Search

This article presents a comprehensive vision of particularities and constraints of the Paja Formation in the Northern Andes of Colombia, supported by personal, institutional, and academic experiences, including a doctoral thesis in completion (geomorphology and risks research line). Such fine-grained marine rocks cause severe damage in diverse zones, with little spread, and are very unfavorable, especially within the Eastern Cordillera (departments of Santander and Cundinamarca), whose socio-environmental problems motivated a popular legal action in the municipality of Vélez due to the cracking and collapse of houses, damage to roads and landslides in the urban area, as well as flows, subsidence, and high hydrogeochemical dynamism or rare earths, although they also presented spontaneous ignition at the rural area. Understanding how these problems originate and interrelate is the main objective of the work. At the beginning, we include some brief definitions, terms, and key approaches to understand the consolidated geomaterials, location, and background of the problem; then, the results of meso–macro–micro studies, obtained by combining the field techniques and conventional instrumental laboratory analyses (tests on the chemistry of water and soil, description of samples with magnifying glasses, petrography with a polarized light microscope, micromorphology of regoliths–colluvions) of nanoscientists (emphasizing RXD-RXF, SEM, IR-Raman spectroscopy, TOC-TS) are presented. These characterizations and new knowledge must be socially and institutionally appropriated and applied in land use planning and risk management for the sustainability of challenging environments with the stratiforms of Lower Cretaceous rocks and associated Quaternary deposits in populated mountainous areas and contrasting intertropical hydroclimatological regimes, geologically active, so unstable and insecure.

This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, pyrophyllite, kaolinite and chlorite group minerals, framboidal and cubic pyrite, as well as marcasite, with minor feldspar, sulphates, and phosphates. Total organic carbon (TOC), total sulfur (TS), and millimeter fragments of algae are high, whereas few centimeters and not biodiverse small ammonite fossils, and other allochemical components are subordinated. Na–A zeolite and associated mineral phases as sodalite occur just beside the interparticle micropores (honeycomb from framboidal, cube molds, and amorphous cavities). It is facilitated by petrophysical properties alterations, due to processes of high diagenesis, temperatures up to 80–100 °C, with weathering contributions, which increase the porosity and permeability, as well as the transmissivity (fluid flow), allowing the geochemistry remobilization and/or recrystallization of pre-existing silica, muscovite, kaolinite minerals group, salts, carbonates, oxides and peroxides. X-ray diffraction analyses reveal the mineral composition of the mudstones and scanning electron micrographs show the typical cubic morphology of Na–A zeolite of approximately 0.45 mμ in particle size. Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate → sodalite → Na–A zeolite. A literature review shows that this is an unusual example of the occurrence of natural zeolites in sedimentary marine rocks recognized around the world.