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Facies and paleoenvironmental analyses of two stratigraphic sections in the El Azogue, region, Sonora, Mexico
This paper presents the analysis of facies and paleoenvironments of two stratigraphic sections at the El Azogue locality the Plutarco Elías Calles dam (approximately 2 km to the east of San Pedro de la Cueva, Sonora, Mexico). The facies analysis consisted of the identification of allochemicals present in both sections describing the textural and compositional features in the analyzed samples. Both sections show a certain compositional homogeneity; however, systematic changes occur throughout the sections. The Cerro El Azogue section exhibits greater lithological variation toward its upper part. The Arroyo El Azogue section shows marked variations in the lower and middle strata, with progressive increases in the abundance of brachiopods, cortoids, and intraclasts. The facies correspond to supratidal, intertidal, and subtidal sedimentary environments.
Copyright (c) 2026 José Carlos Jiménez López, Blanca Estela Buitrón Sánchez, Iván Manuel Cuadros Mendoza, Juan José Palafox Reyes (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
3D modeling of the internal structure of Poás volcano, Costa Rica: using Leapfrog Geo software
Poás Volcano, one of the most active and studied volcanoes in Central America, exhibits high activity and complexity in its geodynamic processes, making the study of its internal structure essential. This work focuses on the three-dimensional modeling of the magmatic reservoir of Poás Volcano, using various publications dedicated to the volcano. Relevant maps and profiles were selected, georeferenced, and integrated into the Leapfrog Geo software. Additionally, seismic data were incorporated to confirm the general location of the reservoir. A total volume of 16 km³ was modeled, encompassing both Poás Volcano and nearby volcanic edifices and structures, while also representing the interaction between volcanism and the subduction zone. This study highlights the potential of 3D modeling as a tool for synthesizing and visualizing complex geological structures such as Poás Volcano. Although the presented model is based on inferences drawn from limited data, it represents significant progress in understanding the internal structure of the volcano. Moreover, it highlights the need for future research to improve the model’s accuracy and to unravel both its processes and geological evolution.
Copyright (c) 2025 Marianela Molina, Carlos Vargas, Percy Denyer (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
Automatic lineament extraction: comparison between two digital elevation models of the Caribbean region of Costa Rica
This study examines the influence of spatial resolution on the automatic detection of lineaments in the northern and southern Limón basins, Costa Rica, by comparing the digital elevation models SRTM-CRTDM2020 (30 m) and ALOS PALSAR (12.5 m). The results demonstrate that the higher-resolution model allows for the identification of a greater number of lineaments, especially in flat and low-altitude areas, providing a more detailed view of the region’s geomorphology and tectonics. A predominant NW-SE orientation is observed in the lineaments extracted from both models, consistent with previously identified tectonic structures. However, the higher resolution introduces methodological challenges, such as the possibility of fragmenting larger structures into smaller segments. The highest density of lineaments is recorded in the southern Limón basin, mainly associated with Paleogene sedimentary geological units and active tectonic deformations, while the density in the northern Limón basin is lower. The automatic extraction of lineaments can be highly beneficial for regional studies, allowing for a relatively rapid analysis without disregarding geological and geomorphological criteria.
Copyright (c) 2026 Fabio Piedra (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
Sedimentology of the Basal Section of the Montezuma Formation (Plio-Pleistocene), Cóbano, Puntarenas, Costa Rica
The lithofacies of coastal cliffs are documented in the Catarata (C) section of the Quebrada El Chorro, the Punta Quizales (Q) section, and the Acantilado (A) section in the Cóbano area of the Nicoya Peninsula, Costa Rica. The surveyed sections are stratigraphically correlated with the basal facies of the Montezuma Formation from the Middle Pliocene to the Early Pleistocene. Sedimentologically, these facies are characterized by strong lithological variability, both vertically and laterally, ranging from shallow marine to transitional coastal sediments, including fine to coarse sandstones and conglomerates. The facies association is related to environments such as river mouths in intertidal coastal plains, beaches, and fan deltas. At least two stages of marine transgressions were defined. A third stage is not well defined in the studied sedimentological sections and could not be characterized. The present-day coastal cliffs show evidence of significant regional tectonic uplift, and consequently, a marked relative fall in sea level and erosive retreat caused by wave action.
Copyright (c) 2026 Luis G. Obando-Acuña, Giovanni Bottazzi-Basti (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
Sedimentology of Eocene-Miocene deposits of the Reventazón river in a transect from las Ánimas to Peralta, Cartago province, Costa Rica
This study presents a facies and architecture analysis of sedimentary deposits exposed along the middle fluvial valley of the Reventazón River, located between Las Ánimas (Turrialba) and the provincial border of Cartago and Limón, Costa Rica. Thirteen metric-scale stratigraphic columns were surveyed and correlated across the study area. Eleven lithofacies and lithofacies associations were identified, including grainstone, rudstone, and packstone-type limestones, interbedded with shales, sandstones, and brecciated conglomerates. These records document a progradational transition from Eocene–Oligocene carbonate-dominated systems to Miocene siliciclastic deltaic environments. Facies association analysis, supported by petrographic studies and micropaleontological tests of foraminifera, led to the recognition of three paleoenvironmental models: a middle to outer carbonate platform in the Eocene; a coral patch reef system and a mixed carbonate-siliciclastic platform slope in the Oligocene; and proximal delta front to prodelta–offshore environments in the Miocene. This work provides a high-resolution stratigraphic framework that enhances the understanding of the depositional and tectonostratigraphic evolution of the South Limón Basin, integrating changes relative sea-level change and continental sediment supply.
Copyright (c) 2025 Daniel Monge-Badilla, Valentin Chesnel (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
Geology, hydrothermal alteration, and mineralogy of Cerro Minas (Santa Ana, Costa Rica): Subvolcanic bodies coeval with the sedimentation of the Pacacua Formation (Lower Miocene)
Cerro Minas, located on the NNW flank of the Escazú hills, corresponds to lava bodies with a fluidal structure (andesites to slightly porphyritic trachytes) associated with the Pacacua Formation. They are interpreted as cryptodomes and apophysis that intruded into the sediments during the Early Miocene. They have an intense silicification and calcification alteration. During the exploitation of the quarry (former Bretaña quarry), the largest geodes recorded so far nationwide (ca. 0.5 to 2 m diameter) with large decametric amethyst crystals were found; in addition, crystalline quartz, smoky quartz and citrines were reported, as well as an anhydrous micro to cryptocrystalline quartz (calcedony, agate, and jasper). Other minerals with very striking shapes and colors were pink, yellow to brown calcite/Mg-calcite and iron-bearing dolomite (ferroan dolomite) roses (a rare occurrence worldwide referring its aspect), associated with barite. The hydrothermal alteration can be classified as silicifying and carbonatic type in an alkaline system rich in Mg at a temperature of about 150 °C. Much of the fine-grained whitish matrix corresponds to calcite, montmorillonite, illite and quartz with the subordinate presence of zeolites (laumontite, mordenite). Among the rare occurrence metal ore minerals, such as specularite, bornite, chalcopyrite and, to a lesser extent, malachite, chalcosine and sphalerite appeared in small quantities.
Copyright (c) 2025 Guillermo E. Alvarado, Luis A. Zeledón, Leonardo Quesada, Gerardo A. Rodríguez, Peter C. Ryan, Paulo León, Christian Solano (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
The “puzolana” quarry of Llano Grande, SW flank of the Irazú Volcano (Costa Rica): geological and mineralogical characterization
The Llano Grande quarry, located on the southwestern flank of the Irazú volcano (Costa Rica), is used for the extraction of pozzolan for cement manufacturing by the company Holcim. The protolithic volcanic rocks (coherent lavas, pyroclastic rocks, and lahars) exhibit advanced to complete obliteration of their original textures, resulting from pervasive alteration characterized by the replacement of most of the original rock components by silica (primarily alpha-quartz, alpha- and beta-tridymite, and cristobalite). This transformation has led to the formation of vuggy silica and pseudo-perlitic-textured rocks. Iron oxide and hydroxide minerals are present in fractures (goethite and minor magnetite) and in hydrothermal breccia chimneys, often associated with gypsum, or occurring as disseminated phases, predominantly in the middle to upper parts of the quarry. In these areas, the rocks also contain cavities filled with vacuolar native sulfur. The abundance of quartz and quartz-pyrite-marcasite assemblage indicates a silicic alteration transitioning to an argillic type, with the presence of clay minerals (kaolinite and calcic montmorillonite) due to intense H⁺ metasomatism with acidic leaching, estimated to have occurred in a vapor-heated environment at approximately 100°C. In addition, sanidine facies, a type of metamorphic contact, were also observed. The tectonic context of the area, characterized by its proximity to the continental divide, its relationship with extinct volcanic centers, and its emplacement within a pull-apart system, suggests that hydrothermal alteration took place near an ancient eruptive center, in proximal volcanic facies and under hyperacidic conditions, possibly during the Middle Pleistocene. A porphyritic basaltic andesite dike intrudes the altered volcanic sequence, evidencing a late-stage phase within the hydrothermal system.
Copyright (c) 2025 Andrés Ulloa, Guillermo E. Alvarado, Federico Rivera, Gerardo Rodríguez, Evelyn Rodríguez (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
The Pleistocene Coyote from the Río Nacaome, Costa Rica
In 1997, we identified as coyote (Canis latrans) a dentulous left dentary of a canid from the Upper Pleistocene of the Río Nacaome in northwestern Costa Rica. This identification has been questioned based on misconceptions about features of the dentary that supposedly diagnose C. latrans. We reaffirm the identity of the Río Nacaome canid as C. latrans based on long established features of the lower dentition that are diagnostic of C. latrans. We also refute the idea that certain features of the dentary are diagnostic of coyotes. The Nacaome coyote fossil is the only fossil of a coyote from Central America and establishes their late Pleistocene presence well south of records in southern Mexico.
Copyright (c) 2025 Spencer G. Lucas, Guillermo E. Alvarado (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
Petrographic, mineralogical, and geochemical aspects of the Zulay pit gossan (Turrubares, Costa Rica)
The Zulay quarry located by San Pedro de Turrubares (San José), represents an excellent example of gossan (supergene modification process), where the iron cap (leached cap) is represented by lavas and breccias pervasively silicified (micro-vuggy silica, alfa quartz and rare moganite) with secondary minerals as zeolites, goethite and hematite (iridescent and earthy) forming a type of iron rock that collectors called turgite or turite, and traces of microrutiles. Rarer is the presence of alum-K. The geological unit is part of Grifo Alto Formation, part of an area of intense past hydrothermal activity (high-sulfidation epithermal), perhaps in correspondence with the proximal facies of an ancient eruptive focus.
Copyright (c) 2025 Guillermo E. Alvarado, Andrés Ulloa, Leonardo Quesada, Carl Nelson, Paulo León, Manuel Barrantes, Daniel Gebregiorgis, Bryan E. Moncada-Villegas, Luis E. Morales-Cambronero (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
Field observations on the evolution of the effusive eruption of Pacaya Volcano, Guatemala, from March 5 to April 24, 2021
Pacaya is a composite stratovolcano with a predominantly strombolian eruptive style. Located south of Lake Amatitlán and 30 kilometers south-southwest of Guatemala City. Since 1961, it has experienced periods of high and low surface activity. By the end of 2020, its activity increased significantly, marking the beginning of another highly active phase. This escalation is inferred to have been triggered by volcanic seismic events that occurred in June 2020. This paper describes the effusive eruption that took place between March 5 and April 24, 2021, during which the activity alternated between effusive activity (lava) and explosive activity (ash columns).
Copyright (c) 2025 José L. Méndez Soto, Gustavo Chigna, William Chigna, Sara S. Fuentes, Juan P. Castañeda (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0
The Turín mining prospect, Tilarán Range: a gold-bearing zone with a mineralization age of 2.0 Ma
To the east of the town of Turin (Tilaran range), there is a gold mineralization consisting of a series of quartz/adularia veins, stockwork zones, and hydrothermal alteration (propylitic, argillic, and phyllic) which outcrop along the Cañita creek valley and in several old underground workings. An adularia concentrate was dated by K-Ar providing an age of 2.0 ± 0.1 Ma, corresponding to the most recent date of gold mineralization of economic interest at the national level, just in correspondence with the beginning of the Monteverde Formation volcanism, metallogenetically barren.
Copyright (c) 2025 Alejandro Arauz, Guillermo E. Alvarado (Autor/a) https://creativecommons.org/licenses/by-nc-sa/4.0