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Abstract

The Cao Bang Basin is the northernmost of the basins related to the Cao Bang-Tien Yen Fault Zone in northern Vietnam. The basin is filled with a thick series of continental deposits. However, the exact age of the sedimentary basin infill has been under discussion for a long time. Because of new published data, the authors have decided to revisit this basin. Palynological data has allowed us to assign the Cao Bang Basin infill to the Lower Oligocene PC1 complex of the Shangcun Fm. (southern China). Among the saccate grains of gymnosperms, the domination of Cathaya and Pinus was observed, whereas angiosperms are represented by Carya, Celtis, Hammamelidaceae, Ulmus and also Pterocarya, Quercus, the Castanea–Castanopsis–Lithocarpus group, and the Loranthaceae. Among pteridophytes occur Laevigatosporites, Osmundaceae, and Pteris. The sedimentological features of the Cao Bang Basin are distinct from those of other basins from the Cao Bang-Tien Yen Fault Zone. The basin is filled with a wide variety of clastic deposits, from some of coarse-grained, alluvial-fan origin, through sandy beds of fluvial origin up to fine, organic-rich lacustrine deposits. The coarse-grained lithofacies are built of clasts derived mainly from local sources. The sandstones from the basin equally are submature or immature. They contain a lot of lithoclasts, the composition of which depends on the sample location within the basin. The potential source area is composed of older sedimentary units and of granitic rocks. The geochemical samples studied reflect the geochemical composition of silicic source rocks with only a minor contribution of basic components. The succession that fills the basin is interpreted as a typical fill for relatively long-lasting evolving half-graben or strike-slip basins. Moreover, the basin is partly occupied by a subsequent present-day sedimentary basin of Quaternary age.
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Abstract

Triceratium barbadense Greville, 1861a, T. brachiatum Brightwell, 1856, T. inconspicuum Greville, 1861b and T. kanayae Fenner, 1984a, are among the most common diatoms reported worldwide from lower to middle Eocene biosiliceous sediments. Due to complicated nomenclatural histories, however, they are often confused. A morphometric analysis performed herein indicates that T. brachiatum is conspecific with T. inconspicuum, and that both were previously often misidentified as T. barbadense. Triceratium barbadense sensu stricto is a distinct species similar to Triceratium castellatum West, 1860. Triceratium brachiatum and T. kanayae are transferred herein to a new genus, Fenneria, for which a close phylogenetic relationship with Medlinia Sims, 1998 is proposed. A review of the geographic and stratigraphic distribution of Fenneria shows that the best constrained records of its occurrences are found at DSDP Site 338, and ODP Sites 1051 and 1260. The ages of the base (B) and top (T) of each species’ stratigraphic range are calibrated here to the Geomagnetic Polarity Timescale either directly or inferred via correlation with dinocyst biostratigraphy. Latitudinal diachroneity of ~7 million years is documented for F. brachiata, which disappears earlier in tropical and mid-latitude sites than in the northern high latitudes. These observations, coupled with a preliminary compilation of the Chron C20n taxonomic composition of pelagic diatom assemblages for Sites 338, 1051 and 1260, indicate that diatoms diversified palaeobiogeographically considerably earlier than the Eocene−Oligocene Transition, as commonly believed. This study also emphasizes the importance of the detailed examination of specimens from both museum collections and deep-sea cores as a step toward enhancing the utility of Palaeogene diatoms in palaeoceanographic and palaeoenvironmental reconstructions.
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Abstract

The Carpathian Orava Basin is a tectonic structure filled with Neogene and Quaternary deposits superimposed on the collision zone between the ALCAPA and European plates. Tectonic features of the south-eastern margin of the Orava Basin and the adjoining part of the fore-arc Central Carpathian Palaeogene Basin were studied. Field observations of mesoscopic structures, analyses of digital elevation models and geological maps, supplemented with electrical resistivity tomography surveys were performed. Particular attention was paid to joint network analysis. The NE-SW-trending Krowiarki and Hruštinka-Biela Orava sinistral fault zones were recognized as key tectonic features that influenced the Orava Basin development. They constitute the north-eastern part of a larger Mur-Mürz-Žilina fault system that separates the Western Carpathians from the Eastern Alps. The interaction of these sinistral fault zones with the older tectonic structures of the collision zone caused the initiation and further development of the Orava Basin as a strike-slip-related basin. The Krowiarki Fault Zone subdivides areas with a different deformation pattern within the sediments of the Central Carpathian Palaeogene Basin and was active at least from the time of cessation of its sedimentation in the early Miocene. Comparison of structural data with the recent tectonic stress field, earthquake focal mechanisms and GPS measurements allows us to conclude that the Krowiarki Fault Zone shows a stable general pattern of tectonic activity for more than the last 20 myr and is presently still active.
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