17 research outputs found
Using highâresolution XRF analyses as a sequence stratigraphic tool in a mudstoneâdominated succession (Early Cretaceous, Lower Saxony Basin, Northern Germany)
Delineation of stratigraphic sequences and their component systems tracts in mudstoneâdominated successions is challenging due to the relatively homogenous, fineâgrained nature of the strata. Highâresolution elemental intensity data from Xâray fluorescence core scanning is used in order to develop a sequence stratigraphic framework for the Lower Cretaceous monotonous mudstone succession in the eastern Lower Saxony Basin. The study is based on four drill cores covering the Berriasian to Aptian interval. In addition, carbon isotope (ÎŽ13Corg), grain size and CaCO3 analyses were carried out on discrete samples. The studied cores represent both proximal and distal basinal environments of the eastern Lower Saxony Basin and can be reliably correlated by utilizing variations in selected Xâray flourescence elemental ratios, K/Ti data have proven to be particularly suitable in this regard. The core correlation shows that chemostratigraphic variability within the studied succession is laterally reproducible in the eastern Lower Saxony Basin, and can be used to establish a sequence stratigraphic framework. Further, Si/Al and Ca/Ti ratios have been applied to characterize the cores in terms of variation in grain size and CaCO3 content, respectively. Vertical grading trends inferred from Si/Al changes were used to identify transgressive and regressive systems tracts within the studied succession. An important regression in the uppermost lower Valanginian coincides with the onset of the Valanginian Weissert Event, as indicated by the wellâknown positive ÎŽ13C shift, and, thus, supports the idea that the initial interval of this event corresponds to enhanced supply of terrigenous material. The results of this study are also in agreement with previously recognized transgressiveâregressive trends in the Lower Saxony Basin and adjacent areas. This clearly shows that systematic geochemical variations recorded in mudstoneâdominated basinal settings are suitable to establish sequence stratigraphic frameworks
The type locality of the Kellwasser-Horizons in the Upper Harz Mountains, Germany
The stratigraphic section âKellwasser-Talâ is the type locality of the Late Devonian Kellwasser Horizons. The locality, which was already badly preserved shortly after its discovery in the middle of the 19 th century by F.A. Roemer, has recently been re-opened and widened. The newly created section ranges from the upper Frasnian to the Lower Carboniferous âKulm-Kieselschieferâ. Although some parts of the outcrop are highly tectonised it is nonetheless possible to reconstruct the sedimentary sequence. The Kellwasser Horizons, connected to one of the five most severe mass-extinction events in Earth History (Kellwasser Crisis), can now be studied again in detail. Conodonts sampled by O.H. Walliser (Göttingen) in the 1980s as well as new samples were investigated with respect to conodont biostratigraphy and microfacies. The type locality is situated in the European Geopark Harz-Braunschweiger Land-Ostfalen and should be protected as a geosite.
Das Profil Kellwasser-Tal (NW-Harz) ist die TyplokalitĂ€t der oberdevonischen Kellwasser-Horizonte. Die LokalitĂ€t, schon bald nach ihrer Entdeckung durch F.A. Roemer Mitte des 19. Jahrhunderts verfallen, ist maschinell erneut freigelegt worden. Es liegt nun ein zusammenhĂ€ngendes Profil vom höheren Frasnium bis in die Kulm-Kieselschiefer des Unterkarbons vor. Obwohl Teile des Aufschlusses tektonisch sehr stark beansprucht sind, ist die Rekonstruktion der sedimentĂ€ren Abfolge möglich. Die beiden Kellwasser-Horizonte, zwei isochrone, global nachweisbare Litho-Einheiten (,,Kellwasser-Kalkeâ), sind wieder gut aufgeschlossen. Sie bezeugen eines der fĂŒnf gröĂten Aussterbe-Ereignisse der Erdgeschichte (Kellwasser-Krise). Im Zusammenhang mit den GelĂ€ndeaktivitĂ€ten ist Sammlungsmaterial (Conodontenfaunen, An- und DĂŒnnschliffe) aufgearbeitet worden, so dass der gegenwĂ€rtige Bearbeitungsstand der LokalitĂ€t dargestellt werden kann. Grundlage der stratigrafischen Bearbeitung waren insbesondere Conodontenproben, welche unter Leitung von O.H. Walliser (Göttingen) in den 1980er Jahren gesammelt wurden. ZusĂ€tzliches, in den letzten Jahren entnommenes Material (Conodonten- und sedimentologisch-fazielle Proben) lieĂ sich mit den Banknummern von Walliser korrelieren. Diese TyplokalitĂ€t ist Teil des EuropĂ€ischen Geoparks Harz-Braunschweiger Land-Ostfalen und sollte als Geotop geschĂŒtzt und erhalten bleiben