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Dissertation zugänglich unter
The Upper Jurassic shallow marine siliciclastic-carbonate deposits in the North German Basin
Die klastisch-karbonatischen Flachwasser-Ablagerungen des oberen Juras im Norddeutschen Becken
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Sequenzstratigraphie , Jura <Geologie> , Karbonate , Lithofazies
Freie Schlagwörter (Deutsch):
Norddeutschen Becken , Oberjura
Freie Schlagwörter (Englisch):
Sequence stratigraphy , Carbonate , Upper Jurassic , Microfacies , North German Basin
38.16 , 38.41 , 38.28
Betzler, Christian (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
This thesis aims to establish the sequence stratigraphic framework of the Upper Jurassic deposits in the North German Basin, which makes a sequence stratigraphic correlation a possible supplement to the limited biostratigraphic correlation in this area. This study also aims to reveal the paleoclimate control on the evolution of the sequences, as well as to decipher how the diagenetic processes were affected by the sequence stratigraphy and facies evolution. To achieve these goals, the Eulenflucht-1 core drilled in Süntel Mountains and the Wendhausen-6 core drilled in Hildesheimer Wald were studied by core description, microfacies analysis, isotopic and element analysis, and cathodoluminescence imaging.
The Upper Jurassic deposits in the North German Basin consist of a mixture of siliciclastic and carbonate deposits. Thirteen facies were identified in the Eulenflucht-1 core and were interpreted to be deposited in a carbonate ramp ranging from the outer ramp into the restricted lagoon. Eight facies were identified in the Wendhausen-6 core and were considered to be deposited in a transition area between a delta setting and a carbonate ramp. Sequences of three different hierarchies were recognized both in the Eulenflucht-1 core and the Wendhausen-6 core. Small-scale sequences were delineated by the changes in grain size, variations in the amount of components, fluctuations of the matrix content, and the vertical facies stacking patterns. Medium-scale sequences were identified by the changes in facies combinations of the constituent small-scale sequences, and were confined by the distinctive hardgrounds or exposure surfaces, characterized by the occurrence of iron minerals or lowstand channel-fill sandstones. Sequence stratigraphic correlation across the North German Basin of the Korallenoolith Formation was achieved at the medium-scale sequence level, as some of the medium-scale sequence boundaries are basin-wide traceable. Large-scale sequences were differentiated by the facies proportion statistics in the distinct medium-scale sequences，which mirror the relative sea-level fluctuations. The shallowing trend in the Lower and Middle Oxfordian deposits is consistent with that of the global sea level change during the Early and Middle Oxfordian age. But the continuous shallowing trend from the Late Oxfordian to the Tithonian age in the Eulenflucht-1 core, is in contrast with the global sea-level rise during that time, and is considered due to the local uplifting tectonic movement.
Specific facies are indicators of specific paleoclimate to some extent, e.g., ooid grainstone and coral boundstone are indicators of warm climate. Therefore, the large-scale sequences, documented by the facies statistic curves recording facies changes, were postulated to be 4 controlled by regional climate. The warm period during the Middle Oxfordian and Late Kimmeridgian was recorded by the development of the ooid grainstone and coral boundstone facies. This is also recorded by the carbon isotopic and the Mg/Ca data. The stable carbon isotope variations of the Eulenflucht-1 core were well correlated with those of the other European Basins, which were interpreted as a result of climate change during the Late Jurassic to Early Cretaceous. In-phase variations of the facies statistic curve and δ13C curve manifest the climate control on the large-scale sequences. The high paleotemperatures during the Middle Oxfordian and Late Kimmeridgian time were also documented by the positive excursion of the Mg/Ca curves detected from the well-preserved oyster shells, which also evidence the climate control on the deposits at that time.
Facies and sequence stratigraphy framework have a great control on the development of diagenesis processes. Diagenetic elements with different optical characteristics under polarized and cathodoluminescence microscopes were logged in the Eulenflucht-1 core. Cement with twin crystals or poikilotopic fabrics and non-luminescence implies late burial diagenesis. It is constrained in the facies with grain-supported texture, e.g., ooid grainstone and coral boundstone, which is resistant to compaction and can provide good water circulation for the formation of the deep burial cement. Micrite rims composed of microcrystalline calcite with dull luminescence represent the marine to early diagenetic products, whereas cement with equant or blocky morphologies and sub-bright to bright luminescence indicate meteoric phreatic or early burial diagenesis. These cement are observed throughout the Eulenflucht-1 core, and not constrained to any specific facies. Dolomite with euhedral to sub-euhedral morphologies and dull to no luminescence is of marine to deep burial diagenetic origin. The dolomite in wackestone or mudstone deposited under the storm wave base is related to bacterial induced sulfate reduction, whereas the dolomite constrained in the ooid grainstone and oyster-serpulid rudstone deposited around the fare weather wave base is precipitated from the mixture of meteoric and marine water in the vicinity of sequences boundaries. Another diagenetic element associated with sequence boundary is microkarst.