Unconformity on Neranleigh Fernvale beds EarthCache

In this area you can see a really good example of an unconformity (a junction surface between a younger rock sequence overlying and and older, usually with an anglular difference between the two) of the Woogaroo Subgroup (a series of rocks that are gently inclined mainly sandy sedimentary rocks) overlying Neranleigh Fernvale beds (these are a belt of medium to fine-grained sediments that stretches from Hamilton to the Gold Coast).

The lower part of the cutting shows interbedded shale (a very fine-grained sedimentary rock with a pronounced thin layering) and siltstone (a fine-grained sedimentary rock intermediate in grain size between midstone and sandstone) and thicker beds of bleached weathered greywacke (a course sedimentary rock composed of small fragments of other rocks, feldspar and quartz).

Despite some small scale faulting (a break in the rock along which movement has occured), they are relatively undeformed, and show the original sedimentary features. 

You can see there are rhythmically banded dark shales and white siltstones and fine sandstones, whose bedding is disrupted and contains small folds. This is interpreted as being the result of slumping while the sediments were still soft; such banded sediments are typical of deep-water, continental slope sequences. 

Fractures or joints in the rock and some thin sandstone layers have been cemented by hard, brown iron oxides (from groundwaters), leaving them standing out from the rest of the rock.

The unconformity occurs as a clearly visable line about 30m from the top of the hill. Almost horizontal conlomerates and sandstones of the Woogaroo Subgroup rest at a slight angle on the older rocks down hill. The lowermost bed is a coarse sedimentary breccia of anguar blocks of chert/quartzite and other rocks from the web. It is succeeded by thin beds of sandstone and more breccia several metres of siltstone and shale, and then a thick bed of sandstone and pebble conglomerate which can be seen outcropping around the hillside. 

From a distance, the unconformity can be seen on a much larger scale in the high wall of the old quarry to the left (GC677X7). 

To log this cache, please answer the following questions and email them to the cache owner.

There are 3 primary colours of rock (white, dark grey, reddish brown) which you can access without climbing the hill. Feel each one and answer the following questions:

1. Feeling each colour, which one has the roughest texture? After reading this this listing - what rock type do you think this is?
2. How thick is the brown layer (the iron oxide layer on the sandstone)?