Examinando por Materia "Miocene"
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Ítem Detrital zircon fission-track thermochronology and magnetic fabric of the Amagá Formation (Colombia): Intracontinental deformation and exhumation events in the northwestern Andes(ELSEVIER SCIENCE BV, 2017-07-01) Piedrahita, V.A.; Bernet, M.; Chadima, M.; Sierra, G.M.; Marín-Cerón, M.I.; Toro, G.E.; Piedrahita, V.A.; Bernet, M.; Chadima, M.; Sierra, G.M.; Marín-Cerón, M.I.; Toro, G.E.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaNew detrital zircon-fission track (ZFT) and magnetic fabric data are presented to constrain the time of deposition, provenance and deformation of the of Lower and Upper members of the Amagá Formation in the Amagá Basin. The Amagá Basin is located in the northern Andes, between the Western and Central Cordilleras of Colombia. The Amagá Formation was deposited in a transpressive geodynamic context and is allegedly synchronous with tectonic events such as the Andean orogeny and the Panama-Choco Block collision with the northwestern South American Plate. Detrital ZFT data confirm an Oligocene age for the Lower Member and a middle-Miocene age for the Upper Member of the Amagá Formation. In addition to constraining the depositional age, the ZFT data presented in this study also reflect Paleocene-Eocene, late to early Oligocene and late to middle Miocene cooling in sediment source areas mainly located in the Central and Western Cordilleras of Colombia. These ages can be associated with regional exhumation events in the central and northern Andes of South America. Collisional stages of the Panama-Choco Block against northwestern South America, subduction of the Farallon-Nazca Plate and strike-slip reactivation periods of the Cauca-Romeral fault system, caused NW-SE compression and NE-SW simple shear in the Amagá Basin. This deformational regime, identified by magnetic fabric data, induces syn- and post-depositional deformation over the Amagá Formation. © 2017 Elsevier B.V.Ítem Early Miocene CO2 estimates from a Neotropical fossil leaf assemblage exceed 400 ppm(Wiley-Blackwell Publishing Ltd, 2018-11-01) Londoño L.; Royer D.L.; Jaramillo C.; Escobar J.; Foster D.A.; Cárdenas-Rozo A.L.; Wood A.; Universidad EAFIT. Departamento de Ciencias; Biodiversidad, Evolución y ConservaciónPremise of the Study: The global climate during the early Miocene was warmer than the present and preceded the even warmer middle Miocene climatic optimum. The paleo-CO2 records for this interval suggest paradoxically low concentrations (<450 ppm) that are difficult to reconcile with a warmer-than-present global climate. Methods: In this study, we use a leaf gas-exchange model to estimate CO2 concentrations using stomatal characteristics of fossil leaves from a late early Miocene Neotropical assemblage from Panama that we date to 18.01 ± 0.17 Ma via 238U/206Pb zircon geochronology. We first validated the model for Neotropical environments by estimating CO2 from canopy leaves of 21 extant species in a natural Panamanian forest and from leaves of seven Neotropical species in greenhouse experiments at 400 and 700 ppm. Key Results: The results showed that the most probable combined CO2 estimate from the natural forests and 400 ppm experiments is 475 ppm, and for the 700 ppm experiments is 665 ppm. CO2 estimates from the five fossil species exhibit bimodality, with two species most consistent with a low mode (528 ppm) and three with a high mode (912 ppm). Conclusions: Despite uncertainties, it is very likely (at >95% confidence) that CO2 during the late early Miocene exceeded 400 ppm. These results revise upwards the likely CO2 concentration at this time, more in keeping with a CO2-forced greenhouse climate. © 2018 Botanical Society of AmericaÍtem Early Miocene CO2 estimates from a Neotropical fossil leaf assemblage exceed 400 ppm(Wiley-Blackwell, 2018-11-01) Londoño L.; Royer D.L.; Jaramillo C.; Escobar J.; Foster D.A.; Cárdenas-Rozo A.L.; Wood A.; Universidad EAFIT. Departamento de Geología; Ciencias del MarPremise of the Study: The global climate during the early Miocene was warmer than the present and preceded the even warmer middle Miocene climatic optimum. The paleo-CO2 records for this interval suggest paradoxically low concentrations (<450 ppm) that are difficult to reconcile with a warmer-than-present global climate. Methods: In this study, we use a leaf gas-exchange model to estimate CO2 concentrations using stomatal characteristics of fossil leaves from a late early Miocene Neotropical assemblage from Panama that we date to 18.01 ± 0.17 Ma via 238U/206Pb zircon geochronology. We first validated the model for Neotropical environments by estimating CO2 from canopy leaves of 21 extant species in a natural Panamanian forest and from leaves of seven Neotropical species in greenhouse experiments at 400 and 700 ppm. Key Results: The results showed that the most probable combined CO2 estimate from the natural forests and 400 ppm experiments is 475 ppm, and for the 700 ppm experiments is 665 ppm. CO2 estimates from the five fossil species exhibit bimodality, with two species most consistent with a low mode (528 ppm) and three with a high mode (912 ppm). Conclusions: Despite uncertainties, it is very likely (at >95% confidence) that CO2 during the late early Miocene exceeded 400 ppm. These results revise upwards the likely CO2 concentration at this time, more in keeping with a CO2-forced greenhouse climate. © 2018 Botanical Society of AmericaÍtem Hydrogeochemical characteristics at Doña Juana Complex (SW Colombia): A new area for geothermal exploration in the Northern Andes region(Elsevier Ltd., 2020-01-01) Gómez Diaz E.; Marín Cerón M.I.; Gómez Diaz E.; Marín Cerón M.I.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaThe Doña Juana Volcanic Complex (DJVC) is an active volcanic zone located in southern Colombia, an area lacking geothermal exploration data. Using the results of hydrogeochemical analyses of hot springs, thermal waters were divided into two groups: Doña Juana System (DJS) and Las Animas System (AS). The DJS thermal waters are sulphate-bicarbonate and the AS dilute-chloride waters with relatively high concentrations of alkalis. The stable isotope and some element ratios suggested a mixing process between geothermal fluids and meteoric waters where AS is related to the upflow with a reservoir temperature around 180 °C estimated through solute geothermometers and mineral equilibrium geothermometry, showing a high temperature system in which the fault systems apparently play an important role in the flow of the geothermal fluids. © 2019 Elsevier LtdÍtem Improved gasoline-powered soft-sediment cutter(SEPM-SOC SEDIMENTARY GEOLOGY, 2013-09-01) Sierra, Gloria M.; Marin-Ceron, Maria I.; Ramirez, Jackeline; Uribe, Camilo; Sierra, Gloria M.; Marin-Ceron, Maria I.; Ramirez, Jackeline; Uribe, Camilo; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaA device used for paleomagnetic sampling has been improved which allows sampling friable, poorly to moderate lithified sedimentary and volcanic materials. The new device attaches to a portable gasoline drill and employs two steel cutting disks with a 2 cm separation, which cuts two parallel slots in the material being sampled. A second set of cuts orthogonal to the first set produces a square pedestal over which a plastic sample box can be placed and oriented to extract a cubic sample; this procedure permits using the same orientation parameters as for conventionally drilled cylindrical samples. The method allows sampling at localities where conventional drilling fails in weak materials. To test the method, sedimentary sandstones of the Amaga' Formation (Eocene-Miocene) in the NW portion of the Central Colombian Andes were sampled. The anisotropy of magnetic susceptibility (AMS) was measured on samples using the new method and compared with results from conventionally drilled cores at the same sites. Results show better AMS within-site precision for box samples compared with the drilled cores. This device improves on previous battery-powered samplers used for sampling by the double-slot procedure. Also the new device can be used with the same gasoline-powered motor for standard core drilling. Copyright © 2013, SEPM (Society for Sedimentary Geology).Ítem Revised stratigraphy of Neogene strata in the Cocinetas Basin, La Guajira, Colombia(Springer International Publishing, 2015-01-01) Universidad EAFIT. Departamento de Geología; Ciencias del MarThe Cocinetas Basin of Colombia provides a valuable window into the geological and paleontological history of northern South America during the Neogene. Two major findings provide new insights into the Neogene history of this Cocinetas Basin: (1) a formal re-description of the Jimol and Castilletes formations, including a revised contact; and (2) the description of a new lithostratigraphic unit, the Ware Formation (Late Pliocene). We conducted extensive fieldwork to develop a basin-scale stratigraphy, made exhaustive paleontological collections, and performed Sr-87/Sr-86 geochronology to document the transition from the fully marine environment of the Jimol Formation (ca. 17.9-16.7 Ma) to the fluvio-deltaic environment of the Castilletes (ca. 16.7-14.2 Ma) and Ware (ca. 3.5-2.8 Ma) formations. We also describe evidence for short-term periodic changes in depositional environments in the Jimol and Castilletes formations. The marine invertebrate fauna of the Jimol and Castilletes formations are among the richest yet recorded from Colombia during the Neogene. The Castilletes and Ware formations have also yielded diverse and biogeographically significant fossil vertebrate assemblages. The revised lithostratigraphy and chronostratigraphy presented here provides the necessary background information to explore the complete evolutionary and biogeographic significance of the excellent fossil record of the Cocinetas Basin.Ítem Timing of rifting in the southern Gulf of California and its conjugate margins: Insights from the plutonic record(Geological Society of America, 2015-05-01) Duque-Trujillo, J.F.; Duque-Trujillo, J.F.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaThe Gulf of California is a young example of crustal stretching and transtensional shearing leading to the birth of a new oceanic basin at a formerly convergent margin. Previous studies focused along the southwestern rifted margin in Baja California...