Multiring impact basins have profoundly influenced the geologic evolution of Mars. We compile and summarize the evidence for Martian impact basins and suggest eight new examples. Multiring basins on Mars define three morphologic subclasses with increasing basin size. Basins having diameters 3003600 km) have extremely shallow topographic profiles and numerous concentric structures expressed as scarps, massifs, and channels. Radial and concentric structures analogous to those associated with Orientale are not apparent for basins of Argyre size or larger. These variations in basin morphology and structure may be associated with mechanical interactions between basin-forming impacts, relatively thin, weak lithosphere, and, for the largest impacts, spherical target geometry.

Multiring basins are recognized on all parts of Mars, including Tharsis, Elysium, and the northern lowlands. Much of the subsequent resurfacing of cratered terrain such as Lunae Planum ridge plains is associated spatially with multiring basins. Nucleation of long-lived volcanic complexes in Tharsis and Elysium was probably aided by early impact basins. The planetary terrain dichotomy was probably established during the period of heavy meteoritic bombardment, and subsequent processes in the northern plains region were not sufficiently vigorous to destroy or completely obscure the underlying multiring basin fabric. The revised population of multiring basins is consistent with the size frequency distribution of craters <500 km in diameter on Mars. Basins having diameters ~500<D<1850 km are characterized by a cumulative frequency slope of -0.75¿0.16, whereas the larger basins define a slope of -1.7¿0.45. This change in slope occurs over the same diameter range as the significant change from Orientale type basin morphology at smaller diameters to Argyre and Chryse type basin morphology. The population of craters and basins on Mars confirms that the relative crater densities on the terrestrial planets due to heavy bombardment are comparable, perhaps suggesting a common source for the impacting objects. ¿ American Geophysical Union 1990