Results from a Multi-disciplinary Sedimentary Pilot Study of Tectonic Lake Iznik (NW Turkey) – Geochemistry and Paleolimnology of the Recent Past     

Sven O. Franz  Lorenz Schwark  Cathrin Brüchmann  Burkhard Scharf  Ralf Klingel  Jon D. Van Alstine  Namık Çagatay  Umut B. Ülgen 《Journal of Paleolimnology》2006,35(4):715-736

A limnogeological reconnaissance study was carried out on Lake Iznik, located in the southeast of the Marmara region of Turkey, involving a seismic survey and collection of short sediment cores. This lake is located on the middle branch of the North Anatolian Fault Zone (NAFZ), a transform plate boundary between the Eurasian and Anatolian Plates. It is, therefore, tectonically active and offers an opportunity to investigate the interplay of sedimentary and seismo-tectonic processes, as well as climate change and human impact in the region. Short cores of the three sub-basins, maximum length of 35.5 cm, recovered non-laminated, blackish clays and silts with varying amounts of biogenic and minerogenic (allochthonous, autochthonous) material, which documented almost the last 80 years of deposition and environmental history. High sedimentation rates in the deeper core sections are accompanied by changes in land use (conversion of woodland to farmland) in the northern areas of Lake Iznik, which caused the deposition of more weathered material (high K/Na ratios) and higher contents of Mn in the lake. A tendency towards eutrophic conditions within the last 20 years is indicated by high nutrient content (N, TOC, P), decreasing C/N-ratios, and characteristic diatom and cladoceran associations. Also increased pollution is revealed by higher Pb, Cu, and Zn contents and increased supply of human and animal faeces (high coprostanol content) during the last two decades. But simultaneous lower sedimentation rates towards the core tops complicate the reconstruction of recent and past eutrophication and pollution states of Lake Iznik. This requires an extension of the pilot study and deeper sediment cores, to recover non-anthropogenic influenced sediment levels.  相似文献   

Analysis of the modes of directional data with particular reference to palaeomagnetism     

David R. Van  Alstine 《Geophysical Journal International》1980,61(1):101-113

Summary. Advantages of using the mode in analysis of palaeomagnetic vectors are discussed, and a computer technique is described for contouring and precisely locating the modes of vector distributions that may be highly skewed. In contrast to conventional determinations of the mode, unit vectors from a given data set are treated not as discrete points, but as identical Fisherian probability density functions defined (at an angle θ from the unit vector) by: p = exp [ sk (cos θ– 1)], where kis the estimate of the Fisherian concentration parameter, and s is an arbitrarily assigned 'smoothing parameter'. A grid, representing the cumulative probability distribution of the total sample of vectors, is contoured to provide a graphical display of the distribution around the most probable value, the mode. By repeatedly contouring the same sample of vectors with successively larger values of s, and by treating the mode as a vector with length given by the total probability value at the mode, 'progressive modal diagrams' can be constructed, to aid in determining the stable position of the mode of skewed distributions. In addition, a new statistic β₉₅ is suggested as an error estimator for the mode. The statistic β₉₅ is derived from the largest subset of the total sample that has a mean identical with the mode of the total sample; this statistic is defined as the Fisherian half-angle of the cone of 95 per cent confidence for the mean of this subset.  相似文献