Abstract

JARAMILLO JUSTINICO, ALEXIS; PARRA SANCHEZ, LUIS NORBERTO  and  RANGEL-CH., J. ORLANDO. Climate changes in the stratigraphy of the Colombian Amazonian region I. Neogene - Quaternary early. Caldasia [online]. 2011, vol.33, n.2, pp.539-572. ISSN 0366-5232.

Stratigraphic units of the Colombian Amazon region are composed of the following geological formations: Solimões late Miocene age (Neogene period 23.03 to 2.6 Ma Miocene-Pliocene), the Formation Jericó described herein and that was deposited between the Pliocene and Pleistocene, and the formation Isa (Içá), which has been considered of Pleistocene age. In the Holocene is predominant sedimentary material directly related or not with the influence of the Amazon River. Although much of the sedimentary environments of the Solimões Formation of Tertiary age correspond to rivers and floodplain forest vegetation, lakes and marshes (pantanales) are also present. Some of them have high concentration of salts in solution and sequences of hardened paleosoils that covers positive landforms formed in environments where some vegetation types are similar to the present types but with woodland savannas. The evidence suggests a warm climate with a prolonged dry season. The following stratigraphic unit, which is described herein Jericó, lies in a discordant form on the Solimões Formation and correspons to fluvial sediments that have been affected by the processes of generation of bauxites after his deposition. This action requires warm climates with a long rainy period, followed by a short dry season. The evidence of processes occurring in the two formations indicates that during the Neogene, the Amazon region (at least the Colombian part) experienced a climate with a dry season, being very long during Solimões Formation and short in Jericó Formation, but in both cases the climatic conditions were different to the actual climate. Isa Formation has a fluvial origin, with hilly topography that protrudes 2 or 3 meters above the terrace of Leticia, and the nearby Brazilian territory is not covered by the existing terrace. The detritus of the Isa formation have been contributed by reworking of the Jericó Formation and were deposited under very humid condition, with higher rainfall amounts than today. There are materials that directly depend on the involvement of the Amazon River while others are not affected by these dynamics. Among the materials that are not affected by the current cycle are the terrace of Leticia, which covers the Içá Formation. This terrace is the highest of the geological units among those that still retain their original flat morphology. On this terrace there are deposits of drainage channels associated with drainage of the terrace and the floodplain that are important to recognize the differential processes of erosion. Other geologic units are associated to flooded areas by the annual cycle of the Amazon River belong to the Quaternary and can be differentiated according to the relative age, spatial position, development over the water surface, and the dynamics of the Amazon River in the Colombian territory. A description about these units will be treated in a forthcoming paper.

Keywords : Geological formations; Solimões- Jericó and- Içá; Amazonian region; Palaeoecology.

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