During the Lower Miocene Era high ocean levels periodically inundated the Lower Murray Basin, creating a warm tropical sea in which coral and shellfish proliferated. Mannum Formation limestone deposits have their origin in the ancient sea bed debris laid down during this era between 26 and 20 million years ago. The process is clearly evident in the limestone and calcareous sandstone structure, which is the residual concreted mass of coral, shell and the skeletal debris of ocean creatures mixed with sand. Though originally whitish, ground water and soakage has stained the strata a orange/yellow/beige colour.
At the earthcache location in Mannum you will see a fine example of the tertiary limestone Mannum Formation. The rock face is in a man made quarry. Close examination of the strata will reveal a variety of shells including bivalves, gastropods, brackiopods and bryozoa. The limestone is mostly a deep yellow colour. The stone at this location is friable and the exposed surface contains numerous weathered holes.
Please walk over to the wall from GZ as GZ will have you in the car park, GZ is here otherwise the cache emblem will be on top of the traditional cache here.
You are welcome to log a "Found it" log when you message or email the answers for the following questions. any "Found it" logs without the answers being sent will be deleted.
Q1. At the base of yellow face there is an area with a different colour. What colour? What is your opinion on why this particular colour has formed?
Q2. There are masses of shells embedded in the face. What is the typical size of the shells?
Q3. This question is optional as it is quite hard to spot the coral. There is a piece of coral embedded in the face at GZ. Approximately how high from ground level is the coral?