Fossils of San Juan province

Se mencionan los principales fósiles que se hallan en el actual territorio de la provincia de San Juan, agrupados según las Eras Paleozoica, Mesozoica y Cenozoica. Se describen brevemente las características morfológicas de los fósiles más representativos, indicando su lugar de hallazgo, su edad y el ambiente sedimentario que lo caracteriza. También se definen y describen algunos conceptos y procesos geológicos utilizados en las ciencias paleontológicas.The main fossils of San Juan province are mentioned. They are grouped into the Paleozoic, Mesozoic and Cenozoic Eras. The morphological features of the most representative fossils are briefly described, with indication of their ages, localities and characteristic sedimentary environments. Also defined are some concepts and geological processes used in paleontological sciences.Fil: Bordonaro, Osvaldo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Raviolo, Mariana M.. No especifíca

Revisión estratigráfica y litofacial de la Formación La Silla (Ordovícico Inferior) en la Precordillera Oriental de San Juan, Argentina

La Formación La Silla (Cámbrico Superior - Ordovícico Inferior) fue definida en 1994 por Keller et al. a partir de los niveles inferiores de la Formación San Juan. Esta Formación consiste en una sucesión distintiva de calizas claras, con escasos fósiles y muy explotadas por su alta pureza. Basados en estudios detallados en la sección tipo cercana a Jáchal y siete secciones en el área sur cercana a la ciudad de San Juan, proponemos una subdivisión formal para la Formación La Silla en tres miembros. La división de la unidad está basada en la ubicación preferencial de bancos dolomíticos en el sector central de la Formación mientras que el sector superior e inferior son calizas monótonas. Los miembros se denominan, de base a techo: Miembro Río del Agua, Miembro Río Blanco y Miembro Río Salado (85, 140 y 81 m, respectivamente). Las dolomías en el Miembro Río Blanco son de dos tipos: macizas, potentes y generalmente asociadas a chert; y dolomías con laminación planar y/o entrecruzada, ambas fácilmente distinguibles a simple vista, otorgándole a este Miembro un aspecto bandeado debido a la alternancia entre calizas y dolomías. Esto contrasta con el aspecto macizo y monótono de los Miembros restantes con estratificación tabular y a veces suavemente ondulante. Se reconocen las facies de grainstone peloidal, grainstone oolítico, rudstone intraclástico, packstone peloidal, mudstone, microbiales laminadas y trombolíticas. Además se describen las nuevas facies de dolomías laminadas y dolomías macizas. De la misma manera que lo observado por Keller et al. (1994), la Formación La Silla representa una fase distinta en la sucesión cambro-ordovícica, con las dolomías perimareales de la Formación La Flecha por debajo y las calizas fosilíferas de plataforma abierta de la Formación San Juan por encima

Trilobite-based biostratigraphic model (biofacies and biozonation) for the Middle Cambrian carbonate platform of the Argentine Precordillera

A preliminary biostratigraphic model that combines trilobite biofacies and biozonation is proposed for the early Marjumian (Middle Cambrian) of the Precordillera of western Argentina. This interval involves a variety of paleogeographic-paleoenvironmental settings across the carbonate platform, ranging from its interior to exterior areas beyond the platform margin and including both open-marine and near-shore environments. This model is based on three stratigraphic sections of the basal part of the Alojamiento Formation, which crops out in the Cordón del Alojamiento (Provincia de Mendoza) and Cordón de Santa Clara (Provincia de San Juan); and three sections of the Soldano Member of La Laja Formation in the Sierra Chica de Zonda (Provincia de San Juan).Three biofacies were recognized on the basis of trilobite associations that show a marked environmental distribution: 1) The Ptychagnostidae Biofacies is represented by an assemblage exclusively dominated by agnostoids, most of them belonging to Ptychagnostus; this assemblage occurs in mudstones and calcareous shales deposited below storm wave-base seaward of the platform margin; 2) the Peronopsidae Biofacies also developed in the external areas but it occurs in limestones deposited between fair-weather and storm wave-base; this assemblage is likewise dominated by agnostoids, but instead belonging to Peronopsis, with the rest of the fauna comprising polymeroids (Dolichometopidae, Oryctocephalidae, Zacanthoididae and Alokistocaridae); 3) the Alokistocaridae Biofacies occurs in grainstones, mudstones and calcareous shales deposited between fair-weather and storm wave-base under changeable conditions located near the platform margin and in the interior. It is dominated by alokistocarids whose relative abundance increases landward from 52% to 58% and to 95%. The remaining components belong to Dorypygidae, Zacanthoididae and Oryctocephalidae; Eodiscidae and Peronopsidae comprise minor proportions in the most seaward location. Due to the contrasting, environmentally mediated associations, these sections belong to three essentially synchronous biozones erected previously for the Middle Cambrian of western Laurentia, the Ptychagnostus gibbus, Oryctocephalus and Ehmaniella Biozones

Characteristics, distribution and diagenetic stages of chert in the La Silla Formation (Lower Ordovician), Argentine Precordillera

The late Cambrian - late Tremadocian La Silla Formation is a carbonate unit of the eastern Precordillera in Argentina whose facies indicate a shallow platform environment. Until this moment, there were no studies that referred to the diagenetic evolution of these rocks. The present study involves the characteristics and distribution of the silicification that affects this unit and determines its different diagenetic stages through petrographic (with cathodoluminescence support) and stratigraphic analyses. An early diagenetic chert, in a stage previous to the compactation, was observed. This chert is related to silica-rich seawater in contact with permeable and porous sediments. A later pulse of chert, associated with fracturing, also occurs. The knowledge provided by the characteristics and distribution of chert in these carbonates is significant, especially when considering that the La Silla Formation in San Juan province is the most quarried unit for the elaboration of lime.A Formação La Silla (Neo Cambriano-Neo Tremadociano) é formada por depósitos carbonáticos da região da Pré-Cordilheira leste, Argentina. As faciologias encontradas em tais depósitos indicam um ambiente de deposição caracterizado por uma plataforma rasa. Até o momento, nenhum estudo tratou especificamente da evolução diagenética dessas rochas. O presente estudo envolve as características e distribuição da silicificação que afeta esta formação e apresenta os diferentes estágios diagenéticos ocorridos, através de análises petrográficas (auxiliadas por catodoluminescência) e estratigráficas. Foi identificado um pulso precoce de silicificação, anterior ao processo de compactação das rochas afetadas. Esta silicificação foi favorecida pela presença de água do mar rica em sílica em contato com sedimentos porosos e permeáveis. Também foi identificado um pulso de silicificação tardia, associado a eventos de fraturamento das rochas. O conhecimento adquirido sobre as características e a distribuição da silicificação nestes depósitos carbonáticos é importante, especialmente quando se considera que a Formação La Silla, na Província de San Juan, é a formação mais minerada para a produção de calcário

Trilobite-based biostratigraphic model (biofacies and biozonation) for the Middle Cambrian carbonate platform of the Argentine Precordillera

A preliminary biostratigraphic model that combines trilobite biofacies and biozonation is proposed for the early Marjumian (Middle Cambrian) of the Precordillera of western Argentina. This interval involves a variety of paleogeographic–paleoenvironmental settings across the carbonate platform, ranging from its interior to exterior areas beyond the platform margin and including both open-marine and near-shore environments. This model is based on three stratigraphic sections of the basal part of the Alojamiento Formation, which crops out in the Cordón del Alojamiento (Provincia de Mendoza) and Cordón de Santa Clara (Provincia de San Juan); and three sections of the Soldano Member of La Laja Formation in the Sierra Chica de Zonda (Provincia de San Juan). Three biofacies were recognized on the basis of trilobite associations that show a marked environmental distribution: 1) The Ptychagnostidae Biofacies is represented by an assemblage exclusively dominated by agnostoids, most of them belonging to Ptychagnostus; this assemblage occurs in mudstones and calcareous shales deposited below storm wave-base seaward of the platform margin; 2) the Peronopsidae Biofacies also developed in the external areas but it occurs in limestones deposited between fair-weather and storm wave-base; this assemblage is likewise dominated by agnostoids, but instead belonging to Peronopsis, with the rest of the fauna comprising polymeroids (Dolichometopidae, Oryctocephalidae, Zacanthoididae and Alokistocaridae); 3) the Alokistocaridae Biofacies occurs in grainstones, mudstones and calcareous shales deposited between fair-weather and storm wave-base under changeable conditions located near the platform margin and in the interior. It is dominated by alokistocarids whose relative abundance increases landward from 52% to 58% and to 95%. The remaining components belong to Dorypygidae, Zacanthoididae and Oryctocephalidae; Eodiscidae and Peronopsidae comprise minor proportions in the most seaward location. Due to the contrasting, environmentally mediated associations, these sections belong to three essentially synchronous biozones erected previously for the Middle Cambrian of western Laurentia, the Ptychagnostus gibbus, Oryctocephalus and Ehmaniella Biozones

Trilobite-based biostratigraphic model (biofacies and biozonation) for the Middle Cambrian carbonate platform of the Argentine Precordillera

A preliminary biostratigraphic model that combines trilobite biofacies and biozonation is proposed for the early Marjumian (Middle Cambrian) of the Precordillera of western Argentina. This interval involves a variety of paleogeographic-paleoenvironmental settings across the carbonate platform, ranging from its interior to exterior areas beyond the platform margin and including both open-marine and near-shore environments. This model is based on three stratigraphic sections of the basal part of the Alojamiento Formation, which crops out in the Cordón del Alojamiento (Provincia de Mendoza) and Cordón de Santa Clara (Provincia de San Juan); and three sections of the Soldano Member of La Laja Formation in the Sierra Chica de Zonda (Provincia de San Juan).Three biofacies were recognized on the basis of trilobite associations that show a marked environmental distribution: 1) The Ptychagnostidae Biofacies is represented by an assemblage exclusively dominated by agnostoids, most of them belonging to Ptychagnostus; this assemblage occurs in mudstones and calcareous shales deposited below storm wave-base seaward of the platform margin; 2) the Peronopsidae Biofacies also developed in the external areas but it occurs in limestones deposited between fair-weather and storm wave-base; this assemblage is likewise dominated by agnostoids, but instead belonging to Peronopsis, with the rest of the fauna comprising polymeroids (Dolichometopidae, Oryctocephalidae, Zacanthoididae and Alokistocaridae); 3) the Alokistocaridae Biofacies occurs in grainstones, mudstones and calcareous shales deposited between fair-weather and storm wave-base under changeable conditions located near the platform margin and in the interior. It is dominated by alokistocarids whose relative abundance increases landward from 52% to 58% and to 95%. The remaining components belong to Dorypygidae, Zacanthoididae and Oryctocephalidae; Eodiscidae and Peronopsidae comprise minor proportions in the most seaward location. Due to the contrasting, environmentally mediated associations, these sections belong to three essentially synchronous biozones erected previously for the Middle Cambrian of western Laurentia, the Ptychagnostus gibbus, Oryctocephalus and Ehmaniella Biozones