Mineralogía y sedimentología de la formación Sierras Bayas en el núcleo septentrional de las sierras homónimas, partido de Olavarría, provincia de Buenos Aires

Tesis presentada para optar al Grado de Doctor en Ciencias NaturalesFil: Poiré, Daniel Gustavo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentin

Diversity, taphonomy and palaeoecology of an angiosperm flora from the cretaceous (Cenomanian-Coniacian) in Southern Patagonia, Argentina

This paper describes the diversity, taphonomy and palaeoecology of angiosperm leaves that dominate a palaeoflora of Cretaceous (Cenomanian-Coniacian) age from the Mata Amarilla Formation in the Austral Basin, south-west Patagonia, Argentina. Twelve morphotypes of angiosperm leaves are recognized based on foliar morphotype analysis of more than 500 specimens. These were divided into six morphological groups based on major architectural patterns. The relative dominance of these morphotypes, mode of preservation and relationship with sedimentary facies were evaluated from two levels within the formation. This analysis identified two different plant palaeocommunities. The lower, María Elena, level (MEL) was deposited in a marine coastal area on a subaerial delta plain; the dominant angiosperm morphotypes preserved in it are group 1 (MA100) and group 2 (MA101, 102); morphotypes MA109 and 110 are scarce but exclusive to this level. The upper, Mata Amarilla, level (MAL), accumulated inland in flood-plain environments; the most abundant angiosperm morphotypes are groups 3 (MA103-105), 4 (MA106) and 1 (MA100); morphotypes MA103-105 and 108 are exclusive to this level. Comparisons with other floras of similar age from Antarctica, Australia and New Zealand indicate that the Mata Amarilla flora has a slightly higher morphological diversity of angiosperm leaves, providing the first evidence for an angiosperm-dominated early Late Cretaceous macroflora in south-west Gondwana.Facultad de Ciencias Naturales y Muse

Rocks For Grinding: Lithic Raw Material Provenience Studies Of Grinding Technology, Interserrana Area Of Buenos Aires Province, Argentina

Los artefactos de molienda representan frecuentemente grandes volúmenes de roca trasportados a los sitios arqueológicos del área Interserrana Bonaerense. En el contexto de los recientes estudios sistemáticos en relación a estos artefactos, en este trabajo se presentan los resultados de los análisis petrográficos macroscópicos, de cortes delgados y de difracción de rayos X de una muestra de instrumentos confeccionados sobre materias primas sedimentarias y metamórficas. De manera complementaria, se consideran características de las formas-base y los pesos de parte de los artefactos estudiados. Los datos obtenidos se discuten respecto a la procedencia y estrategias de explotación de estos recursos líticos utilizados para los artefactos de molienda. Se identificó en los conjuntos estudiados el uso de rocas disponibles en afloramientos de los sistemas serranos pampeanos de Tandilia y Ventania e interserranos. El trasladado de estas materias primas líticas a los contextos bajo estudio implicaron diferentes esfuerzos de aprovisionamiento (locales, de media y de larga distancia). Las características petrográficas de las rocas seleccionadas para la producción de los artefactos de molienda se relacionan principalmente con una alta capacidad abrasiva. En algunos casos, se habrían aprovechado formas-base naturales aptas para ser usadas sin modificaciones previas. Estos datos comprenden un primer acercamiento a la gestión de recursos líticos para la manufactura y/o uso de artefactos de molienda por parte de grupos cazadores-recolectores prehispánicos pampeanos durante el Holoceno tardío.Grinding tools frequently comprise great volumes of rocks transported to the archaeological sites of the Interserrana area of Buenos Aires Province. The results from thin section and X-ray diffraction analyses of a sample of grinding artifacts manufactured from sedimentary and metamorphic raw material are presented in this paper in the context of recent systematic studies in relation to these tools. In addition, characteristics of blanks and weights of part of the sample studied are considered. These data are discussed in relation to provenience and exploitation strategies of the lithic raw material used for grinding tools. The use of rocks available on the Pampean ranges of Tandilia and Ventania and minor outcrops in the Interserrana area were identifi ed for the studied assemblages. The transport of these raw materials implied different procurements efforts (of local, middle and long distance). The rocks selected for the production of grinding tools had the petrographic characteristic of a high abrasive capacity. In some cases, natural blanks have been selected for use without any previous modifi cation. These data comprise a preliminary approach to the management of lithic resources for the manufacture and/or use of grinding tools by prehispanic Pampean hunter-gatherers during the Late Holocene.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones Geológica

Diversity, taphonomy and palaeoecology of an angiosperm flora from the cretaceous (Cenomanian-Coniacian) in Southern Patagonia, Argentina

This paper describes the diversity, taphonomy and palaeoecology of angiosperm leaves that dominate a palaeoflora of Cretaceous (Cenomanian-Coniacian) age from the Mata Amarilla Formation in the Austral Basin, south-west Patagonia, Argentina. Twelve morphotypes of angiosperm leaves are recognized based on foliar morphotype analysis of more than 500 specimens. These were divided into six morphological groups based on major architectural patterns. The relative dominance of these morphotypes, mode of preservation and relationship with sedimentary facies were evaluated from two levels within the formation. This analysis identified two different plant palaeocommunities. The lower, María Elena, level (MEL) was deposited in a marine coastal area on a subaerial delta plain; the dominant angiosperm morphotypes preserved in it are group 1 (MA100) and group 2 (MA101, 102); morphotypes MA109 and 110 are scarce but exclusive to this level. The upper, Mata Amarilla, level (MAL), accumulated inland in flood-plain environments; the most abundant angiosperm morphotypes are groups 3 (MA103-105), 4 (MA106) and 1 (MA100); morphotypes MA103-105 and 108 are exclusive to this level. Comparisons with other floras of similar age from Antarctica, Australia and New Zealand indicate that the Mata Amarilla flora has a slightly higher morphological diversity of angiosperm leaves, providing the first evidence for an angiosperm-dominated early Late Cretaceous macroflora in south-west Gondwana.Facultad de Ciencias Naturales y Muse

Rocks For Grinding: Lithic Raw Material Provenience Studies Of Grinding Technology, Interserrana Area Of Buenos Aires Province, Argentina

Los artefactos de molienda representan frecuentemente grandes volúmenes de roca trasportados a los sitios arqueológicos del área Interserrana Bonaerense. En el contexto de los recientes estudios sistemáticos en relación a estos artefactos, en este trabajo se presentan los resultados de los análisis petrográficos macroscópicos, de cortes delgados y de difracción de rayos X de una muestra de instrumentos confeccionados sobre materias primas sedimentarias y metamórficas. De manera complementaria, se consideran características de las formas-base y los pesos de parte de los artefactos estudiados. Los datos obtenidos se discuten respecto a la procedencia y estrategias de explotación de estos recursos líticos utilizados para los artefactos de molienda. Se identificó en los conjuntos estudiados el uso de rocas disponibles en afloramientos de los sistemas serranos pampeanos de Tandilia y Ventania e interserranos. El trasladado de estas materias primas líticas a los contextos bajo estudio implicaron diferentes esfuerzos de aprovisionamiento (locales, de media y de larga distancia). Las características petrográficas de las rocas seleccionadas para la producción de los artefactos de molienda se relacionan principalmente con una alta capacidad abrasiva. En algunos casos, se habrían aprovechado formas-base naturales aptas para ser usadas sin modificaciones previas. Estos datos comprenden un primer acercamiento a la gestión de recursos líticos para la manufactura y/o uso de artefactos de molienda por parte de grupos cazadores-recolectores prehispánicos pampeanos durante el Holoceno tardío.Grinding tools frequently comprise great volumes of rocks transported to the archaeological sites of the Interserrana area of Buenos Aires Province. The results from thin section and X-ray diffraction analyses of a sample of grinding artifacts manufactured from sedimentary and metamorphic raw material are presented in this paper in the context of recent systematic studies in relation to these tools. In addition, characteristics of blanks and weights of part of the sample studied are considered. These data are discussed in relation to provenience and exploitation strategies of the lithic raw material used for grinding tools. The use of rocks available on the Pampean ranges of Tandilia and Ventania and minor outcrops in the Interserrana area were identifi ed for the studied assemblages. The transport of these raw materials implied different procurements efforts (of local, middle and long distance). The rocks selected for the production of grinding tools had the petrographic characteristic of a high abrasive capacity. In some cases, natural blanks have been selected for use without any previous modifi cation. These data comprise a preliminary approach to the management of lithic resources for the manufacture and/or use of grinding tools by prehispanic Pampean hunter-gatherers during the Late Holocene.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones Geológica

Atlantocerus, a new genus of lungfish from the upper cretaceous of South America and Africa

Fil: Cione, Alberto Luis. Departamento Paleontología Vertebrados, Museo de La PlataFil: Gouiric-Cavalli, Soledad. Departamento Paleontología Vertebrados, Museo de La PlataFil: Goin, Francisco Javier. Departamento Paleontología Vertebrados, Museo de La PlataFil: Poiré, Daniel Gustavo. Departamento Paleontología Vertebrados, Museo de La Plat

Trace fossils in subtidal bars from the Balcarce Formation (Cambrian/Ordovician), Cabo Corrientes, Mar del Plata, Argentina

Cambrian/Ordovician trace fossil assemblages from the Balcarce Formation are described. In the Cabo Corrientes outcrops at the Atlantic coast, four sedimentary facies are distinguished as follows: a) Pebble Sandstone Facies with progradation surfaces and no evidence of bioturbation; b) Crossbedded Sandstone Facies in tabular and lenticular sand bodies with rare Palaeophycus isp.; c) Heterolithic Facies with wavy bedding bearing Daedalus labeckei, Herradurichnus scagliai, Rusophycus isp.. Scolicia isp., and Teichichnus isp.; and d) Sandy Heterolithic Facies with Herradurichnus scagliai and Scalicia isp. This sedimentary succession is considered here as interbar, bar margin, and central bar facies in a subtidal environment on an open marine shelf. Ethologically, two principal trace fossil assemblages are recognised. Both assemblages are closely associated with sedimentary facies and specific colonising events may be distinguished. The first assemblage consists of Rusophycus isp. and Herradurichnus scagliai, which occur as furrows on the substrate at the water-sediment interface. The second one is composed of Daedalus labeckei, Scalicia isp. and Teichichnus isp., which are post-depositional burrows developed a few centimeters below the sediment surface by sediment feeding organisms. From this study, the palaeoenvironmental history of the bioturbation of this shelf bar deposit can be summarised. Firstly synsedimentary ichnofossils developed in interbar and bar margin heterolithic deposits. Secondly, these deposits were buried by vertical accretion of migrating sand waves, and then mud feeding organisms started working below the sediment surface living on the available nutrients in the wavy bedded heterolithic facies. Simultaneously, in the overlying new interbar and bar margin facies similar syndepositational traces were developed.Cambrian/Ordovician trace fossil assemblages from the Balcarce Formation are described. In the Cabo Corrientes outcrops at the Atlantic coast, four sedimentary facies are distinguished as follows: a) Pebble Sandstone Facies with progradation surfaces and no evidence of bioturbation; b) Crossbedded Sandstone Facies in tabular and lenticular sand bodies with rare Palaeophycus isp.; c) Heterolithic Facies with wavy bedding bearing Daedalus labeckei, Herradurichnus scagliai, Rusophycus isp.. Scolicia isp., and Teichichnus isp.; and d) Sandy Heterolithic Facies with Herradurichnus scagliai and Scalicia isp. This sedimentary succession is considered here as interbar, bar margin, and central bar facies in a subtidal environment on an open marine shelf. Ethologically, two principal trace fossil assemblages are recognised. Both assemblages are closely associated with sedimentary facies and specific colonising events may be distinguished. The first assemblage consists of Rusophycus isp. and Herradurichnus scagliai, which occur as furrows on the substrate at the water-sediment interface. The second one is composed of Daedalus labeckei, Scalicia isp. and Teichichnus isp., which are post-depositional burrows developed a few centimeters below the sediment surface by sediment feeding organisms. From this study, the palaeoenvironmental history of the bioturbation of this shelf bar deposit can be summarised. Firstly synsedimentary ichnofossils developed in interbar and bar margin heterolithic deposits. Secondly, these deposits were buried by vertical accretion of migrating sand waves, and then mud feeding organisms started working below the sediment surface living on the available nutrients in the wavy bedded heterolithic facies. Simultaneously, in the overlying new interbar and bar margin facies similar syndepositational traces were developed.Facultad de Ciencias Naturales y Muse

Atlantoceratodus a new genus of lungfish from the upper Cretaceous of South America and Africa

The only previously known material of “Ceratodus” iheringi Ameghino, 1898 (the hoiotype, a tooth píate) was collected by Carlos Ameghino along with other marine and freshwater fossils in the “Piso Shehuenense” in Pari Aike, Río Shehuen, Southern Patagonia. The material was figured but not described. Fortunately, the hoiotype was preserved in the Museo de La Plata. The bearing beds are presently included in the Mata Amarilla Formation which is considered Cenomanian-Coniasian in age. Additional lungfish material from the Southern part of Mendoza and Río Negro provinces was erroneously reponed by several authors to this species.In the present contribution, based on about 200 complete and fragmentary tooth plates from the type locality, we describe and diagnose the species “Ceratodus ” iheringi and a new genus, Atlantoceratodus. The species appears to be only known in the type area. Atlantoceratodus iheringi most closely resembles “Ceratodus " madagascariensis Priem, 1924 from the upper Cretaceous (Campanian) of Madagascar and we suggest that both species pertain to the same genus.Facultad de Ciencias Naturales y Muse

Miembro psamopelitas de la Formación Sierras Bayas, partido de Olavarría, provincia de Buenos Aires

Fil: Poiré, Daniel Gustavo. Centro de Investigaciones Geológicas, Facultad de Ciencias Naturales y Museo, UNLPFil: Iñiguez Rodríguez, Adrián Mario. Centro de Investigaciones Geológicas, Facultad de Ciencias Naturales y Museo, UNL

Evolución paleoambiental de la Formación Río Mayer, Cretácico Inferior, Cuenca Austral, Provincia de Santa Cruz, Argentina.

La Formación Río Mayer es parte del relleno inicial de la Cuenca Austral, la cual se ubica en el sector más austral de la Patagonia. El área de estudio se encuentra entre los lagos San Martín y Argentino (Provincia de Santa Cruz), donde se relevaron diez perfiles sedimentológicos de detalle en los que se describieron 18 facies sedimentarias. Estas facies responden a diferentes procesos sedimentarios, principalmente autigénicos, hemipelágicos y episódicos. A partir de la distribución de las facies y del origen del material fósil se reconocieron tres asociaciones de facies que representan paleoambientes sedimentarios: marino de plataforma externa, marino de plataforma externa con influencia deltaica y prodelta. El análisis de la distribución espacial y temporal de las facies condujo a la elaboración de un esquema de evolución paleoambiental para el Cretácico Inferior de la Cuenca Austral en la zona estudiada. La depositación de la Formación Río Mayer, por encima de la Formación Springhill, en el área de la Seccional Río Guanaco, comenzó durante el Berriasiano. En el Valanginiano la transgresión generó los depósitos incluidos en la Formación Springhill en la región de Lago San Martín, mientras que en el intervalo Hauteriviano-Barremiano toda el área de estudio presentaba características de plataforma externa distal. Durante el lapso temporal Aptiano-Albiano, se produjo la instalación de un sistema deltaico (Formación Piedra Clavada / Kachaike) en el norte del área de estudio entre los lagos San Martín y Viedma. Para este intervalo temporal la Formación Río Mayer en las regiones de Lago San Martín y Estancia La Vega, representa un ambiente de prodelta. Paralelamente, en la región sur del área de estudio se produjo la sedimentación de los niveles incluidos en un ambiente de plataforma externa influenciada por flujos turbidíticos distales de frente deltaico. Finalmente durante el Albiano superior-Cenomaniano inferior se desarrolló una transgresión marina, que marca el comienzo de la etapa de antepaís de la Cuenca Austral. En la región de los lagos San Martín y Viedma, la transgresión está evidenciada por los depósitos litorales de la Formación Mata Amarilla, mientras que en la región de Río Guanaco es representada por los depósitos de la Formación Cerro Toro