Inversion of the geomagnetic field determined by palaeomagnetic investigations of quaternary sediments

Résumé Au cours des recherches paléomagnétiques en Tchécoslovaquie, on a constaté und double polarité de la magnétisation rémanente des sédiments quaternaires. Des recherches plus détaillées de la localité Červeny kopec près de Brno, qui représente une région de sédiments avec une suite initerrompue de couches déposées au cours d'un million d'années dernières, datées par la méthode de correlation astronomique, fournissent certains résultats importants sur l'époque au cours de laquelle s'est passé l'inversion du champ géomagnétique. Selon nos recherches de jusqu'à présent, on peut déterminer la fin de l'époque inverse de Matuyama par 0,930 million d'années environ. Après elle succède la pèriode de transition, dont la durée est de 60 000 ans environ, au cours de laquelle se sont passé des changements rapides dans le champ géomagnétique et au cours de laquelle existent des roches possédant une magnétisation avec inclinaison soit positive, soit négative. L'époque de polarité normale de Brunhes commence selon nos constatations autour de 0,870 million d'années.

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Microencruster-microbial-cement framework of the Upper Jurassic reef developed on the slope of the intra-Tethyan carbonate platform (Bulgaria)

The carbonate succession in the Lyalintsi section of the western Moesian Platform (western Bulgaria) displays a shallowing-upward trend. Growth of the Tithonian–Valanginian coral biostromes and low-relief bioherms was preceded by Oxfordian–Kimmeridgian sedimentation of fine-grained peloidal-bioclastic limestones and Saccocoma-bearing limestones on the homoclinal ramp and the carbonate platform slope. In the late Kimmeridgian, boundstones with very rare corals, but with easily recognisable biohermal morphology, were developed. The main components of this reef are encrusting microorganisms, microbial crusts and synsedimentary cements. Microencrusters Labes atramentosa, Crescentiella morronensis, Perturbatacrusta leini and Radiomura cautica, as well as thin crusts of calcified sponges (sclerosponges), are the main biotic components. Corals (almost exclusively microsolenids) are sparse, whereas photophilic microencrusters (e.g., “Lithocodium–Bacinella”), are absent, although they are common in the overlying shallow-water part of the Lyalintsi sequence. Microbialites and synsedimentary cements provided additional support for the reef framework. The framework, especially the biotic components, and the reefal facies position within the sedimentary succession, implies that the high-energy upper slope of the carbonate platform was the depositional setting of the microencruster-microbial-cement reef studied. Encrusting microorganisms, except for C. morronensis and sponges, are only known from the intra-Tethyan platforms. This study supports conclusion of studies of coeval Alpine reefs that the presence of the microencruster-microbial-cement framework provides insight into the palaeobathymetry, palaeogeography and tectonic configuration of the intra-Tethyan carbonate platforms.     

Information effect on remediation design of contaminated aquifers using the pump and treat method

We examine the effect of uncertainty due to limited information on the remediation design of a contaminated aquifer using the pump and treat method. The hydraulic conductivity and contaminant concentration distributions for a fictitious contaminated aquifer are generated assuming a limited number of sampling locations. Stochastic optimization with multiple realizations is used to account for aquifer uncertainty. The optimization process involves a genetic algorithm (GA). As the number of realizations increases, a greater extraction rate and more wells are needed. There was a total cost increase, but the optimal remediation designs became more reliable. Stochastic optimization analysis also determines the locations for extraction wells, the variation in extraction rates as a function of the change of well locations, and the reliability of the optimal designs. The number of realizations (stack number) that caused the design factors to converge could be determined. Effective stochastic optimization may be achieved by reducing computational resources. An increase in the variability of the conductivity distribution requires more extraction wells. Information about potential extraction wells can be used to prevent failure of the remediation task.     

Paleomagnetic records and mineral-magnetic properties of deep-sea sediments in the NW pacific: Paleoenvironmental implication

The paleomagnetic records and mineral-magnetic properties of unconsolidated core sediment from the east Mariana Basin of the western Pacific have been analyzed to trace the time-dependent variations in sedimentary environments. Progressive alternating field demagnetization effectively extracts a stable remanent magnetization showing both normal and reverse polarities. Comparison of successive polarity changes, recorded in the sediment core, with reference magnetic polarity time-scale, reveals that the recovered sediment column was deposited since the late Pliocene. From the sediment age model, calculated sedimentation rate during the late Pliocene was 9.8 times higher than that during the Pleistocene. Considering the oceanic environments and geologic setting in the study area, the anomalous high sediment flux during the late Pliocene was probably caused by enhanced current flows, such as North Equatorial Current, associated with atmospheric circulation as well as by debris flows from adjacent sea mounts. In addition, the systematic variation of mineral-magnetic properties indicates periodical fluxes of coarse and magnetically stable particles, on the fine-grained dominant sedimentary environments. Such influxes, however, would not be related to syn-volcanic activities, because the summits of seamounts were totally blanketed by biogenic Pliocene-Pleistocene sediments. It is, hence, reasonable to interpret that paleomagnetic and mineral-magnetic data probably reflect drastic paleoenvironmental changes at the boundary between the Pliocene and Pleistocene, where strong current and atmospheric circulations decreased.     

Relationship between polymetallic nodule genesis and sediment distribution in the KODOS (Korea Deep Ocean Study) Area, Northeastern Pacific

Polymetallic nodule and sediment characteristics were investigated for two blocks (KR2 and KR5) in the Korea Deep Ocean Study (KODOS) area in order to better understand nodule distribution and the potential effects of sediments on nodule genesis. The northern block (KR2) is dominated by hydrogenetic nodules, whereas the southern block (KR5) is dominated by diagenetic nodules. Sediments in the study area are assigned to three major lithologic units which are distinctive in color and texture. The northern block is characterized by a thick, metalpoor Unit 1 sediment, which is thin in the southern block, where metal-rich Units 2b and 3 occur close to the surface. The distribution of different nodule genetic types in the northern and southern blocks can be attributed to topographic variations (topographic high near seamounts in KR2 and abyssal plain in KR5) and different sedimentation rates (0.1 and 0.32 mm/kyr in blocks KR2 and KR5, respectively). The southern block has a geologic setting more conducive to diagenetic nodule formation, such as flat topography and sediment composition. Nodule distribution in the studied blocks might also be explained by the distribution of the sediment units of different metal contents. The northern block, in which Unit 1 is thicker, has more abundant hydrogenetic nodules, possibly because Unit 1 prevents metals that are remobilized from the underlying sediments from reaching the seabed where the nodules are forming.     

Influence of local geological pattern on values of vibrations induced by road traffic

Buildings in the proximity of roads can be affected by vibrations induced by traffic. Local geological pattern is necessary to be taken into account because it has significant influence on values of vibrations and their characteristics. This paper summarizes results of experimental measurements. Four different types of buildings in different types of local geology were used for this purpose. The obtained results document that the generation of significant vibrations is mostly due to heavy vehicles. Some maximum velocity values exceed acceptable limits according to the Czech Technical Standard 73 0040 for evaluation of technical seismicity effect on buildings. Cosmetic damage, meaning the cracking of plaster, might occur due to traffic vibrations.     

Assessment of the Global and Regional Land Hydrosphere and Its Impact on the Balance of the Geophysical Excitation Function of Polar Motion

The impact of continental hydrological loading from land water, snow and ice on polar motion excitation, calculated as hydrological angular momentum (HAM), is difficult to estimate, and not as much is known about it as about atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). In this paper, regional hydrological excitations to polar motion are investigated using monthly terrestrial water storage data derived from the Gravity Recovery and Climate Experiment (GRACE) mission and from the five models of land hydrology. The results show that the areas where the variance shows large variability are similar for the different models of land hydrology and for the GRACE data. Areas which have a small amplitude on the maps make an important contribution to the global hydrological excitation function of polar motion. The comparison of geodetic residuals and global hydrological excitation functions of polar motion shows that none of the hydrological excitation has enough energy to significantly improve the agreement between the observed geodetic excitation and geophysical ones.