Age,stratigraphy, sedimentology and tectonic setting of the Sigri Pyroclastic Formation and its fossil forests,Early Miocene,Lesbos, Greece     

Georgia Pe‐Piper  David J.W. Piper  Nickolas Zouros  George Anastasakis 《Basin Research》2019,31(6):1178-1197

The Petrified Forest of Lesbos comprises silicified tree fossils at multiple stratigraphic levels within the Lower Miocene Sigri Pyroclastic Formation. Our objective was to understand the interplay of tectonic setting, structural evolution, volcanological setting and basin evolution in the preservation of this remarkable natural monument. Sections were logged for lithology, sedimentary structures and hydrothermal alteration. Orientations of fallen fossil trees were measured. Samples were taken for mineralogical and geochemical analysis. ⁴⁰Ar/³⁹Ar dating was carried out on mineral separates from four samples. Widespread andesite‐dacite domes, the Eressos Formation, intrude and overlie metamorphic basement and are overlain by the Sigri Pyroclastic Formation, which comprises several hundreds of metres of pyroclastic flow tuffs (unwelded ignimbrites) interbedded with fluvial conglomerate and volcaniclastic sandstone. The Sigri Pyroclastic Formation ranges in age from 21.5 to 22 Ma, where it overlies the lacustrine Gavathas Formation, to younger than 18.4 Ma. Tuffs and fluvial conglomerates in the Sigri Pyroclastic Formation coarsen eastwards, and petrified trees and soil horizons occur throughout the Formation. The recurrence of pyroclastic flows was approximately one every 20 ka, so destructive flows were relatively infrequent, allowing the development of climax vegetation between most eruptions. Conglomerate‐filled channels show that rivers flowed westwards. Tree fall directions indicate NW to N movement of pyroclastic flows, implying a source near the younger Mesotopos–Tavari caldera to the south. The basin, which formed in a NNE‐trending dextral strike‐slip regime, provided some topographic steering. Following the Sigri Pyroclastic Formation at ca. 18 Ma, there was a rapid increase in the pace of volcanic activity, with the eruption of thick lava sequences and welded ignimbrites, and intrusion of dykes and laccoliths in SW Lesbos. Rapid burial by permeable tuffs, silica from alteration of volcanic ash, and later hydrothermal circulation all contributed to the preservation of the petrified trees.  相似文献   

Seasonal changes in the daily emission rates of terpenes by Quercus ilex and the atmospheric concentrations of terpenes in the natural park of Montseny, NE Spain     

Joan Llusia  Josep Pe?uelas  Roger Seco  Iolanda Filella 《Journal of Atmospheric Chemistry》2012,69(3):215-230

We studied the daily patterns in the rates of terpene emissions by the montane holm oak, Quercus ilex, in three typical days of winter and three typical days of summer in Montseny, a natural park near Barcelona, and related them to the air concentrations of terpenes, ozone and NO₂. Terpene emission rates were about 10 times higher in summer than in winter. Emissions virtually stopped in the dark. In both seasons, rates of terpene emissions were well correlated with light, air temperature and relative humidity. Rates of emissions were also correlated with stomatal conductance and the rates of transpiration and photosynthesis. Almost all the individual terpenes identified followed the same pattern as total terpenes. The most abundant terpene was ??-pinene, followed by sabinene + ??-pinene, limonene, myrcene, camphene and ??-phellandrene. Atmospheric terpene concentrations were also about 10 times higher in summer than in winter. A significant diurnal pattern with maxima at midday was observed, especially in summer. The increase by one order of magnitude in the concentrations of these volatile isoprenoids highlights the importance of local biogenic summer emissions in these Mediterranean forested areas which also receive polluted air masses from nearby or distant anthropic sources. Atmospheric concentrations of O₃ and NO₂ were also significantly higher in summer and at midday hours. In both seasons, concentrations of O₃ were significantly correlated with concentrations of terpenes and NO₂ in the air and with rates of terpene emission.  相似文献   

Trends of AOT40 at three sites in the Catalan Pyrenees over the last 16 years     

Maria Díaz-de-Quijano  Josep Peñuelas  Àngela Ribas 《Journal of Atmospheric Chemistry》2011,68(4):317-330

Ozone mixing ratios were monitored at three stations at different altitudes along the Catalan Pyrenees from 1994 to 2009. The AOT40 greatly exceeded the critical level for the protection of forest and semi-natural vegetation set by the UNECE’s CLRTAP and the target value and long-term objective for the protection of vegetation set by the European Directive 2008/50/EC. The AOT40 showed an overall increasing trend over time with a slight decrease during the last 3 years, although longer-term records of ozone levels are required before affirming with certainty a declining or stabilising trend. These results indicate that plant life in the Pyrenean region can be at risk of ozone damage due to the high ozone mixing ratios detected. Nevertheless, more effort is warranted to determine the uptake of ozone by vegetation in this mountainous range. An ozone flux-based index that takes into account the local environmental conditions, plant phenology, and nocturnal uptake of ozone would provide a more accurate assessment of the risk from ozone for the particular vegetation in each area.  相似文献   

Comparative study of digestion methods EPA 3050B (HNO₃--H₂O₂--HCl) and ISO 11466.3 (aqua regia) for Cu, Ni and Pb contamination assessment in marine sediments     

Peña-Icart M  Villanueva Tagle ME  Alonso-Hernández C  Rodríguez Hernández J  Behar M  Pomares Alfonso MS 《Marine environmental research》2011,72(1-2):60-66

Knowing the metal extraction capacity of a digestion method is crucial for a better environmental interpretation of metal concentrations determined in sediments. One of the main problems at the present is the lack of harmonization of information obtained by two of the most popular sediment partial digestion methods: ISO 11466.3 (aqua regia) and EPA 3050B (HNO?--H?O?--HCl). In the present work, the amount of Cu, Ni and Pb leached by using both methods was compared with the total content of those elements in marine sediments collected, as an example, from the Cienfuegos Bay, Cuba. Similar amounts of Cu were extracted by both methods; while leaching of Ni and Pb were different. Generally, the EPA method extracted more Ni than the ISO method. In contrast, Pb was extracted in a larger amount by the ISO method. Some explanations are given for the observed results. X-ray Diffraction, X-ray Fluorescence, Particle Induced X-ray Emission Spectrometry and Energy Dispersive X-ray coupled to Scanning Electron Microscopy were employed for this purpose. On the other hand, none of the methods studied extracted simultaneously the fraction of all the metals, probably provided by human activity (Theoretical Anthropogenic Fraction) in both sediments studied. The use of ISO 11466.3 or EPA 3050B is recommended since the analytical performance parameters of both, in combination with Flame Atomic Absorption Spectrometry, are adequate. For a better environmental interpretation of the analytical results, information on the extraction efficiency of the selected method for specific elements and sediments under study should also be provided, together with the determined concentrations.  相似文献   

Recent observations of the WR central star of the planetary nebula LMC-N66     

Miriam Peña  Manuel Peimbert  Silvia Torres-Peimbert  Maria Teresa Ruiz  Jose Maza 《Astrophysics and Space Science》1996,238(1):55-58

The recent evolution of the central star of the planetary nebula LMC-N66 is presented. Before 1987, it showed a weak continuum with aT _eff120 000 K andL _bol25 000L and in a few years it developed strong WR features (P Cygni line profiles in N v at 124.0 nm and C IV at 155.0 nm, wide Heii emission, etc.) typical of a WN 4.5. Additionally the stellar continuum increased by a large factor and the absolute visual magnitude of the star changed from + 1.24 in 1987 to–2.57 in January, 1995. The WR features and enhanced continuum, evidencing a powerful mass-loss event remained with small variations for more than 5 years. Recent ultraviolet and optical data shows that the mass-loss seems to have diminished abruptly in the last three months.  相似文献   

Impacts of in-stream aggregate mining on the distributary channels of the alluvial fans of Tafí valley (Northwest Argentina)     

María Marta Sampietro-Vattuone  José Luis Peña-Monné  Graciela Rodríguez  Paula Lucía Medina  Marta Amelia Vattuone 《地球表面变化过程与地形》2021,46(14):2930-2945

In-stream mining is a common aggregate mining practice around the world. However, the impacts of such practice are not always taken into account when the mines are established, and the environmental cost of in-stream aggregate mining is generally not assessed. The purpose of this study was to evaluate the impacts of aggregate mining conducted in La Puerta River (Tafí valley, Northwest Argentina), a dry-pit in-stream mine, by considering the geomorphological, geoarchaeological, and human effects. Multitemporal analysis of the area using remote sensors (aerial photographs and satellite images 1970–2020), high-resolution drone digital elevation models and orthomosaics (2018–2019), and an intensive survey demonstrated that the mining area grew exponentially between 2002 and 2020 under unregulated mining. As a result, this practice exerts great environmental impact, including channel section alterations and destabilization of riverbanks, soil loss, river profile changes, and the formation of lag deposits of discarded materials, thus increasing environmental hazard under unpredictable flows. Finally, this is a highly touristic area that has suffered substantial landscape degradation and irreversible archaeological damage.  相似文献   

Glacial and Fluvial Deposits in the Aragón Valley,Central‐Western Pyrenees: Chronology of the Pyrenean Late Pleistocene Glaciers     

José M. García‐Ruiz  Carlos Martí‐Bono  José L. Peña‐Monné  Carlos Sancho  Edward J. Rhodes  Blas Valero‐Garcés  Penélope González‐Sampériz  Ana Moreno 《Geografiska Annaler: Series A, Physical Geography》2013,95(1):15-32

The Aragón Valley glacier (Central Western Pyrenees) has been studied since the late nineteenth century and has become one of the best areas in the Pyrenees to study the occurrence of Pleistocene glaciations and the relationships between moraines and fluvial terraces. New morphological studies and absolute ages for moraines and fluvial terraces in the Aragón Valley allow a correlation with other Pyrenean glaciers and provide solid chronologies about the asynchroneity between global last glacial maximum (LGM) and the maximum ice extent (MIE). Six frontal arcs and three lateral morainic ridges were identified in the Villanúa basin terminal glacial complex. The main moraines (M1 and M2) correspond to two glacial stages (oxygen isotopic stages MIS 6 and MIS 4), dated at 171 ± 22 ka and 68 ± 7 ka, respectively. From a topographical point of view, moraine M1 appears to be linked to the 60 m fluvioglacial terrace, dated in a tributary of the Aragón River at 263 ± 21 ka. The difference in age between M1 moraine and the 60 m fluvioglacial terrace suggests that the latter belongs to an earlier glacial stage (MIS 8). Moraine M2 was clearly linked to the fluvioglacial 20 m terrace. Other minor internal moraines were related to the 7–8 m terrace. The dates obtained for the last glacial cycle (20–18 ka) are similar to other chronologies for Mediterranean mountains, and confirm the occurrence of an early MIE in the Central Pyrenees that does not coincide with the global LGM.  相似文献   

Decadal Trends in Oxygen Concentration in Subsurface Waters of the Northeast Pacific Ocean     

William R. Crawford  M. Angelica Peña 《大气与海洋》2016,54(2):171-192

Previous studies have shown decreasing oxygen concentration (O₂) in subsurface waters of the continental slope from California to Canada since about 1980. With longer time series we show that from southern California to northern Canada increasing O₂ preceded these decreases from 1950 to about 1980. Because there has been no clear trend since 1950, we cannot yet conclude that anthropogenic climate change is the cause of these decreasing trends after 1980. These findings are based mainly on O₂ on the 26.7 potential density (σ_θ) surface in the region north of 30°N and east of 170°W, covering both the continental margin and deep-sea regions. On the continental slope, O₂ increased at most locations by 10 to 20?µmol?kg^?1 to about 1980, followed by declines of similar magnitude in recent years. Changes in O₂ were associated with changes in temperature of the opposite sign south of 37°N, but correlation of temperature and O₂ is irregular in more northerly locations. At all locations, temperature-related solubility change was a minor cause of these O₂ trends. In deep-sea waters, O₂ decreased with time with a more rapid decrease from about 1995 to about 2003. At Ocean Station P (OSP; 50°N, 145°W), which has the longest uninterrupted record of observations, significant linear trends of ?0.4 to ?0.5?µmol?kg^?1?y^?1 were found on the 26.5, 26.7, and 26.9 σ_θ surfaces. In addition, a significant sinusoidal oscillation of period 18.61 years and amplitude of 18?µmol?kg^?1 was found on the 26.9 σ_θ surface at OSP and a station 400?km to the east, which fits reasonably well with the lunar nodal cycle. The phase of this oscillation was identical at both locations. Clear evidence of similar variability did not emerge at other open-ocean locations or along the continental slope.  相似文献   

Fold-Axis Parallel Extension along the Southern Ending of the Quito (Ecuadorian Andes) Fault System: Implications in River Network and Aquifer Geometry     

Peñafiel  L. A.  Reyes  P. S. B.  Alcalá  F. J.  Ramírez  M. R.  Cabero  A. 《Geotectonics》2020,54(2):256-265

Geotectonics - Extension parallel to fold axis represents a rarely documented tectonic process that occur in different tectonic settings such as large-scale orogenic belts, mountain ranges, and...  相似文献   

Satellite Remote Sensing as a Reconnaissance Tool for Assessing Nautical Chart Adequacy and Completeness     

Shachak Pe’eri  Christopher Parrish  Chukwuma Azuike  Lee Alexander  Andrew Armstrong 《Marine Geodesy》2013,36(3):293-314

National hydrographic offices need a better means of assessing the adequacy of existing nautical charts in order to plan and prioritize future hydrographic surveys. The ability to derive bathymetry from multispectral satellite imagery is a topic that has received considerable attention in scientific literature. However, published studies have not addressed the ability of satellite-derived bathymetry to meet specific hydrographic survey requirements. Specifically, the bathymetry needs to be referenced to a chart datum and statistical uncertainty estimates of the bathymetry should be provided. Ideally, the procedure should be based on readily-available, low-cost software, tools, and data. This paper describes the development and testing of a procedure using publicly-available, multispectral satellite imagery to map and portray shallow-water bathymetry in a GIS environment for three study sites: Northeast United States, Nigeria, and Belize. Landsat imagery and published algorithms were used to derive estimates of the bathymetry in shallow waters, and uncertainty of the satellite-derived bathymetry was then assessed using a Monte Carlo method. Results indicate that the practical procedures developed in this study are suitable for use by national hydrographic offices.  相似文献