The stratigraphy of the Guadalupe Formation and gravity structures in the Serrania of Chia (Sabana de Bogota)

Abstract

The Guadalupe Formation in the "Serranía de Chía" is, starting from the oldest, formed by the following levels: Raizal Member (= Dura Sandstone), 200 m; level of Plaeners, 100 m; Labor Sandstone, 70m; Tierna Sandstone, 50 m. Between the Labor and Tierna Sandstones there are about 1:01 m of lutites and porcelanites (Bürgl's Upper Plaeners). This section is similar both, in lithology and in thickness to the observed sections in another regions of the Sabana of Bogotá, so there are not important variations on the thickness of the levels of the Guadalupe, and for this reason is unacceptable the idea of the existence of an individualized basin in the region of the Sabana of Bogotá, formed by the Upper Plaeners. Tectonically the "Serranía de Chía" is formed by the eastern flank of a narrow anticline which can be saw in the half S of the "Serranía", in spite that his W flank is not as clear as his E flank. Gravity produced collapse structures in both flanks but specially in the East flank. These structures were formed by slidings aIl along the dip, especially in the Plaeners level; the dips which produced such slidings are around 35-60° These gravitational structures are produced mainly in sections in which erosion made disappear the thick levels of sandstones which are superposed to the Plaeners level. In the regions in which such sandstones are present, there are lack of slidings or they are not important because the plastic layers 01 clays and porcelanites ol the Plaeners Ievel cannot slide freely due to their position between two levels of thick sandstones.