ABSTRACT Formation of the Central European tektites, known as moldavites, has been associated with a large meteorite impact in southern Germany 14.8 m.y. ago. The geochemical link between moldavites and their source materials, and the processes of their possible chemical differentiation still remain uncertain. Some differences in chemical composition between moldavites and sediments of corresponding age from the surroundings of the Ries crater could be explained by a hypothesis according to which biomass covering the pre-impact area contributed to the source materials. In a comparison of the geochemical compositions of a large representative set of moldavites and suitable Ries sediments, enrichment in elements K, Ca, Mg, and Mn and depletion of Na in moldavites, similar to redistribution of these elements during their transfer from soil to plants, could indicate the unconventional biogenic component in moldavite source materials. Simple mixing calculations of the most suitable Ries sediments and a model biogenic component represented by burned biomass residue are presented. The plausibility of the estimated biomass contribution considering reconstructions of the middle Miocene paleoenvironment in the pre-impact Ries area is discussed. No significant vapor fractionation is required to explain the observed variability of moldavite chemical composition.

ABSTRACT Quantitative insights into the geochemistry and petrology of proximal impactites are fundamental to understand the complex processes that affected target lithologies during and after hypervelocity impact events. Traditional analytical techniques used to obtain major- and trace-element data sets focus predominantly on either destructive whole-rock analysis or laboratory-intensive phase-specific micro-analysis. Here, we present micro–X-ray fluorescence (µXRF) as a state-of-the-art, time-efficient, and nondestructive alternative for major- and trace-element analysis for both small and large samples (up to 20 cm wide) of proximal impactites. We applied µXRF element mapping on 44 samples from the Chicxulub, Popigai, and Ries impact structures, including impact breccias, impact melt rocks, and shocked target lithologies. The µXRF mapping required limited to no sample preparation and rapidly generated high-resolution major- and trace-element maps (~1 h for 8 cm 2 , with a spatial resolution of 25 µm). These chemical distribution maps can be used as qualitative multi-element maps, as semiquantitative single-element heat maps, and as a basis for a novel image analysis workflow quantifying the modal abundance, size, shape, and degree of sorting of segmented components. The standardless fundamental parameters method was used to quantify the µXRF maps, and the results were compared with bulk powder techniques. Concentrations of most major elements (Na 2 O–CaO) were found to be accurate within 10% for thick sections. Overall, we demonstrate that µXRF is more than only a screening tool for heterogeneous impactites, because it rapidly produces bulk and phase-specific geochemical data sets that are suitable for various applications within the earth sciences.

ABSTRACT Rampart craters are omnipresent features on volatile-rich solid planetary surfaces. This raises the question whether, and how many, rampart craters are present on Earth. We reviewed the terrestrial impact crater record with regard to possible rampart morphologies and present detailed morphological analyses of these terrestrial craters here. Our results show that the Ries crater in Germany, Bosumtwi crater in Ghana, Tenoumer crater in Mauritania, Lonar crater in India, and Meteor crater in the United States are terrestrial rampart craters. The Ries and Bosumtwi craters can be classified as double-layer ejecta (DLE) craters, whereas Tenoumer, Lonar, and Meteor craters can be classified as single-layer ejecta (SLE) craters. Tenoumer and Meteor craters show rampart as well as common lunar-like ejecta characteristics within their ejecta blankets and, thus, appear to be hybrid craters. In addition, we discuss seven crater structures that show at least some morphological or lithological peculiarities that could provide evidence for possible ejecta ramparts. Considering the low number of terrestrial impact craters with well-preserved ejecta blankets, the relatively high proportion of rampart craters is astonishing. Obviously, the formation of layered or rampart craters is a common and not a rare process on Earth.

A detailed total intensity magnetic survey of a local negative magnetic anomaly located in the southern sector of the inner ring in the Ries impact structure was carried out in 2006–2007. As the suevite of the Ries crater is known to have an often strong reverse remanent magnetization causing negative magnetic anomalies, a suevite body lying below shallow lake sediments upon the crystalline basement rocks of the inner ring was suspected to be the cause of the anomaly. A drilling program conducted by the Geological Service of Bavaria offered the opportunity to drill a 100-m-deep core hole into this anomaly in 2006. The core stratigraphy involves from 0 to 4.5 m fluviatile Quaternary lake sediments, from 4.5 to 21 m Neogene clays of the Ries crater lake, and from 21 to 100 m suevite and impact melt rock. The suevite and the impact melt rock have a strong reverse remanent magnetization and very high Koenigsberger ratios. Thermomagnetic and coercivity analyses indicate that magnetite is the dominant carrier of the magnetization. The borehole unfortunately did not penetrate the crystalline basement rocks of the inner ring, but modeling of the magnetic source body indicates that the bottom of the hole could not be far from the contact. A macroscopic survey shows suevite from 21 to 87 m, highly diverse in terms of suevite types, and a gradational transition to massive impact melt rock constituting the lowermost 13 m of the drill core. A detailed macroscopic description and first results of microscopic observations reveal that suevite groundmass is substantially altered to secondary phyllosilicates (mostly smectite, minor chlorite) and locally extensive development of calcite. Crystalline basement–derived lithic clasts and minerals dominate the clast population, and only traces of clastic material derived from the upper sediment parts of the target could be recorded. Macroscopically and microscopically, melt fragments have mostly irregular shapes, which lead to the tentative conclusion that only part of the melt—and by implication suevite—mass is derived from fallout of the ejecta curtain. On the other hand, most melt fragments and larger lithic clasts are seemingly oriented subperpendicular to the core axis. This could be interpreted as being due alternatively to settling through air or lateral movement within the actual crater. The gradational zone between proper suevite and massive impact melt rock is characterized by increasing enrichment of melt component and concomitant reduction of suevitic groundmass, until in the uppermost impact melt rock, only millimeter-wide stringers of groundmass remain between densely packed centimeter- to decimeter-size melt fragments.