The Raleigh, North Carolina area is a peneplain. The area has been devoid of any mountain building events for quite some time so the land surface has very low relief. As a result, outcrops of exposed metamorphic bedrock across the Piedmont physiographic province are few and far between. Additionally, bedrock may be covered by a literal veneer of dense soil and/or saprolite which conceals the bedrock below by mere inches.
But fear not! I am a trained geologist and have become adept at finding these obscure bedrock outcrops. So for reference, and in case anyone wants to go and visit, lets start with a map that I cobbed together.
Site Location of Bedrock Outcrop along US-401 South, Raleigh, North Carolina - photo by J. Sents, 2012
I used the Wake County iMAPS GIS [Beta] for the base layers used to create the map above. The location presents itself as an unpaved, unmarked parking lot. Along the southern edge of the lot, a stand of trees and bushes conceals the exposed bedrock. So a few days after the initial identification of this site, I made first contact with my camera and compass.
Bedrock Outcrop Photograph facing South - photo by J. Sents, 2012
You can see my Brunton compass just to the right of center [the bright object]. Don’t ask what string was for. I can’t imagine anyone went out of their way to hold that scrawny tree upright but who really knows? I’ve seen weirder things across this state. Note as the outcrop starts to become saprolite [extremely weathered bedrock] to the right [west]. See what I mean about how little soil cover is required to start obscuring the bedrock? This is very common across this whole Piedmont region.
Another thing to note is the set of joints and fractures. I sampled these and collected the strike and dip data. I will present those below. For those of you who have no idea what strike and dip are, I’ll explain that in a follow-up post very shortly after, if not immediately following, this post. Here are some strikes and dips of the two predominant fracture sets:
- 255° 75°NW
- 258° 73°NW
- 256° 75°NW
- 317° 65°SW
- 315° 72°SW
- 318° 69°SW
I’m far more concerned with the strikes [bold] than the dips [gray]. What I’m hoping to accomplish is to present you all with a better idea of what I find, how it compares to the work the North Carolina Geologic Survey is currently conducting, and what it tells us with respect to the regional Piedmont metamorphic bedrock in central North Carolina. Stay tuned. I’ll get to the strike and dip definitions tomorrow most likely.
