Browsing by Author "Salazar, Christian"
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Item Ammonite biostratigraphy and bioevents in the Jurassic e Cretaceous boundary of central Chile(2019) Salazar, Christian; Stinnesbeck, Wolfgang; Alvarez, MiguelAmmonites are abundant and well preserved in the Tithonian-Valanginian (Upper Jurassic eLowerCretaceous) sedimentary successions of the central Chilean Andes, known as the Lo Valdes and Ba~nos delFlaco Formations. A total of 1429 ammonites were collected from these stratigraphic units and thefollowing index zones based on ammonites are here proposed, from base to top: Virgatosphinctes mex-icanus/Pseudolissoceras cf. zitteli,Windhauseniceras internispinosum,Micracanthoceras microcanthum/Corongoceras alternans,Substeueroceras koeneni (Berriasella fraudans and Groebericeras rocardi sub-zones)and Thurmanniceras thurmanni/Argentiniceras fasciculatum.Our analyses indicate that “Ammonite Richness”is high in the middle and upper Tithonian and intothe lower Berriasian part of the succession, but decreases towards the lower Valanginian. Highest sim-ilarity values are established for the upper Tithonian, coincident with a high diversity; similarity declinesin the lower Berriasian. The main faunal turnover occurred between the early and late Berriasian fol-lowed by a secondary bioevent between the late Berriasian and early ValanginianItem Palaeoredox conditions and sequence stratigraphy of the Cretaceous storm-dominated, mixed siliciclastic-carbonate ramp in the Eastern Cordillera Basin (Colombia): Evidence from sedimentary geochemical proxies and facies analysis(2018) Rivera, Huber A.; Le Roux, Jacobus P.; Sánchez, L. Katherine; Mariño-Martínez, Jorge E.; Salazar, Christian; Barragán, J. CarolinaThe Cretaceous black shales of Colombia are among the most important successions in the north of South America and have attracted the attention of many geoscientists and exploration companies over the last few decades, because of their high hydrocarbon potential and the presence of emerald deposits. However, many uncertainties still remain with regard to their tectonic setting, sequence stratigraphy, depositional environments, palaeoxygenation conditions, and organic matter preservation. In order to develop a more integrated picture of these different processes and conditions, we conducted a detailed sedimentological, inorganic geochemical (U, V, Ni, Zn, Mn, Fe, Ti, Mo, Cu, Cr, Cd, Ba) and sequence stratigraphic analysis of the Cretaceous black shales in the Magdalena-Tablazo Sub-Basin (Eastern Cordillera Basin) of Colombia. Eleven lithofacies and five lithofacies associations of a storm-dominated, siliciclastic-carbonate ramp were identified, which range from basin to shallow inner ramp environments. These facies were grouped into six third-order stratigraphic sequences showing high-order cycles of marine transgression with constrained regressive pulses during the late Valanginian to early Coniacian. The black shales succession represents deposition under anoxic bottom water with some intervals representing dysoxic-suboxic conditions. The evolution of the sedimentary environments and their palaeoxygenation history reflect tectonic and eustatic sea-level controls that 1) produced a variable orientation and position of the coastline throughout the Cretaceous; 2) conditioned the low-gradient ramp geometry (b0.3°) and 3) modified the oxygenation conditions in the Magdalena-Tablazo Sub-Basin. An improved under- standing of the sedimentary setting during deposition of the Cretaceous black shales in the Magdalena-Tablazo Sub-Basin assists in highlighting the interplay between the mechanism of sedimentation and continuum anoxic conditions prevailing in a basin, as well the important role of nutrient input from continental runoff as a trigger of high productivity and extended anoxia conditions.Item Release of gliotransmitters through astroglial connexin 43 hemichannels is necessary for fear memory consolidation in the basolateral amygdala(Federation of American Societies for Experimental Biology, 2012) Stehberg, Jimmy; Moraga-Amaro, Rodrigo; Salazar, Christian; Becerra, Alvaro; Echeverría, Cesar; Orellana, Juan; Bultynck, Geert; Ponsaerts, Raf; Leybaert, Luc; Simon, Felipe; Sáez, Juan; Retamal, MauricioRecent in vitro evidence indicates that astrocytes can modulate synaptic plasticity by releasing neuroactive substances (gliotransmitters). However, whether gliotransmitter release from astrocytes is necessary for higher brain function in vivo, particularly for memory, as well as the contribution of connexin (Cx) hemichannels to gliotransmitter release, remain elusive. Here, we microinfused into the rat basolateral amygdala (BLA) TAT-Cx43L2, a peptide that selectively inhibits Cx43-hemichannel opening while maintaining synaptic transmission or interastrocyte gap junctional communication. In vivo blockade of Cx43 hemichannels during memory consolidation induced amnesia for auditory fear conditioning, as assessed 24 h after training, without affecting short-term memory, locomotion, or shock reactivity. The amnesic effect was transitory, specific for memory consolidation, and was confirmed after microinfusion of Gap27, another Cx43-hemichannel blocker. Learning capacity was recovered after coinfusion of TAT-Cx43L2 and a mixture of putative gliotransmitters (glutamate, glutamine, lactate, d-serine, glycine, and ATP). We propose that gliotransmitter release from astrocytes through Cx43 hemichannels is necessary for fear memory consolidation at the BLA. Thus, the present study is the first to demonstrate a physiological role for astroglial Cx43 hemichannels in brain function, making these channels a novel pharmacological target for the treatment of psychiatric disorders, including post-traumatic stress disorder.Item Taguatagua 1: New insights into the late Pleistocene fauna, paleoenvironment, and human subsistence in a unique lacustrine context in central Chile(2020) Labarca, Rafael; González Guarda, Erwin; Lizama Catalán, Álvaro; Villavicencio, Natalia A.; Alarcón Muñoz, Jhonatan; Suazo Lara, Felipe; Oyanadel Urbina, Pablo; Soto Huenchumán, Paula; Salazar, Christian; Soto Acuña, Sergio; Buldrinia, Karina E.The Laguna de Tagua Tagua has yielded two important late Pleistocene archaeological sites, Taguatagua 1 and Taguatagua 2, in which a clear early human exploitation of megafauna has been recorded. Particularly in Taguatagua 1 (TT-1), here re-dated around 12,600 cal yr BP, an abundant small faunal assemblage was also recovered, which had not been previously studied in detail. Here we report the first comprehensive taxonomic and taphonomic analysis of this site. We identified 28 different taxa, including mollusks, fish, anurans, reptiles, birds, marsupials, rodents, carnivores, gomphotheres, horses and cervids, making this the richest late Pleistocene site in Chile so far. Among these, sixteen taxa are new for the Chilean late Pleistocene. Birds are the richest group, with ten taxa, followed by rodents with eight taxa. Most of the species currently inhabit the area, but we identified some locally extirpated taxa, together with extinct taxa (exclusively megamammals). Taphonomic analysis suggests a very complex depositional scenario, mostly related to lake-level oscillations which covered and exposed a mainly natural deposited small faunal assemblage. So far, we detected human-made modifications exclusively in horse and cervid bones. Current habitat requirements of the extant fauna, as well as dietary reconstruction of extinct fauna, suggest a highly variable climate and vegetation during the formation of TT-1 since taxa with preferences from semiarid to humid/wooded environments were identified. These results can be related to the changes from cold/wet to dry/warm conditions documented during the Pleistocene - Holocene transition.