Pub Date : 2020-01-31DOI: 10.5027/andgeov47n1-3229
Fernanda Serra, Nicolás A. Feltes, M. Mango, Miles A. Henderson, G. Albanesi, G. Ortega
The Ordovician System is extensively represented in the Precordillera of San Juan Province, Argentina. At the Cerro La Chilca in the Jachal area, the limestone of the San Juan Formation is paraconformably overlain by interbedded limestone and shale of the Gualcamayo Formation. The present contribution reports new data on the conodont fauna and biostratigraphy of these darriwilian units, revising local and regional chronostratigraphic relationships. New information on the composition of conodont and graptolite associations through the stratigraphic sequence is presented. The presence of Paroistodus horridus horridus, Yangtzeplacognathus crassus, and Histiodella sinuosa constrain the uppermost strata of the San Juan Formation to the lower part of the Y. crassus Zone, according to the Baltoscandian scheme, and to the H. sinuosa Subzone of the Periodon macrodentatus Zone of the North American scheme. In the overlying Gualcamayo Formation the co-occurrence of Y. crassus with Histiodella holodentata enable the recognition of the Y. crassus Zone and the H. holodentata Subzone of the P. macrodentatus Zone. The identification of these zones allows for precise global and regional correlation. A graptolite assemblage that belongs to the epipelagic and deep-water biotopes with some components restricted to low paleolatitudes is recognized. This diverse assemblage is characteristic of the pelagic biofacies. The important diversity of graptolites in this section suggests a favorable environment for their development. Local changes in the taxonomic composition are recognized through the Gualcamayo Formation. When comparing this fauna with that of different study localities from the Central Precordillera (Cerro Potrerillo, Oculta Creek, Cerro Viejo de Huaco and Las Aguaditas Creek) slight differences in the generic composition are observed. Taxonomic differences support the preference of certain associations for particular environments; though, graptolites are more diverse in black shales facies, which represent deeper environments (the Los Azules Formation), in relation to the calcareous-shale facies of the Gualcamayo Formation from Cerro La Chilca and correlative unit at Las Aguaditas Creek.
奥陶系广泛分布于阿根廷圣胡安省的Precordillera地区。在Jachal地区的Cerro La Chilca，圣胡安组的灰岩被Gualcamayo组的互层灰岩和页岩顺整合覆盖。本文报道了这些达里威利单位牙形石动物群和生物地层学的新资料，修订了当地和区域的年代地层关系。通过地层层序对牙形石和笔石组合的组成提供了新的信息。paristodus horridus horridus、Yangtzeplacognathus crassus和Histiodella sinuosa的存在，将圣胡安组的最上层地层限制在Baltoscandian模式下的Y. crassus带的下部，以及北美模式下的Periodon macrodentatus带的H. sinuosa亚带。在其上的Gualcamayo组中，粗齿杨与holododella holodentata的共存使得粗齿杨区和大齿杨区holodentata亚区得以识别。这些区域的识别允许进行精确的全球和区域关联。笔石组合属于上层海洋和深水生物群落，其中一些成分仅限于低古纬度。这种多样化的组合是远洋生物相的特征。该剖面笔石的重要多样性表明其具有良好的发育环境。分类组成的局部变化是通过瓜尔卡马约组来识别的。将该区系与中部Precordillera不同研究地点(Cerro Potrerillo、Oculta Creek、Cerro Viejo de Huaco和Las Aguaditas Creek)的区系进行比较，发现其属组成略有差异。分类学上的差异支持了某些种群对特定环境的偏好;然而，与Cerro La Chilca的Gualcamayo组的钙质页岩相和Las Aguaditas Creek的相关单元相比，黑色页岩相(Los Azules组)的笔石更加多样化，代表了更深的环境(Los Azules组)。
{"title":"Darriwilian (Middle Ordovician) conodonts and graptolites from the Cerro La Chilca Section, Central Precordillera, Argentina","authors":"Fernanda Serra, Nicolás A. Feltes, M. Mango, Miles A. Henderson, G. Albanesi, G. Ortega","doi":"10.5027/andgeov47n1-3229","DOIUrl":"https://doi.org/10.5027/andgeov47n1-3229","url":null,"abstract":"The Ordovician System is extensively represented in the Precordillera of San Juan Province, Argentina. At the Cerro La Chilca in the Jachal area, the limestone of the San Juan Formation is paraconformably overlain by interbedded limestone and shale of the Gualcamayo Formation. The present contribution reports new data on the conodont fauna and biostratigraphy of these darriwilian units, revising local and regional chronostratigraphic relationships. New information on the composition of conodont and graptolite associations through the stratigraphic sequence is presented. The presence of Paroistodus horridus horridus, Yangtzeplacognathus crassus, and Histiodella sinuosa constrain the uppermost strata of the San Juan Formation to the lower part of the Y. crassus Zone, according to the Baltoscandian scheme, and to the H. sinuosa Subzone of the Periodon macrodentatus Zone of the North American scheme. In the overlying Gualcamayo Formation the co-occurrence of Y. crassus with Histiodella holodentata enable the recognition of the Y. crassus Zone and the H. holodentata Subzone of the P. macrodentatus Zone. The identification of these zones allows for precise global and regional correlation. A graptolite assemblage that belongs to the epipelagic and deep-water biotopes with some components restricted to low paleolatitudes is recognized. This diverse assemblage is characteristic of the pelagic biofacies. The important diversity of graptolites in this section suggests a favorable environment for their development. Local changes in the taxonomic composition are recognized through the Gualcamayo Formation. When comparing this fauna with that of different study localities from the Central Precordillera (Cerro Potrerillo, Oculta Creek, Cerro Viejo de Huaco and Las Aguaditas Creek) slight differences in the generic composition are observed. Taxonomic differences support the preference of certain associations for particular environments; though, graptolites are more diverse in black shales facies, which represent deeper environments (the Los Azules Formation), in relation to the calcareous-shale facies of the Gualcamayo Formation from Cerro La Chilca and correlative unit at Las Aguaditas Creek.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2020-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42502468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-31DOI: 10.5027/andgeov47n1-3193
Nerina Canale, J. J. Ponce, Noelia B. Carmona, Martín N. Parada, Daniel I. Drittanti
Sedimentologic and ichnologic analysis of the Middle Jurassic Lajas Formation in Bajada de Los Molles area allow recognizing upper offshore-lower shoreface deposits in transition to prodelta, delta front and interdistributary bay succesions. This system is classified as a river-dominated delta due to the presence of distributary channel deposits with huge amounts of particulate organic matter and low diversity and abundance of trace fossils. Hyperpycnites are common in the basal and upper part of the studied section, and form channel-levee and distributary-channel systems, integrated by massive sandstones and load deformation structures, or transitional and recurrent passages of tractive sedimentary structures with abundant particulate organic matter on the foresets. The greatest diversity and abundance of trace fossils are recognized in the upper offshore-lower shoreface deposits where Skolithos and Cruziana ichnofacies occur. Deltaic deposits show trace fossil associations with lower diversity and abundance than the fully marine ones, whereas the hyperpycnite deposits are either unbioturbated or show the lowest diversity and abundance of trace fossils, reflecting the most stressed conditions within the system.
Bajada de Los Molles地区中侏罗世Lajas组的沉积学和考古学分析使我们能够识别向前三角洲、三角洲前缘和分流间湾序列过渡的上近海下滨面矿床。该系统被归类为河流主导的三角洲，因为存在大量颗粒有机物的分流河道沉积物，微量化石的多样性和丰度较低。高pycnite常见于研究剖面的基底和上部，形成河道-堤坝和分流河道系统，由块状砂岩和负载变形结构整合在一起，或形成牵引沉积结构的过渡和复发通道，在前缘具有丰富的颗粒有机质。在Skolithos和Cruziana遗迹相所在的上近海下滨面矿床中，发现了最大的多样性和丰度的痕迹化石。三角洲矿床显示出微量化石组合，其多样性和丰度低于全海洋矿床，而超硬质岩矿床要么未受扰动，要么显示出最低的微量化石多样性和丰富度，反映了系统内最受压力的条件。
{"title":"Sedimentología e icnología de un delta fluvio-dominado, Formación Lajas (Jurásico Medio), cuenca Neuquina, Argentina","authors":"Nerina Canale, J. J. Ponce, Noelia B. Carmona, Martín N. Parada, Daniel I. Drittanti","doi":"10.5027/andgeov47n1-3193","DOIUrl":"https://doi.org/10.5027/andgeov47n1-3193","url":null,"abstract":"Sedimentologic and ichnologic analysis of the Middle Jurassic Lajas Formation in Bajada de Los Molles area allow recognizing upper offshore-lower shoreface deposits in transition to prodelta, delta front and interdistributary bay succesions. This system is classified as a river-dominated delta due to the presence of distributary channel deposits with huge amounts of particulate organic matter and low diversity and abundance of trace fossils. Hyperpycnites are common in the basal and upper part of the studied section, and form channel-levee and distributary-channel systems, integrated by massive sandstones and load deformation structures, or transitional and recurrent passages of tractive sedimentary structures with abundant particulate organic matter on the foresets. The greatest diversity and abundance of trace fossils are recognized in the upper offshore-lower shoreface deposits where Skolithos and Cruziana ichnofacies occur. Deltaic deposits show trace fossil associations with lower diversity and abundance than the fully marine ones, whereas the hyperpycnite deposits are either unbioturbated or show the lowest diversity and abundance of trace fossils, reflecting the most stressed conditions within the system.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2020-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45541774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-31DOI: 10.5027/andgeov47n1-3260
Marcelo H. García, J. Correa, V. Maksaev, B. Townley
El subsuelo marino comprendido por la Zona Economica Exclusiva(ZEE) de Chile tiene condiciones propicias para originar y hospedar diferentes depositos minerales, pero su conocimiento geologico es escaso y disperso. Los estudios existentes son muy limitados en cuanto a analisis geoquimicos y mineralogicos. Los recursos minerales no-energeticos mas significativos, costa afuera de Chile, corresponden a: nodulos y costras de Fe-Mn, depositos de fosforitas, depositos de placeres de oro y titanio y depositos de sulfuros masivos. Los sitios de nodulos de Fe-Mn se encuentran en planicies abisales y montes submarinos, y alrededor de islas volcanicas, a profundidades de 2.890 a 4.332 m, y pueden tener concentraciones importantes de Cu y Ni (hasta 1,38% de Cu+Ni) and Co (hasta 0,53%). Ocurrencias de costras de Mn ricas en Co han sido reportadas alrededor de las islas Rapanui y Salas y Gomez, con contenidos de Cu+Ni de hasta 0,3%. Sitios con depositos de fosforitas aparecen en estratos holocenos de la plataforma continental de Peru y norte de Chile, con un contenido promedio de P2O5 de 22,6%. Depositos de placeres de oro se encuentran en playas y canales del sur de Chile y podrian extenderse mar afuera, probablemente en canones submarinos. Depositos de placeres de titanio han sido evaluados en diferentes playas de Chile y tambien podrian continuarse mar afuera. Anomalias de platino han sido encontradas en canales y bahias del extremo sur de Chile. Muestras de mineralizacion de Sulfuros Masivos Volcanogenicos (VMS) no se conocen a la fecha en la ZEE de Chile. Sin embargo, muestras de depositos hidrotermales, con potencial para mineralizacion polimetalica del tipo VMS, han sido colectadas alrededor de la isla Rapanui, y varias cadenas de montes submarinos e islas volcanicas indican condiciones favorables para la formacion y preservacion de estos depositos. La informacion geologica, actualmente disponible, sobre el fondo marino de la ZEE de Chile es insuficiente para estimar el real potencial de sus recursos minerales no-energeticos.
{"title":"Potential mineral resources of the Chilean offshore: an overview","authors":"Marcelo H. García, J. Correa, V. Maksaev, B. Townley","doi":"10.5027/andgeov47n1-3260","DOIUrl":"https://doi.org/10.5027/andgeov47n1-3260","url":null,"abstract":"El subsuelo marino comprendido por la Zona Economica Exclusiva(ZEE) de Chile tiene condiciones propicias para originar y hospedar diferentes depositos minerales, pero su conocimiento geologico es escaso y disperso. Los estudios existentes son muy limitados en cuanto a analisis geoquimicos y mineralogicos. Los recursos minerales no-energeticos mas significativos, costa afuera de Chile, corresponden a: nodulos y costras de Fe-Mn, depositos de fosforitas, depositos de placeres de oro y titanio y depositos de sulfuros masivos. Los sitios de nodulos de Fe-Mn se encuentran en planicies abisales y montes submarinos, y alrededor de islas volcanicas, a profundidades de 2.890 a 4.332 m, y pueden tener concentraciones importantes de Cu y Ni (hasta 1,38% de Cu+Ni) and Co (hasta 0,53%). Ocurrencias de costras de Mn ricas en Co han sido reportadas alrededor de las islas Rapanui y Salas y Gomez, con contenidos de Cu+Ni de hasta 0,3%. Sitios con depositos de fosforitas aparecen en estratos holocenos de la plataforma continental de Peru y norte de Chile, con un contenido promedio de P2O5 de 22,6%. Depositos de placeres de oro se encuentran en playas y canales del sur de Chile y podrian extenderse mar afuera, probablemente en canones submarinos. Depositos de placeres de titanio han sido evaluados en diferentes playas de Chile y tambien podrian continuarse mar afuera. Anomalias de platino han sido encontradas en canales y bahias del extremo sur de Chile. Muestras de mineralizacion de Sulfuros Masivos Volcanogenicos (VMS) no se conocen a la fecha en la ZEE de Chile. Sin embargo, muestras de depositos hidrotermales, con potencial para mineralizacion polimetalica del tipo VMS, han sido colectadas alrededor de la isla Rapanui, y varias cadenas de montes submarinos e islas volcanicas indican condiciones favorables para la formacion y preservacion de estos depositos. La informacion geologica, actualmente disponible, sobre el fondo marino de la ZEE de Chile es insuficiente para estimar el real potencial de sus recursos minerales no-energeticos.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2020-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43213487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-31DOI: 10.5027/ANDGEOV47N1-3261
B. A. Toro, S. Heredia, Nexxys C. Herrera Sánchez, F. Moreno
Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindstrom) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.
{"title":"First Middle Ordovician conodont record related to key graptolites from the western Puna, Argentina: perspectives for an integrated biostratigraphy and correlation of the Central Andean Basin","authors":"B. A. Toro, S. Heredia, Nexxys C. Herrera Sánchez, F. Moreno","doi":"10.5027/ANDGEOV47N1-3261","DOIUrl":"https://doi.org/10.5027/ANDGEOV47N1-3261","url":null,"abstract":"Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindstrom) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2020-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45447001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-30DOI: 10.5027/andgeov46n3-3143
A. Taboada, M. A. Pagani, M. K. Pinilla, Franco Tortello, C. A. Taboada
A narrow upper Paleozoic belt crops out in the northern tip of Sierra de Tecka through the Quebrada de Güera-Peña (Patagonia, Argentina). There, black shales of the Pampa de Tepuel Formation contain marine fossil invertebrates previously listed as belonging to the “Levipustula” fauna. Material recently recorded by the authors comprises, in order of abundance, gastropods [Glabrocingulum (Glabrocingulum) poperimense (Maxwell), G. (Stenozone) argentinum (Reed), G. (Stenozone) sp., Peruvispira teckaensis sp. nov., Ananias riccardii Pinilla], bivalves [Nuculopsis (Nuculopsis) patagoniensis González, Phestia tepuelensis González, Streblochondria sueroi González, Streblopteria sp.], conulariids [Paraconularia cf. ugartei Cúneo and Sabattini], brachiopods [Amosia sueroi Simanauskas, Languigneotus laevicaudatum (Amos), Beecheria patagonica Amos], trilobites [Australosutura argentinensis Hahn and Hahn], cephalopods [Pseudoorthoceratidae Flower and Caster, Sueroceras? sp., Mitorthoceras? sp.], and rugose corals [?Lophophyllidiidae Moore and Jeffords]. In addition, the present study includes the new key brachiopods Languigneotus dammanorum gen. et sp. nov. and Tuberculatella waterhousei sp. nov. from younger localities of the Tepuel-Genoa Basin. The Languigneotus laevicaudatum and Languigneotus-Verchojania subzones (late Pennsylvanian) are proposed herein to replace the former Tuberculatella Zone. In addition, previous stratigraphic relationships and correlations of the study section with the Arroyo Pescado (Estancia Ap Iwan) and Esquel areas are discussed. The general stratigraphic profile of a glacial-related section cropping out at Estancia Ap Iwan includes lower conglomeradic beds, which are reinterpreted as early Jurassic in age, and glacimarine levels that are partially equivalent to the Pampa de Tepuel Formation but older than those of Quebrada de Güera-Peña. A correlation of the Esquel Formation with the Arroyo Pescado Formation and other contemporaneous units on the paleopacific margin is assessed, implying that the Esquel Formation should be segregated from the Tepuel Group. The Esquel and Arroyo Pescado formations can be regarded as the basement of the glaciomarine column of the Tepuel-Genoa Basin.
一条狭窄的上古生界带穿过Quebrada de Güera-Peña(阿根廷巴塔哥尼亚)，在Sierra de Tecka的北端延伸出来。在那里，Pampa de Tepuel组的黑色页岩含有以前被列为“Levipustula”动物群的海洋无脊椎动物化石。作者最近记录的材料，按丰度顺序包括腹足类[Glabrocingulum (Glabrocingulum) poperimense (Maxwell)， G. (Stenozone) argentinum (Reed)， G. (Stenozone) sp.， Peruvispira teckaensis sp. nov.， Ananias riccardii Pinilla]，双壳类[Nuculopsis (Nuculopsis) patagoniensis González, Phestia tepuelensis González, Streblochondria sueroi González, Streblopteria sp.]，圆锥类[Paraconularia cf.ugartei Cúneo和Sabattini]，腕足类[Amosia sueroi Simanauskas，三叶虫[Australosutura argentinensis Hahn and Hahn]，头足类[pseudothoceratidae Flower and Caster]， superoceras ?sp, Mitorthoceras ?[Sp .]和红珊瑚[?][j]。此外，本研究还包括了在特普埃尔-热那亚盆地年轻地区发现的新的关键腕足动物Languigneotus dammanorum gen. et sp. 11和Tuberculatella waterhousei sp. 11。本文提出了langigneotus laevicaudatum和langigneotus - verchojania亚区(宾夕法尼亚州晚期)来取代以前的结核区。此外，还讨论了研究剖面与Arroyo Pescado (Estancia Ap Iwan)和Esquel地区的地层关系和对比。在Estancia Ap Iwan剪出的冰川相关剖面的总体地层剖面包括较低的砾岩层，其年龄被重新解释为早侏罗世，以及部分相当于Pampa de Tepuel组但比Quebrada de Güera-Peña组更古老的冰川海相层。通过对Esquel组与Arroyo Pescado组及古太平洋边缘其他同时期单元的对比分析，认为Esquel组应与Tepuel群相分离。Esquel组和Arroyo Pescado组可视为Tepuel-Genoa盆地冰海柱的基底。
{"title":"Carboniferous deposits of northern Sierra de Tecka, central-western Patagonia, Argentina: paleontology, biostratigraphy and correlations","authors":"A. Taboada, M. A. Pagani, M. K. Pinilla, Franco Tortello, C. A. Taboada","doi":"10.5027/andgeov46n3-3143","DOIUrl":"https://doi.org/10.5027/andgeov46n3-3143","url":null,"abstract":"A narrow upper Paleozoic belt crops out in the northern tip of Sierra de Tecka through the Quebrada de Güera-Peña (Patagonia, Argentina). There, black shales of the Pampa de Tepuel Formation contain marine fossil invertebrates previously listed as belonging to the “Levipustula” fauna. Material recently recorded by the authors comprises, in order of abundance, gastropods [Glabrocingulum (Glabrocingulum) poperimense (Maxwell), G. (Stenozone) argentinum (Reed), G. (Stenozone) sp., Peruvispira teckaensis sp. nov., Ananias riccardii Pinilla], bivalves [Nuculopsis (Nuculopsis) patagoniensis González, Phestia tepuelensis González, Streblochondria sueroi González, Streblopteria sp.], conulariids [Paraconularia cf. ugartei Cúneo and Sabattini], brachiopods [Amosia sueroi Simanauskas, Languigneotus laevicaudatum (Amos), Beecheria patagonica Amos], trilobites [Australosutura argentinensis Hahn and Hahn], cephalopods [Pseudoorthoceratidae Flower and Caster, Sueroceras? sp., Mitorthoceras? sp.], and rugose corals [?Lophophyllidiidae Moore and Jeffords]. In addition, the present study includes the new key brachiopods Languigneotus dammanorum gen. et sp. nov. and Tuberculatella waterhousei sp. nov. from younger localities of the Tepuel-Genoa Basin. The Languigneotus laevicaudatum and Languigneotus-Verchojania subzones (late Pennsylvanian) are proposed herein to replace the former Tuberculatella Zone. In addition, previous stratigraphic relationships and correlations of the study section with the Arroyo Pescado (Estancia Ap Iwan) and Esquel areas are discussed. The general stratigraphic profile of a glacial-related section cropping out at Estancia Ap Iwan includes lower conglomeradic beds, which are reinterpreted as early Jurassic in age, and glacimarine levels that are partially equivalent to the Pampa de Tepuel Formation but older than those of Quebrada de Güera-Peña. A correlation of the Esquel Formation with the Arroyo Pescado Formation and other contemporaneous units on the paleopacific margin is assessed, implying that the Esquel Formation should be segregated from the Tepuel Group. The Esquel and Arroyo Pescado formations can be regarded as the basement of the glaciomarine column of the Tepuel-Genoa Basin.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2019-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46038438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-30DOI: 10.5027/andgeov46n3-3228
T. Pedernera, E. Ottone, A. Mancuso, C. Benavente, F. Abarzúa
In the North of Mendoza Province, at Paramillos de Uspallata locality, Triassic sedimentary rocks outcrop. These Triassic beds are grouped in four formations: Paramillos, Agua de la Zorra, Portezuelo Bayo and Los Colorados. The Agua de la Zorra Formation is characterized by deposition in a deltaic and lacustrine system. The aims of this contribution are: (1) to realize a systematic study of new plant remains found in the Agua de la Zorra Formation and (2) to analize the influence of the potential of preservation and the volcanism in the Agua de la Zorra taphoflora in contrast with other Triassic units. Plant remains were systematically collected and compared with taphofloras from other Triassic formations of the Cuyana Basin. The systematic study from the Agua de la Zorra Formation allowed the determination of 21 taxa, nine of which have been cited in a previous contribution and 12 were described for the first time for the Agua de la Zorra Formation. There are differences in the taxonomic diversity between the taphofloras recovered from Potrerillos and Paramillos formations and these differences are linking with differences in biostratinomic process in each fluvial system and linked with the evidence of volcanic processes in these areas. The differences in diversity in the taphofloras of the Cacheuta and Agua de la Zorra formations can be more associated to ecological differences than variations in the taphonomic processes in each of the lake systems.
在门多萨省北部的Paramillos de Uspallata地区，三叠纪沉积岩露头。这些三叠纪地层分为四个地层：Paramillos、Agua de la Zorra、Portezuelo Bayo和Los Colorados。Agua de la Zorra组的特征是沉积在三角洲和湖泊系统中。这一贡献的目的是：（1）实现对在Agua de la Zorra组中发现的新植物遗骸的系统研究；（2）与其他三叠纪单元相比，分析Agua de la Zorra taphoflora的保存潜力和火山活动的影响。系统地收集了植物遗骸，并将其与库亚纳盆地其他三叠纪地层的taphofloras进行了比较。Agua de la Zorra组的系统研究确定了21个分类群，其中9个分类群已在以前的文章中被引用，12个分类群首次被描述为Agua de la Zorra地层。从Potrerillos和Paramillos地层中发现的taphofloras在分类多样性上存在差异，这些差异与每个河流系统的生物地层学过程的差异有关，并与这些地区火山作用的证据有关。Cacheuta和Agua de la Zorra组taphofloras多样性的差异可能更多地与生态差异有关，而不是与每个湖泊系统的taphonomic过程的变化有关。
{"title":"Syn-Eruptive Taphoflora From The Agua De La Zorra Formation (Upper Triassic) Cuyana Basin, Mendoza, Argentina","authors":"T. Pedernera, E. Ottone, A. Mancuso, C. Benavente, F. Abarzúa","doi":"10.5027/andgeov46n3-3228","DOIUrl":"https://doi.org/10.5027/andgeov46n3-3228","url":null,"abstract":"In the North of Mendoza Province, at Paramillos de Uspallata locality, Triassic sedimentary rocks outcrop. These Triassic beds are grouped in four formations: Paramillos, Agua de la Zorra, Portezuelo Bayo and Los Colorados. The Agua de la Zorra Formation is characterized by deposition in a deltaic and lacustrine system. The aims of this contribution are: (1) to realize a systematic study of new plant remains found in the Agua de la Zorra Formation and (2) to analize the influence of the potential of preservation and the volcanism in the Agua de la Zorra taphoflora in contrast with other Triassic units. Plant remains were systematically collected and compared with taphofloras from other Triassic formations of the Cuyana Basin. The systematic study from the Agua de la Zorra Formation allowed the determination of 21 taxa, nine of which have been cited in a previous contribution and 12 were described for the first time for the Agua de la Zorra Formation. There are differences in the taxonomic diversity between the taphofloras recovered from Potrerillos and Paramillos formations and these differences are linking with differences in biostratinomic process in each fluvial system and linked with the evidence of volcanic processes in these areas. The differences in diversity in the taphofloras of the Cacheuta and Agua de la Zorra formations can be more associated to ecological differences than variations in the taphonomic processes in each of the lake systems.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2019-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41988436","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-30DOI: 10.5027/ANDGEOV46N3-3221
Javiera Peralta-Prato, A. Solórzano
The aquatic sloth, Thalassocnus, is one of the most intriguing lineage of mammal known from the southern pacific coast of South America during the late Neogene. It was initially recognized in Perú, but recent paleontological surveys also recorded its presence in Chile. However, the determination of how many species of Thalassocnus were actually present in Chile remains as an open question. Here, we provide a detailed morphological description of an isolated distal fragment of humerus recovered at the Mina Fosforita member (ca. 7 Ma), Bahía Inglesa Formation (Atacama Region, northern Chile), which is referred to Thalassocnus. Morphological comparisons with others forms from Chile and Perú allow us to attribute the CPUC/C/557 specimen to Thalassocnus cf. T. natans, though some degree of intraspecific variation is acknowledged. The assessment of the stratigraphic provenance of the materials with previously assigned to Thalassocnus from the Bahía Inglesa, Horcón and Coquimbo formations, permits us to propose that the taxonomic diversity of Thalassocnus in Chile is unequivocal conformed by T. carolomartini, and T. natans. We also admitted the likely presence of T. antiquus and probably T. yaucensis. Futures discoveries of more complete specimens, and/or the detailed analysis of undescribed specimens from Chile will undoubtedly contribute to illustrate the evolutionary history of the Thalassocnus radiation in Chile.
{"title":"How many species of the aquatic sloth Thalassocnus (Xenarthra: Megatheriidae) were in Chile?: new evidences from the Bahía Inglesa Formation, with a reappraisal of their biochronological affinities","authors":"Javiera Peralta-Prato, A. Solórzano","doi":"10.5027/ANDGEOV46N3-3221","DOIUrl":"https://doi.org/10.5027/ANDGEOV46N3-3221","url":null,"abstract":"The aquatic sloth, Thalassocnus, is one of the most intriguing lineage of mammal known from the southern pacific coast of South America during the late Neogene. It was initially recognized in Perú, but recent paleontological surveys also recorded its presence in Chile. However, the determination of how many species of Thalassocnus were actually present in Chile remains as an open question. Here, we provide a detailed morphological description of an isolated distal fragment of humerus recovered at the Mina Fosforita member (ca. 7 Ma), Bahía Inglesa Formation (Atacama Region, northern Chile), which is referred to Thalassocnus. Morphological comparisons with others forms from Chile and Perú allow us to attribute the CPUC/C/557 specimen to Thalassocnus cf. T. natans, though some degree of intraspecific variation is acknowledged. The assessment of the stratigraphic provenance of the materials with previously assigned to Thalassocnus from the Bahía Inglesa, Horcón and Coquimbo formations, permits us to propose that the taxonomic diversity of Thalassocnus in Chile is unequivocal conformed by T. carolomartini, and T. natans. We also admitted the likely presence of T. antiquus and probably T. yaucensis. Futures discoveries of more complete specimens, and/or the detailed analysis of undescribed specimens from Chile will undoubtedly contribute to illustrate the evolutionary history of the Thalassocnus radiation in Chile.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2019-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45839873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-30DOI: 10.5027/andgeov46n3-3127
J. Bodnar, A. Iglesias, C. Colombi, J. Drovandi
The northern area of Cuyo Basin (west‐central Argentina) corresponds to the Rincón Blanco half-graben, whose filling is arranged into the Rincón Blanco and Sorocayense groups. In the present study, we propose a new stratigraphic scheme for the Sorocayense Group in the Barreal depocenter (San Juan Province), revise the palaeoenvironmental interpretations, and organize and analyse the plant assemblages of previous and new fossiliferous levels. We defined three tectosedimentary sequences. The basal sequence represents the initial graben filling with pyroclastic flows, alluvial fan, and ephemeral fluvial systems, and is arranged in a new unit, the Cerro Colorado del Cementerio Formation. The middle sequence, including Barreal and Cortaderita formations, is characterized by sediment gravity flow deposits and different fluvial systems, with development of floodplains with vertisols and calcisols, and temporal ponds/lakes. In turn, the Cortaderita Formation was divided into the following lithostratigraphic members: Don Raúl and La Emilia. The upper sequence, represented by Cepeda Formation, was deposited by distributary fluvial and ephemeral fluvial systems. Twelve fossiliferous strata (EF) were recognized, which were all identified in the middle sequence: EF1 to EF3 in the Barreal Formation, EF4 to EF8 in the Don Raúl Member, and EF9 to EF12 in the La Emilia Member, both of Cortaderita Formation. The taphocoenosis found in the Barreal and Cortaderita formations were dominated by corystosperms, with conifers, cycadales, and peltasperms as subordinate forms. The available evidence from the taphofloras, palaeosols and palaeonvironments indicate the development of seasonal subtropical climates, which vary from arid or semi-arid in the basal sequence, sub-humid to semi-arid in the middle sequence, and arid or semi-arid in the upper sequence. On the basis of the new information, geological correlation and age of the lithostratigraphic units were accurately re-evaluated. Based on the palaeofloristic content and the correlation with the Rincón Blanco Group, it is possible to infer that the basal sequence was accumulated during late Early Triassic-early Middle Triassic, the middle sequence during the Middle Triassic, while the upper sequence was deposited in the early Late Triassic.
{"title":"Stratigraphical, sedimentological and palaeofloristic characterization of the Sorocayense Group (Triassic) in Barreal depocenter, San Juan Province, Argentina","authors":"J. Bodnar, A. Iglesias, C. Colombi, J. Drovandi","doi":"10.5027/andgeov46n3-3127","DOIUrl":"https://doi.org/10.5027/andgeov46n3-3127","url":null,"abstract":"The northern area of Cuyo Basin (west‐central Argentina) corresponds to the Rincón Blanco half-graben, whose filling is arranged into the Rincón Blanco and Sorocayense groups. In the present study, we propose a new stratigraphic scheme for the Sorocayense Group in the Barreal depocenter (San Juan Province), revise the palaeoenvironmental interpretations, and organize and analyse the plant assemblages of previous and new fossiliferous levels. We defined three tectosedimentary sequences. The basal sequence represents the initial graben filling with pyroclastic flows, alluvial fan, and ephemeral fluvial systems, and is arranged in a new unit, the Cerro Colorado del Cementerio Formation. The middle sequence, including Barreal and Cortaderita formations, is characterized by sediment gravity flow deposits and different fluvial systems, with development of floodplains with vertisols and calcisols, and temporal ponds/lakes. In turn, the Cortaderita Formation was divided into the following lithostratigraphic members: Don Raúl and La Emilia. The upper sequence, represented by Cepeda Formation, was deposited by distributary fluvial and ephemeral fluvial systems. Twelve fossiliferous strata (EF) were recognized, which were all identified in the middle sequence: EF1 to EF3 in the Barreal Formation, EF4 to EF8 in the Don Raúl Member, and EF9 to EF12 in the La Emilia Member, both of Cortaderita Formation. The taphocoenosis found in the Barreal and Cortaderita formations were dominated by corystosperms, with conifers, cycadales, and peltasperms as subordinate forms. The available evidence from the taphofloras, palaeosols and palaeonvironments indicate the development of seasonal subtropical climates, which vary from arid or semi-arid in the basal sequence, sub-humid to semi-arid in the middle sequence, and arid or semi-arid in the upper sequence. On the basis of the new information, geological correlation and age of the lithostratigraphic units were accurately re-evaluated. Based on the palaeofloristic content and the correlation with the Rincón Blanco Group, it is possible to infer that the basal sequence was accumulated during late Early Triassic-early Middle Triassic, the middle sequence during the Middle Triassic, while the upper sequence was deposited in the early Late Triassic.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2019-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47412599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-30DOI: 10.5027/ANDGEOV46N3-3189
S. Heredia, Ana Mestre
The Middle-Upper Ordovician Ponón Trehué Formation cropping out in the San Rafael Block (Argentina) provided a large collection of conodonts which have been published years ago. The species Eoplacognathus robustus and Eoplacognathus lindstroemi recovered from these strata have been revised and restudied. In this contribution we describe M and S elements that were assigned previously to Baltoniodus prevariabilis and Baltoniodus variabilis as belonging to the E. robustus and E. lindstroemi apparatuses. The morphological characters of the P, S and M elements as part of these late Eoplacognathus apparatus were analyzed and support the proposal of a new reconstruction of it. We have compared this apparatus with the Baltoniodus apparatus and suggest the inclusion of the Eoplacognathus genus into the Balognathidae family. The new architecture of the Eoplacognathus apparatus is comparable to the genus Lenodus. This analysis improves the knowledge about this index conodont group allowing a new insight on the evolution, phylogeny and paleobiology of this linage.
San Rafael地块（阿根廷）中上奥陶世Ponón Trehué组提供了多年前出版的大量牙形石。对从这些地层中恢复的Eoplaconagnathus robustus和Eoplacanagnathus lindstroemi物种进行了修订和重新研究。在这篇文章中，我们描述了以前分配给前变巴尔托诺杜和可变巴尔托诺杜属的M和S元素，它们属于粗壮E.robustus和林氏E.lindstroemi装置。分析了作为这些晚期始氏器一部分的P、S和M元素的形态特征，并支持对其进行新的重建的建议。我们将该器与Baltoniodus器进行了比较，并建议将始氏器属纳入Balognatidae科。Eoplancognathus装置的新结构可与Lenodus属相媲美。这一分析提高了对该指数牙形石群的了解，从而对该谱系的进化、系统发育和古生物学有了新的认识。
{"title":"The Middle Ordovician conodonts Eoplacognathus robustus Bergström and E. lindstroemi (Hamar): Taxonomy and apparatus reconstruction","authors":"S. Heredia, Ana Mestre","doi":"10.5027/ANDGEOV46N3-3189","DOIUrl":"https://doi.org/10.5027/ANDGEOV46N3-3189","url":null,"abstract":"The Middle-Upper Ordovician Ponón Trehué Formation cropping out in the San Rafael Block (Argentina) provided a large collection of conodonts which have been published years ago. The species Eoplacognathus robustus and Eoplacognathus lindstroemi recovered from these strata have been revised and restudied. In this contribution we describe M and S elements that were assigned previously to Baltoniodus prevariabilis and Baltoniodus variabilis as belonging to the E. robustus and E. lindstroemi apparatuses. The morphological characters of the P, S and M elements as part of these late Eoplacognathus apparatus were analyzed and support the proposal of a new reconstruction of it. We have compared this apparatus with the Baltoniodus apparatus and suggest the inclusion of the Eoplacognathus genus into the Balognathidae family. The new architecture of the Eoplacognathus apparatus is comparable to the genus Lenodus. This analysis improves the knowledge about this index conodont group allowing a new insight on the evolution, phylogeny and paleobiology of this linage.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2019-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44662150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-30DOI: 10.5027/andgeov46n3-3198
Carlos D. Ramacciotti, C. Casquet, Edgardo G. Baldo, Sebastián O. Verdecchia, Matías Martín Morales, Priscila Soledad Zandomeni
The Sierra de Pie de Palo (SPP, Western Sierras Pampeanas) shows evidence of two regional metamorphisms: one Mesoproterozoic attributed to the Grenvillian orogeny and other of Ordovician age related to the Famatinian orogeny. The Neoproterozoic-to-Cambrian sedimentary successions that cover the Grenvillian basement only record the Ordovician event. One staurolite-schist from the Ediacaran Difunta Correa Metasedimentary Sequence collected in the southeastern side of the SPP allows to constrain, by means of pseudosections, a prograde evolution from ca. 3 kbar and 515 ºC up to ca. 9 kbar and 640 ºC corresponding to a high P/T gradient. The SPP and the immediately east Loma de Las Chacras outcrop were part of the famatinian forearc which shows a progressive decrease of P (from ca. 13 kbar to 6 kbar), T (from ca. 900 ºC to 450 ºC), and P/T gradient (from ca. 85 ºC/kbar to 35 ºC/kbar) towards the active continental margin on the west. The Caucete Group, in the western side of the SPP, represents the westernmost part of the forearc, near to the active continental margin. Metamorphism was apparently coeval with the Famatinian magmatism and with ductile underthrusting at ca. 470-465 Ma, which led to burial of the forearc beneath the magmatic arc.
Sierra de Pie de Palo（SPP，West Sierras Pampeanas）显示了两种区域变质作用的证据：一种是属于格伦维尔造山运动的中元古代，另一种是与法马汀造山运动有关的奥陶纪。覆盖格伦维尔期基底的新元古代至寒武纪沉积序列仅记录了奥陶纪事件。SPP东南侧采集的埃迪卡拉纪Difunta Correa变质沉积序列中的一片十字石片岩，可通过假剖面限制从约3kbar和515ºC到约9kbar和640ºC的前进演化，对应于高P/T梯度。SPP和紧邻东部的Loma de Las Chacras露头是法马汀阶前弧的一部分，该前弧显示P（从约13 kbar到6 kbar）、T（从约900ºC到450ºC）和P/T梯度（从约85ºC/kbar到35ºC/kbal）向西部活动大陆边缘逐渐降低。位于SPP西侧的Caucet群代表弧前最西部，靠近活动大陆边缘。变质作用显然与大约470-465Ma的法马汀期岩浆作用和韧性低推力同时发生，这导致弧前埋藏在岩浆弧下。
{"title":"Metamorfismo de alto gradiente P/T en la Sierra de Pie de Palo (Sierras Pampeanas, Argentina): modelado de equilibrio de fases minerales e implicancias geodinámicas en el antearco famatiniano","authors":"Carlos D. Ramacciotti, C. Casquet, Edgardo G. Baldo, Sebastián O. Verdecchia, Matías Martín Morales, Priscila Soledad Zandomeni","doi":"10.5027/andgeov46n3-3198","DOIUrl":"https://doi.org/10.5027/andgeov46n3-3198","url":null,"abstract":"The Sierra de Pie de Palo (SPP, Western Sierras Pampeanas) shows evidence of two regional metamorphisms: one Mesoproterozoic attributed to the Grenvillian orogeny and other of Ordovician age related to the Famatinian orogeny. The Neoproterozoic-to-Cambrian sedimentary successions that cover the Grenvillian basement only record the Ordovician event. One staurolite-schist from the Ediacaran Difunta Correa Metasedimentary Sequence collected in the southeastern side of the SPP allows to constrain, by means of pseudosections, a prograde evolution from ca. 3 kbar and 515 ºC up to ca. 9 kbar and 640 ºC corresponding to a high P/T gradient. The SPP and the immediately east Loma de Las Chacras outcrop were part of the famatinian forearc which shows a progressive decrease of P (from ca. 13 kbar to 6 kbar), T (from ca. 900 ºC to 450 ºC), and P/T gradient (from ca. 85 ºC/kbar to 35 ºC/kbar) towards the active continental margin on the west. The Caucete Group, in the western side of the SPP, represents the westernmost part of the forearc, near to the active continental margin. Metamorphism was apparently coeval with the Famatinian magmatism and with ductile underthrusting at ca. 470-465 Ma, which led to burial of the forearc beneath the magmatic arc.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2019-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46321397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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