Conference Agenda

The formation of peak rings in large meteorite impact craters is not well understood. The IODP-ICDP Expedition 364 drill core revealed that shocked target rock of the peak ring of the Chicxulub impact crater is pervasively affected by decimeter-scale brittle shear faults, apparently formed toward the end of peak ring formation. Shear faults lend themselves excellently to infer the deformation kinematics under which they formed. Hence, the orientations and slip senses of 602 shear faults extracted from the drill core were kinematically analyzed to better understand peak ring formation, a novel approach in impact cratering studies. Specifically, the inversion of the fault slip data allowed us to determine the orientations of principal kinematic axes and their variation with depth. The results revealed that overall, the peak ring formed by horizontal shortening and vertical extension. However, horizontal concentric extension prevails at greater depths within the drill core. Collectively, the deformation kinematics are consistent with rock flow during peak ring formation characterized by simultaneous rollback of the crater margin and outward displacement of collapsed central peak material. Not only do these results refine current numerical models of peak ring crater formation, they also support gravity-controlled cratering of the dynamic collapse model.

Paleoclimate research is needed to understand long-term climate variability. Terrestrial longterm climate archives are sparse but relevant to reconstruct continental climate. This study aims to assess the suitability of paleosols within a 400 m sediment core from the Namibian Cuvelai Etosha Basin as archive of paleoclimate data. The core penetrates a succession of two megafans that formed over 60 Ma years of the Cenozoic in a stable system. The older Olukonda Fan (Olukonda Fm.) is dominated by fine grained sediments to pebble conglomerates, representing 118 fining upwards cycles including several depositional environments from channel to long-lasting pool. The younger Cubango Fan (Andoni Fm.) consists largely of massive sands with variying silt and clay content. Both fans show signs of pedogenesis that vary in intensity and postdepositional overprint.

Our study represents a review and new interpretation of pedogenesis in both formations. Additionally to paleosol classification, weathering intensity, i.e. the loss of Na and K associated with chemical weathering, is examined as a function of grain size, provenance, and extent of pedogenesis. Preliminary results indicate that while pedogenesis is evident from sedimentological observations, it is not observed in the geochemical data. This is interpreted as resulting from constant recycling of sediment within the system that leads to significant chemical weathering prior to pedogenesis, limiting the chemical alterations during pedogenesis. In the end, the only suitable archive of paleoclimate information may be pedogenic carbonate, which will be at the centre of future work, but needs to be carefully seperated from diagenetic carbonate.

The south of Germany is famous for the exceptionally well-preserved fossils including Archaeopteryx. These fossils originate from several formations within the Germany Weißjura Group. Some of them comprise important, famous and sustainable construction materials like the Lithographic Limestone or the Treuchtlingen (Jura) Limestone, both of them certified as GeoHeritage Rocks by the IUGS.

However, data and studies beyond taxonomic and palaeontolgical analyses are scarce, or hardly accessible. In fact much work has been done, but mostly in isolated studies and attempts. This talk gives an overview over the existing data and the potential for integrated stratigraphy in this thick succession of Late Jurassic limestone.

Cross-strata on Mars are expressions of ancient bedforms formed due to sediment transport by either wind or water. Some of these cross-strata show peculiar features, including intercalated mudstone drapes, discontinuity surfaces and cyclic patterns in lamina thickness (i.e. bundled cross-strata). In this study, we evaluated the sedimentary features of five of these bundled cross-strata using images from the Curiosity rover in Gale Crater. These cross-strata are generally 0.08–0.20 m thick and up to 1.6 m wide. They accumulated in fluvial, deltaic-lacustrine and aeolian depositional environments approximately 3.6–3.1 Ga. These cross-strata were analysed with statistical methods with a focus on three parameters of the internal laminae: thickness, angle and shape. Our results show variations in all these parameters, some of which are confirmed having a moderate to strong cyclic imprint at different scales. These cyclic patterns were attributed to a self-organisation related to the migration of superimposed bedforms over the host bedform under mostly unidirectional riverine- and wind-driven flows, similarly to what is observed in bedforms on Earth depositional systems and reproduced in flume experiments. Both high- and low-angle discontinuity surfaces were identified and were attributed to the migration of different-scale superimposed bedforms. This study shows how Martian sediment transport in the past had similar dynamics as on Earth also at the bed scale. At the same time, it helps to better understand the full range of depositional mechanisms on both Earth and other planets that are able to produce cyclicities not necessarily under varying flow strength and/or direction.

The Saale Basin is an Upper Paleozoic intermontane basin filled with continental deposits of the Mansfeld Subgroup and Halle Formation. Despite extensive previous work, the role of autogenic and allogenic forcing factors on its stratigraphic architecture remains unclear. In this study, detailed sedimentological analysis was integrated with portable X-Ray Fluorescence (XRF) data from the Querfurt 1/64 core at 50 cm resolution. Four facies associations were identified: fluvial channels, crevasse splays, floodplains, and shallow lacustrine deposits. Fluvial channels are divided into two subtypes based on their infill: (1) sandstone bodies with trough cross-bedding and reactivation surfaces, interpreted as perennial channels, and (2) structureless or parallel-laminated sandstones, interpreted as ephemeral channels. Floodplains consist of reddish mudstones interpreted as subaerial deposits, and grey-greenish, locally coaly mudstones interpreted as waterlogged/palustrine settings. Crevasse splays are composed of massive to rippled sandstones that prograde onto both floodplain types, while shallow lacustrine deposits consist of grey mudstones and carbonates interbedded with ripple-laminated and mud-cracked sandstones. Paleohydrological analysis of cross-bedding indicates seasonal discharge variability and a decrease in channel dimensions and water depth upsection. XRF-derived weathering proxies (K/Al; Rb/Ti) display hierarchical cyclicity interpreted as wet–dry climatic fluctuations, consistent with sedimentological observations and previous interpretations. Provenance proxies (Zr/Cr; Rb/K) suggest a relatively homogeneous sediment source, with subtle trends from mafic/intermediate to felsic compositions and from metamorphic to volcanic sources. Further outcrop studies are required to assess lateral continuity of the identified cycles, constrain their controls and duration, and better understand basin evolution.

High-grade metamorphic rocks in Saxony were historically interpreted as supracrustal rocks, implying that their protolith have been formed by direct deposition on pre-existing basement. This fixistic working hypothesis has been widely applied in many mapping campaigns and has led to a lithostratigraphic subdivision of these metamorphic suites, which is presented on numerous geological maps. State of the art geological evidence, however, suggests that lithostratigraphic models for mapping metamorphic high-grade terrains should be rejected, and, instead, metamorphic rock characterisation in the field should follow international guidelines recently established for lithodemic units. In Saxony, metamorphic high-grade rocks can be classified and mapped in a lithodemic sense as gneisses, micaschists, phyllites, eclogites, serpentinites, etc. based upon observable rock characteristics such as mineralogical, textural and structural features. In contrast to lithostratigraphic models, lithodemic nomenclature for metamorphic rocks should be independent of the inferred geologic history, and basic field criteria should be strictly separated from the laboratory data obtained from the mapped rocks. To establish a full hierarchical lithodemic classification, approved lithodemes may be ranked within metamorphic suites according to their tectono-metamorphic evolution. The interaction between sedimentary strata, deposited on a subaerial exposed basement, and lithodemic basement rocks is always characterised by the absence of stratigraphic coherency between the two geologic levels. Hence, metamorphic lithodemes should be treated separately from official stratigraphic tables and can be assigned to time intervals where tectonic emplacement within their present structural position took place, which typically coincides with the last major regional metamorphic event in the respective area.