Aalenian sedimentary deposits in southern Germany have accumulated in a shallow-marine, epicontinental shelf environment. These accumulations are dominated by thick claystones and argillaceous siltstones, with increasing percentages of sandstones towards the top. Aalenian sediments are likely to represent a relatively complete stratigraphic record, however, the sedimentary evolution and paleoclimatic significance of these typically poorly exposed deposits remain largely unexplored. Here we present a suite of high-resolution x-ray fluorescence (XRF) core scanning data from southern Germany to identify Transgressive-Regressive cycles during the Aalenian stage. Results are based on three scientific drill cores of 200 – 250 m length that have been analyzed with an Avaatech XRF Core Scanner at a 10 mm sampling interval (10 keV, 500 µA). Resulting trends in elemental Si/Al ratios, which are indicative for subtle grain-size variations, combined with sedimentological observations on ichnofacies and bedform development were used to reconstruct shoreline trajectories and establish a sequence stratigraphic framework for the thick and largely homogenous lower Aalenian Opalinuston Formation.

In Central Europe, the about 1 km thick Buntsandstein was deposited in the large intracratonic Central European Basin (CEB). The Buntsandstein sedimentary succession displays a striking cyclicity of varying magnitude. The most obvious cycle is the 10 to 20 m thick small-scale cycle (wet-dry cycle) that is ascribed to changes in lake level (base-level) and assumed to be controlled by astronomical forcing of climate.

Combined with wireline logs, these cycles can be mapped over large parts of the Central European Basin providing a high-resolution cyclostratigraphic framework. Hence, the cycles represent basin-wide events. The isochronous character of this framework has been proven by magneto- and biostratigraphic means. The detailed magnetostratigraphy spans the upper Zechstein to lowermost Muschelkalk. Compared with available radioisotopic ages for the base and top of the marine Early Triassic, a Buntsandstein duration of about 6 Ma is derived.

Within the more central part of the CEB, the synchronous character of the cyclostratigraphic framework has been proven by magnetostratigraphic and biostratigraphic means. Based on an integrated comparison, radioisotopic ages obtained from Tethyan sections, have been referred successfully to the Buntsandstein cyclostratigraphy, substantiating the hypothesis that the pronounced small-scale cycles correspond to solar-induced ~100 ka eccentricity cycles. Hence, the duration of the Buntsandstein has been calculated to span some 6 Ma. The Buntsandstein cyclostratigraphy offers good potential to constructing a reliable astronomically calibrated Early Triassic geomagnetic polarity timescale.

Time indications in the Rotliegend Group of Germany are integrated and presented in a new way (Menning et al. 2022, ZDDG 173: 3–139). (1) U-Pb CA-ID-TIMS radio-isotopic age determinations from the Thüringer Wald (Lützner et al. 2021, Int. J. Earth Sci.), (2) the recalculated Rb-Sr age for the Donnersberg-Formation of the Saar-Nahe Basin (Menning et al. 2022) utilizing the recently revised ⁸⁷Rb decay constant (Villa et al. 2016, Geochim. Cosmochim. Acta), (3) the newly calculated mean age for the U-Pb SHRIMP data of Breitkreuz & Kennedy (1999, Tectonophysics) of 298.6 ± 1.9 Ma for the Central European Basin (CEB), which reduces the time span for the Altmark Subgroup volcanic succession from 302–290 Ma to ≈ 300.5–296.5 Ma, (4) the Re-Os age of 257.3 ± 1.1 Ma for the Kupferschiefer (base Zechstein Group), (5) the age of ≈ 265 Ma of the Illawarra Reversal of the Earth´ magnetic field, and (6) highly different palaeomagnetic properties of the sediments of the underlying Müritz Subgroup and the hanging Havel Subgroup are significant evidence for an extensive stratigraphic gap or a very gap-rich time span (≈ 295/293.5–266 Ma = Middle Rotliegend). In Central Europe, this gap forms part of the longest Phanerozoic time span without significant marine layers (≈ 311 Ma to ≈ 257.3 Ma = ≈ 54 Ma). The gap is most probably related to the amalgamation and the associated immense uplift of Pangaea in Central and Western Europe and thus termed the ‘Pangaea Gap’.

The Global Time Scale of the International Commission on Stratigraphy includes subdivisions of systems down to stages but substages can be recognized once all stages are ratified. Devonian substage progress slowed down since the inevitable Pragian/Emsian boundary revision has not yet been achieved. Formal substage definitions are urgent since variable versions are used widely, in different regions, and by different authors. This hampers the precise correlation of climatic changes, sea-level fluctuations, geochemical cycles, rates of evolution, and extinction/radiation events. Precise and unequivocal time-scales are the pre-condition for advances in multidisciplinary Earth System research and geological mapping. Our recent studies led to progress in the case of Givetian to Tournaisian substages, which all shall be placed close to 2^nd/3^rd order global events, which importance is often hidden by their timing within stages.

The future Upper Givetian base shall be placed at the top of the global Taghanic Crises (base of hermanni Zone) while the Lower/Middle Frasnian boundary should coincide with the anoxic Middlesex Event. The best boundary marker, Ancyrodella nodosa, provides correlation with the Alamo Impact of Nevada. Revision of the controversial conodont scale at Martenberg, a potential GSSP, confirmed the semichatovae Transgression (nasuta Subzone) as the best Upper Frasnian base. Other Rhenish sections are suitable for the definitions of the Middle (base marginifera Zone, Beringhauser Tunnel), Upper (Lower Annulata Event, Effenberg), and Uppermost Famennian (e.g. Oese, base ultimus ultimus Zone). The anoxic Lower Alum Shale (base crenulata Zone) should re-define a Middle Tournaisian substage following the classical Belgium chronostratigraphic scale.

The distinction between sedimentary and tectonic processes in the formation of chaotic rock units is especially difficult in orogenic belts, where sedimentary structures are usually strongly overprinted by tectonic deformation (e.g. Fiesta et al. 2019). This also applies to the chaotic rock units, which are widespread in the allochthonous domain of the Harz Mountains. For these units, it has been assumed that their chaotic rock fabric was initially sedimentary in origin and was merely tectonically overprinted by subsequent Variscan deformation (e.g. Schwab & Ehling 2008). In contrast, it could be shown, that tectonic processes were crucial for the formation of the chaotic rock fabric (Friedel et al. 2019). This is particularly evident in the structural characteristics of Devonian limestone blocks.

In chaotic units, blocks of (hemi)pelagic condensed limestone of different Devonian age are widely incorporated in a slaty-clayey matrix. So far, the blocks were mostly regarded as olistoliths and thus considered as clear evidence for a sedimentary origin of the chaotic rock units (olistostromes). However, our investigations show that the limestone blocks are fault-bounded, folded and internally imbricated stacks of limestone strata, whose final fragmentation and isolation occurred subsequently to tectonic folding.

Such blocks of fault-bounded imbricate stacks of rock strata are a diagnostic field-criterion to identify a strong tectonic overprint or even a tectonic origin of chaotic rock fabrics. Since such blocks are regionally distributed, they support, together with other structural features, a predominantly tectonic origin of these units and argue against widespread submarine mass-flow deposits.

References:
Fiesta et al. 2019, Gondwana Research, 74, 7-30
Friedel et al. 2019, Intern. Journal of Earth Science, 108, 2295-2323
Schwab & Ehling 2008, Karbon, 110-140; in Bachmann et al. (Hrsg.) Geologie von Sachsen-Anhalt, Schweizerbart

The Rhenish Slate Mountains are one of the classical outcrop areas for stratigraphic research in Devonian and Carboniferous strata. Lithostratigraphic mapping of German parts of the Rhenish Slate Mountains has been performed systematically for over 100 years starting with a mapping campaign implemented by the Prussian Geological Survey in the 1920s. Today, geological mapping is performed by the Geological Survey of North Rhine-Westphalia and published in an output scale of 1 : 50 000. Results are made available via a modern geodata infrastructure for the use by digital map display. We present sedimentological facies models for the time spans of the Middle to Upper Devonian and the Mississippian. On the one hand the lithostratigraphic lexicon LithoLex is the data source of definitions of lithostratigraphic units and on the other hand results of field mapping are needed to classify lithostratigraphic units that are not yet implemented in the lexicon. Our models can work as links between results of field mapping of the northern Rhenish Slate Mountains east of the river Rhine and help to classify lithostratigraphic units, where it is still needful.