Low-temperature partial magnetic self-reversal in marine sediments by magnetostatic interaction of titanomagnetite and titanohematite intergrowths

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Biogenic silica microfossils in sediments of the Permian - Carboniferous Unayzah Formation, Saudi Arabia

Biogenic silica particles (BSPs) have been discovered in sediments of the Permian - Carboniferous Unayzah Formation of Saudi Arabia. The BSPs are extracted from sediments that are generally barren of macro- or microfossils. BSPs have been found in the Basal Khuff Clastics (BKC), and the Unayzah A, B, and C members, that were sampled in six different wells over a large geographic area. More than 3,500 BSPs have been identified in 83 samples examined and have been classified into 14 different BSP morphotypes. Furthermore, three outcrop samples of the Permian - Carboniferous Al Khlata and Gharif formations of Oman were analysed. Herein seven BSP morphotypes were identified. For comparison of the Paleozoic BSPs with modern analogues, recent plant material from the Rub' Al Khali Desert was studied. The presence of BSPs in Paleozoic deposits and their morphological difference is encouraging. Variations in morphotype abundance and occurrence may ultimately provide a means of subdividing and correlating the Unayzah Formation. Research presently underway is testing the distribution of morphotypes in terms of stratigraphic position, depositional facies, and paleoclimatic setting

A new biostratigraphical tool for reservoir characterisation and well correlation in permo-carboniferous sandstones

Permo-Carboniferous sandstones are important reservoir rocks for natural gas in the Southern North Sea basin. This is a mature area which makes tools for reservoir characterization and well to well correlation important for field optimalisation and ongoing exploration activities. Within the Permo-Carboniferous sandstone reservoirs of the Dutch on- and offshore there are two key questions which still need to be resolved. One regards the geological model for the basin infill, another is the detection of the Base Permian Unconformity (BPU), an important regional unconformity. Biostratigraphy is classically used to address these problems. As the traditional microfossil groups are absent in the Permo-Carboniferous redbed deposits, the application of biostratigraphy is seriously hampered. In this study, we present a new biostratigraphical tool based on biogenic silica microfossils (BSPs). This fossil group consists of siliceous plant remains which are preserved even under extreme oxidizing conditions. BSPs are present in the Permo-Carboniferous redbed sequences and are now for the first time used for biostratigraphical correlations. This new tool holds great potential for independent chronostratigraphical correlations in economically important redbed deposits worldwide. In this study the initial results from a case study in the Southern North Sea basin will be presented

Identification of magnetic Fe-Ti oxides in marine sediments by electron backscatter diffraction in scanning electron microscopy

In paleomagnetic and environmental magnetic studies the magnetomineralogical identification is usually based on a set of rock magnetic parameters, complemented by crystallographic and chemical information retrieved from X-ray diffraction (XRD), (electron) microscopy or energy dispersive spectroscopy (EDS) of selected samples. While very useful, each of these supplementary techniques has its limitations when applied to natural sample material which are related to low particle concentrations (down to the ppm range in marine sediments) and very fine grain sizes (down to the nm scale). Therefore, meaningful application of such techniques depends on sample quality. Electron backscatter diffraction (EBSD) of individual grains in scanning electron microscopy (SEM) enables mineralogical identification of grains down to ∼0.2 micrometer and is particularly powerful when combined with EDS. In this study, we show the merits of EBSD for rock magnetic investigations by analyzing titanomagnetites and hemoilmenites of various compositions and submicron lamella of titanomagnetite-hemoilmenite intergrowths. Such particles often occur in natural marine sediments where EDS often has a semi-quantitative character and compositionally similar intergrowths may be difficult to distinguish. With the mineralogical information provided by EBSD unambiguous identification of spinel-type and trigonal oxides is obtained. Optimal EBSD patterns are gathered from smooth, polished surfaces, but here we show that interpretable EBSD patterns can be obtained directly from the surface of unconsolidated, so called 'non-embedded' particles from marine sediments. This information enhances the interpretative value of rock magnetic parameters. © 2007 The Authors Journal compilation © 2007 RAS

Identification of magnetic Fe-Ti-oxides in marine sediments by electron backscatter diffraction in scanning electron microscopy

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