In the east of Venezuela, along the border with Guyana and Brazil, lies a chain of table mountains called "tepuis" which are the eroded remains on the Guyana shield, a layer of rocks from the earliest known geological formations. Experts debate whether they are remnants of Gondwana (the super-continent in which half the earth’s landmasses were grouped some 2000 million years ago) or the even earlier super-continent, Pangaea (which contained all the landmasses and existed between 570 and 200 million years ago, splitting to form Gondwana and Laurasia). Part of the difficulty of dating the rocks here lies in the fact that whatever their origin, they are empty of any fossils, having been formed before life first appeared on the planet. The Guyana shield was itself split when the Atlantic opened up and divided the Americas from Africa, so the table mountains of this area are matched by similar, smaller structures in the western Sahara. Mount Roraima is the southernmost tepui and on its summit plateau the borders of Venezuela, Guyana and Brazil meet at the "Triple Point".
To log this cache you will have to reach the Triple Point. This is usually done from the Venezuelan side where the only known non-climbing route up the walls of the tepui is to be found. The trip which will take several days to walk across the Gran Sabana to base camp and then ascend the mountain through the rain forest and up the vertical sandstone cliffs. Once on top of the mountain, the Triple Point is about an 8 hour round trip from the caves where mountain top camps are usually made.
Roraima is made of sandstone, the sand being the eroded remains of unimaginably old mountains washed down into shallow lakes and seas on the margins of the oldest continents known to geology. You can see the ripple marks in some of the layers of rock on Roraima's plateau which show that it was laid down under shallow water. You are walking on sand from a time before life existed on this planet. It is an awe-inspiring thought.
Like the other tepuis, Roraima stands high and isolated because its sandstone rock is hard enough to withstand hundreds of millions of years of erosion by wind and water. All the sandstone layers have been hardened by pressure from the layers of rock laid down above them. Some have been hardened by exposure to the effects of igneous rocks (molten rocks extruded from the liquid mantle of the earth). But the key to the formation of the tepuis is the chemical effect of "petrification". Water leaking down through the sandstone layers has carried chemicals which turned the sand to stone before the other hardening effects had an influence. As a result these areas have become "super-hardened" and so they now stand above the surrounding landscape as huge table mountains.
For the local people, the tepuis have always been the homes of gods and demons. For generations, they would never visit them. The Venezuelan government has made the tepuis national monuments which no-one should access. You are allowed to go there because the local people have petitioned to allow access in order to bring work and money to the local area. So you should respect the mountain and the local people on your visit.
When you are at the Triple Point find the small round plaque on the plinth and note the 5 digit number. To log this cache, please email us with the answers to the questions below. If correct, you will receive permission to log the cache. Logs without permission will be deleted.
1. Allowing for the academic debate about the formation of the Guyana Shield, what is the oldest possible date estimated for the rocks of Roraima?
2. Why are there no fossils in the rocks of Roraima?
3. The tepuis have been formed by erosion of the Guyana Shield by wind and water. What is the other key factor in the formation of the tepuis?
4. What is the 5 digit number on the small round plaque on the plinth (corner of Guyana/Brazil border)?
5. The rocks are coloured black by lichen, but near the Triple Point there are exposures that show the true colour of the rock. What is it and why is it that colour?
A photo of yourself at the Triple Point in your log like the one below is appreciated.
