Geology of the La Tatacoa "Desert" (Huila, Colombia) : Precisions on the Stratigraphy of the Honda Group, the Evolution of the "Pata High" and the Presence of the La Venta Fauna

Abstract

Middle Miocene fluviatile sequences are developed over a wide area of the La Tatacoa "desert" (the La Victoria and Villavieja Formations of the Honda Group). In contrast, pre-Miocene rocks, which range from possible Upper Palaeozoic calcareous deposits to Jurassic volcanics of the Prado Member (Saldaña Formation) and the Cretaceous sediments of the Monserrate Formation, outcrop only in small and irregular patches. Since the 1950's many different stratigraphic schemes have been proposed for the La Tatacoa Neogene sequence. A critical analysis and discussion of these various proposals is needed to establish a stratigraphic scheme that meets the requirements of both scientific accuracy and practical need. Based on the analysis of this kind, it is suggested that the level "group" must be retained for the Honda lithostratigraphic unit. Similar considerations suggest that the Honda Group can be subdivided into two formations: La Victoria (sensu Guerrero, 1994) and Villavieja. The validity of defining Baraya and Cerro Colorado Members, occupying the lowest and highest part of the sequence respectively, can also be established. However the previously defined informal divisions that involve treating other units as members and/or beds are disregarded, because they are considered superfluous and serve only to create confusion. Geological research of the region has reached a detailed level of understanding, and this combined with the present geographic location, can be used to discuss various aspects of the tectonosedimentary development of the northern part of the Upper Magdalena Valley. Based on the characteristics of the stratigraphic sequence and on the results of radiometric dating, different stages in the geological development of the region during the Neogene can be defined. This geological development has to be set in a context, which includes the influence of the Central Cordillera, the elevation of the "Patά High" (=Natagaima High or Natagaima Arch) and the uplifting of the Eastern Cordillera. Finally, aspects related to the presence (appearence?), expansion and extinction of the La Venta Fauna are considered within the context of the proposed tectonosedimentary scheme.