Deep-Sea Research II 49 (2002) 951–957 Oceanic impactsFa growing field of fundamental geoscience Rainer Gersonde a, *, Alexander Deutsch b , Boris A. Ivanov c , Frank T. Kyte d a Alfred Wegener Institute for Polar and Marine Research, P.B. 120161, D-27515 Bremerhaven, Germany b Institut f . ur Planetologie, Westf . alische Wilhelms-Universit . at M. unster, Wilhelm-Klemm-Str. 10, D-48149 M. unster, Germany c Institute for Dynamics of Geospheres, Russian Academy of Science, Leninsky Prospect 38, Korpus 6, Moscow 117321, Russia d Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA 1. ImpactFa fundamental geologic process in our solar system The heavily cratered surfaces of almost all solid bodies in our solar system testify the general importance of collisional events. Impacts release enormous amounts of energy within a time-scale of up to a few seconds. This complex process results on solid targets in cratering, ejecta of material, and in irreversible changes in rocks and minerals, generally referred to as impact (orFless favorableFshock) metamorphism. Impact as geo- logic process came into the focus of public interest only in the context of the mass extinction at the Cretaceous–Tertiary (K/T) boundary, 65 Ma ago. Yet it needed the discovery of the about 180 km sized Chicxulub impact structure, buried under roughly 1 km of Tertiary sediments of the Yucat ! an Peninsula, Mexico, to realize what a fundamental role impacts may have played for the evolution of the atmosphere and life. Witnessing the crash of comet Shoemaker–Levi 9 into Jupiter in July 1994 finally convinced a broad audience that impacts are dangerous or even lethal. This collision as well as the need to better understand the ultimate cause for the mass extinction in the aftermath of the Chicxulub ‘‘K/T’’ event initiated a bloom in modeling of cratering eventsFnow a major field in impact researchFas well as a renewal of elaborate research for terrestrial impact structures. The current rate of discovery is about five structures per year totaling to about 165 known terrestrial impact structures. The about 250-km sized, 2023 Ma deeply eroded Vredefort structure is the oldest and largest known terrestrial crater, yet about 60% of the population are younger than 200 Ma reflecting the highly dynamic nature of the Earth’s crust. More than 80% of the known impact structures were formed on continental targets, and they are concentrated on stable shield areas, the rest originated in marine environment. Pioneer studies to understand the physics of a deep-ocean impact and to generate strategies for the detection of such structures have been presented by Melosh (1982) and McKinnon (1982). The context for these papers in the 1980s was the intense search for an impact structure large enough to produce the world-wide enrichment of iridium in K/T bound- ary sediments. The K/T crater Chicxulub, finally discovered beneath more than 1 km of post-impact sediments (Penfield and Camargo, 1981; Hilde- brand et al., 1991), is the largest known crater formed in a marine environment. As for all other identified marine impact structures, the target at Chicxulub was a shallow-water environment. Shallow-water impacts still result in characteristic crater-form structures although morphological differences to structures on the continents are developed. To date, only one impact into deep *Corresponding author. Tel.: +49-471-4831-1203; fax: +49- 471-4831-149. E-mail addresses: rgersonde@awi-bremerhaven.de (R. Ger- sonde), deutsca@uni-muenster.de (A. Deutsch), baivanov@- glasnet.ru (B.A. Ivanov), kyte@igpp.ucla.edu (F.T. Kyte). 0967-0645/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0967-0645(01)00134-5