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11.
In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age
Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed
by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary
lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper,
late-deposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope
of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts
of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part
of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular
magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between
breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity.
We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a
rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity
to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease
in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite
was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and
unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic
material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or
erosion of the tuff ring caused a return to normal shallow marine conditions. 相似文献
12.
Sonia Jerez Juan Pedro Montavez Pedro Jimenez-Guerrero Juan Jose Gomez-Navarro Raquel Lorente-Plazas Eduardo Zorita 《Climate Dynamics》2013,40(11-12):3023-3046
This work assesses the influence of the model physics in present-day regional climate simulations. It is based on a multi-phyiscs ensemble of 30-year long MM5 hindcasted simulations performed over a complex and climatically heterogeneous domain as the Iberian Peninsula. The ensemble consists of eight members that results from combining different parametrization schemes for modeling the Planetary Boundary Layer, the cumulus and the microphysics processes. The analysis is made at the seasonal time scale and focuses on mean values and interannual variability of temperature and precipitation. The objectives are (1) to evaluate and characterize differences among the simulations attributable to changes in the physical options of the regional model, and (2) to identify the most suitable parametrization schemes and understand the underlying mechanisms causing that some schemes perform better than others. The results confirm the paramount importance of the model physics, showing that the spread among the various simulations is of comparable magnitude to the spread obtained in similar multi-model ensembles. This suggests that most of the spread obtained in multi-model ensembles could be attributable to the different physical configurations employed in the various models. Second, we obtain that no single ensemble member outperforms the others in every situation. Nevertheless, some particular schemes display a better performance. On the one hand, the non-local MRF PBL scheme reduces the cold bias of the simulations throughout the year compared to the local Eta model. The reason is that the former simulates deeper mixing layers. On the other hand, the Grell parametrization scheme for cumulus produces smaller amount of precipitation in the summer season compared to the more complex Kain-Fritsch scheme by reducing the overestimation in the simulated frequency of the convective precipitation events. Consequently, the interannual variability of precipitation (temperature) diminishes (increases), which implies a better agreement with the observations in both cases. Although these features improve in general the accuracy of the simulations, controversial nuances are also highlighted. 相似文献
13.
Wave–current laboratory experiments have shown that the logarithmic current profile observed in pure current flows is modified due to the presence of waves. When waves propagate opposite the current, an increase in the current intensity is achieved near the mean water level, while a reduction is obtained for following waves and currents. With the aim of analyzing these nonlinear effects along the whole water column, an Eulerian wave–current model is presented. In contrast to previously presented wave–current models, the present is able to include the variation of the free surface elevation due to the wave motion and the effect of a non hydrostatic pressure field. Therefore it does not restrict its application to waves in shallow waters. Moreover, the model is able to simulate all the possible angles between waves and currents. 相似文献
14.
Michel G. Houlé Sonia Préfontaine Anthony D. Fowler Harold L. Gibson 《Bulletin of Volcanology》2009,71(8):881-901
Spinifex-textured sills (i.e., veins) characterized by komatiitic magmas that have intruded their own volcanic-piles have
long been recognized. For instance, in the early 1970s, Pyke and coworkers, in their classic work at Pyke Hill in Munro Township,
noted that not all spinifex-bearing ultramafic rocks formed as lava flows, rather some were clearly emplaced as small dikes
and sills. Several hypotheses have been proposed to explain spinifex-textured sills: intrusion into a cold host, filter pressing,
or drainage of residual liquid. However, these do not satisfactorily explain the phenomenon. Field and petrographic observations
at Pyke Hill and Serpentine Mountain demonstrate that spinifex-bearing komatiite sills and dikes were emplaced during channel
inflation processes when new magma was intruded into a cooler, semi-consolidated but permeable cumulate material. Komatiitic
liquids were intruded into the olivine cumulate rocks near the boundary between the spinifex and the cumulate zones of well-organized
to organized komatiite flows. Spinifex-textured sills are generally tabular in morphology, stacked one above another, with
curviplanar contacts sub-parallel to stratigraphy. Some sills exhibit complex digitated apophyses. Thinner sills typically
have a random olivine spinifex texture similar, though generally composed of coarser crystals, to that of komatiite lava flows.
Thicker sills exhibit more complex organization of their constituent crystals characterized by zones of random olivine spinifex,
overlying zones of organized coarse spinifex crystals similar to those found in lava flows. They have striking coarse dendritic
spinifex zones composed of very large olivine crystals, up to several centimetres long and up to 1 cm wide that are not observed
in lava flows. Typically, at the sill margins, the cumulate material of the host flow is composed of euhedral to subhedral
olivine crystals that are larger than those distal to the contact. Many of these margin-crystals have either concentric overgrowth
shells or dendritic olivine overgrowths that grew from the cumulate-sill contact toward the sill interior. The dendrites grew
on pre-existing olivine cumulate at the contact in response to a sharp temperature gradient imposed by the intrusion of hot
material, whereas the concentric overgrowths formed as new melt percolated into the unconsolidated groundmass of the host-flow
cumulate material. Spinifex-textured sills and dikes occur in well-organized to organized flows that are interpreted to have
formed by “breakouts” above and peripheral to lava pathways (channels/conduits) as a result of inflation that accompanied
voluminous komatiitic eruptions responsible for the construction and channelization of komatiitic flow fields. The spinifex-textured
dikes and sills represent komatiitic lava that was originally emplaced into the channel roof during periods of episodic inflation
that resulted in lava breakouts and was subsequently trapped in the “roof rocks” during periods of channel deflation. Accordingly,
the occurrence of spinifex-textured sills and dikes may indicate proximity to, and aid in the identification and delineation
of lava channel-ways that could potentially host Ni–Cu–(PGE) mineralization within komatiitic lava flow-fields. 相似文献
15.
Juan Andrés García-Valero Juan Pedro Montavez Sonia Jerez Juan José Gómez-Navarro Raquel Lorente-Plazas Pedro Jiménez-Guerrero 《Theoretical and Applied Climatology》2012,110(1-2):291-310
A seasonal analysis of the atmospheric circulation over the Iberian Peninsula (IP) based on circulation types (CTs) obtained from sea level pressure and 500-hPa geopotential height is presented. The study covers the period of 1958–2008, when a high variability and important changes in winter and spring precipitation and temperature have been reported. Frequency, persistence, and the most probable transitions of the circulation types are analyzed. Among the clustering methods available in the literature, two of the most reliable classification methods have been tested, K-means and simulated annealing and diversified randomization. A comparison of both methods over the IP is presented for winter (DJF). The quality of the circulation types obtained through both methods as well as the better stability achieved by K-means suggest this method as more appropriated for our target area. Twelve CTs were obtained for each season and were analyzed. The patterns obtained were regrouped in five general situations: anticyclonic, cyclonic, zonal, summertime, and hybrid-mixed. The analysis of frequencies of these situations offers a similar characterization of the atmospheric circulation that others previously obtained by subjective methods. The analysis of the trends in frequency and persistence for each CT shows few significant trends, mainly in winter and spring with a general decrease of the cyclonic patterns and an increase of the anticyclonic situations. This can be related to the negative precipitation trends reported by other authors. Regarding the persistence, an interesting result is that there is a high interannual variability of the persistence in autumn and spring, when patterns can persist longer than in other seasons. An analysis of the most probable transitions between the CTs has been performed, revealing the existence of cyclic sequences in all seasons. These sequences are related to the high frequency of certain patterns such as the anticyclonic situations in winter. Finally, a clear seasonal dependence of the transitions between cyclonic situations associated with extratropical disturbances was found. This dependence suggests that the transitions of low-pressure systems towards the south of the IP are more likely in spring and autumn than in winter. 相似文献
16.
This study systematically analyzes the complete IPCC AR4 (CMIP3) ensemble of GCM simulations with respect to changes in extreme event characteristics at the end of the 21st century compared to present-day conditions. It complements previous studies by investigating a more comprehensive database and considering seasonal changes beside the annual time scale. Confirming previous studies, the agreement between the GCMs is generally high for temperature-related extremes, indicating increases of warm day occurrences and heatwave lengths, and decreases of cold extremes. However, we identify issues with the choice of indices used to quantify heatwave lengths, which do overall not affect the sign of the changes, but strongly impact the magnitude and patterns of projected changes in heatwave characteristics. Projected changes in precipitation and dryness extremes are more ambiguous than those in temperature extremes, despite some robust features, such as increasing dryness over the Mediterranean and increasing heavy precipitation over the Northern high latitudes. We also find that the assessment of projected changes in dryness depends on the index choice, and that models show less agreement regarding changes in soil moisture than in the commonly used ‘consecutive dry days’ index, which is based on precipitation data only. Finally an analysis of the scaling of changes of extreme temperature quantiles with global, regional and seasonal warming shows that much of the extreme quantile changes are due to a seasonal scaling of the regional annual-mean warming. This emphasizes the importance of the seasonal time scale also for extremes. Changes in extreme quantiles of temperature on land scale with changes in global annual mean temperature by a factor of more than 2 in some regions and seasons, implying large changes in extremes in several countries, even for the commonly discussed global 2°C-warming target. 相似文献
17.
P. Pato M. Otero M. Válega C.B. Lopes M.E. Pereira A.C. Duarte 《Marine pollution bulletin》2010,60(10):1658-1666
After having estimated the patterns of flow to the ocean and found some seasonal and tidal differences, mainly with regard to the relative importance of dissolved and particulate fractions, mercury partitioning at the interface between a contaminated lagoon and the Atlantic Ocean was investigated during four tidal cycles in contrasting season and tidal regimes. Mercury was found to be located predominantely in the particulate fraction throughout the year, contributing to its retention within the system. Seasonal conditions, variations in marine and fluvial signals and processes affecting bed sediment resuspension influenced the character and concentration of suspended particulate matter in the water column. Variation in the nature, levels and partitioning of organic carbon in the particulate fraction affected levels of particulate mercury as well as mercury partitioning. These results highlight the dominant role of suspended particulate matter in the distribution of anthropogenic mercury and reinforce the importance of competitive behavior related to organic carbon in mercury scavenging. 相似文献
18.
Wagner José Barreto Dilson Norio Ishikawa Ieda Spacino Scarminio João de Souza Costa Paulo dos Santos Nora Miriam de Fatima Soares Romilaine Mansano Nicolau Adriana Celeste Esteves Gonçalves Sonia Regina Giancoli Barreto 《洁净——土壤、空气、水》2008,36(4):353-359
The conservation of large water resources is essential for the preservation of human life. The quantification and, more importantly, the speciation of chemical substances that indicate the presence of anthropogenic contamination in water resources are of great importance. This paper presents the results of analysis for the determination of organic, inorganic and total phosphorus, pseudo‐sulfur, and iron and manganese, in five fractions, in water sediments collected from the Capivara Hydroelectric Power Plant, Brazil. A study on the seasonal variation of these parameters was conducted, with data having been collected in the winter and in the summer, at two sites along the dam, 5 km apart, close to the city of Primeiro de Maio. Phosphorous was found in sediments and adjacent soil in the organic form (OP), and was used as an indicator of anthropogenic influence on the reservoir banks. Speciation of potentially toxic Mn showed that it is present in the exchangeable fraction of the 0–5 cm depth layer (sediment/water interface), making its transfer to the water column possible. Results from this study showed that domestic and industrial effluent treatment measures are needed for the preservation of the quality of aquatic environments. 相似文献
19.
Morgan Ganerd Mark A. Smethurst Sonia Rousse Trond H. Torsvik Tore Prestvik 《Earth and Planetary Science Letters》2008,272(1-2):464-475
The paleomagnetic data sets from the British Tertiary Igneous Province (BTIP) have recently been criticized as being unreliable and discordant with data from elsewhere in the North Atlantic Igneous Province (NAIP) [Riisager et al. Earth Planet. Sci. Lett. 201 (2002) 261–276; Riisager et al. Earth Planet. Sci. Lett. 214 (2003) 409–425]. We offer new paleomagnetic data for the extensive lava flow sequence on the Isle of Mull, Scotland, and can confirm the paleomagnetic pole positions emanating from important earlier studies. Our new north paleomagnetic pole position for Eurasia at 59 ± 0.2 Ma has latitude 73.3°N, longitude 166.2°E (dp/dm = 5.2/7.0).A re-evaluation and an inter-comparison of the paleomagnetic database emanating from the NAIP were carried out to test for sub-province consistency. We find a general agreement between the Eurasian part of NAIP (BTIP and Faeroes) and East Greenland data. However a compilation of West Greenland data displays a large and unexplained dispersion. We speculate on if this is related to different sense of block rotation of the Tertiary West Greenland constituents. Combining all data from the NAIP constituents, give a pole position at 75.0°N, 169.9°E (N = 25, K = 84.3, A95 = 3.2) in Eurasian reference frame. 相似文献
20.
A growing body of evidence implies that the concept of 'treeless tundra' in eastern and northern Europe fails to explain the rapidity of Lateglacial and postglacial tree population dynamics of the region, yet the knowledge of the geographic locations and shifting of tree populations is fragmentary. Pollen, stomata and plant macrofossil stratigraphies from Lake Kurjanovas in the poorly studied eastern Baltic region provide improved knowledge of ranges of north‐eastern European trees during the Lateglacial and subsequent plant population responses to the abrupt climatic changes of the Lateglacial/Holocene transition. The results prove the Lateglacial presence of tree populations (Betula, Pinus and Picea) in the eastern Baltic region. Particularly relevant is the stomatal and plant macrofossil evidence showing the local presence of reproductive Picea populations during the Younger Dryas stadial at 12 900–11 700 cal. a BP, occurring along with Dryas octopetala and arctic herbs, indicating semi‐open vegetation. The spread of Pinus–Betula forest at ca. 14 400 cal. a BP, the rise of Picea at ca. 12 800 cal. a BP and the re‐establishment of Pinus–Betula forest at ca. 11 700 cal. a BP within a span of centuries further suggest strikingly rapid, climate‐driven ecosystem changes rather than gradual plant succession on a newly deglaciated land. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献