Gathering clues

Location:  N38°59.542’  W077°14.790

Elevation: 132ft

Our first stop on the Billy Goat trail was at an outcrop with abundant jointing.  Here I took several measurements of strike and dip, trends and plunge, foliation and bedding.  I am gathering this information to compile a steronet which should shed light on what stresses and changes this area has undergone.  I will also use the collected data to try and solve the mystery that have plagued geologists which is why are the Lamprophyre Dikes offset and whether Mather Gorge (an stretch along the river that is abnormally straight compared to the rest of the river) was cut by a dike.

  In order to get a large amount of data trials, my classmates helped to take measurements and later we combined our data.

Look at the dip on that.  These beds are dipping at 150°, 41°

The primary rock type here is a greywacke.  Greywacke is an intersesting rock because its presence tells us that it came from a low-oxygen environment in the deep sea.  One interesting feature about greywacke is that in many cases, one can find graded bedding in the rock.  This is because as sediment is weathered from its source and carried out to the ocean, it can be deposited in alluvial fans. The largest grains drop out first followed by finer and finer sediments.  Turbidity currents are what drive the sediment onto the alluvial fans as its deposited.  Notice the presence of a large quartz vein in the picture above.  I will address how this came to be injected into the greywacke later on.  So my mission was to find evidence of graded bedding.  Depicted below are some images of just what I found.

I have to say I got a little too excited when I found my first fold...the first of many.  I think how silly it is now as I called the professor over with so much pride inside when I triumphantly announced "Look at this fold I found!!"  Little did I know at the time how pathetic this little guy was.  Professor Bentley was so gracious to play along with a quick pat on the back and a small grin "yeah...look at that little guy.  Very good."  Thanks professor.



And we found some bedding!
What a nice bedrock sample this is.  Just look at the grading on it.  We can see several successions of deposition.  Love It!  So now we know that this was probably deposited in an alluvial fan in the deep ocean.  Oh...and lets not forget about composition...this greywacke is a dark grey mafic rock lending itself even more support as to the deep depths at which deposition most likely occurred.  So how did all of this greywacke get to be 132ft above sea level?  Lets go find more clues of the geologic past that might help better explain how it all went down...or should I say up.