Acta Geológica Lilloana

Coastal alluvial environments on active margins recorded in the Zapotal Formation, Santa Elena, Ecuador

2025-11-27T09:38:39-03:00

Coastal alluvial environments on active margins recorded in the Zapotal Formation, Santa Elena, Ecuador. I In the Santa Elena Peninsula, located in the southwest of Ecuador, the Zapotal Formation represents the sedimentary cycle of the Upper Oligocene to Lower Miocene. The stratigraphic definition of the Zapotal Formation varies among different authors, depending on the area of the basin where it was reported. This variation creates uncertainty in the regional geological evolution model. Therefore, this research studies the Zapotal Formation in the Ballenita, Farrallón de Dillon, Santa María, San Marcos, La Chacra, and Cerro La Tapa sections, considering detailed lithostratigraphic, petrographic, and geochemical analyses framed within the interpretation of the sedimentation environment and determination of the detrital provenance.

This study identified eight lithofacies: massive clast-supported conglomerate (Gcm), massive matrix-supported conglomerate (Gmm), litharenite with parallel cross-stratification (Sp), parallel lamination (Sl), current ripples (Sr), and massive litharenite (Sm), laminated siltstone with organic matter (Fl), and massive siltstone (Fm). Based on the stratigraphic architecture, this sequence was interpreted as braided fluvial and coastal meandering systems. Petrographic and geochemical data indicate that the Zapotal Formation was deposited in an active continental margin, linked to the erosion of transitional and dissected arcs and recycled orogenic provinces.

Nearby Geology: Geotourism as an Added Value for Greater San Miguel de Tucumán, Argentina.

2025-11-27T09:38:31-03:00

The landscape and natural aesthetic value of large cities are closely related to the geographic setting in which they are located, associated to their urban development process. The city growth tends to obliterate the natural scenery, with geology being the element that most frequently goes unnoticed due to various factors. It is within this context that the presence of notable geological features—which can be considered heritage elements—should be incorporated as significant tourist resources to enrich the natural and cultural values of the area. Geotourism as such remains as an underdeveloped activity in Argentina and is closely related to geological heritage, focusing on valuable elements of a geological nature by characterizing geology as heritage, the aim is both to ensure the long-term preservation of geological assets and to leverage their potential for social development. This contribution proposes the enhancement of geological heritage elements in the vicinity of the Sierra de San Javier (Circuito Chico, Greater San Miguel de Tucumán), through the identification of notable features, and the proposal of a geo-tourism route that seeks comprehensive use of the area, associated to the classic tourism, and thus contributing to local community development.

Cartographic model to optimize the identification process of mineral deposits in Macará, Loja (Ecuador)

2025-11-27T09:38:33-03:00

The identification of mineral deposits has traditionally relied on field surveys and analog map overlays, which constrain exploration efficiency. This study proposes a cartographic model based on the integration of geological variables through the Analytic Hierarchy Process (AHP) of Saaty (1994), applied in the Macará region, Loja province, Ecuador.
Four variables were considered: geological units/formations, structures, stream-sediment geochemistry, and hydrothermal alteration. Results show that geological units and stream-sediment geochemistry were the most influential factors in defining prospective zones. Multicriteria evaluation was applied using standard deviation, natural breaks, geometric intervals, and quantiles methods in ArcGIS. The resulting maps delineate areas with favorable characteristics for mineral exploration. Classifications based on natural breaks, geometric intervals, and quantiles converged on reducing exploration to specific sites, whereas the standard deviation method identified broader prospective zones at the regional scale. This methodological approach demonstrates the effectiveness of cartographic integration and multicriteria analysis as robust
tools for prioritizing exploration areas, optimizing both time and resources compared to traditional method.

Petrographic and geochemical perspectives of the Azafrán Unit in the Río Blanco – La Esperanza section, Baños, Ecuador

2025-11-27T09:38:35-03:00

Previous investigations documented the best exposures of the Azafrán Unit in the Río Blanco–La Esperanza section; however, detailed information regarding its petrography, geochemistry, and the degree and type of metamorphism is lacking. The present study aims to characterize the
lithostratigraphy, petrography, geochemistry, and metamorphic grade of the Azafrán Unit in order to understand its geological and tectonic evolution. The research examines the lithological and metamorphic
variability observed in the field, evaluating its relationship with magmatic processes and tectonic deformation. Through detailed geological mapping, twelve representative samples of the Azafrán Unit were collected. The results indicate that the unit is composed of monzogranites,
schists, and gneisses, with phaneritic and granoblastic textures. Geochemical analyses reveal a high-K calc-alkaline affinity and enrichment in incompatible elements, indicating a magmatic origin associated with subduction processes. Metamorphism is characterized by greenschist facies, with temperature and pressure gradients ranging from 350 °C to
500 °C and from 3 to 8 kbar, respectively. In this context, the findings confirm that the metamorphosed granitoid series of the Azafrán Unit was subjected to dynamic tectono-metamorphic environments, where deformation and magmatism interacted within an active continental
margin framework. The identified structural heterogeneity rules out homogeneous metamorphic episodes and constitutes evidence of spatial and temporal variations in the intensity of tectonic and metamorphic events.

Geomorphology of the northern section Cutucú mountain range, Subandean Zone, Ecuador

2025-11-27T09:38:36-03:00

The Cutucú Cordillera represents a morphostructural subdomain of the Sub-Andean Zone that extends to the southeast of Ecuador. It is limited by the Santiago River basin to the south, by the Pastaza River to the north, to the west by the eastern foothills of the Cordillera Real, and to
the east by the Amazon Plain. The scarce previous research on the geomorphological aspects of the northern section of the Cutucú Mountain Range has limited the comprehensive interpretation of its geological structures and regional lithostratigraphy. In this context, the present investigation details the geomorphological characteristics of this area
from DTM photointerpretation techniques, satellite images, and their relationship with the lithostratigraphy lifted for the present investigation in the northern segment of the Cutucú Cordillera. This geomorphological analysis describes the Macuma Anticline with northward dipping, where Cretaceous quartz-sandstones of the Hollín
Formation outcrop as part of the flanks of the anticline, overlain by sandstones, calcareous mudstones, limestones of the Napo Formation, while at its core are volcanic breccias, volcanic litharenites, and arkoses
of the Chapiza Formation from the Middle Jurassic to Early Cretaceous and fossiliferous calcareous shales of the Macuma Formation of the Paleozoic. Likewise, the Pumbuis Anticline is described, which extends from south to north, from the Tayuntsa River to the Macuma River,
characterized by the presence of chevron-type structures arranged as elongated and stepped bands dipping towards the east, where volcanosediments of the Chapiza Formation outcrop, unconformably overlain by quartz-sandstones of the Hollín Formation.