Basic remote sensing signatures of large, deeply eroded impact structures

Abstract

Orbital remote sensing has discovered a number of impact structures on Earth. Complex structures eroded below allochthonous breccias and sheets of impact melt typically reveal a multicircular bull‘s-eye pattern when the projectile struck a subhorizontally bedded sedimentary target. These structures are striking because of steeply dipping strata in the central uplift, sometimes encircling a crystalline plug. The central anomaly is usually surrounded by an annulus representing a shallow ring-shaped syncline that develops during the cratering process. If not exposed, vegetation, drainage, and weathering products can delineate the bedrock geology. In crystalline targets, the signatures of central uplift and ring syncline are much more subtle, and hard to recognize by satellite imagery. At large structures, however, traces of slumping faults at the crater rim may remain perceptible as curved drainage or scarps. In particular radar systems are potentially useful for detecting such features. The presently known cratering record indicates that more deeply eroded impact structures exist, and this especially in crystalline terrains.