Post-depositional effects on the microstructure and stable isotopes composition of planktic foraminiferal tests from the Miocene of the Pelotas Basin, south Brazilian continental margin

An integrated study of planktic foraminiferal tests (Orbulina universa and Globigerinoides trilobus) imaging techniques and chemical/isotopic analyses has been carried out at the Miocene section of the Pelotas Basin (South Brazil) with the purpose of record and evaluate the effects of the diagenesis in its wall texture and isotopic composition. The characterization of the foraminiferal tests preservation prior performing isotopic analysis for paleoceanographic studies is essential to ensure the choice of suitable material for obtaining reliable data. Scanning electron microscopy, backscatter scanning electron microscopy, energy-dispersive X-ray spectrometry and stable isotope measurements were used to evaluate the post-depositional effects on the tests. It was possible to identify features of dissolution, neomorphism (recrystallization) and coating of autigenic minerals. The stable isotopic data defi ne two compositional groups. The heavier and less scattered values characterize a preserved paleoenvironmental signal as the lighter and scattered ones indicate a signal derived from post-depositional alterations. Additionally, the characterization of the distinct types of diagenetic changes and their textural products provide a guideline for the evaluation of the diagenetic effects of deeply buried fossil foraminifera.Un estudio integrado de las características de textura y composición química e isotópica de foraminíferos planctónicos (Orbulina universa y Globigerinoides trilobus) del Mioceno de la Cuenca de Pelotas (sur de Brasil) fue llevado a cabo con el propósito de registrar y evaluar los efectos de la diagénesis. La caracterización del grado de preservación de los foraminíferos, previa a la obtención de análisis isotópicos para estudios paleoceanográfi cos, es esencial para asegurar una selección adecuada del material y así obtener datos fi ables. Se empleó microscopía electrónica de barrido, imágenes con Planktic foraminiferal tests: Post-depositional effects on the microstructure and isotopic composition electrones retrodispersados, espectroscopía de rayos X de dispersión de energía y mediciones de isótopos estables para evaluar los efectos post-depósito en los caparazones. Esos estudios permitieron identifi car características de disolución, recristalización y revestimiento de minerales autigénicos. Los datos de isótopos estables permitieron defi nir dos grupos de composición: los valores más pesados y menos dispersos caracterizan señales paleoambientales preservadas, mientras que los datos más dispersos y correspondientes a composiciones más ligeras indican una señal derivada de las alteraciones postdepósito. Además, la caracterización de los distintos tipos de cambios diagenéticos y sus productos texturales proporciona una guía para la evaluación de los efectos diagenéticos en los foraminíferos fósiles provenientes de secciones sedimentarias de gran espesor

Metallogeny of Cerro dos Martins Cu-Deposit, RS: Review and Isotopic Geochemistry of Sr, S, O and C

This paper presents the geology, chemical data, Pb-Pb zircon ages, sulfur, carbon, oxygen, strontium isotopes and fluid inclusions of Cerro dos Martins copper deposit. The deposit is hosted by the Neoproterozoic volcano-sedimentary sequence of the Camaquã Basin in the Rio Grande do Sul Shield, southern Brazil. The ores consist of a set of Cu-sulfide NW-trending veins and disseminations within of the Bom Jardim Group. Chalcocite and bornite are the main ore minerals, whereas carbonates, barite, quartz and hematite are the gangue. The volcanic host rocks show an alkaline affinity. An intrusive quartz-diorite body, also shown alkaline affinity, yield a 550±5 Ma zircon age (initial 87Sr/86Sr of 0,704), which is considered the minimum age of the copper mineralization. The δ34SCDT of sulfides ranges from –6.2 to +0.9‰. Hematite in the mineral paragenesis suggests oxidizing conditions, which would shift the original magmatic sulfur isotopic compositions (δ34S ~ 0‰) to negative values. Barite with δ34SCDT from +9.25 to +10.65‰ may also indicate oxidation due to mixing of a hot rising fluid with cold meteoric water. The δ13CPDB of calcite from gangue, in the range of – 1,90 to – 4,45% is interpreted as originated from mixing sources – magmatic and fluids contaminated by basement marbles. Studies on primary aqueous biphasic fluid inclusions show homogenisation temperatures with average of 215°C. Water in equilibrium with calcite from hydrothermal fluid show calculated values of δ O18 SMOW between 3 and 14‰, suggesting derivation from a magmatic source with some contributions from meteoric water. 87Sr/86Sr from these calcite show values between 0, 7068 – 0, 7087, typical from upper crust. Hence, the Cerro dos Martins copper deposit is interpreted to have had origin by a mixing between a magmatic-hydrotermal fluids related to the alkaline-shoshonitic, post-collisional magmatic event (595-550 Ma) of the Dom Feliciano Orogeny and basement rocks. Exploration models for copper deposits in this shield should consider the alkaline magmatism in the genesis of deposits

Metalogênese do depósito de cobre Cerro dos Martins, RS: revisão e geoquímica isotópica de SR, O e C-

This paper presents the geology, chemical data, Pb-Pb zircon ages, sulfur, carbon, oxygen, strontium isotopes and fluid inclusions of Cerro dos Martins copper deposit. The deposit is hosted by the Neoproterozoic volcano-sedimentary sequence of the Camaquã Basin in the Rio Grande do Sul Shield, southern Brazil. The ores consist of a set of Cu-sulfide NW-trending veins and disseminations within of the Bom Jardim Group. Chalcocite and bornite are the main ore minerals, whereas carbonates, barite, quartz and hematite are the gangue. The volcanic host rocks show an alkaline affinity. An intrusive quartz-diorite body, also shown alkaline affinity, yield a 550±5 Ma zircon age (initial 87Sr/86Sr of 0,704), which is considered the minimum age of the copper mineralization. The d34SCDT of sulfides ranges from –6.2 to +0.9‰. Hematite in the mineral paragenesis suggests oxidizing conditions, which would shift the original magmatic sulfur isotopic compositions (d34S ~ 0‰) to negative values. Barite with d34SCDT from +9.25 to +10.65‰ may also indicate oxidation due to mixing of a hot rising fluid with cold meteoric water. The d13CPDB of calcite from gangue, in the range of – 1,90 to – 4,45% is interpreted as originated from mixing sources – magmatic and fluids contaminated by basement marbles. Studies on primary aqueous biphasic fluid inclusions show homogenisation temperatures with average of 215°C. Water in equilibrium with calcite from hydrothermal fluid show calculated values of d O18 SMOW between 3 and 14‰, suggesting derivation from a magmatic source with some contributions from meteoric water. 87Sr/86Sr from these calcite show values between 0, 7068 – 0, 7087, typical from upper crust. Hence, the Cerro dos Martins copper deposit is interpreted to have had origin by a mixing between a magmatic-hydrotermal fluids related to the alkaline-shoshonitic, post-collisional magmatic event (595-550 Ma) of the Dom Feliciano Orogeny and basement rocks. Exploration models for copper deposits in this shield should consider the alkaline magmatism in the genesis of deposits

Metalogênese do depósito de cobre Cerro dos Martins, RS: revisão e geoquímica isotópica de SR, O e C-

This paper presents the geology, chemical data, Pb-Pb zircon ages, sulfur, carbon, oxygen, strontium isotopes and fluid inclusions of Cerro dos Martins copper deposit. The deposit is hosted by the Neoproterozoic volcano-sedimentary sequence of the Camaquã Basin in the Rio Grande do Sul Shield, southern Brazil. The ores consist of a set of Cu-sulfide NW-trending veins and disseminations within of the Bom Jardim Group. Chalcocite and bornite are the main ore minerals, whereas carbonates, barite, quartz and hematite are the gangue. The volcanic host rocks show an alkaline affinity. An intrusive quartz-diorite body, also shown alkaline affinity, yield a 550±5 Ma zircon age (initial 87Sr/86Sr of 0,704), which is considered the minimum age of the copper mineralization. The d34SCDT of sulfides ranges from –6.2 to +0.9‰. Hematite in the mineral paragenesis suggests oxidizing conditions, which would shift the original magmatic sulfur isotopic compositions (d34S ~ 0‰) to negative values. Barite with d34SCDT from +9.25 to +10.65‰ may also indicate oxidation due to mixing of a hot rising fluid with cold meteoric water. The d13CPDB of calcite from gangue, in the range of – 1,90 to – 4,45% is interpreted as originated from mixing sources – magmatic and fluids contaminated by basement marbles. Studies on primary aqueous biphasic fluid inclusions show homogenisation temperatures with average of 215°C. Water in equilibrium with calcite from hydrothermal fluid show calculated values of d O18 SMOW between 3 and 14‰, suggesting derivation from a magmatic source with some contributions from meteoric water. 87Sr/86Sr from these calcite show values between 0, 7068 – 0, 7087, typical from upper crust. Hence, the Cerro dos Martins copper deposit is interpreted to have had origin by a mixing between a magmatic-hydrotermal fluids related to the alkaline-shoshonitic, post-collisional magmatic event (595-550 Ma) of the Dom Feliciano Orogeny and basement rocks. Exploration models for copper deposits in this shield should consider the alkaline magmatism in the genesis of deposits

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved