Boletin Geologico

According to the relative sea level (RSL) data series from Tumaco 1953-2006, the positive sea-level anomalies show a good coherence with the Southern Oscillation lndex (SOI). The variability of the SOI explains 61 % of the seasonal variability in the water level data (r2 = 0.61, &lt; 0.05). Maximum peaks appear in the 1982-1983 and 1997-1998 El Nino years, which were approximately 30 cm above the interannual monthly mean. The long term sea-level trend was decreasing at 0.60 mm/yr. Two subgroups of sea-level data with changing trends were identified: first (1953-1979), a decreasing trend of 4.7 mm/yr; second, an increasing trend rising at a rate of 4.7 mm/yr. The break of the series coincides with the occurrence of the 1979 great Tu maco earthquake (Mw = 8.2). That rate of change in the RSL subgroups could be explained through the theoretical dislocation model of strain accumulation and release at a subduction zone. Moreover, anomalies in water discharge of the Mira River (1981-2002) show an incrementally higher discharge in the drainage river basin between 1981 and 1987 and a diminishing trend in the discharge between 1988 and 2002. Recent delta dynamics show a continuous progradation proceeding between 1958 and 1987. After the 1979 earthquake, relative sea leve! rise, the 1982-1983 El Nino events and decreased river input may explain the change to a slow coastal erosion stage at the delta front.

Sergio A. López

Héctor Mora Páez

Camilo A. Monroy

Juan D. Restrepo

Efraín Rodríguez Rubio

Boletín Geológico

Nivel relativo del mar en la costa pacífica sur de Colombia: variabilidad, tendencias e implicaciones en la dinámica deltaica

哥伦比亚太平洋南部海岸的相对海平面：变异性、趋势及其对三角洲动态的影响

Currently the Venezuelan glaciers are restricted to the northwest slopes of the Humboldt-Bonpland and Bolívar peaks of the Sierra Nevada de Merida. Only a few glaciological observations have been completed and so many parameters of their dynamics are still unknown. In 1952 the total glacial cover was calculated at 3 km2. However, their evolution until 2008, their rate of retreat and response to the climatic variability are not well understood. This work presents the first results using satellite observations made on the Siniguis glacier which is the largest in the region located on the Humboldt-Bonpland peaks. The covered area calculated from the multi-spectral analysis of the SPOT-5 images is 0.33 km2. This indicates that since 1952 the glacier has lost an area of approximately 1.7 km2 with and average retreat rate of 30.3 m/year which corresponds to 83.74% of its coverage area. lf this trend continues, the glaciers of the Venezuelan Andes could disappear in ten years.

Eduardo Carrillo

Evolución de los glaciares en los Andes venezolanos: picos Humboldt y Bonpland

委内瑞拉安第斯山脉冰川演变：洪堡峰和邦普朗峰

This work presents a review and description of sorne methods _and concepts which explain the application of methodologies to the granulometric evaluation of volcaniclastic deposits. Point counting, sieve and pipette methods are described along with a unification methodology which combines the results of each method in an equivalent distribution curve. Equally, an emphasis on the importance of this type off analysis is made taking into account the increasingly common development and utilization of empirical classification diagrams. In this way, the information given by these methods do not discriminate among different processes and make a quantitative description of the volcaniclastic deposits.

Hugo F. Murcia

Gloria P. Cortez

Blanca O. Hurtado

Métodos e integración de análisis granulométrico para depósitos volcaniclásticos

火山碎屑沉积物的粒度分析方法与集成

The Ocaña-Curumani relief of the Bucaramanga Fault System is distributed asymmetrically through different deformative phases: high degree (mylonites) near the main fault; shear cataclastic systems to the west. The deformation is defined by a cataclastic series of rocks with quartzfeldespathic protoliths associated with the Bucaramanga Gneiss (mapped in sheet 55 El Banco) with a mineralogical composition that includes orthoclase, microcline and plagioclase feldspars, quartz biotite epidote apatite sphene and opaque minerals. The cataclastic texture is demonstrated by the accumulation of combined intracrystalline deformation along with grain size reduction where the microstructures that display the minerals register the deformation to which the rock has been exposed. This suggests cataclastic flow in sites of tangential breakup by the generation and distribution of orthogonal adjustments of fractures, in addition to intragranular, transgranular and circumgranular microfractures, Riedel shears, extensional structures and microfaults.

Mario Andrés Cuéllar Cárdenas

Julián Andrés López Isaza

Microestructuras asociadas a deformación frágil del relevo Ocaña-Curumaní. Sistema de Fallas de Bucaramanga

奥卡尼亚-库鲁马尼断层系统中与脆性变形相关的微观结构

A combined hydrogeological study using hydrochemistry and environmental isotopes (deuterium, oxygen 18, tritium, carbon 13, and radiocarbon) has been completed in the region of Maicao (Colombia). The study area encompasses 650 km2 and includes three aquifers: the Cretaceous Aquifer (limestones), south of the Oca fault, the Tertiary Aquifer (semi-consolidated marine sediments) and the Quaternary Aquifer (unconsolidated sediments of continental and marine origins). Both the Quaternary and Tertiary aquifers are located just to the north of the same fault (elevation between 40 and 600 m above sea level). The Quaternary Aquifer is an unconfined aquifer underlain by the Mongui Formation (a confined Tertiary Aquifer). Lts regional groundwater flow is northward. The climatic conditions are semiarid, with an average temperature of 27 C, annual average precipitation of 350 mm in the north and 1200 mm in the south (September to November). Two types of groundwater have been found in Maicao: the first, low salinity and young (less than 50 years), is located in the Cretaceous Aquifer and in the sector of the Quaternary Aquifer adjacent to the Carraipia River (main superficial water body in the project area), the second, moderately mineralized, isotopically depleted with respect to the first group and older (more than 7900 years), is located in the Tertiary Aquifer and in the central and northern sectors of the Quaternary Aquifer. Results of this study show that the recharge of the Quaternary Aquifer which is the aquifer most extensively used by the inhabitants of Maicao is slow and is, therefore, susceptible to depletion if no measures are taken to insure rational use.

Jean Denis Taupin

Luis Eduardo Toro

María Consuelo Vargas

Estudio hidrogeoquímico e isotópico en los acuíferos de la zona de Maicao, Colombia

哥伦比亚迈考地区含水层的水文地球化学和同位素研究

El Servicio Geológico Colombiano, en su transformación a centro de investigación científica, continúa desarrollando sus propósitos de mejoramiento de las publicaciones institucionales, en particular, las relacionadas con la producción científica en el área de las geociencias. En este emprendimiento se mantiene el objetivo de volver realidad el sueño de convertir el Boletín Geológico en una revista científica de alto impacto y con un amplio reconocimiento a nivel nacional e internacional.

Editorial

社论

In the department of Cesar, Municipality of Becerril, there are extensive outcroppings of Cretaceous rocks with calcareous sequences belonging to the Lagunitas and Aguas Blancas Formations, the Cogollo Group, and the La Luna Formation. This study presents the mapping of a 25 km2 are in the eastern sector of the Municipality of Becerril, intended to contribute geological knowledge of this area through field work, identification of geomorphological units and petrographic descriptions at a scale 1:25,000. The Lagunitas Formation is characterized by a succession of dark gray massive fossiliferous limestone intercalated with calcareous mudstone and lumachellic limestone. From the Aguas Blancas Formation, the Ánimas Member is identified in detail, consisting of calcareous mudstone with abundant organic matter interbedded with black micritic limestones that grades horizontally to sandstones with fine-grained calcareous cement. The Tucuy Member consists of calcareous siltstone, fine-grained sandstone and carbonated claystone. The Maracas Member consists mainly of massive lumachellic limestone. Similarly, four geomorphological environments were identified: structural, identifying units of hog-backs, homoclinal ridges and cuestas; denudation, identifying units such as erosion scarps, lightly bisected hills and undulating interfluves; karstic, with units of karstic valley and karstic slope; and fluvial, with the floodplain unit.

Milton David Lozada Molina

Frank David Lascarro Navarro

Luisa Fernanda León Díaz

Elías Ernesto Rojas Martínez

Fabio enrique Carrillo Bolaño

Luis Carlos Tapia Tavera

Dino Carmelo Manco Jaraba

Contribución al conocimiento geológico de la Serranía del Perijá mediante cartografía a escala 1:25.000 del Grupo Cogollo, en el sector oriental del municipio de Becerril, Cesar

通过1:25,000比例尺的Cogollo组地质图对塞拉尼亚德尔佩里哈地区地质知识的贡献——以塞萨尔省贝塞里尔市东部地区为例

With the aim of expanding the reference materials of the Geochronology Laboratory of the Colombian&nbsp;Geological Survey (LG-SGC, in Spanish), zircons were collected from the nepheline syenite of&nbsp;San José del Guaviare, Jordán locality (Colombia). The SNG-1 sample was composed of 24 zircons&nbsp;selected from the fraction between 2 and 5 millimeters long, which were mounted and polished in&nbsp;an epoxy resin block. The zircons were dated by analyzing the isotopic ratios of uranium and lead&nbsp;using the LA-ICPMS method. In the LG-SGC, 92 points on the zircons were selected for analysis,&nbsp;and at the University of Rennes in France (LG-URF), 24 points from crystals found nearby were&nbsp;selected for analysis from a previous cathodoluminescence study. Concordant ages for the zircons&nbsp;for both laboratories corresponded to a crystallization age of 608 ± 1.2 Ma and 602 ± 3 Ma,&nbsp;respectively, which differ by less than 1% despite the difference in instrumentation and analytical&nbsp;procedures. For systematic error correction and quality control, international reference material,&nbsp;such as Plešovice, GJ-1, FC-5 Duluth and Mount Dromedary zircon, was used. The uncertainties&nbsp;generated during the analyses are similar (1.2 and 3.2 Ma), and the mean square-weighted deviation (MSWD) of the concordia diagrams was &lt; 1 in both cases, indicating low dispersion of the&nbsp;results. Some discordant ages show that the U/Pb ratios are not uniform, as expected for a primary&nbsp;reference material. However, we believe that the zircons of the Jordán syenite have potential use as&nbsp;a secondary reference material for the LG-SGC provided they are carefully selected and prepared,&nbsp;their geochemical content (including rare earth elements, REE) is characterized, and quality monitoring&nbsp;of U/Pb dating is performed, as these zircons are large, reaching up to 4 cm, abundant, and&nbsp;possible to collect in the Colombian territory.

Jimmy Alejandro Muñoz Rocha

Alejandro Piraquive

José Alejandro Franco Victoria

Amed Bonilla Pérez

Luz Mary Peña Urueña

Thomas Heinrich Cramer

Lorena del Pilar Rayo Rocha

Nicolás Villamizar Escalante

Megacircones ediacáricos de la sienita nefelínica de San José del Guaviare y su potencial como material de referencia para datación U/Pb mediante LA-ICP-MS

瓜维亚雷省圣何塞霓霞正长岩中的埃迪卡拉纪巨型锥体及其作为LA-ICP-MS铀铅测年参考材料的潜力

The geological explorations carried out by the Colombian Geological Survey (SGC, in Spanish)&nbsp;between 2005 and 2008 show that the potential areas for exploration and exploitation of emeralds&nbsp;in the Western Emerald Belt (CEOC, in Spanish) are closely related to the Muzo (Hauterivian-Barremian&nbsp;age) and Rosa Blanca (Valanginian age) geological formations, and in the Eastern Emerald&nbsp;Belt (CEOR, in Spanish), are associated to the Santa Rosa and Chivor formations (Berriasian&nbsp;age). Mineralization is associated with various mesoscopic tectonic structures with hydrothermal&nbsp;alteration.

Roberto Terraza Melo

Notas sobre el contexto tectonoestratigráfico de formación de las esmeraldas colombianas

关于哥伦比亚祖母绿形成的地质构造背景的注记

This work presents the boundaries of a new area of interest for the detailed exploration of emeralds&nbsp;in Colombia, identified through the interpretation of geobotanical anomalies in areas of dense&nbsp;vegetation. A methodology was designed in which fifteen vegetation indices were calculated. The&nbsp;anomalies correlated most with the lineaments detected from the interpretation of a shaded-relief&nbsp;model generated from a digital terrain model (DTM) were selected. A detailed spectral analysis in&nbsp;the mineralized zones of the area with the highest correlation showed a halo of vegetative stress in&nbsp;all studied cases; moreover, the analysis corroborated a direct relationship between the albitization&nbsp;present in the mineralized zones, the lineaments and the degree of vegetative stress. A sector between&nbsp;the Coscuez mine and the La Pita mine was identified as a target for detailed exploration,&nbsp;where the vegetation indexes indicate less vegetative stress and correlate better with the natural&nbsp;terrain lineaments. It was found that the proposed methodology based on geobotanical anomalies&nbsp;yields consistent results and can be used as a tool for emerald exploration.

Manuel Guillermo Zafra Dulcey

Análisis de anomalías geobotánicas a partir del procesamiento e interpretación de productos de sensores remotos, estudio de caso: occidente de Boyacá (Colombia)

基于遥感产品处理与解释的地球生物异常分析，案例研究：博亚卡西部（哥伦比亚）

Publication Information	Publisher: Colombian Geological Service，Publishing cycle: ，Journal Type: journal，Open Access Journals: Yes
Basic data	Year of publication: 2021，Proportion of original research papers: ，Self Citation Rate:， Gold OA Rate:
Average review cycle	24 weeks

Boletin Geologico

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