From back-arc to rifted margin: Geochemical and Nd isotopic records in Neoproterozoic?-Cambrian metabasites of the Bystrzyckie and Orlickie Mountains (Sudetes,SW Poland)

Metamorphosed during the Variscan orogeny, sediments of the ca. 560 Ma M?ynowiec Formation and ca. 530 Ma Stronie Formation in the Bystrzyckie and Orlickie Mountains (Central Sudetes, Poland) contain metabasites with a range of basaltic compositions. Immobile trace element and Nd isotope features allow distinction of dominant, either E-MORB-like (Group 1: Zr/Nb 9–20, εNd₅₃₀ +2.6 to +6.7) or mildly enriched N-MORB-like tholeiites (Group 2: Zr/Nb 21–27, εNd₅₃₀ +0.2 to +6.7), and scarce but genetically important OIB-like alkaline (Group 3: Zr/Nb 5, εNd₅₃₀ +2.2) or depleted tholeiitic rocks (Group 4: Zr/Nb 67, εNd₅₃₀ +7.9). Neither the radiogenic age nor age relationships between these four groups are known. However, field evidence suggests that the metabasites are younger than the M?ynowiec Formation and that their emplacement must have been coeval with the accumulation of the Stronie Formation sediments. The OIB affinity of Group 3 is interpreted to reflect an enriched mantle (EM)-type asthenopheric source whilst the groups of tholeiitic rocks indicate involvement of depleted (locally slightly residual) MORB-type mantle (DMM). Several geochemical signatures, the decoupling between Nd isotope and trace element characteristics, and melting models indicate variable enrichment of the DMM-like source, here ascribed to asthenosphere-derived OIB-like melts (Group 1 and 2) and a contribution from a supra-subduction zone (Group 2 and 4). Based on contrasting back-arc basin (BAB)- and within-plate-like affinities of the metabasites, and on petrogenetic constraints from the spatially related infill of the Stronie Formation rift basin, the studied magmatic episode is suggested be related to cessation of the supra-subduction zone activity, presumably induced by ridge-trench collision. This event might have led to slab break-off, the development of a transform plate boundary, opening of a slab window and upward migration of sub-slab enriched asthenosphere. Decompression melting of the upwelling asthenosphere could then have produced OIB-like melts which segregated and infiltrated into the mantle of the former subduction zone, with randomly distributed slab-derived components. In an extensional regime, magmas generated at shallow levels from heterogeneous mantle regions were emplaced within sedimentary rocks of the overlying rift basin. The vestiges of subduction-related processes and within-plate style of mantle enrichment suggest that the metabasites could be related to final stages of the Cadomian orogeny and incipient Early Palaeozoic rifting of Gondwana that heralded the opening of the Rheic Ocean.     

Exploring desiccation cracks in soils using a 2D profile laser device

The study of desiccation cracks in soils has been a subject of increasing attention in recent research. This paper presents the use of a 2D profile laser that is coupled with a motion controller (that allows scanning the overall surface of a drying soil) and electronic balance (to measure the water loss). The aim is to accurately track the three most relevant variables associated with the behavior of soils during desiccation: volume change, water loss and evolving crack network’s morphology. The paper presents the methodology to obtain a digital model of the soil using the experimental setup described above. The main results of a natural soil subjected to drying are presented and discussed, including evolution of cracks aperture; evolution of cracks depth, surface contour levels (at different times); and evolution of volume change. It is shown that the proposed methodology provides very useful information for studying the behavior of soils subjected to desiccation.     

The significance of Chara vegetation in the precipitation of lacustrine calcium carbonate

A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north‐east Poland), is characterized by: (i) carbonate sediments with a CaCO₃ content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO₃^? and forming thick CaCO₃ encrustations. Thus, this study was aimed at evaluating the CaCO₃ production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO₃ per 1 m² were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0·0625 m²) per transect. The composition and structure of phytoplankton and the physico‐chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m^?2 and CaCO₃ encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685·5 and 438 g m^?2, respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m^?2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO₃ sedimentation.     

ALTERNATIVE METHODS FOR CONDUCTING COMPARATIVE ANALYSES OF CADASTRAL SYSTEMS

The conception of an efficient cadastral system is an important element in the development of each coun-try. It is crucial for the efficient operation of the real estate market—the security and liberty of making transactions, register-ing a property, planning operations, the introduction of an ad valorem tax on property and more rational use of space. InEurope there are different types of cadastral systems, because the countries in Europe have different cultural back-grounds, different economical and social backgrounds. Through the centuries, many types of cadastral systems evolvedand their differences often depend upon local cultural heritage, physical geography, land use, technology, etc. Compara-tive analyses of cadastral systems have been the subjects of many publications and studies in world literature. It was as-sessed that the useful tools in conducting comparative analyses of various cadastral systems include the procedures of statisti-cal inference. This paper presents the results of a project to compare the performance of ten cadastral systems international-ly by creating appropriate integrated indicators of a cadastral system using statistical technique. Such indicators willmake it possible to compare different cadastral systems and present them hierarchically in relation to their quality, struc-ture, as well as legal, organizational and technological solutions. From a good number of methods available, techniquesoriginating from two spheres of statistic inference were selected: distribution free methods and multivariate analysis meth-ods. For analyses with the distribution free methods, FRIEDMAN‘‘s test (FRIENDMAN‘‘s non-parametric variance analy-sis) as well as KENDALL‘‘s test ( KENDALL‘‘s compatibility ratio) were selected. For analyses with the multivariate analy-sis methods, factor analysis was selected.     

Ellipsoids, material points and material segments

Simple models of potential based on material points and material segments are confronted with a homogeneous ellipsoid potential. A spheroid is approximated with a pair of material points or with one material segment. The segment model proves to be more accurate. For a triaxial ellipsoid, two models are considered: one with five material points and one with two material segments and a point. When their parameters are determined with the fourth sectorial harmonic ignored, both simple models have a similar approximation error. Numerical tests indicate that the approximate models of a triaxial ellipsoid are 5 to 10 times faster than exact formulation, whereas for a spheroid the approximate models are at most twice as fast as the exact formulae.     

The Influence of Selected Meteorological Parameters on the Concentration of Surface Ozone in the Central Region of Poland

Abstract?This paper presents the results of measurements of the concentration of surface ozone and concurrent standard meteorological parameters: total solar radiation, temperature, relative humidity, pressure, wind speed, and vertical and horizontal components of the wind. The data were collected from 2005 to 2010 at stations located in central Poland (Mazowieckie voivodeship): Warszawa (urban), Legionowo (suburban), Granica and Belsk (rural). Furthermore, Granica is situated in the forested area of Kampinoski National Park. Continuously measured surface ozone concentrations demonstrated the well-known diurnal cycle of surface ozone concentration with a maximum in the afternoon and a minimum in the early morning hours. The averaged diurnal variations over six years reveal that the highest concentrations appear at rural stations (Belsk: 55?µg?m^?3 and Granica: 50?µg?m^?3) and the lowest at the urban station (Warszawa: 41?µg?m^?3). The threshold for high levels of surface ozone (120?µg?m^?3 per 8?h) was exceeded most often at Granica and Belsk. The occurrence of the ozone “weekend effect,” especially at urban stations, has been identified. The difference between weekend and weekday surface ozone concentrations at urban and rural stations was as high as 6.5?µg?m^?3 and approximately 2?µg?m^?3, respectively. Using appropriate statistical tools, it has been shown that meteorological conditions have a significant influence on ozone concentration. High correlation coefficients were found between ozone concentration and solar radiation, temperature, relative humidity, and wind speed. The forward stepwise regression model explains up to 75% of the variations in daily surface ozone concentration in terms of meteorological variability in summer and up to 70% in winter. At the same time, a multilayer perceptron neural network model was used to reconstruct the concentration of surface ozone. High correlation coefficients (up to 0.89) indicate that, on the basis of standard meteorological parameters and NO₂ concentration, we can determine ozone concentration with high accuracy.     

Tithonian–Early Valanginian evolution of deposition along the proto-Caribbean margin of North America recorded in Guaniguanico successions (western Cuba)

In the Guaniguanico Mountains of western Cuba, the Late Jurassic–Early Cretaceous limestones occur in three stratigraphic successions, which have accumulated along the proto-Caribbean margin of North America. The Late Jurassic subsidence and shallow-water carbonate deposition of the Guaniguanico successions have no counterpart on the northeastern Maya block, but some distant similarities with the southeastern Gulf of Mexico may exist. Four facies types have been distinguished in the Tithonian–Lower Valanginian deposits of the Guaniguanico tectonic units. Drowning of the Late Jurassic carbonate bank of the Sierra de los Organos occurred at the Kimmeridgian/Tithonian boundary. During this boundary interval, sedimentation in the west Cuban area and southwestern margin of the Maya block (Mexico) has evolved in a similar way in response to a major second-order transgression.The Lower Tithonian ammonite assemblages of the Guaniguanico successions indicate, in general, the neritic zone. Presence of juvenile gastropods and lack of adult specimens suggest unfavorable environment for these molluscs, probably related to low oxygenation levels. The Early Tithonian transgressive phase terminated about the lower boundary of the Chitinoidella Zone. The Late Tithonian “regressive” phase is weakly marked, whereas the latest Tithonian–earliest Berriasian strata were deposited during a deepening phase. The latter transgressive phase has ended in the Late Berriasian Oblonga Subzone. We correlate the bioturbated pelagic biomicrites of the Tumbitas Member of the Guasasa Formation with a significant fall of the sea level during the latest Berriasian–Early Valanginian. The average sedimentation rate for the Tumbitas Member biomicrites was about three times faster than for the Berriasian Tumbadero Member limestones. Sedimentation rates for the Tumbitas Member and the Valanginian limestones at the DSDP Site 535 in the southeastern Gulf of Mexico were similar. In the Los Organos succession, the Late Valanginian transgressive interval is associated with radiolarian limestones and black chert interbeds in the lower part of the Pons Formation. In the Southern Rosario succession, the pelagic limestones pass into the radiolarian cherts of the Santa Teresa Formation indicating a proximity of CCD during Late Valanginian–Hauterivian times.     

Explicit stress integration with error control for the Barcelona Basic Model.: Part II: Algorithms efficiency and accuracy

The paper compares the accuracy and efficiency of explicit stress integration schemes for elasto-plastic unsaturated soil models with automatic error control. Numerical tests are performed with reference to the Barcelona Basic Model (BBM), one of the most popular elasto-plastic models for unsaturated soils, by using eight explicit Runge–Kutta algorithms of various order as well as a novel application of the extrapolation method described in the companion paper. Initially, the results obtained from the lowest order Runge–Kutta scheme (i.e. Modified Euler) as well as the extrapolation method are checked against accurate solutions of a number of BBM paths involving changes of strains and suction. Subsequently, the efficiency and accuracy of all algorithms are assessed for generic increments of strains and suction, while the difference between two alternative error control methods is also analysed. The results presented, although strictly valid for the Barcelona Basic Model, are expected to be general and relevant to other similar unsaturated elasto-plastic models formulated in terms of two independent stress variables such as net stress and suction.     

A combined neural network/gradient‐based approach for the identification of constitutive model parameters using self‐boring pressuremeter tests

This paper presents a numerical procedure of material parameter identification for the coupled hydro‐mechanical boundary value problem (BVP) of the self‐boring pressuremeter test (SBPT) in clay. First, the neural network (NN) technique is applied to obtain an initial estimate of model parameters, taking into account the possible drainage conditions during the expansion test. This technique is used to avoid potential pitfalls related to the conventional gradient‐based optimization techniques, considered here as a corrector that improves predicted parameters. Parameter identification based on measurements obtained through the pressuremeter expansion test and two types of holding tests is illustrated on the Modified Cam clay model. NNs are trained using a set of test samples, which are generated by means of finite element simulations of SBPT. The measurements obtained through expansion and consolidation tests are normalized so that NN predictors operate independently of the testing depth. Examples of parameter determination are demonstrated on both numerical and field data. The efficiency of the combined parameter identification in terms of accuracy, effectiveness and computational effort is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.