8 January 2013

Hoerikwaggo Trail 2: the Table Mountain Sandstone

Posted by Callan

Yesterday I introduced you to the Hoerikwaggo Trail. Today, we’ll start looking in detail at the geology. The predominant rock unit is the Table Mountain Sandstone, or more properly, the Peninsula Formation of the Table Mountain Group, a super clean quartz sandstone with scattered pebbles in it. It’s Cambrian in age. The pebbles are VERY well rounded, almost like Easter eggs:

I saw plenty of isolated pebbles like the previous two, plus there were areas that were more or less “conglomeratic”…

The sandstone is named for Table Mountain (the prominent flat-topped peak immediately south of the “City Bowl” of Cape Town), but it’s a regionally extensive unit, extending both north and east of Table Mountain proper.

As we hiked along, there were plenty of fine examples of cross-bedding, such as seen here:

Remember how we used this cross-bedding to determine that many of the Table Mountain Sandstone strata at Cape Agulhas were overturned?

Annotated:

I saw a sole example of soft-sediment deformation:

…And I even found a brecciated piece, implying some serious tectonic disturbance, but that’s a subject for a later post in this series…

More on that tomorrow…