Prinz, Linda: Syn- and post-depositional sand bodies in lignite : The interrelationship of tectonics and sedimentation in the Lower Rhine Embayment. - Bonn, 2018. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc:
author = {{Linda Prinz}},
title = {Syn- and post-depositional sand bodies in lignite : The interrelationship of tectonics and sedimentation in the Lower Rhine Embayment},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2018,
month = jun,

note = {The Cenozoic-age Lower Rhine Embayment is part of the European Cenozoic Rift System, which initiated in Eocene times as a result of passive, intracontinental rifting. The Lower Rhine Embayment formed in an extensional regime, related to the reactivation of Late Variscan fracture systems located to the NW of the Rhenish Massif. The Lower Rhine Embayment extends along the Rhine River from Bonn in the SE through to Belgium and the North Sea Basin in the NW Netherlands.
Deposition of the Cenozoic-age basin infill of the Lower Rhine Embayment was controlled by the interaction of tectonic activity and sedimentary processes related to sea-level fluctuations and climatic changes. In the subtropical climatic conditions of Miocene times, extensive paralic mires formed across the basin, and as a result of continuous basin subsidence, extremely thick (up to 270 m) peat deposits accumulated in the Lower Rhine Embayment. These lignite seams (up to 100 m thick) have been mined for more than 150 years in the so-called Rhenish Lignite District.
Within the Garzweiler mining area, one of the three active lignite open-cast mines in the Lower Rhine Embayment (which are run by the RWE Power AG), the presence of sand bodies affect the industrial exploitation of the lignite. Due to the variable dimensions and irregular distribution of these sand bodies, the processing of future lignite volumes is difficult and often problematic. Therefore, this study aims to improve the understanding of sand body emplacement within the Miocene-age Frimmersdorf Seam, and to facilitate the early and precise recognition of sand bodies within the future mining area.
The analyses of sand bodies within the Miocene-age Frimmersdorf Seam is mainly based on three years of fieldwork within the constantly refreshed outcrops of the Garzweiler open-cast mine, but also includes older data from the RWE Power AG archive, for example, maps, geophysical measurements and drilling well data. The interpretation of the various fieldwork and analytical approaches revealed that a variety of both syn- and post-depositional mechanisms were responsible for the emplacement of the various sand bodies within the peat/lignites of the Frimmersdorf Seam, providing evidence of the extreme complexity of the depositional and post-depositional systems. Syn-depositional sand bodies were formed in fluvial and estuarine channels in the extensive mires, or by episodic flooding events from the adjacent North Sea. The presence of post-depositional sand injectites within the Frimmersdorf Seam is related to liquefaction and fluidization of unconsolidated, overpressurized sands (i.e. the Frimmersdorf and Neurath sands), and the natural hydraulic fracturing of the sealing host strata, i.e. the Frimmersdorf Seam.
Organic petrological and inorganic geochemical analyses were carried out on lignite and sand samples to investigate the influence of sand body emplacement on the adjacent lignite. The ash contents, as well as thin section analyses revealed that the lignite was not influenced by sand body deposition, not even at the direct contact areas. Additionally, this study provided some useful information on the depositional environment, for example the mineralisation of the water, which was present during peat/lignite formation. The analyses of sulphur and ash contents of the lignite samples indicate that the depositional environment was controlled by freshwaters. On the other hand, the presence of glauconite minerals in one of the sand sample, and low Ca/Mg ratios would suggest that the sand body emplacement was controlled by marine currents. The organic petrological and inorganic geochemical analyses, therefore, provide evidence of the complex interaction of marine processes (tides, waves, storm events) with the river systems in the paralic mires.
Finally, a three-dimensional reconstruction of the Frimmersdorf Seam was modelled. This integrated model was based on pre-existing contour line maps of the lignite boundaries, as well as information on lignite thicknesses (based on the RWE Power AG reservoir model), and measurements of the sand body distributions and orientations. The interpretation of the 3D model revealed a close interrelationship between sand bodies and seam morphology on the one hand, and between sand injectites and the occurrence and orientation of the fault systems on the other. The hydraulic fracturing of the lignite, and, therefore, the orientation of the sand injectites, were largely controlled by tectonic activity within the study area. Fracturing of the peat/lignite occurred under the stress field that prevailed during the time of sand injectite formation.},

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