The Orinoco Basin, extending from the Andes and the plains of the Llanos and the Guiana shield of Colombia and Venezuela to the Atlantic, covers 980,000km2. The river flows 2,140km from its source in the extreme south of the Guianan massif until reaching the ocean.
The "Oriniquia" as it's known locally, represents one of the most biologically and hydrologically diverse areas of the world.
At over 33,000 m3/sec, it ranks fourth worldwide in average discharge.
The Orinoco through the seasons:
The Orinoco changes greatly from season to season. Between May and August, rainfall oscillating between 5,000 and 7,000mm and the relatively flat topographic conditions of the basin generate a flooded area covering almost 10% of the basin. This creates new habitats and resources for many aquatic species. In Ciudad Bolivar (the capital of the eastern Venezuelan state of Bolivar), the annual variation in water level ranges from 15m to 18m and the discharge rate varies from one season to the next. A tributary of the Orinoco River called the Casiquiare connects with the Rio Negro, a tributary of the Amazon River, forming a 'natural canal' between the Orinoco and the Amazon River.
Geological history:
The Orinoco River runs through two distinct geological areas: one is the oldest geological formation on the continent, to the south of the river, and the other is a relatively recent formation of land, created by sediment washed down from the Andes. Over time, the eroding action of the river has contributed to the isolation of an area of high sandstone mesas, locally known as the tepuis, some with an altitude of 1,500m. One of these is home to Angel Falls, which at nearly 1,000m is the highest free-falling waterfall on Earth.
The geologic construction of South America is determined by three big geologic regions which form at the same time also tectonic and physical-spatial great unities: The old shields, the young highmountains and the also young sedimantation tank. Along the whole Pacific coast the young mountains of the Andes rise. High in the tertiary, it is marked certainly by the tectonic active continental edge, and, hence, by intensive volcanism and violent earthquakes. In contrast to the Andes the low mountain ranges are tectonic quiet crust parts. Originated in older mountain formations, in the meantime, they are "kratonic", that means not more folding and in general tectonic quietly. These are the old shields and the rests praecambrian basement, but also of the variscian mountain formation. There steps either the upcoming depth rock in the surface by days, or it is overlaid from mostly thin mesozoican and caneozoican asediment series. Finally, the young sedimantation tank are to be called which are named as a rule after the main receiving stream, the Orinocobasin, the Amazon basin and the La Plata system with the decisive rivers of Paraguay and Paraná.
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Please answer following questions via mail and wait for my logpermission!
1. How is the oldest geolocial formation of South America called?
2. How are the Indians called living in Orinoco Delta?
