Contact (geology)

[4] Gradational contacts occur where the change in depositional environment takes place over a longer period of time.

Closely related to intercalated contacts is interfingering (also known as intertonguing,[7] interdigitating, or interlocking[8]) of laterally adjacent sedimentary rock bodies.

Here the contact breaks down into a series of wedges or tongues that penetrate the adjacent rock body and pinch out individually.

Depending on the composition of the magma, the intrusive body may have a complex internal structure which can provide insight into its emplacement.

[1] Identifying and understanding the relationship between contacts is important in determining relative ages of rocks and formations.

These contacts have been identified by the International Commission on Stratigraphy and they are known as GSSPs, or global boundary stratotype section and points.

Some of these boundary points are at physical locations, while others are in ice drill core sections, or have been defined chronometrically.

This reddish layer is the Iridium Anomaly, representative of the fallout of the major impact that resulted in the mass extinction event that ended the Cretaceous.