Terrestrial Impact Structures

Die Einschläge von Asteroiden, verbunden mit der Entstehung von Einschlagkratern, sind ein fundamentaler Prozess im Sonnensystem; mit ziemlicher Sicherheit sogar darüber hinaus. Als die Planeten und ihre Monde in der protoplanetaren Scheibe des sich gerade bildenden Sonnensystems am Entstehen waren, spielten Einschläge auf ihren Oberflächen eine wichtige Rolle. Auch später beeinflussten sie die Entwicklung der Planeten. Der Einschlag großer Projektile wirkte sich auf der Erde sogar auf die Entwicklung des Lebens aus. In den zurückliegenden 50 Jahren hat uns die interplanetare Raumfahrt die Kartierung der kraterübersäten alten Oberflächen unserer Nachbarn im Sonnensystem ermöglicht. Auf unserem Heimatplaneten repräsentiert die heutige Anzahl der weltweiten Einschlagkrater dagegen nur einen Bruchteil dessen, was die Erde im Lauf ihrer Geschichte an Einschlägen erfahren hat. Tektonische Aktivität, Erosion und Verwitterung sowie Sedimentation hat den Großteil dieser Einschlaghistorie ausgelöscht. Der übrig gebliebene Anteil ist von diesen geologischen Prozessen oft bis zur Unkenntlichkeit verändert oder im Untergrund unseren Blicken entzogen. Die Kartierung dessen, was von den Einschlägen der Vergangenheit heute noch auf der Erdoberfläche zu sehen ist kann von Satelliten aus erdnahen Umlaufbahnen vorgenommen werden. Oft behindert dabei die Erdatmosphäre infolge dichter Bewölkung oder starker Luftverschmutzung den freien Blick oder fehlende Ausleuchtung durch die Sonne entzieht den Erdboden einer genauen Betrachtung. Jedoch können wir heute mit Methoden der Fernerkundung, entwickelt in den zurückliegenden Jahren, die Herausforderung, die Erdoberfläche mit hoher Präzision zu kartieren, erfolgreich bewältigen. Zwischen 2010 und 2016 hat die deutsche X-Band Radarmission TanDEM-X, geleitet und betrieben vom DLR, dem Deutschen Zentrum für Luft- und Raumfahrt, das erste hochaufgelöste globale digitale Höhenmodell der festen Erdoberfläche erstellt. Es basiert auf der Methode der Interferometrie mittels Synthetischen Aperturradars. Wir haben mit Hilfe dieser Daten den ersten topografischen Atlas aller heute bekannten terrestrischen Einschlagkrater erstellt. Er vermittelt den Leserinnen und Lesern die Grundlagen des Einschlagprozesses, der Radarfernerkundung im Allgemeinen sowie der TanDEM-X Raumfahrtmission im Speziellen. Er zeigt die Einschlagkrater der Erde in mehr als 200 hochaufgelösten topografischen Karten, ergänzt durch geologische Beschreibungen sowie einer Vielzahl von Aufnahmen dieser Strukturen. Der Atlas vermittelt für jeden Kontinent einen umfassenden Überblick über dessen Inventar an Einschlagkratern.

Autorentext
Wolf Uwe Reimold holds M.Sc. (1977) and Ph.D. (1980) degrees in Mineralogy from the University of Münster (Germany). Post-doctoral research at NASA Johnson Space Center in Houston (USA) was followed by research positions and then a Professorship in Mineralogy at the University of the Witwatersrand (Johannesburg, South Africa, 1984­2005). Uwe's main research interests have been multidisciplinary Impact Crater and Shock Metamorphism studies, besides some Economic Geology and Regional Geology exploits in southern Africa and Ethiopia. Impact research was mainly focused on structures in Africa, Europe, and North America, including a major contribution to the understanding of the Vredefort impact structure in South Africa. Other main research targets were Bosumtwi (Ghana), Roter Kamm (Namibia), and various structures in Scandinavia, and in recent years in Brazil. In 2006, Uwe transferred to Humboldt University and the Museum für Naturkunde in Berlin, where he served as Professor of Mineralogy and Petrography, and Head of the Evolution and Geosciences Division of the Museum. In 2018 Uwe took retirement in Berlin, and a new position as Professor Titular at the Institute of Geosciences at the University of Brasília, Brasil.

Leseprobe
The idea for this atlas was born already several years ago. Then, a precise topographic atlas presenting terrestrial impact craters, the scars of the impacts of solid bodies onto the Earth's surface, had not been established yet. This was astonishing, as such impacts had long been considered as the most fundamental process on the surfaces of the terrestrial planets, as the late Eugene Shoemaker, one of the pioneers of impact geology, had put it. But when the first digital elevation data had been processed from the early phase of the TanDEM-X mission, they immediately showed their great potential for mapping applications. We were particularly excited, because the objective of this space-borne undertaking of generating a precise high-resolution digital elevation model for the entire solid surface of Earth would allow, for the first time, to map the morphology of all terrestrial impact structures with a topographic expression, in detail. What had been the limiting factor of the existing datasets for such an exercise in the past no global coverage, data gaps, or data artefacts would no longer hamper the cartographic work. Only very small impact craters below the resolution of the TanDEM-X data would escape recognition in the TanDEM-X maps. Patience, however, was required before the final TanDEM-X Digital Elevation Model (DEM) was released and access to the data for science applications was granted. In the meantime, we had investigated the workflow to present the topography of an impact structure and its environs by using Raw DEM scenes. Because our intention was not to merely publish a sequence of high-quality maps, our atlas concept foresaw to additionally provide short and concise, illustrated text sections for each impact structure. As two of us, Thomas Kenkmann and Wolf Uwe Reimold, have throughout their careers as impact geologists confirmed the impact origin of a considerable number of structures and participated in the studies of many more, these so-called fact sheets also reflect personal experience. Clearly this is the reason why these texts sometimes differ in style this is indeed intended. What is more, the fact sheets also reflect the varied degrees of detailed study that different impact structures have permitted to date. The individual texts also provide information about the location of a structure and how to access it. For those structures in very remote parts of the globe, the access notes can, however, be limited. A list of selected references completes each text. These are the main references that were used by the authors of the individual fact sheets who are acknowledged at the top of each structure's first page. These references are also intended to provide the layperson with a strategic entry into the literature pertaining to any of these impact structures. The atlas consists of three parts: introductory chapters, the physical maps with corresponding texts for all impact structures covered herein, and an annexure with supplementary information. The first introductory chapter briefly explains why interplanetary space is filled with small bodies and why they sometimes approach Earth's orbit. Chapter 2 goes a bit deeper into the principles of hypervelocity impact. It explains crater formation, shock metamorphism, and specific impact-related lithologies. This chapter introduces impact related concepts that are addressed in more detail in the subsequent impact structure-related fact sheets. The third chapter describes the terrestrial impact crater record. A short account on its completeness or rather lack thereof is followed by its status at the time of the manuscript deadline as of February 2020. As the last two years have been very productive in identifying previously unknown impact structures, we have thrived towards a status that is as complete as possible. Our atlas, however, has a differentiated view on some alleged impact structures. Where we feel that the evidence for an impact origin is still incomplete or ambiguous, we treat these structures separately, ev…

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