If you're doing this EarthCache now you are in the Montsec in the pre Aragonese Pyrenees on the banks of the Canelles reservoir located in the town of Finestras, now abandoned.
Where we are, exists a curious geological formation and very rare of this size in Spain, which is popularly known as the "Chinese Wall" known. It is not similar of the giant in Asian country, but seeing these two vertical walls of rock, located in two parallel lines, immediately comes to mind the Great Wall.
But before to talk about how it was formed, we have to know what is the stratigraphy and for what we need to make a recap to understand more easily this phenomenon.
Stratigraphy
Stratigraphy is the branch of geology is about the study and interpretation of the vertical and horizontal stratified sedimentary rocks. The units are based on their characteristics or qualities to establish its distribution and relationship in space and succession in time, and to interpret the geological history, here, the basic principles of stratigraphy:
Relative
Organize the stratum and the events in a sequence according to their age.
- - Principle of original horizontality: In normal conditions, the sediments are deposited that they acquire a horizontal arrangement.
- - Principle of lateral continuity: Sedimentary bodies are extend in all directions and senses until its thickness becomes zero or reach the edge of the basin sedimentation. (Sedimentary bodies are not infinite).
- - Superposition principle: The layers are deposited horizontal on each other and so that the entire layer is superimposed on another and inversely.
- - Principle of uniformity: The laws and natural laws governing these processes have remained uniform throughout geologic time.
- - Principle of actualism: The phenomenon and processes that are acting today are the same who have acted during the geological times, and produce the same effects that occurred in the past.
- - Principle of faunal succession or correlation: Fossil organisms groups occur in a defined and particular order, so that each period can be recognized by their corresponding fossil, Example: trilobites correspond to the primary era; ammonites, secondary; and nummulites, to tertiary.
Absolute
It allows to find the age of a stratum or geological event determined by the following method (there are three, here only discuss what interests us):
- - Sedimentological: Analyzed sediment deposits that follow regular time intervals, such as: the varvites glaciers are sediments at the bottom of glacial lakes. In winter a thin, dark sediment is deposited; and in summer, one thick and clear. So, each pair of layers corresponding to a year.
Formation
This rock formation that you have in front of you, it has been originated millions of years ago during the Cretaceous. The strata of this rock formation are closely linked to the Geotectonics of the Pyrenees because they were formed 80 million years ago when the Iberian and Eurasian plates collided to form the Pyrenees.
Seeing them today in this vertically, is also due to Milla anticline, syncline of the Blancafort and the anticline of Canelles. These forces exerted to each other through the years, they have raised the strata until completely vertical.
They consist mainly of alveoline limestone sediments, consolidated in rocks when theen the sea still covered these lands.
The alveolinas limestones are formed by fossils of foraminifera with a shell fusiform with numerous spirally arranged chambers. Its size is usually half a centimeter long by one or two millimeters wide. Because of its great development during the Paleogene, they have formed thick layers of limestone formed almost exclusively by their shells. If we look closely, we can see some of them.
The concept of this Earthcache is that the geocacher learn how the strata in this area are created. I could explain more about the subject but I like my Earthcaches to be brief and concise so visitors leave the place having learned something new. Enjoy it!
At the indicated coordinates, you can find an infoboard, to validate your log, please send me the answers to the following questions. You can log without waiting for my reply, if a problem occurs we will try to find a solution together. You can contact me in English, French, Spanish or Catalan :)
Log this cache as a "found it" and send me your answers via my profile or via message on geocaching.com, and I will contact you in case of problem.
1-. Seeing these two walls (strata) that form the "Wall", can you tell me which one was deposited before (oldest) on the seabed?
2-. Due to what geological phenomenon can we see these layers as if they were a wall?
3-. Finish this sentence with the help of the info board: Es imposible mostrarse indiferente ante...