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.