Antietam Breccia 2 by Alan Pitts

This is an outcrop of brecciated quartzite located along the Shenendoah River near Ashby Gap Virginia. The quartzite is from the Cambrian Antietam formattion, the upper most clastic unit in the Blue Ridge stratigraphic stack. The Antietam Formation is a clean orthoquartzite containing skolithos trace fossils and is interpreted as a beach/barrier island. The sequence of rocks that the Antietam belongs to, the Chilhowee group is a transgressive sequence which marks the break up of Rodinia and transition towards a passive margin on the proto- North American east coast. The brecciation of the rock is thought to have occured as a result of the westward thrusting and folding of the Blue Ridge province during Allehenian mountian building.

This breccia occurs at the top of the Antietam near the contact with the overlying Tomstown Formation and could be local evidence of the larger Blue Ridge Thust Fault system.

Image made as part of the MAGIC project (Mid-Atlantic Geo-Imagery Collection)