Geological History

More than 600 million years ago rocks were forming in the Cape Town area. During the following hundred million years they went through trauma and reformation, which you can see the affects of today. You can see the layers of granite and sandstone that remain today and that for three main rock formations in the Cape Peninsula area. Those formations are:

Screen Shot 2013-03-24 at 2.00.01 PM

Figure 1: Crustal evolution [Available From: http://web.uct.ac.za/depts/geolsci/cape.htm]

The Malmesbury Group

  • Late-Precambrian age
  • 540 million years old – oldest rock formation in the area
  • Dark grey mudstone and lighter sandstone
  • Originally deposited on an ancient continental slope by submarine slumping and currents
  • Metamorphosed by heat and pressure and folding
  • Foundation of many buildings


malms03

 

 
 
 
 
 
Figure 2: Malmesbury Group sediments on the eastern side of False Bay [Available From: http://blogs.agu.org/mountainbeltway/2012/03/26/malmesbury-group-sediments-on-the-eastern-side-of-false-bay/]
saf03
Figure 3: Sea Point migmatite [Available From: http://blogs.agu.org/mountainbeltway/2012/03/01/sea-point-migmatite/]

Cape Granite

  • Batholith intruded into the Malmesbury Group 630 million years ago as magma
  • Hard and coarse-grained large white or pink feldspar crystals
  • Flakes of black mica and glassy grey/brown quartz
  • The foundation for most of the Table Mountain Chain
  • Exposed to erosion
  • Granite boulders are a result of weathering

800px-Swimmers_at_Boulders_Beach__Cape_Town

Figure 4: Granite Boulders [Available From: http://www.cape-town-helicopter-tours.com/cape-town-attractions.html]
boulders_beach_south_africa_01
 
Figure 5: Granite Boulders on Boulders Beach [Available From: http://oursurprisingworld.com/boulders-beach-south-africa-photo-gallery/]

Table Mountain Group

  • Eroded surface of granite basement in stream channels and tidal flats 450 million years ago
  • Weather-resistant sedimentary rocks
  • Approximately 2 km thick
  • Sand, silt, and mud deposits lithified by pressure and folding

Table_Mountain

Figure 6: Table Mountain sediments [Available From: https://www.e-education.psu.edu/earth106/content/l6_p2.html]

sandstone1

Figure 7: Table Mountain sandstone [Available From: http://www.earth.ox.ac.uk/~oesis/field/]

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s