Boletín de Geología

Mineralogical and geochemical evidence of the Caribbean Large Igneous Province (CLIP) in the submarine basement of the Guajira Basin, Colombia

Tue, 06 May 2025 00:00:00 +0000

The origin and composition of the basement offshore of the northern South American margin are somewhat controversial as it results from the complex interaction of the Caribbean, South American, and Nazca tectonic plates through geologic time. One of the major issues that have limited a proper comprehension is the difficulty in acquiring sampling from submerged igneous and metamorphic rocks. The basement sequence of the Orca-1 exploratory well, located offshore of the Guajira Peninsula in northern Colombia, consists of a sequence at least 200 m thick, characterized by basalts and andesites. Occasional extrusive episodes are marked by the presence of pyroclastic rocks deposited in a subaqueous environment. The mineralogical alteration of the Orca-1 rocks points to a significant role played by low- temperature hydrothermal fluids in their formation. Its geochemical signature indicates a tholeiitic affinity and a plume source without any evidence of a subduction component or mantle-crust interaction in its petrogenesis. Based on their composition, we propose that the Orca-1 basement rocks correspond to a fragment of the oceanic crust that formed the Caribbean Large Igneous Province (CLIP) and were later accreted to the margin of the Guajira Peninsula, north of the Chimare suture which seems to be northern boundary of the autochthonous South American blocks.

Lithologic and biostratigraphical characterization of the Toluviejo Formation: Contributions about the paleoenvironments of the Eocene carbonate platforms from northern Colombia

Tue, 06 May 2025 00:00:00 +0000

This study aims to understand the paleoenvironmental conditions of the Toluviejo Formation (San Jacinto Fold Belt, Colombian Caribbean). To achieve this a petrographic analysis of the El Hueso section (Córdoba, Colombia), as well as a geochemical evaluation of some elements present in the rock (Sr, Ba, Fe, Ca, V, Cu, Al) were conducted. The petrographic analyses reveal that the sedimentary succession is mainly composed of bioclastic limestones (grainstone), dominated by large benthic foraminifers (families Nummulitidae, Lepidocyclinidae, Soritiidae, and Discocyclinidae), and calcareous algae, with a moderate to low degree of diagenesis in some samples. The foraminiferal assemblages indicate a middle Eocene (Late Lutetian to Bartonian) age, which agrees with age definitions for other sections of this unit. Petrofacial analysis identifies 3 groups based on variations in the proportions of large benthic foraminifers and calcareous algae, indicative of a middle carbonate ramp. Although the lithology and composition of the El Hueso section are generally homogeneous, the variations in its main bioclasts, as well as the Fe/Ca and Sr/Ba geochemical ratios, suggest minor changes in the energy conditions, terrigenous input, and paleosalinity (probably linked to eustatic variations) for the basal part of the succession. Furthermore, the degree of bioclast preservation and the distribution of elements sensitive to bottom water oxygenation variations (V/Al, Cu/Al) indicate low-stress paleoenvironmental conditions.

Exploration methods and geothermal systems in Colombia with emphasis on the Nevado del Ruiz volcano, Valle de Nereidas geothermal Project

Tue, 06 May 2025 00:00:00 +0000

Geothermal conceptual models generally comprise four essential elements in convective geothermal systems: a heat source, a reservoir, a fluid source, and an impermeable rock. A comprehensive geothermal model is developed based on the available data at a given stage, which involves various studies such as geophysical surveys, heat anomaly mapping, geological analysis, and hydrochemical assessments. In Colombia, geothermal resources are predominantly associated with the active volcanic arc along the Central Cordillera, although non-volcanic areas also hold potential. The main application of geothermal energy in the country has been low-enthalpy systems, primarily for balneology and ecotourism. However, exploration efforts are currently underway to identify medium- to high-enthalpy systems with potential for electricity generation. This work outlines common methods in geothermal exploration and highlights the exploration progress in Colombia, with emphasis on the Nevado del Ruiz volcano as a case study for geothermal energy use. Additionally, this work demonstrates how in the most advanced project in the country, the Valle de Nereidas, on the western flank of the Nevado del Ruiz volcano, thermal springs have led to a high-enthalpy geothermal project. These hot springs are related to an increase in permeability in the rocks, associated with the interaction of fault systems in a NW-SE direction that are intersected by regional N-S faults such as the San Jerónimo fault. The circulation pattern of geothermal fluids in the area of interest is proposed to follow the SEE to the NWW, according to the structural pattern of the area related to the Nereidas-Río Claro fault system.

Geological modelling for CO2 storage potential estimation in an area located south of the Lower Magdalena Valley Basin, Colombia

Tue, 06 May 2025 00:00:00 +0000

The results of geological modeling to assess the CO₂ sequestration potential in the southern part of the Lower Magdalena Valley are presented. Using correlations, petrophysical analysis, evaluation of pressure and temperature gradients, seismic interpretation, and statistical calculations, a deterministic capacity of 7,58 MtCO₂eq was estimated. In a stochastic approach, significant variability is revealed, indicating that the storage capacity could range from 0,82 MtCO₂eq (P₉₀) to 15,28 MtCO₂eq (P₁₀). The data support the Ciénaga de Oro Formation as a suitable reservoir for CO₂ sequestration. However, detailed analysis of the structure, corresponding to an inversion anticline, and capacity estimates lead to the dismissal of the project’s feasibility in the area. In summary, while the reservoir’s suitability is confirmed, considerations suggest significant limitations for the implementation of CO₂ sequestration in the studied area.

Intermediate-depth seismicity of the lesser Antilles subduction slab, close to the Paria peninsula, Venezuela

Tue, 06 May 2025 00:00:00 +0000

From a macroseismic investigation of earthquakes ranging between 45 and 150 km in depth and magnitudes Mw ≥ 5.0 since year 2000, related to the South American-Atlantic (SAA) subduction in the region of the southeastern Caribbean STEP, we have determined that the cities of Ciudad Guayana and Ciudad Bolívar, sitting at the northernmost edge of competent rock outcrops of the Precambrian craton of Guyana, show seismic intensities which do not comply with a normal attenuation pattern of decreasing intensities with increasing distance. This necessarily leads to the revision of the current Venezuelan seismic-resistant code (COVENIN 1756-1:2019), since the seismic Hazard estimations for this southern region of Venezuela appear to be clearly underestimated.

Comparative results obtained for coal bed methane from different types of sampling in the Sinifaná basin (Antioquia, Colombia)

Astrid Blandón-Montes, Jorge Martín Molina-Escobar, Luis Dethere Caro-González — Tue, 06 May 2025 00:00:00 +0000

The objective of this work was to compare the coal bed methane obtained from different types of sampling: channel by ply, lateral, and vertical drilling cores at the San Fernando Mine in the Municipality of Amagá – Antioquia, Colombia. These samples were subjected to gas desorption, gas chromatography, porosity, permeability and high-pressure adsorption analyses. The studied coals are classified as subbituminous A coal and high-volatile C bituminous coal, according to the ASTM D388-19a standard classification of coal by rank. The average of total gas desorbed in the samples varied between 0.2 and 33.7 ft3/ton, which are low values compared to the other coal mining areas of Colombia and the world. Gas composition was primarily methane (C1) ranging from 92.2% to 98.98%, carbon dioxide (CO2) ranging from 0.30% and 4.27%, and amounts typically less than 1.0% other hydrocarbons. At a pressure of 1500 psi, the CH4 adsorption isotherms for the different types of samples varied between 45 and 340 ft3/ton. According to the results, it can be established that there is a lateral variability in depth of the methane gas contents and with a tendency to decrease in coal seam 2 and 3. Vertical variability was also found in the vertical drilling and in the samples taken from the channel per ply of the exploitation front faces. When comparing the results with those of previous studies, the gas contents were generally low (less than 60 ft3/ton). On the other hand, it can be determined in a simple way and at a low-cost manner in samples taken from the exploitation fronts faces.