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1.
The Antola Formation of Upper Cretaceous age crops out extensively in the Northern Apennines and consists of graded units of calcareous sandstones, sandstones, marlstones, and shales. It can be subdivided into the Cerreto, Antola Marlstone, Bruggi, and S. Donato Members on the basis of bed thicknesses and percentage of shales. Although the whole formation is interpreted as a deep-sea basin plain deposit, the members constitute lateral facies subdivisions which range from proximal, thick-bedded turbidities that show a prevalence of thinning upward cycles in bed thicknesses to distal turbidites that show predominantly thickening upward cycles and have a high percentage of shale. Repetitive patterns in the lithological sequence of the turbidite association are generally distinctive and are satisfactorily described as first order Markov chains. Only the Antola Marlstone Member has an additional second order Markov property. Imaginary eigenvalues of the transition probability matrices of all but the Bruggi Member demonstrate a strong cyclic character in the lithologic ordering within the formation. The behaviour of the Antola Marlstone and of the Bruggi may reflect the influence of a secondary ophiolitic intra-basinal source of clastics that contributed sandy turbidites and olistostromes. Systematic long-term variations in the sequence of bed thickness development in some sections of the Antola Formation are often subtle and equivocal, and pose special problems in interpretation. Fourier analysis was applied to the task of partitioning fundamental wavelengths from “background noise” introduced by essentially random depositional processes. In all members there is (1) strong short-term wavelength of two to three beds indicative of alternating thin and thick beds and judged to be typical of turbidite sequences; (2) an intermediate wavelength ranging from about five beds (proximal facies), eight beds (distal) to nine beds (very distal), which have both thinning and thickening upward trends, interpreted respectively as valley fill due to shifting talwegs of low density turbidity currents, and to progradational, flat turbidite lobes; (3) a poorly defined long-term wave-length of from thirty to greater than sixty beds that may be related to an unspecified trend in the evolution of the sedimentary basin. Phase angles associated with the coniputed power spectra give indications as to the asymmetry (thickening or thinning upward) or symmetry of the representative units. 相似文献
2.
The prograde disappearance of staurolite can be described inthe model system K2O-FeO-MgO-Al2O3-SiO2-H2O (KFMASH) by thereaction: staurolite + muscovite + quartz = biotite + aluminumsilicate + garnet + water. The common occurrence and world—widedistribution of the assemblage staurolite-biotite-aluminum silicate-garnet(SBAG) in quartz-mica-schist suggest that the model reactionmay be over-simplified. Previous workers have suggested thatthe SBAG assemblage (1) is a strictly divariant assemblage thatbuffered water activity, (2) is stabilized by non-KFMASH components,and (3) did not attain equilibrium. We used least-squares regression to show that balanced reactionsdo not exist among the minerals in samples of SBAG assemblagesfrom Califonia and New England. The absence of reaction relationshipscan be explained by imbalances in two or three of the minorelements Zn, Mn, and either Ca or Na. The assemblage is apparentlystabilized by non-KFMASH components. Criteria for mapping staurolite-out isograds that representthe conditions of the KFMASH staurolite-out reaction dependon which of the four phases is the ‘extra’ phase,and require an understanding of the thermodynamic effects ofall the ‘extra’ components. Our results suggestthat transition zones of SBAG assemblages near staurolite-outisograds are the result of ‘extra’ components. However,it is uncertain whether µH2O of fluids in equilibriumwith SBAG assemblages varied across such zones. 相似文献
3.
DARIO TERRIBILINI OTTO EUGSTER MARIO BURGER ALFRED JAKOB URS KrHENBÜHL 《Meteoritics & planetary science》1998,33(4):677-684
Abstract— We report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene, maskelynite/mesostasis glass, and bulk material of Shergotty and of bulk samples from Chassigny and Yamato 793605. The 40K-40Ar isochron for the Shergotty minerals yields a gas retention age of 196 Ma, which is, within errors, in agreement with previously determined Rb-Sr internal isochron ages. Argon that was trapped at this time has a 40Ar/36Ar ratio of 1100. For Chassigny and Y-793605, we obtain trapped 40Ar/36Ar ratios of 1380 and 950, respectively. Using these results and literature data, we show that the three shergottites, Shergotty, Zagami, and QUE 94001; the lherzolites ALH 77005, LEW 88516, and Y-793605; as well as Chassigny and ALH 84001 contain a mixture of Martian mantle and atmospheric Ar; whereas, the trapped 40Ar/36Ar ratio of the nakhlites, Nakhla, Lafayette, and Governador Valadares cannot be determined with the present data. We show that Martian atmospheric trapped Ar in Martian meteorites is correlated with the shock pressure that they experienced. Hence, we conclude that the Martian atmospheric gases were introduced by shock into the meteoritic material. For the Shergotty minerals, we obtain 3He-, 21Ne-, and 38Ar-based cosmic-ray exposure ages of 3.0 Ma, and for the lherzolite Y-793605, 4.0 Ma, which confirms our earlier conclusion that the lherzolites were ejected from Mars ～1 Ma before the shergottites. Chassigny yields the previously known ejection age of 11.6 Ma. 相似文献
4.
Abstract The effects induced on the climate by human activity have become a major issue for the new millennium. In order to arrive at sustainable conclusions it is necessary, first of all, to assess and quantify natural climatic changes. In general this is done by analysing available time series. In the case of historical hydrometeorological data sets, a comparative analysis with solar cycles is not usually conducted. This work, however, demonstrates that the effect of solar cycles observed at the Equator is also visible at middle and high latitudes with multiple periodicity of the basic solar frequency (roughly 11 years). This could well be due to the interaction between solar forcing and circulation mechanisms within the atmosphere, i.e. water-air-soil interactions coupled with anthropogenic forcing. This theory has been tested by comparing different types of historical data series with the River Po discharges and cyclic appearance of slime bloom in the Adriatic Sea. 相似文献
5.
MARIO CONIGLIO 《Sedimentology》1987,34(5):813-823
Chert in the Cow Head Group is mainly a replacement of limestone and shale and, to a lesser extent, an interparticle cement. Its field occurrences are distinct as: (1) silicified margins on coarse conglomerates and thinly bedded limestones; (2) nodules within limestone and shale; (3) pervasively silicified beds of limestone and shale; and (4) clasts or partial replacement of clasts within conglomerate. Radiolarians and sponge spicules are composed of microquartz or calcite and are particularly common in the Ordovician part of the succession where most chert occurs. In limestone spatially associated with chert, the use of cathodoluminescence demonstrates that calcite-replaced radiolarians and spicules are volumetrically more important than realized through transmitted-light petrography. Petrographic relations between siliceous and rare pyritized radiolarians further indicate that these particles may be dissolved prior to compaction. No trace of their former existence remains, other than indirectly through the presence of silicified limestone and shale. Crushed grains cemented by chalcedony indicate that chert was precipitated during or after compaction. The history of silicification and the replacement or dissolution of siliceous bioclasts is protracted, ranging from near the sediment-water interface, where it is concomitant with early limestone lithification, to deeper burial, postdating mechanical compaction. 相似文献
6.
GIOVANNA SCOPELLITI RODOLFO NERI ADRIANA BELLANCA PIETRO DI STEFANO† MARIO BARBIERI‡ 《Sedimentology》2009,56(2):591-607
In this study, the Pietra di Billiemi , a famous dimension stone, is investigated because it records the tectonic evolution of the south Tethys continental margin and preserves a record of major environmental changes occurring near the Triassic/Jurassic boundary. The Pietra di Billiemi is a grey, coarse-grained and clast-supported limestone breccia cropping out in an area of the Palermo Mountains representing a segment of the Apennine–Maghrebian chain in western Sicily. The rock consists of metre-sized to centimetre-sized angular clasts, derived from Upper Triassic sponge boundstones and rudstones, with a differently coloured, silt-grained matrix. Fitted fragments are observed commonly which suggest an in situ origin for the bulk of the breccia. The matrix is characterized by the absence of biogenic components and by variable mineralogy and geochemistry. Petrographic features and Sr-isotope values indicate that the most important and earliest fillings of the breccia consist of black matrix and white matrix temporally referable to Hettangian–Sinemurian times. Clotted micrite, carbonate fluorapatite and abundant pyrite, in addition to relatively high contents of redox-sensitive elements (V, Ni, Zn and S), are consistent with deposition in anoxic conditions that favoured microbial mediation for authigenic carbonate (calcite and dolomite) precipitation in the matrix. As a whole, the Billiemi breccia can be considered a product of tectonic fragmentation of a Tethyan carbonate platform edge around the Triassic/Jurassic boundary, formed when the drowned platform edge was covered by hemipelagic mudstones recording the anoxic conditions existing during Early Jurassic times. 相似文献
7.
This work aims to contribute to the characterization and understanding of infragravity waves on two beaches with erosion problems. For this reason, we have used an array of ADCP and a pressure sensor to measure wave parameters and pressure inside and outside of the surf zone during the dry and rainy period in the beaches of Galerazamba and Manzanillo del Mar (both dissipative and eroded beaches) located in the Colombian Caribbean coast. Based on these measurements, we have carried out a spectral analysis in order to identify the frequency components that characterize the wave and its energy; thus, we identified the characteristic frequencies of infragravity waves to finally filter the infragravity signal on each beach in different seasonal periods. Among the results of the Welch spectrum applied to surface elevation time series, we found that, the frequencies'' energy of the sea-swell band decreases due to bottom friction and wave breaking as the wave approaches the shore, while the frequencies'' energy of the infragravity band increases significantly. In addition, for the wavelet analysis, we could observe how the energy of the infragravity band, especially the lowest frequencies gain energy as the waves approaches the coast. Furthermore, based on the infragravity wave obtained from the extreme wave event registered during the field campaign we can conclude that the contribution of this signal is important in the erosion problems presented in the beaches of Galerazamba and Manzanillo del Mar. Finally, these results show the need to realize other studies that allow us to understand deeply, the role of infragravity waves on the morphological changes that occurs in these beaches. 相似文献
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9.
MARIO TRIELOFF ALEXANDER DEUTSCH ELMAR K. JESSBERGER 《Meteoritics & planetary science》1998,33(2):361-372
Abstract— For the ～65 km sized Kara impact structure close to the polar Ural, we report an age of 70.3 ± 2.2 Ma (2s?), defined by the mean of 40Ar-39Ar plateau ages for three glassy or crystalline impact melt rocks cleaned from mineral and rock clasts. The fine structure of the age spectra of these samples can quantitatively be simulated by modeling taking into account 39Ar recoil effects, without assuming the presence of excess Ar. The calculations corroborate our age results by showing that 39Ar recoil does not affect the plateau fractions. Previously, Kara has been proposed as a probable K/T impact site or was related to the Campanian-Maastrichtian boundary at 73 Ma. At the 2s? level, both suggestions are ruled out by the well-constrained age for the Kara impact structure. 相似文献
10.
MARIO MORELLÓN BLAS VALERO-GARCÉS FLAVIO ANSELMETTI† DANIEL ARIZTEGUI‡ MICHAEL SCHNELLMANN§ ANA MORENO¶ PILAR MATA MAYTE RICO JUAN PABLO CORELLA 《Sedimentology》2009,56(5):1505-1534
Lake Estanya is a small (19 ha), freshwater to brackish, monomictic lake formed by the coalescence of two karstic sinkholes with maximum water depths of 12 and 20 m, located in the Pre‐Pyrenean Ranges (North‐eastern Spain). The lake is hydrologically closed and the water balance is controlled mostly by groundwater input and evaporation. Three main modern depositional sub‐environments can be recognized as: (i) a carbonate‐producing ‘littoral platform’; (ii) a steep ‘talus’ dominated by reworking of littoral sediments and mass‐wasting processes; and (iii) an ‘offshore, distal area’, seasonally affected by anoxia with fine‐grained, clastic sediment deposition. A seismic survey identified up to 15 m thick sedimentary infill comprising: (i) a ‘basal unit’, seismically transparent and restricted to the depocentres of both sub‐basins; (ii) an ‘intermediate unit’ characterized by continuous high‐amplitude reflections; and (iii) an ‘upper unit’ with strong parallel reflectors. Several mass‐wasting deposits occur in both sub‐basins. Five sediment cores were analysed using sedimentological, microscopic, geochemical and physical techniques. The chronological model for the sediment sequence is based on 17 accelerator mass spectrometry 14C dates. Five depositional environments were characterized by their respective sedimentary facies associations. The depositional history of Lake Estanya during the last ca 21 kyr comprises five stages: (i) a brackish, shallow, calcite‐producing lake during full glacial times (21 to 17·3 kyr bp ); (ii) a saline, permanent, relatively deep lake during the late glacial (17·3 to 11·6 kyr bp ); (iii) an ephemeral, saline lake and saline mudflat complex during the transition to the Holocene (11·6 to 9·4 kyr bp ); (iv) a saline lake with gypsum‐rich, laminated facies and abundant microbial mats punctuated by periods of more frequent flooding episodes and clastic‐dominated deposition during the Holocene (9·4 to 0·8 kyr bp ); and (v) a deep, freshwater to brackish lake with high clastic input during the last 800 years. Climate‐driven hydrological fluctuations are the main internal control in the evolution of the lake during the last 21 kyr, affecting water salinity, lake‐level changes and water stratification. However, external factors, such as karstic processes, clastic input and the occurrence of mass‐flows, are also significant. The facies model defined for Lake Estanya is an essential tool for deciphering the main factors influencing lake deposition and to evaluate the most suitable proxies for lake level, climate and environmental reconstructions, and it is applicable to modern karstic lakes and to ancient lacustrine formations. 相似文献