SEDIMENTOLOGICAL AND PETROGRAPHIC CHARACTERIZATION OF THE GALEMBO FORMATION IN LANDAZURI, SANTANDER (MIDDLE MAGDALENA VALLEY BASIN, COLOMBIA)

The sedimentary succession of the Middle Magdalena Valley Basin (MMVB) in Colombia includes Mesozoic and Cenozoic formations associated with a retroarc foreland basin [E1] (Gómez et al., 2003). Among these, the Upper Cretaceous Galembo Formation is particularly notable for its organic-rich marine shales, mudstones, calcareous mudstones, chert beds, bentonites, and limestones [E2] , which contain a variety of fossils, including phyto-debris, foraminifera, fish remains, ammonoids, bivalves, and gastropods. Understanding the stratigraphy and sedimentology of the Galembo Formation is essential as it offers a window into past climatic, environmental, and ecological conditions, aiding in the reconstruction of both local and global environmental history during the Upper Cretaceous.

This study focuses on a poorly explored stratigraphic section of the Galembo Formation along the road from Landazuri to Cimitarra, Santander Department, Colombia, previously described by Torres-Parada (2013). Twenty-six samples were collected from this section for detailed petrographic analysis using an Olympus BH-2 Polarizing microscope. The samples were classified based on their textural, structural, and compositional characteristics, following the classification schemes of Folk (1962) and Dunham (1962).

The lithological, sedimentological, and fossil assemblages suggest that the Galembo Formation in this region was deposited in shallow marine, low bioturbation, and low-oxygen conditions, likely corresponding to periods of deficient oxygenation (reducing conditions). These conditions may have been influenced by global warming and oceanic stagnation during the Cretaceous, contributing to the preservation of organic-rich shales. This study provides valuable insights into the geological evolution of the MMVB during the Upper Cretaceous and enhances our understanding of regional paleoenvironmental conditions.