.Paper presented at the 11 th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain     

The Hei D 3 5876 Å line as an activity and structural indicator in F-type Hyades stars

We give the first results of a study in F-type MS stars using the Hei D ₃ absorption feature at 5876 Å as an indicator of stellar activity and structure. The observations were obtained with the QUB echelle spectrograph at the Cassegrain focus of the 4.2 m William Herschel telescope, and have spectral resolution /6×10⁴, and signal-to-noise ratios 200. We chose as a first sample 17 F-stars of the Hyades Main Sequence. It was found that Hei D ₃ and X-ray emission appear aroundB-V 0.3, indicating the onset of sub-surface convection zones. Below this value, in stars withB-V0.42–0.44 the behaviour of the Hei D ₃ equivalent width against Rossby number is different from that observed in later type stars, indicating that the presence of nonradiative mechanisms other than dynamo must be important in heating the chromospheres of these hotter stars.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.Based on observations made with the William Herschel telescope, operated on the island of La Palma by the Royal Greenwich Observatory, in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias.     

Visible and near-infrared monitoring of 3C 279 in 1988–1989

We present near-infrared monitoring taken with the 1.5 m Carlos Sánchez Telescope in Tenerife and CCD photometry taken with the Jacobus Kapteyn Telescope in La Palma of the 1988 outburst of 3C 279. This is combined with archival data to examine the behaviour of the light curve fromB toK.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.