To log this Earth Cache you have to answer the following questions by contacting me via my profile (erenei):
1) When were the fossils deposited?
2) As per the display, how many species of molluscs were discovered in the Alexandria Formation? Display missing - there were more than 170 species found.
3) How was the Alexandria Formation formed?
4) Describe the look, size, content and texture of the rock. Please do not touch.
Tertiary Alexandria Formation
By the end of the Cretaceous Period (about 80 million years ago), the present configuration of the Southern African coastline was established. The evolution of the landscape from this time onwards was dictated to to a large extent by fluctuating sea-levels. You will understand that climatic cooling results in more seawater freezing in the polar regions, which will correspond with a dropping of global sea level. By the same token, sea level rise will be associated with global warming. One such sea level rise from about 20 to 2 million years ago, resulted in the flooding of the Eastern Cape coastline to form the marine Alexandria Formation.
This formation has deposited 10’s of kilometres inland of the present coastline and has resulted in a fairly level wave-cut platform. These levels occur in about three different heights (each representing a different sea level), each formed during a still-stand followed by further lowering of sea level. The maximum landward extent of the raised sea level resulted in the development of the Grassridge Platform, which occurs at heights of 245 - 320 metres above mean sea level.
The shoreline of this sea level curved inland from the vicinity of Port Elizabeth to Paterson and Port Alfred. Under the water of the fluctuating sea levels, were deposited the sediments of the Alexandria Formation. The lower Coega Platform occurs further seawards, at an average height of about 200 metres above mean sea level. This Platform ends inland against a former cliff line that is exposed near the N2 highway in the vicinity of the Coega salt pans, between Colchester and Port Elizabeth.
The Alexandria Formation near Colchester would form part of the Coega Platform, whilst the same formation within the Addo Elephant Park near Addo Heights, would form part of the older Grassridge Platform. The Tertiary Alexandria Formation generally attains a maximum thickness of about 13 metres near Colchester and comprises calcareous sandstone, coquinite (cemented shell-rock) and quartzitic sandstone gravel. The Tertiary Period (65 to 2 million years ago) also coincides with the rise of the mammals. Dinosaurs became extinct at the end of the Cretaceous Period (about 65 million years ago) and small quadrupeds and flowering plants dominated the landscape.
The Alexandria Formation is easily discernable within the current Addo Elephant National Park and stands out as a white-coloured band near the upper portions of the hills. The best outcrop within the Park would be at the Zuurkop Lookout, where this material was previously mined to produce the white coloured material used to surface the gravel road in this part of the Park. In 3-D it should be remembered that this formation represents a fairly flat sea-level deposit, so it extrapolates as a thin disk into the landscape beneath the overlying cover material such as at Addo Heights. This cover material is known as the Nanaga Formation in the Park.
(Source: http://www.sanparks.co.za/parks/addo/conservation/ff/geology.php )