Geometries of Gilbert-type deltas and large channels in the Meteora Conglomerate, Meso-Hellenic basin (Oligo-Miocene), central Greece

The Meteora conglomerate is a thick, coarse-grained unit of Oligo-Miocene age in the Meso-Hellenic basin consisting of Gilbert-type delta deposits (wedge-shaped bodies) and deep channel fills. Gilbert-type deltas prograded from the eastern margin basinward, perpendicular to the NW-SE basin axis. Delta bodies are thicker in the distal portion, where the dip of the foresets is lower than in the proximal area. Organized and disorganized conglomerates coexist, suggesting a mixture of mass- and turbulent-flow processes. The mass flow deposits seem to prevail in the uppermost part of the foresets. Channels (up to 25 m deep) are cut into the Gilbert-type delta deposits, and have axes perpendicular to the progradational trend of the deltas. Giant bars displaying accretion of the downstream side formed inside the channels. The channels were probably cut into Gilbert-delta deposits due to uplift of the source area or to a fall in sea-level. Although large cross-sets of both Gilbert delta and channels have been formed by progradation, they can be distinguished by: (i) angle of foreset bed dips, (ii) facies and textures and (iii) vertical sequences. Differences in these features aid in distinguishing Gilbert-type deltas from in-channel bars.     

THE FLUCTUATIONS OF ITALIAN GLACIERS DURING THE LAST CENTURY: A CONTRIBUTION TO KNOWLEDGE ABOUT ALPINE GLACIER CHANGES

This paper describes the recent evolution of Italian glaciers through an analysis of all available terminus fluctuation data that the authors have entered in a glaciers database (named GLAD) containing 883 records collected on glaciers from 1908 to 2002. Furthermore, a representative subset of data (249 glaciers located in Lombardy) was analysed regarding surface area changes. For the analysis of terminus fluctuations, the glaciers were sorted by size classes according to length. The data showed that during the 20th century Italian Alpine glaciers underwent a generalized retreat, with one distinct and well documented readvance episode that occurred between the 1970s and mid‐1980s, and a poorly documented one around the early 1920s. The rates of terminus advance and retreat have changed without significant delays for the larger glaciers with respect to the smaller ones. However, the smaller the glacier, the more limited the advance (if any) during the 1970s and early 1980s. The behaviour of glaciers shorter than 1 km appears to have changed in the last decade, and between 1993 and 2002 they retreated at a very high rate. The analysis of the subset of data led to a quanti‐fication of surface reduction of c. 10% from 1992 to 1999 for glaciers in Lombardy. Small glaciers proved to contribute strongly to total area loss: in 1999, 232 glaciers (c. 90% of the total) were smaller than 1 km², covering 27.2 km² (less than 30% of the total area), but accounted for 58% of the total loss in area (they had lost 7.4 km²).     

Effect of Phosphatization on Element Concentration of Cobalt-Rich Ferromanganese Crusts

1 Introduction Co-rich ferromanganese crusts occurring on submarine guyots have received much attention from scientists since the beginning of the 1980’s because they are enriched in Co, Mn, Pt, and rare earth elements (REEs), and have large potential mineral resources, occurring as they do on topographic highs relative to polymetallic nodules in the C-C (Clarion-Clipperton) zone (Halbach et al., 1982, 1989; Hein et al., 1992, 1999; Usui and Someya, 1997; Yamazaki and Sharma, 1998, 2000…     

西太平洋富钴结壳生长与富集特征

通过对西太平洋麦哲伦海山区富钴结壳的大尺度细致研究 ,笔者较为深入地探讨了该区结壳的生长与富集特征。研究表明 ,该区结壳自古近纪开始生长 ,生长速率变化范围为 1.5～ 12 .3mm/Ma,速率相差近一个数量级 ,平均生长速率为 3.81m m/Ma;生长过程中成矿元素的地球化学行为呈现明显差异 ;环境发生“骤变”的 O/M界面 ,可能是结壳生长过程中其构造和色泽发生“突变”的一个重要年代 ;成矿元素成分的时序演化主要受控于海水化学和各种不同地质作用的综合影响 ,成矿与非成矿地质作用在生长过程中呈现为互为消长的特征。研究发现 ,该区结壳和太平洋深海粘土元素的分配系数间存在着显著的线性相关关系 ,相关系数为 0 .89,显示它们有相近的元素富集机理。此外 ,笔者还从元素的滞留时间、阳离子的电子键能及其在海水中的水解行为与结壳富集特征间的关系进行了探讨。     

Stratal patterns: a proposal of classification and examples from the Dolomites

Abstract A classification of stratal patterns is proposed from outcrop analysis of the Middle-Upper Triassic succession of the Dolomites (northern Italy). Stratal patterns are classified into two groups: stratal discontinuities and internal geometries. The stratal discontinuities are further subdivided into unconformities and synsedimentary stratal discontinuities on the basis of whether significant time is missing at the discontinuity. Internal geometries are further subdivided into planes and internal patterns.     

Experimental Crystallization of a High-K Arc Basalt: the Golden Pumice, Stromboli Volcano (Italy)

The near-liquidus crystallization of a high-K basalt (PST-9golden pumice, 49·4 wt % SiO₂, 1·85 wt % K₂O,7·96 wt % MgO) from the present-day activity of Stromboli(Aeolian Islands, Italy) has been experimentally investigatedbetween 1050 and 1175°C, at pressures from 50 to 400 MPa,for melt H₂O concentrations between 1·2 and 5·5wt % and NNO ranging from –0·07 to +2·32.A drop-quench device was systematically used. AuPd alloys wereused as containers in most cases, resulting in an average Feloss of 13% for the 34 charges studied. Major crystallizingphases include clinopyroxene, olivine and plagioclase. Fe–Tioxide was encountered in a few charges. Clinopyroxene is theliquidus phase at 400 MPa down to at least 200 MPa, followedby olivine and plagioclase. The compositions of all major phasesand glass vary systematically with the proportion of crystals.Ca in clinopyroxene sensitively depends on the H₂O concentrationof the coexisting melt, and clinopyroxene Mg-number shows aweak negative correlation with NNO. The experimental data allowthe liquidus surface of PST-9 to be defined. When used in combinationwith melt inclusion data, a consistent set of pre-eruptive pressures(100–270 MPa), temperatures (1140–1160°C) andmelt H₂O concentrations is obtained. Near-liquidus phase equilibriaand clinopyroxene Ca contents require melt H₂O concentrations<2·7–3·6 and 3 ± 1 wt %, respectively,overlapping with the maximum frequency of glass inclusion data(2·5–2·7 wt % H₂O). For olivine to crystallizeclose to the liquidus, pressures close to 200 MPa are needed.Redox conditions around NNO = +0·5 are inferred fromclinopyroxene compositions. The determined pre-eruptive parametersrefer to the storage region of golden pumice melts, which islocated at a depth of around 7·5 km, within the metamorphicarc crust. Golden pumice melts ascending from their storagezone along an adiabat will not experience crystallization ontheir way to the surface. KEY WORDS: basalt; pumice; experiment; phase equilibria; Stromboli     

Sedimentation, fracturing and sliding on a pelagic plateau margin: the Middle Jurassic to Lower Cretaceous succession of Rocca Busambra (Western Sicily, Italy)

The Jurassic succession of Rocca Busambra consists of two lithostratigraphic units: a pile of peritidal limestones several hundreds of metres thick (Inici Formation: Hettangian to Sinemurian) and a 2 to 15 m thick sequence of Rosso Ammonitico‐type pelagic limestones (Toarcian? to lowermost Berriasian). An extensive interval of non‐deposition is evidenced by a thick Fe–Mn oxide crust on the bounding disconformity and is recorded partially in the material contained within a complex network of neptunian dykes and sills. Seven lithofacies are distinguished in the Rosso Ammonitico. These lithofacies show that the Rosso Ammonitico limestones differ from most analogues both in Sicily and elsewhere: sediments are mostly grain‐supported and non‐nodular; obviously bottom currents were important during deposition of these sediments. These currents were pulsating at different frequencies and induced winnowing, intraclast production and early cement precipitation. Other Rosso Ammonitico lithosomes of Late Jurassic to earliest Cretaceous age, usually decimetre thick and discontinuous, overlie the Inici Formation without any Fe–Mn crust; their anomalous stratigraphical and geometrical relationships show that they were deposited on an inclined, stepped, erosional surface incised in the sub‐horizontal Inici Formation. This ancient escarpment is interpreted as the result of a mainly gravitational collapse of the margin of a pelagic plateau. Such mass wasting was probably due to the backstepping of the tectonic plateau–basin margin that is not observable directly, but may be inferred from circumstantial evidence. This observation clearly shows that tectonic activity affected the Rocca Busambra sector of the West Tethys continental margins a few tens of millions of years after the end of the rifting stage. The anomalous Rosso Ammonitico sediments are the only indication of the escarpment and their occurrence in the stratigraphic record is probably more widespread than reported in the literature. More accurate palaeoenvironmental and palaeogeographic reconstructions may depend on the identification of these sediments.