Continuity and facies heterogeneities of shallow carbonate ramp cycles (Sinemurian,Lower Jurassic,North‐east Spain)

The lateral continuity and facies heterogeneities of metre‐scale cycles in a greenhouse Lower Jurassic (Sinemurian) carbonate ramp from the northern Iberian Basin (Spain) was evaluated from extensive field analysis carried out on a well‐exposed 12 km long outcrop. Eleven high‐frequency continuous cycles and their bounding surfaces are traceable laterally through the entire outcrop. However, three of these cycles are found to split laterally into discontinuous cycles of more limited distribution (up to 3 to 5 km of lateral extent). The continuous and discontinuous cycles have a similar field expression in one‐dimensional logs. As a consequence, the number of cycles that can be differentiated is variable along the logged sections (i.e. from 11 to 16). Cycles have variable facies heterogeneities and sedimentary trends depending on the environment of formation: shallowing‐upward and symmetrical cycles occur in protected lagoon–tidal flat areas and in the open‐marine, high‐energy domain. These cycles show significant facies heterogeneities, which were controlled mainly by lateral migration of a mosaic of facies over an irregular topography. Deepening‐upward and aggradational cycles are generated in low‐energy, sub wave‐base, open‐marine areas. Facies are laterally homogeneous, reflecting low potential for carbonate accumulation and inability to fill the created accommodation space in this low‐relief and relatively deep area. Cycle boundaries are generated by stages of rapid accommodation gain, involving the flooding of the carbonate ramp; they are more likely to originate from regional tectonic pulses (related to the extensional tectonics operating in the northern Iberian Basin) rather than greenhouse low‐amplitude eustacy. Discontinuous cycles tend to occur in thickened areas and are interpreted as originating from the infill of wedge‐shaped accommodation space resulting from differential subsidence (i.e. local tectonic pulses). In conclusion, where thickness variations occur in extensional settings lateral continuity of cycles should not be expected. In less well‐exposed, or in one‐dimensional sections and in wells, it would not be possible to distinguish continuous from discontinuous cycles, or to understand such two‐dimensional heterogeneities. Identification of unique cycle‐forming mechanisms or attempting cyclostratigraphic long‐distance correlation of cycles is unrealistic without a detailed analysis of the architecture of cycles in laterally continuous outcrops.     

20th-CENTURY CHANGES OF TEMPERATURE IN THE MOUNTAIN REGIONS OF CENTRAL EUROPE

Daily maximum and minimum temperatures from 29 low-lying and mountain stations of 7 countries in Central Europe were analyzed. The analysis of the annual variation of diurnal temperature range helps to distinguish unique climatic characteristics of high and low altitude stations. A comparison of the time series of extreme daily temperatures as well as mean temperature shows a good agreement between the low-lying stations and the mountain stations. Many of the pronounced warm and cold periods are present in all time series and are therefore representative for the whole region. A linear trend analysis of the station data for the period 1901–1990 (19 stations) and 1951–1990 (all 29 stations) shows spatial patterns of similar changes in maximum and minimum daily temperatures and diurnal temperature range. Mountain stations show only small changes of the diurnal temperature range over the 1901–1990 period, whereas the low-lying stations in the western part of the Alps show a significant decrease of diurnal temperature range, caused by strong increase of the minimum temperature. For the shorter period 1951–1990, the diurnal temperature range decreases at the western low-lying stations, mainly in spring, whereas it remains roughly constant at the mountain stations. The decrease of diurnal temperature range is stronger in the western part than in the eastern part of the Alps.     

Analyzing the genesis, intensity, and tracks of western Mediterranean cyclones

Midlatitude cyclones are analyzed on a selected region covering most of southern Europe and the western part of the Mediterranean Sea (35–50°N, 10°W–25°E). On the basis of mean sea level pressure fields of the ECMWF (European Centre for Medium-range Weather Forecast) Reanalysis Dataset (ERA-40), detailed evaluation of Mediterranean cyclones is accomplished for the period between 1957 and 2002 on a 1° horizontal resolution grid. Cyclone centers are identified and their paths are tracked with a 6-h time step (using 00 UTC, 06 UTC, 12 UTC, and 18 UTC). Decadal, annual, and seasonal statistical analysis of cyclone tracks includes the study of the genesis, frequency, and activity of the Mediterranean cyclones as well as the variability of cyclone tracks. The results suggest that the cyclone frequency in the western Mediterranean region increased in summer and autumn, and decreased in winter and spring. A special belt-shaped area is identified, which plays a special role in cyclogenesis, and also, the cyclone tracks often remain within this belt. An overall decreasing trend is detected in winter and spring in the entire Mediterranean belt, while cyclone frequency increased in autumn. The largest positive and negative trend coefficients are identified in summer.     

Black crusts on travertine: factors controlling development and stability

The travertine buildings of Budapest show extensive black crust formation, which is related to high concentration of atmospheric pollution and a continental climate. Laminar black crusts, framboidal black crusts and leached white surfaces are compared. Physical properties (Schmidt hammer rebound, Duroscope rebound), mineralogical composition and elemental composition are measured. Framboidal black crusts contain more than 50% of acicular gypsum. The crust surface displays idiomorphic rosette-like gypsum crystals with particulates, calcite and gypsum crystal aggregates. The sulphur isotopic composition of the black crusts pinpoints the involvement of rain and dust in crust formation. Thick framboidal black crust has the lowest strength while thin laminar black crust and white dissolved surfaces show minor decrease in surface strength compared to unaltered travertine. The crusts adhere to the travertine surface and rarely show mechanical decay forms that are typical features of porous limestone ashlars in Budapest.