Truly diagnostic impact signatures in layers of rock that might be distant from the impact site, are shocked quartz containing planar deformation features, and tektites.

Chemical analyses of the suspected impact layer may reveal unusual abundances of certain elements, such as iridium, which are relatively much more abundant in meteorites than in the Earth’s crust, or there could be evidence of hydrothermal alteration consistent with impact-generated hydrothermal circulation.

Impact structures may be buried, in which case more local shock features will be absent or eroded (although deep coring can reveal rocks from the structure itself).

If the structure is eroded, and the original target rocks are accessible, we might see breccias, shatter cones and pseudotachylites within and around the structure. In some cases, we can employ techniques used in geophysical exploration, such as gravity meters and magnetometers, to infer the presence of a buried structure, as illustrated in Figure 4.3.

Figure 4.3

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LPI 100 km