Petrographic study at upper part of the Guadalupe Formation ( upper Cretaceous ) to the east of Bogota

Abstract

The petrographic study of 115 samples of the Labor and Tierna Sandstones (Guadalupe Formation, Upper Cretaceous) shows the existence of a differentiation between both levels, The Labor Sandstone is characterized by the presence of glauconite in the most part of the Iayers of the section, by the presence of the matrix in some layers, and because the median of quartz grains has lower vaIues. The nature of the cement is quite variable with abundance of carbonated cement and higher amount of ferruginous cement. The Tierna Sandstone has as characteristics the low content of glauconite, the existence of some thick grain Iayers of sandstones, and the abundance of quartzitic texture. In the cement predominates the kaolinite and there is very few calcium carbonate cements. Also is important to indicate the absence of the clay matrix.