Pictures of Geologic Contacts

Simply put, a geologic contact is where one rock type touches another --and as it turns out, they only do so in one of three ways. Depositional contacts are those where a sedimentary rock (or a lava flow) was deposited on an older rock; intrusive contacts are those where one rock has intruded another; fault (and shear zone) contacts are those where rocks come into contact across fault zones.

These photos highlight some of the key features associated with each type of geologic contact.

Click on any of the images below to see an enlarged, higher resolution version with a caption.

 

Depositional Contacts
Depositional Contact
Sandstone on Conglomerate, Montana 		depositional contact
Angular Unconformity, Siccar Pt., Scotland 		depositional contact
Paleozoic rock, Nopah Range, California

Click here for pictures of unconformities.

 

Intrusive Contacts
Intrusive Contact
Granodiorite intruding roof pendant, CA 		Intrusive Contact
Pegmatite intruding gneiss 		Intrusive Contact
Purcell Sill, Glacier NP, Montana

Click here for more pictures of intrusive features.

 

Fault Contacts
fault contact
Normal fault in sandstone, Utah 		fault contact
Thrust fault, Kyrgyzstan 		fault contact
Ductile shear zone in gneiss

Click here for more pictures of brittle faults and features.

 

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