Palynological, organic-petrographical and organic-geochemical investigations on coals and sediments of the Duckmantian, Ruhr Basin, Germany

摘要

The idea of the present thesis was to combine different established methods in a high-resolution study on a short-timed interval of Duckmantian strata (Pennsylvanian/Upper Carboniferous) of the Ruhr Basin, Western Germany. Organic petrographical, palynological, sedimentological and organic geochemical techniques were used to obtain a huge data set, to support the argumentations and discussions. In doing so, these investigations were focused on two main goals: (a) the maturity and quality of source rocks and (b) the evolution of swamp environments.(a) Maturity and quality of source rocksThis first part of the study focuses on the quality, quantity and maturity of coal and dispersed terrigenous organic matter. Furthermore, kerogen concentrates and coal-mineral-mixtures also were analysed. For the sampled interval samples show a vitrinite reflectance between 0.75 and 1.0% with an increase of maturity towards the stratigraphic older and deeper seam successions. Average vitrinite reflectance of sediment samples is slightly higher than that of coal samples. The maturity trend also is reflected in the Tmax values of Rock-Eval pyrolysis or the C17/C27-relationship. Investigations on petroleum potential show a kerogen type III respectively II/III for the sampled interval. Differences between Rock-Eval parameters determined on whole rock samples and kerogen concentrates were observed, especially with respect to Hydrogen Index (HI) values. In coals, which were compared with dispersed organic matter of similar maceral composition, the HI is about two times as high as that of the sediment samples. In contrast, Oxygen Indices are much higher for dispersed type III kerogen than for coal, caused by the stronger degradation of organic compounds in the clastic environments as compared to the peat environments. However, Oxygen Indices clearly are influenced by decomposition of carbonate minerals. Furthermore, Hydrogen Indices of dispersed kerogen are influenced by mineral-matrix effects. Experiments with artificial mixtures of coal and minerals show that reactions with pyrite seem to reduce HI values of kerogen concentrates significantly. (b) Evolution of swamp environmentsThe second part of the thesis focuses on palynological investigations on miospores to reconstruct the swamp evolution during the Duckmantian of the Ruhr Basin. In addition, sedimentological and organic petrographical data confirmed the interpretation. Based on published information of in situ spores the encountered miospores were assigned to their parent plants in order to reconstruct the vegetation history. In this study six plant associations were identified by using a Detrended Correspondence Analyses (DCA): lepidocarpacean association I, lepidocarpacean association II, lepidocarpacean – sigillarian association, lepidocarpacean – sphenophyll association, lepidocarpacean – fern association, and the subarborescent lycopsid association. Furthermore, coal petrographical GI/TPI and GWI/VI relationships also reflect these associations. Another new defined index, the water cover index (WCI), based on these palynological interpretations, reflects the ratio of hydrophilous/hygrophilous vs. mesophilous plants and gives additional information on the environment.In the sampled seam successions arborescent lycopsids are the most abundant plants, with a dominance of the miospore Lycospora. In 75% of all samples the genus is represented with more than 50% relative abundance. Hence, lepidocarpaceans such as Lepidophloios and Lepidodendron dominated the vegetation of the Ruhr Basin during the mid and late Duckmantian, forming flood plains and planar forest mires. Some variations are reflected in abundance of other spores. A greater influence of the sigillarian miospores Crassispora was typical for drier swamp margins, whereas densospore producing plants or sphenophylls characterized the stunted respectively scrambling vegetation of domed swamps. By contrast, fern influenced environments were rare during the Duckmantian. Recurring rhythmic successions of plant associations and depositional environments were noted in the studied interval: A lower flood plain is followed by peat substrate topogenous mires, which rise up and build an ombrogenous mire. After subsidence and recurrent flooding an upper flood plain was re-established. This general cycle is temporarily interrupted by other plant associations representing varying local environments. Drier sandbanks and swamp margin zones covered with sigillarians regularly occurred, implicating small environmental variations and a lateral shift of the swamp habitat.