By: magic-gigapans
Image: Chris Johnson, Mid-Atlantic Geo-Image Collection
License: Creative Commons Non Commercial ⧉

Uploaded: 13 May 2020
Last Updated: 19 May 2020

291 megapixels
29,668 x 9,820 pixels
98.9 in X 32.7 in at 300dpi

This is an exposure of the Catoctin formation at Point of Rocks in Maryland, on the north bank of the Potomac River. Point of Rocks is a prominent water gap cut by the Potomac River. The Catoctin formation is Neoproterozoic in age and was erupted as a series of flood basalts during the breakup of the Mesoproterozoic supercontinent Rodinia, and the opening of the Neoproterozoic and Paleozoic aged Iapetus Ocean basin. It overlies the basement complex at the core of the Blue Ridge Anticlinorium. In many places, clastic sedimentary rock occurs between the basement and the Catoctin. A simplified stratigraphic section may be seen here: http://web.wm.edu/geology/virginia/provinces/Blueridge/blue_ridge_strat.html The Catoctin was metamorphosed during Alleghanian mountain-building in the late Paleozoic (during the closure of the Iapetus and the assembly of the supercontinent Pangaea). This metamorphism imparted the characteristic green color as a result of the growth of the minerals chlorite and epidote. The image was taken from the public boat ramp on the Virginia side of the Potomac looking north into Maryland along the strike of the eastern limb of the anticlinorium. This area exhibits numerous veins of milky quartz. The western boundary of the Mesozoic Culpeper Basin lies just to the east of this site, an ancient rift valley that formed as Pangaea broke apart and the Atlantic Ocean basin began opening. The United States Geologic Survey maintains a stream gauge just downstream of the bridge, where data are collected on the Potomac’s discharge: http://waterdata.usgs.gov/usa/nwis/uv?01638500 Thanks go to Callan Bentley for help with such a great description! Thanks Callan!