Cambrian sponge spicules and Chancelloriid sclerites from the Argentine Precordillera : a Review

Spicules of sponges and sclerites of chancelloriids have been collected from in situ Cambrian sections of the La Laja Formation (San Juan Precordillera). They have also been collected from carbonate olistoliths, which were emplaced from the Cambrian units in the Early Ordovician Los Sombreros Formation (San Juan Precordillera) and Empozada Formation (Mendoza Precordillera). The Cambrian La Laja Formation sequences were deposited in a shallow carbonate platform in the eastern part of the Precordillera. The Cambrian carbonate rocks, which make up the olistoliths in the Los Sombreros and Empozada Formations, record deposition in the slope environments which developed in the western Precordillera. Cambrian Porifera and sponge-like chancelloriid assemblages are known mainly from fragments of skeletal nets, dissociated spicules and sclerites, which enable us to define two assemblages. The first assemblage of spicules was defined from the upper Lower to Middle Cambrian sequences of the La Laja Formation. This assemblage consists of a variety of stauractines and sclerites of Chancelloria WALCOTT. The family Protospongiidae is represented by triradiate prodianes, pentactines and hexactines, all belonging to Kiwetinokia WALCOTT. The second assemblage, which consists of isolated hexactines, pentactines, monaxons and skeletal nets, was defined in the Cambrian derived olistholiths of the Los Sombreros and Empozada Formations. Early hexactinellid Protospongiidae with body preservation (Diagoniella ? and Kiwetinokia) also occur. Demosponges have a very limited record in the Cambrian of the Precordillera. Anthaspidellid sponges had been reported from the La Laja Formation and now from the San Martín olistolith (Empozada Formation). The occurrences of these two assemblages of spicules and sclerites in both the Cambrian platform and slope facies of the Precordillera contribute additional data for a better understanding of the relationships between the eastern and the western facies assemblages, which developed in the Precordillera during the Cambrian. Therefore, they are useful for paleoenvironmental and paleogeographical interpretations of the Cambrian depositional framework

Darriwilian Conodont Biostratigraphy of the Las Chacritas Formation, Central Precordillera (San Juan Province, Argentina)

The Las Chacritas Fm in the type section in the Sierra de La Trampa, Central Precordillera (San Juan Province) was deposited in an outer carbonate ramp setting that evolved from relatively deep to shallow water. Samples from this well-exposed Middle Ordovician section yielded collections of low-diversity conodont faunas stratigraphically significant. The top of the underlying San Juan Fm and the lower and middle parts of the Las Chacritas Fm contain conodonts representative of the Lenodus variabilis Zone, and the upper part of the Las Chacritas Fm yields conodonts that correlate with the Paroistodus horridus subzone of the upper part of the Lenodus variabilis Zone. The occurrence of Dzikodus tablepointensis and Eoplacognathus pseudoplanus in the upper part of the Paroistodus horridus subzone is especially significant. The occurrence of Histiodella kristinae in the highest levels indicates that the top of the Las Chacritas Fm correlates with the Eoplacognathus suecicus Zone. Conodont biofacies are analyzed trough the entire section, supporting an outer platform or open sea conditions. Baltic and Sino-Pacific affinities are stated

Cambrian sponge spicules and Chancelloriid sclerites from the Argentine Precordillera : a Review

Spicules of sponges and sclerites of chancelloriids have been collected from in situ Cambrian sections of the La Laja Formation (San Juan Precordillera). They have also been collected from carbonate olistoliths, which were emplaced from the Cambrian units in the Early Ordovician Los Sombreros Formation (San Juan Precordillera) and Empozada Formation (Mendoza Precordillera). The Cambrian La Laja Formation sequences were deposited in a shallow carbonate platform in the eastern part of the Precordillera. The Cambrian carbonate rocks, which make up the olistoliths in the Los Sombreros and Empozada Formations, record deposition in the slope environments which developed in the western Precordillera. Cambrian Porifera and sponge-like chancelloriid assemblages are known mainly from fragments of skeletal nets, dissociated spicules and sclerites, which enable us to define two assemblages. The first assemblage of spicules was defined from the upper Lower to Middle Cambrian sequences of the La Laja Formation. This assemblage consists of a variety of stauractines and sclerites of Chancelloria WALCOTT. The family Protospongiidae is represented by triradiate prodianes, pentactines and hexactines, all belonging to Kiwetinokia WALCOTT. The second assemblage, which consists of isolated hexactines, pentactines, monaxons and skeletal nets, was defined in the Cambrian derived olistholiths of the Los Sombreros and Empozada Formations. Early hexactinellid Protospongiidae with body preservation (Diagoniella ? and Kiwetinokia) also occur. Demosponges have a very limited record in the Cambrian of the Precordillera. Anthaspidellid sponges had been reported from the La Laja Formation and now from the San Martín olistolith (Empozada Formation). The occurrences of these two assemblages of spicules and sclerites in both the Cambrian platform and slope facies of the Precordillera contribute additional data for a better understanding of the relationships between the eastern and the western facies assemblages, which developed in the Precordillera during the Cambrian. Therefore, they are useful for paleoenvironmental and paleogeographical interpretations of the Cambrian depositional framework

Cambrian sponge spicules and Chancelloriid sclerites from the Argentine Precordillera: A Review

Spicules of sponges and sclerites of chancelloriids have been collected from in situ Cambrian sections of the La Laja Formation (San Juan Precordillera). They have also been collected from carbonate olistoliths, which were emplaced from the Cambrian units in the Early Ordovician Los Sombreros Formation (San Juan Precordillera) and Empozada Formation (Mendoza Precordillera). The Cambrian La Laja Formation sequences were deposited in a shallow carbonate platform in the eastern part of the Precordillera. The Cambrian carbonate rocks, which make up the olistoliths in the Los Sombreros and Empozada Formations, record deposition in the slope environments which developed in the western Precordillera. Cambrian Porifera and sponge-like chancelloriid assemblages are known mainly from fragments of skeletal nets, dissociated spicules and sclerites, which enable us to define two assemblages. The first assemblage of spicules was defined from the upper Lower to Middle Cambrian sequences of the La Laja Formation. This assemblage consists of a variety of stauractines and sclerites of Chancelloria WALCOTT. The family Protospongiidae is represented by triradiate prodianes, pentactines and hexactines, all belonging to Kiwetinokia WALCOTT. The second assemblage, which consists of isolated hexactines, pentactines, monaxons and skeletal nets, was defined in the Cambrian derived olistholiths of the Los Sombreros and Empozada Formations. Early hexactinellid Protospongiidae with body preservation (Diagoniella ? and Kiwetinokia) also occur. Demosponges have a very limited record in the Cambrian of the Precordillera. Anthaspidellid sponges had been reported from the La Laja Formation and now from the San Martín olistolith (Empozada Formation). The occurrences of these two assemblages of spicules and sclerites in both the Cambrian platform and slope facies of the Precordillera contribute additional data for a better understanding of the relationships between the eastern and the western facies assemblages, which developed in the Precordillera during the Cambrian. Therefore, they are useful for paleoenvironmental and paleogeographical interpretations of the Cambrian depositional framework

Darriwilian Conodont Biostratigraphy of the Las Chacritas Formation, Central Precordillera (San Juan Province, Argentina)

The Las Chacritas Fm in the type section in the Sierra de La Trampa, Central Precordillera (San Juan Province) was deposited in an outer carbonate ramp setting that evolved from relatively deep to shallow water. Samples from this well-exposed Middle Ordovician section yielded collections of low-diversity conodont faunas stratigraphically significant. The top of the underlying San Juan Fm and the lower and middle parts of the Las Chacritas Fm contain conodonts representative of the Lenodus variabilis Zone, and the upper part of the Las Chacritas Fm yields conodonts that correlate with the Paroistodus horridus subzone of the upper part of the Lenodus variabilis Zone. The occurrence of Dzikodus tablepointensis and Eoplacognathus pseudoplanus in the upper part of the Paroistodus horridus subzone is especially significant. The occurrence of Histiodella kristinae in the highest levels indicates that the top of the Las Chacritas Fm correlates with the Eoplacognathus suecicus Zone. Conodont biofacies are analyzed trough the entire section, supporting an outer platform or open sea conditions. Baltic and Sino-Pacific affinities are stated

Microfacies asociadas a las Zonas de <i>Oepikodus evae</i> y <i>O. intermedius</i> (Conodonta) en el Ordovícico de Salagasta, Mendoza, Argentina

En la localidad de Salagasta, ubicada en el extremo austral de la Sierra de La Higuera, provincia de Mendoza aflora una secuencia eopaleozoica afectada tectónicamente, que forma parte de la Provincia Geológica de Precordillera. La franja de calizas correspondiente a la plataforma ordovícica de la Formación San Juan, ingresa en la Precordillera de Mendoza desde la Sierra de Las Peñas (provincia de San Juan) y aparece en la región septentrional de la Sierra de La Higuera. Se han caracterizado las microfacies y los conodontes asociados para el miembro superior (32m), correspondiente a los tramos medio y superior de la sección carbonática. El miembro superior está caracterizado por microfacies de packstones de pellets que pasan a grainstones fosilíferos y grainstones crinoidales asociadas a estructuras sedimentarias de media a alta energía. En los 4m cuspidales de la Formación San Juan, las microfacies reflejan menor energía y están representadas por mudstones y wackestones pelletoidales. Los conodontes permitieron referir los tramos medio y superior de la sección carbonática a la Zona de Oepikodus evae y los tramos cuspidales a la Zona de Oepikodus intermedius. De acuerdo a las biozonas de conodontes determinadas, los términos superiores de la Formación San Juan en la región de Salagasta, Precordillera de Mendoza se asignan al Floiano más alto. La sección culmina con un paquete mixto calcáreo-pelítico de 7m de espesor correspondiente a la Formación Gualcamayo.Simposio I: 2º Simposio de bioestratigrafía y eventos del Paleozoico inferiorSymposium I: 2nd Symposium of biostratigraphy and Lower Paleozoic eventsSimpósio I: 2 º Simpósio de bioestratigrafia e eventos do Paleozoico InferiorFacultad de Ciencias Naturales y Muse

Microfacies asociadas a las Zonas de Oepikodus evae y O. intermedius (Conodonta) en el Ordovícico de Salagasta, Mendoza, Argentina

En la localidad de Salagasta, ubicada en el extremo austral de la Sierra de La Higuera, provincia de Mendoza aflora una secuencia eopaleozoica afectada tectónicamente, que forma parte de la Provincia Geológica de Precordillera. La franja de calizas correspondiente a la plataforma ordovícica de la Formación San Juan, ingresa en la Precordillera de Mendoza desde la Sierra de Las Peñas (provincia de San Juan) y aparece en la región septentrional de la Sierra de La Higuera. Se han caracterizado las microfacies y los conodontes asociados para el miembro superior (32m), correspondiente a los tramos medio y superior de la sección carbonática. El miembro superior está caracterizado por microfacies de packstones de pellets que pasan a grainstones fosilíferos y grainstones crinoidales asociadas a estructuras sedimentarias de media a alta energía. En los 4m cuspidales de la Formación San Juan, las microfacies reflejan menor energía y están representadas por mudstones y wackestones pelletoidales. Los conodontes permitieron referir los tramos medio y superior de la sección carbonática a la Zona de Oepikodus evae y los tramos cuspidales a la Zona de Oepikodus intermedius. De acuerdo a las biozonas de conodontes determinadas, los términos superiores de la Formación San Juan en la región de Salagasta, Precordillera de Mendoza se asignan al Floiano más alto. La sección culmina con un paquete mixto calcáreo-pelítico de 7m de espesor correspondiente a la Formación Gualcamayo.Simposio I: 2º Simposio de bioestratigrafía y eventos del Paleozoico inferiorSymposium I: 2nd Symposium of biostratigraphy and Lower Paleozoic eventsSimpósio I: 2 º Simpósio de bioestratigrafia e eventos do Paleozoico InferiorFacultad de Ciencias Naturales y Muse

Microfacies, biota y paleoambientes sedimentarios del Ordovícico Temprano-Medio del Cerro Salazar, Sonora central, México

This work shows the results of facies/microfacies and paleoenvironmental analysis of the Pozo Nuevo Formation outcropping at the Cerro Salazar, nearby the Rancho Las Norias (Central Sonora, Mexico). The Pozo Nuevo Formation represents Early-Middle Ordovician deposits of a continental carbonate shelf that developed in the southwestern tip of Laurentia. The conodonts and trilobites described from the unit indicate a late Floian-early Dapingian age. The microfacies analysis enables identifying different sub-environments within the carbonate shelf from minor to major depth: a coastal beach, represented by quartz sandstone and laminated quartzite with desiccation cracks; an inner shelf which includes a supratidal setting constituted by dolomitized wackestone and an intertidal-subtidal lagoon characterized by diffusely laminated microbialites, oncoid mudstone, pelloid packstone grading to biopelloid and bioclastic packstone containing foraminifera and ostracods; and a subtidal setting composed of grainstone and packstone with crinoids and algae (Nuia) and detritic quartz and bioclastic packstone with bryozoans. In the lagoon as well as in the subtidal platform, there are intercalated intraclastic - bioclastic packstone levels, which are interpreted as proximal stormy events. The vertical variation of facies indicates a marked trend toward shallowing. At the base of the section fine micritic sediments deposited in a quiet, low energy lagoon, whereas a deeper subtidal environment with diverse faunas was developed in the middle part. On the other hand, at the top of the succession there is an increased participation of detrital quartz with deposition of coastal quartz sandstone culminating with thick dolomite levels of a vadose environment.En el presente trabajo se da a conocer el resultado de los análisis de facies/microfacies y paleoambientes de la Formación Pozo Nuevo aflorante en el Cerro Salazar, en las cercanías del Rancho Las Norias (Sonora central, México). Esta formación corresponde a depósitos de una plataforma carbonática continental que se desarrolló en el extremo sudoeste de Laurentia en el Ordovícico Inferior- Medio. Los conodontes y trilobites reconocidos indican una edad floiana tardía-dapingiana temprana. Las microfacies permiten identificar distintos subambientes dentro de la plataforma carbonática: costero de playa formado por areniscas cuarzosas y cuarcita laminada con grietas de desecación; plataforma interna: supramareal constituido por facies dolomíticas y laguna caracterizado por microbialitas de laminación difusa, mudstone oncoidal, packstone peloidal que gradúa a biopeloidal y packstone bioclástico con foraminíferos y ostrácodos; plataforma media, submareal compuesto por grainstone y packstone de crinoideos y algas (Nuia) con cuarzo detrítico y packstones bioclásticos con briozoarios. Tanto en el ambiente de laguna como en la plataforma media, se intercalan niveles de packstone intraclástico-bioclástico interpretados como eventos tempestíticos proximales. La variación vertical de facies, indica una tendencia marcada hacia la somerización con areniscas cuarzosas y dolomías en el tope de la sección. En la base, las facies corresponden a sedimentos finos micríticos que se depositaron en un ambiente tranquilo y de baja energía característicos de laguna. En la parte media se desarrolló una plataforma submareal con biota diversificada de crinoideos, briozoarios, algas, braquiópodos, trilobites, nautiloideos y gasterópodos. Estratigráficamente sobre la sección inferior se incrementa la participación de cuarzo detrítico que forma depósitos de arenas cuarzosas acumuladas en ambiente costero de playa, registrando la migración de la línea de costa hacia el depocentro de la cuenca. El tope de la sección culmina con un importante espesor de dolomías originadas en un ambiente vadoso. El modelo de sedimentación representa la gradual somerización de la cuenca desde carbonatos de baja energía hasta de alta energía, con facies de areniscas cuarzosas de playa y dolomías vadosas