Stratigraphy

Ecuador by stratigraphic layers

Stratigraphy could be defined as the science of “the geological order”. It deals with the superposition of the rocks layers from older to younger, from rocks in a lower position to rocks in higher position. However, this order is interrupted by several phenomena such as earthquakes, faults, folds, volcanic explosions, landslides, tsunamis etc.

Consequently, the stratigraphic columns are found in places where none or minimum disturbances have occurred, and have a good accumulation of layers of sediments. These places are within sedimentary basins.

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The mayor stratigraphic records of the Ecuadorian Geology come from coastal cliffs, natural rivers’ cuts, road cuts, and exposures in the front-Andes and the sub-Andes hills. These records are completed with exposures in high mountains. There is also, data of subsurface records of reflection seismic lines of geophysics and records of drilled wells, for the oil industry, in the Oriente and the Costa.

The Principles of Stratigraphy

The video below gives a great overview on stratigraphy

Given the diversity of rivers and waterways in Ecuador its no surprise that some of the most complete stratigraphic records can be found along them. Sections detailed in the book include:

  • The Pastaza River and effluents from Baños to Mera offer almost a complete geological record from Paleozoic on.
  • The Mesozoic is well exposed in the Rio Misahualli section
  • The profile of Rio Cosanga enables you to know the Mesozoic – Cenozoic transition and provides an important volcanic record of the Cordillera Real.
  • The profiles along the Guayllabamba and Mira rivers are quite complete in the transition from Mesozoic to Cenozoic in the Northern Andes.
  • The Paute River also cuts across the Cordillera Real and in doing so it provides an almost complete geological record.
Stratigraphic Column Misahualli River Ecuador

Stratigraphic Column – Misahualli River

Andean Capybara Fossil

The most important vertebrate fossils, reported already at the base of the upper Cangahua have been; mastodons, mylodons and sabertooth tigers of temperate – semi-tropical environment. A new fossil found in the inter-Andean Guayllabamba basin, at the location of Tanda, is the piece corresponding to half of the inferior jaw of a capybara, a tropical rodent.

Capybara with fossil of JawThe modern capybara (hidrochoerus hydrochaeris) is a giant vegetarian rodent from tropical zones off the Andes, found from Colombia to Argentina. It can reach a height of 120cm and a weight of 50Kg, has no tail and lives near the water, as it is an excellent swimmer. It has not been observed above 1300 masl (meters above sea level).

The finding of a jaw of capybara in the dry area of Tanda at a present altitude of 2400m is very significant. It is the first fossil of this kind located in the Ecuadorian inter-Andes. Its discovery implies three important facts:

  • A real connection of the Guayllabamba basin with the coast.
  • A more humid – tropical environment within the basin, before 14Ka.
  • A permanent elevation of the Andes, since then.