Varved (annually laminated) sediments are of great interest for inference of past environmental conditions, as they provide dated records with high time resolution. After deposition, the sediment varves are affected by diagenesis; i.e., chemical, physical and biological changes that occur within the sediment. An important premise when reconstructing past environmental conditions using lake sediments is that the signal of interest is preserved in the sediment. In this thesis I have used a unique collection of ten stored freeze cores of varved lake sediment from Nylandssjön in northern Sweden, collected from 1979 to 2007. The suite of cores made it possible to follow long-term (up to 27 years) changes in iron (Fe), sulfur (S), carbon (C), nitrogen (N), δ13C and δ15N in the sediment caused by processes that occur in the lake bottom as the sediment ages. The sediment geochemistry and resulting changes were followed in years for which there are surface varves in the core series. Fe and S concentrations analyzed by X-ray fluorescence spectroscopy showed no diagenetic front in the sediment and the data do not suggest a substantial vertical transport of Fe and S in the sediment. A model based on thermodynamic, limnological, and sediment data from the lake, showed that there are pe (redox) ranges within which either FeS (reduced specie) or Fe(OH)3/FeOOH oxidized species) is the only solid phase present and there are pe ranges within which the two solid phases co-exist. This supports the hypothesis that blackish and grey-brownish Fe-layers that occur in the varves were formed at the time of deposition. C and N analyzed with an elemental analyzer showed that within the first five years after deposition the C concentration of the sediment decreased by 20% and N by 30%, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. The C:N ratio increased with increasing age of the sediment; from ~ 10 in the surface varves to ~12 after 27 years of aging. δ13C and δ15N analyzed on a mass spectrometer showed that δ13C increased by 0.4-1.5‰ units during the first five years, after that only minor fluctuations in δ13C were recorded. Another pattern was seen for δ15N, with a gradual decrease of 0.3-0.7‰ units over the entire 27-year-period. The diagenetic changes in the stable isotope values that occur in Nylandssjön are minor, but they are of about the same magnitude as the variation in the isotopic signal in the varves deposited between 1950-2006. My results show that diagenesis does not change the visual appearance of the varves, except for varve thickness; the varves get thinner as the sediment ages. As the color of Fe in the varves likely reflects the environmental conditions at the time of deposition this creates possibilities for deciphering high-temporal-resolution information of past hypolimnetic oxygen conditions from varves. My findings on C, N, δ13C and δ15N will have implications for interpretations of paleolimnological data. The diagenetic effects should be carefully taken into consideration when C, N, δ13C and δ15N in sediment cores are used to study organic matter sources or paleoproductivity, in particular when dealing with relatively small and recent changes. In addition to the significance of diagenetic effects on sediment parameters, a comparison of the varves in Nylandssjön and the adjacent lake Koltjärnen, and the two deep basins of Nylandssjön show that subtle features in the lakes and their catchments affect the appearance of the varves, which make interpretation of varves complicated.

Middle Ordovician carbonates in the Lake Simcoe area, south-central Ontario were examined to determine if: (1) The δ18O values of early-stage calcite cement in hardgrounds are useful proxies for Ordovician seawater δ18O values; (2) a regional hydrothermal event affected middle Ordovician strata in the Lake Simcoe area. Whole rock samples of middle Ordovician hardgrounds and immediately overlying limestones containing early calcite cement have δ13C values ranging from -1.7 to +2.9‰ (PDB) and δ18O values ranging from -6.9 to -2.9‰ (PDB). Hardground δ18O values and the similarity of the isotopic composition between the hardgrounds and overlying limestones are consistent with diagenetic alteration during shallow burial, which indicates the hardgrounds are not useful proxies. Late-stage calcite cements have δ13C values from -8.4 to +2.9‰ (PDB) and δ18O values from -11.4 to -6.0‰ (PDB). Late-stage microcrystalline dolomites have δ13C values from -3.9 to +0.4‰ and δ18O values from -10.7 to -7.6‰. Late-stage saddle dolomites have δ13C values from -1.7 to 1.9‰ and δ18O values from -13.8 to -8.5‰. The late-stage carbonate δ18O values are more negative than the early-stage carbonate δ18O values and are interpreted to reflect progressively deeper burial diagenesis. Four types of fluid inclusions were identified in late-stage calcite, saddle dolomite, barite, and quartz. Type 1 inclusions are aqueous liquid-rich with very consistent low to very low vapour-liquid ratios and are of primary, secondary pseudosecondary and indeterminate origins. Type 2 inclusions are aqueous liquid-only and are of primary and secondary origins. Type 3 inclusions are oil-bearing, liquid-rich with low to medium vapor-liquid ratios and are of secondary origin. Type 4 inclusions are vapour-only and are of indeterminate origin. The type 4 inclusions analyzed did not yield any microthermometric data suggesting they are empty cavities that have lost all their fluid. Fluid inclusions of primary, secondary and pseudosecondary origins in calcite, dolomite and quartz have overlapping homogenization temperatures ranging from 43 to 188°C. Fluid inclusions of indeterminate origin in calcite and barite have homogenization temperatures from 80 to greater than 200°C. Petrographic and microthermometric evidence indicates that fluid inclusion homogenization temperatures greater than 150°C most likely are caused by stretching or leaking; therefore, are discounted. Fluid inclusion types 1 and 2 represent two fluid inclusion assemblages (FIA) based on final ice melting temperatures. The high salinity (10 to 30 wt%CaCl2) inclusions in FIA 1 are of primary, secondary, pseudosecondary and indeterminate origin in calcite, dolomite, barite and quartz. Fluid inclusions in FIA 1 are interpreted as reflecting saline basin brines from which the host minerals precipitated during burial diagenesis. The low salinity (0 to 2.7 wt%CaCl2) inclusions in FIA 2 are of secondary and indeterminate origin in calcite. Fluid inclusions in FIA 2 may reflect a meteoric origin such as in a vadose or phreatic environment based on inclusions containing different phases and variable vapor-liquid ratios. Alternatively the low salinity inclusions may reflect alteration from an influx of meteoric fluids that migrated through basement faults and fractures during periods of uplift and erosion. Early and late-stage carbonates from this study precipitated from 18O-depleted pore fluids and/or at progressively higher temperatures accompanying deeper burial. The FIA 1 homogenization temperatures support burial diagenesis at 66 to 80°C if it is assumed the rocks were buried 2 km, the surface temperature was 20°C and the geothermal gradient was between 23 to 30°C/km. An alternative interpretation is mineral precipitation during a regional hydrothermal event. Burial diagenesis does not explain the fluid inclusion homogenization temperatures of 90°C and greater unless geothermal gradients are higher than 35°C/km or burial depth is increased to 3 km or more. However, thermal maturity of organic matter in the Michigan Basin suggests Ordovician strata were never buried more than 2 km. Four models for regional hydrothermal fluid migration are: (1) gravity-driven flow; (2) ‘squeegee-type’ fluid flow; (3) convection cell fluid flow; and (4) structurally-controlled fluid flow. The gravity-driven model relies on continental heat flow and an influx of meteoric water from basin catchment areas. For the ‘squeegee, convection cell and structurally controlled models, hot fluids could have entered the region from several conduits concurrently during episodic reactivation of basement faults and fracture systems in response to intracratonic stresses created by the continuous interaction of tectonic plates. Determining which of the models best explains regional hydrothermal fluid flow in the Michigan Basin is difficult for several reasons; (1) surface temperatures and maximum burial temperatures at the time of mineral precipitation in the Michigan Basin during the Ordovician are unknown; (2) the timing of mineral precipitation in relation to tectonic pulses is undetermined; (3) there is as yet no known deep-seated heat sources in the Michigan Basin for convection to occur; and (4) it is unknown whether advection is a major process in the Michigan Basin. A collaborative multi-disciplinary research project covering geology, geophysics and hydrogeology would provide much more integrated data than is currently available from stable isotopes, fluid inclusions and organic matter.

Reservoir quality of subsurface sandstones depends on the composition, texture and grain size of the initial sediments. These factors are a function of hinterland processes: tectonic setting, provenance, climate and depositional environment, and sediment transportation processes. This study focuses on a modern, dryland, fluvial deposition system from source-to-sink that aims to provide a quantitative dataset analogue to facilitate forward modelling for prediction of subsurface compositions, grain size and textures of reservoir sandstones. Umbum Creek, in the western Lake Eyre Basin of Central Australia, was selected as a small river network (~ 100km²) in order to study source-to-sink sedimentation. The provenance area was analysed using isopach maps derived from a 783 drill-hole dataset, which included stratigraphy and lithology information. Subsequently forty-three samples of different provenance lithotypes from the Umbum Creek catchment were collected for petrographic thin-section analysis. Recent sediments were then sampled from 90 strategically located stream confluences along Umbum Creek and tributaries (proximal, medial and distal subsets). A quantitative textural and compositional dataset was subsequently generated from 34 selected samples. With half-phi sieve analysis (4mm to 32 microns), and an associated petrographic description recognising 72 categories of grain composition was undertaken for each sample. The provenance analysis using isopach maps demonstrated that Palaeozoic and Mesozoic sedimentary basin evolution in the study area was controlled by northeast and northwest-trending structural elements. The regional uplift of the Peake and Denison Inliers that occurred during the Cenozoic had a significant impact on the evolution of the Lake Eyre Basin, causing changes in the provenance of Late Neogene sedimentation and on through to the present. The sink area represents a shallow intracratonic basin whereby a thin veneer of fluvial/lacustrine sediments is accumulating adjacent to a basement uplift. This study has highlighted the importance of multiple sediment provenances. Five different provenance lithotype grains were identified in the Umbum Creek modern sediments: the Gawler Craton plutonic / basement provenance (recycled) the Peake and Denison Inliers Proterozoic volcanic provenance (recycled), the Davenport Ranges metamorphic provenance, the Mesozoic sedimentary provenance and the Cenozoic sedimentary provenance. Whereas a downstream fining of grain size was expected, a general trend of downstream coarsening of grain size was noted being the result of aeolian deflation of fines and intra-basinal coarse-grained sediment contributions. In the sink area, modern sediments from the terminal splay complex comprise 70-80% quartz, 10-20% lithic fragments (of which ~ 7% are ductile lithic grains), < 3% feldspar, and clay (<2%). Grains are sub-angular to well-rounded and moderately well sorted. The compositional and textural maturity of the terminal splay sediments is attributed to reworked plutonic quartz grains, the dissolution and disintegration of feldspar and carbonate grains during transportation, along with the breakdown of lithic fragments due to fluvio-aeolian interactions and subsequent mechanical/ chemical weathering processes. These data were used to build a predictive forward model for modal sandstone analysis that achieved a fair to good correlation between predicted and observed grain lithotypes and provenance categories. These results illustrate that the character of sands in the Umbum Creek catchment are governed by a multiplicity of controls such as tectonic setting, provenance lithotype analysis, climate, regional topographic gradient, hinterland transport distance, basin subsidence rate and depositional environment. The fluvio-aeolian depositional environment along with the current arid to semi-arid playa climatic conditions of Umbum Creek catchment facilitate the growth of clay coatings, however accounts for a low clay matrix within the deposits. In addition, the playa environment also facilitates the alteration of infiltrated detrital clay to kaolinite, the formation of evaporites (gypsum, halite and anhydrite) and the formation of authigenic clays. These factors are all significant in determining the ultimate reservoir quality of reservoir sandstones, emphasising the importance of this study as an analogue for modelling ‘buried’ dryland depositional systems. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337211 / Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2008

Reservoir quality of subsurface sandstones depends on the composition, texture and grain size of the initial sediments. These factors are a function of hinterland processes: tectonic setting, provenance, climate and depositional environment, and sediment transportation processes. This study focuses on a modern, dryland, fluvial deposition system from source-to-sink that aims to provide a quantitative dataset analogue to facilitate forward modelling for prediction of subsurface compositions, grain size and textures of reservoir sandstones. Umbum Creek, in the western Lake Eyre Basin of Central Australia, was selected as a small river network (~ 100km²) in order to study source-to-sink sedimentation. The provenance area was analysed using isopach maps derived from a 783 drill-hole dataset, which included stratigraphy and lithology information. Subsequently forty-three samples of different provenance lithotypes from the Umbum Creek catchment were collected for petrographic thin-section analysis. Recent sediments were then sampled from 90 strategically located stream confluences along Umbum Creek and tributaries (proximal, medial and distal subsets). A quantitative textural and compositional dataset was subsequently generated from 34 selected samples. With half-phi sieve analysis (4mm to 32 microns), and an associated petrographic description recognising 72 categories of grain composition was undertaken for each sample. The provenance analysis using isopach maps demonstrated that Palaeozoic and Mesozoic sedimentary basin evolution in the study area was controlled by northeast and northwest-trending structural elements. The regional uplift of the Peake and Denison Inliers that occurred during the Cenozoic had a significant impact on the evolution of the Lake Eyre Basin, causing changes in the provenance of Late Neogene sedimentation and on through to the present. The sink area represents a shallow intracratonic basin whereby a thin veneer of fluvial/lacustrine sediments is accumulating adjacent to a basement uplift. This study has highlighted the importance of multiple sediment provenances. Five different provenance lithotype grains were identified in the Umbum Creek modern sediments: the Gawler Craton plutonic / basement provenance (recycled) the Peake and Denison Inliers Proterozoic volcanic provenance (recycled), the Davenport Ranges metamorphic provenance, the Mesozoic sedimentary provenance and the Cenozoic sedimentary provenance. Whereas a downstream fining of grain size was expected, a general trend of downstream coarsening of grain size was noted being the result of aeolian deflation of fines and intra-basinal coarse-grained sediment contributions. In the sink area, modern sediments from the terminal splay complex comprise 70-80% quartz, 10-20% lithic fragments (of which ~ 7% are ductile lithic grains), < 3% feldspar, and clay (<2%). Grains are sub-angular to well-rounded and moderately well sorted. The compositional and textural maturity of the terminal splay sediments is attributed to reworked plutonic quartz grains, the dissolution and disintegration of feldspar and carbonate grains during transportation, along with the breakdown of lithic fragments due to fluvio-aeolian interactions and subsequent mechanical/ chemical weathering processes. These data were used to build a predictive forward model for modal sandstone analysis that achieved a fair to good correlation between predicted and observed grain lithotypes and provenance categories. These results illustrate that the character of sands in the Umbum Creek catchment are governed by a multiplicity of controls such as tectonic setting, provenance lithotype analysis, climate, regional topographic gradient, hinterland transport distance, basin subsidence rate and depositional environment. The fluvio-aeolian depositional environment along with the current arid to semi-arid playa climatic conditions of Umbum Creek catchment facilitate the growth of clay coatings, however accounts for a low clay matrix within the deposits. In addition, the playa environment also facilitates the alteration of infiltrated detrital clay to kaolinite, the formation of evaporites (gypsum, halite and anhydrite) and the formation of authigenic clays. These factors are all significant in determining the ultimate reservoir quality of reservoir sandstones, emphasising the importance of this study as an analogue for modelling ‘buried’ dryland depositional systems. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337211 / Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2008

Reservoir quality of subsurface sandstones depends on the composition, texture and grain size of the initial sediments. These factors are a function of hinterland processes: tectonic setting, provenance, climate and depositional environment, and sediment transportation processes. This study focuses on a modern, dryland, fluvial deposition system from source-to-sink that aims to provide a quantitative dataset analogue to facilitate forward modelling for prediction of subsurface compositions, grain size and textures of reservoir sandstones. Umbum Creek, in the western Lake Eyre Basin of Central Australia, was selected as a small river network (~ 100km²) in order to study source-to-sink sedimentation. The provenance area was analysed using isopach maps derived from a 783 drill-hole dataset, which included stratigraphy and lithology information. Subsequently forty-three samples of different provenance lithotypes from the Umbum Creek catchment were collected for petrographic thin-section analysis. Recent sediments were then sampled from 90 strategically located stream confluences along Umbum Creek and tributaries (proximal, medial and distal subsets). A quantitative textural and compositional dataset was subsequently generated from 34 selected samples. With half-phi sieve analysis (4mm to 32 microns), and an associated petrographic description recognising 72 categories of grain composition was undertaken for each sample. The provenance analysis using isopach maps demonstrated that Palaeozoic and Mesozoic sedimentary basin evolution in the study area was controlled by northeast and northwest-trending structural elements. The regional uplift of the Peake and Denison Inliers that occurred during the Cenozoic had a significant impact on the evolution of the Lake Eyre Basin, causing changes in the provenance of Late Neogene sedimentation and on through to the present. The sink area represents a shallow intracratonic basin whereby a thin veneer of fluvial/lacustrine sediments is accumulating adjacent to a basement uplift. This study has highlighted the importance of multiple sediment provenances. Five different provenance lithotype grains were identified in the Umbum Creek modern sediments: the Gawler Craton plutonic / basement provenance (recycled) the Peake and Denison Inliers Proterozoic volcanic provenance (recycled), the Davenport Ranges metamorphic provenance, the Mesozoic sedimentary provenance and the Cenozoic sedimentary provenance. Whereas a downstream fining of grain size was expected, a general trend of downstream coarsening of grain size was noted being the result of aeolian deflation of fines and intra-basinal coarse-grained sediment contributions. In the sink area, modern sediments from the terminal splay complex comprise 70-80% quartz, 10-20% lithic fragments (of which ~ 7% are ductile lithic grains), < 3% feldspar, and clay (<2%). Grains are sub-angular to well-rounded and moderately well sorted. The compositional and textural maturity of the terminal splay sediments is attributed to reworked plutonic quartz grains, the dissolution and disintegration of feldspar and carbonate grains during transportation, along with the breakdown of lithic fragments due to fluvio-aeolian interactions and subsequent mechanical/ chemical weathering processes. These data were used to build a predictive forward model for modal sandstone analysis that achieved a fair to good correlation between predicted and observed grain lithotypes and provenance categories. These results illustrate that the character of sands in the Umbum Creek catchment are governed by a multiplicity of controls such as tectonic setting, provenance lithotype analysis, climate, regional topographic gradient, hinterland transport distance, basin subsidence rate and depositional environment. The fluvio-aeolian depositional environment along with the current arid to semi-arid playa climatic conditions of Umbum Creek catchment facilitate the growth of clay coatings, however accounts for a low clay matrix within the deposits. In addition, the playa environment also facilitates the alteration of infiltrated detrital clay to kaolinite, the formation of evaporites (gypsum, halite and anhydrite) and the formation of authigenic clays. These factors are all significant in determining the ultimate reservoir quality of reservoir sandstones, emphasising the importance of this study as an analogue for modelling ‘buried’ dryland depositional systems. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337211 / Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2008

Made available in DSpace on 2014-12-17T14:08:57Z (GMT). No. of bitstreams: 1 IsabelleTS_DISSERT.pdf: 9676896 bytes, checksum: 211bb77ead98d9be0d4a700bc3a80049 (MD5) Previous issue date: 2014-06-04 / Universidade Federal do Rio Grande do Norte / The Rio do Peixe Basin represents a main basin of northeastern Brazil and pioneering work positioned the rocks of this basin in the Early Cretaceous. However, a recent study, based on integrated pollen analysis from three wells, found an unprecedented siliciclastic sedimentary section, in the region, of early Devonian age. Therefore, the present study aims a detailed petrographic and petrological analysis of this devonian section, in the Rio do Peixe Basin and proposes a diagenetic evolution, to understand the characteristics of the porous system, identify the main reservoir petrofacies with the main factors impacting on the quality of these rocks as reservoirs and a quick study on the provenance of this section. The petrographic study was based on samples obtained from subsurface and surface. The diagenetic evolution of petrofacies and its identification were based only on subsurface samples and the study of provenance was based on surface samples. The thin sections were prepared from sandstones, pelites and sandstones intercalated with pelites. The original detrital composition for this section is arcosean and the main diagenetic processes that affected these rocks occur in various depths and different conditions, which resulted in extensive diagenetic variety. The following processes were identified: early fracture and healing of grains; albitization of K-feldspar and plagioclase; siderite; precipitation of silica and feldspar; mechanical infiltration of clay and its transformation to illite/esmectite and illite; autigenesis of analcime; dissolution; autigenesis of chlorite; dolomite/ferrous dolomite/anquerite; apatite; calcite; pyrite; titanium minerals and iron oxide-hidroxide. The occurrence of a recently discovered volcanism, in the Rio do Peixe Basin, may have influenced the diagenetic evolution of this section. Three diagenetic stages affected the Devonian section: eo, meso and telodiagenesis. This section is compositionally quite feldspathic, indicating provenance from continental blocks, between transitional continental and uplift of the basement. From this study, we observed a wide heterogeneity in the role of the studied sandstones as reservoirs. Seven petrofacies were identified, taking into account the main diagenetic constituent responsible for the reduction of porosity. It is possible that the loss of original porosity was influenced by intense diagenesis in these rocks, where the main constituent for the loss of porosity are clays minerals, oxides and carbonate cement (calcite and dolomite) / A Bacia do Rio do Peixe corresponde a uma das principais bacias interiores do Nordeste do Brasil e trabalhos pioneiros posicionaram as rochas pertencentes a esta bacia, no Cret?ceo Inferior. Entretanto, um estudo mais recente, baseado na an?lise palinol?gica integrada entre tr?s po?os, verificou a exist?ncia de uma se??o sedimentar silicicl?stica, in?dita na regi?o, de idade eodevoniana. Portanto, o presente trabalho tem como objetivo realizar uma an?lise petrogr?fica e petrol?gica detalhada dessa se??o devoniana rec?m-descoberta na Bacia do Rio do Peixe e sugerir uma evolu??o diagen?tica, a fim de auxiliar no entendimento das caracter?sticas do sistema poroso, identificar as principais petrof?cies de reservat?rios, juntamente com os principais fatores impactantes na qualidade das mesmas e um breve estudo sobre a proveni?ncia dos sedimentos desta bacia. O estudo petrogr?fico foi baseado em amostras de subsuperficie e superf?cie, tendo a interpreta??o da evolu??o diagen?tica e a identifica??o das petrof?cies sido baseadas, apenas, nas amostras de subsuperf?cie. As l?minas petrogr?ficas foram confeccionadas a partir de arenitos, pelitos e arenitos intercalados por pelitos. A composi??o detr?tica original dessa se??o ? arcoseana e os principais processos diagen?ticos que a afetaram ocorreram em diversas profundidades e diferentes condi??es, o que resultou na grande variedade diagen?tica de processos: faturamento precoce e cicatriza??o de gr?os; albitiza??o dos K-feldspatos e plagiocl?sios; siderita; precipita??o de s?lica e feldspato; infiltra??o mec?nica de argila e transforma??o da mesma em ilita/esmectita e ilita; analcima; autig?nese de analcima; dissolu??o; precipita??o de caulinita; compacta??o mec?nica e qu?mica; autig?nese de clorita, dolomita/dolomita ferrosa/anquerita, apatita, calcita, pirita, minerais de tit?nio e ?xido/hidr?xido de ferro. A ocorr?ncia de vulcanismo rec?m-descoberto na Bacia do Rio do Peixe pode ter influenciado a evolu??o diagen?tica desta se??o. Foram identificados tr?s est?gios diagen?ticos: eo-, meso- e telodiag?nese. Essa se??o ? composicionalmente bastante feldsp?tica, indicando proveni?ncia de blocos continentais, entre o continental transicional a soerguimento do embasamento. A partir desse estudo, foi poss?vel verificar uma heterogeneidade no papel como reservat?rio dos arenitos estudados, sendo poss?vel a separa??o de sete petrof?cies, identificadas a partir do principal constituinte diagen?tico respons?vel pela redu??o da porosidade. A perda da porosidade original foi influenciada pela diag?nese intensa nessas rochas, sobretudo pela autig?nese de argilominerais, ?xidos e carbonatos (calcita e dolomita)

Made available in DSpace on 2015-03-13T17:08:31Z (GMT). No. of bitstreams: 1 IZAACCN_DISSERT.pdf: 2446448 bytes, checksum: 471b19d7ee3e89cd19644f2868c686c5 (MD5) Previous issue date: 2011-04-14 / Beachrocks s?o rochas sedimentares formadas pela cimenta??o de sedimentos praiais por carbonato de c?lcio em especial, calcita e/ou aragonita em zona de estir?ncio. A ocorr?ncia dessas rochas ? bastante comum em diversas partes do globo, sobretudo em regi?es com latitudes inferiores a 40?. O Rio Grande do Norte possui grande quantidade de beachrocks, os quais afloram tanto em regi?es costeiras quanto em zona costa-afora. Os dep?sitos de beachrocks de zona costeira do referido estado t?m sido estudados por diversos autores, os quais abordaram os mais variados temas desde o in?cio do s?culo XX. Por outro lado, os dep?sitos de zona costa-afora apesar de terem sido estudados por poucos autores t?m ganhado aten??o apenas nos ?ltimos anos. Por?m, nenhum trabalho at? o presente fez algum tipo de estudo comparativo de cunho geol?gico entre os corpos de beachrocks presentes em ambas as zonas: costeira e costa-afora. Sendo assim, a presente disserta??o teve o intuito de correlacionar os corpos de beachrocks que afloram em zona costeira aos que est?o atualmente dispostos em zona costa-afora, pr?ximo a is?bata de 25 m, levando em considera??o seus aspectos petrogr?ficos, diagen?ticos e sedimentol?gicos. Para isso, foram percorridos cerca de 260 km de litoral, correspondendo ao trecho entre os munic?pios de Extremoz e Tibau, em busca de afloramentos de beachrocks. Se??es colunares foram confeccionadas e amostras coletadas em esta??es de amostragem representativas da zona costeira, ao passo que da zona costa-afora apenas se??es delgadas foram analisadas. Trabalhos dispon?veis na literatura sobre o tema e ?rea em pauta tamb?m foram utilizados. A partir dos dados levantados, observou-se que os beachrocks s?o formados por diferentes camadas ao longo de um perfil vertical. Estas camadas s?o claramente identificadas em afloramento pela diferen?a existente na composi??o, textura e estruturas sedimentares peculiares a cada uma delas. Se??es delgadas foram confeccionadas e analisadas a partir de amostras coletadas nas diferentes camadas de diversos afloramentos. Um afloramento foi escolhido como afloramento modelo sendo este o de S?o Bento do Norte por apresentar a maior espessura de rocha aflorante (1,9 m). Este tem sido muito bem estudado tanto no corrente trabalho quanto em trabalhos de outros autores. A este foram comparados todos os outros afloramentos analisados. A partir da an?lise micropetrogr?fica, foram identificadas 03 microf?cies para os beachrocks do Rio Grande do Norte, sendo elas: Quartzaren?tica (< 2,9% de bioclastos), Quartzaren?tica Biocl?stica (entre 3 e 9,9% de bioclastos) e Bio-quartzaren?tica (> 10% de bioclastos). Associando essas microf?cies ?s an?lises sedimentol?gicas realizadas foi poss?vel propor que as microf?cies Quartzaren?tica e Bio-quartzaren?tica foram depositadas em zona de estir?ncio enquanto que a microf?cies Quartzaren?tica Biocl?stica foi depositada em zona de face litor?nea superior. A hist?ria diagen?tica dos beachrocks estudados ? marcada por quatro principais processos: compacta??o mec?nica, cimenta??o, dissolu??o e gera??o de porosidade secund?ria, e oxida??o. Dentre esses, o processo de cimenta??o ? o mais importante, sendo caracterizado por precipita??o de cimento de calcita rica em Mg sob cinco morfologias, a saber: cut?culas criptocristalinas, franjas prism?ticas is?pacas, calcita esp?tica microcristalina, calcita esp?tica equante e agregados pseudo-peloidais. Todas estas morfologias foram formadas durante o est?gio de eodiag?nese, nas zonas fre?tica marinha ativa ou fre?tica mete?rica ativa, corroborando assim com a id?ia de que beachrocks t?m sua litifica??o completa a pequenas profundidades. Associando as an?lises microfaciol?gicas ?s diagen?ticas foi poss?vel sugerir que a sucess?o vertical de camadas vista em alguns beachrocks costeiros representam registros de varia??es de mais alta frequ?ncia do n?vel do mar durante o Holoceno. A partir da?, baseando-se em informa??es obtidas atrav?s de curvas de varia??o do n?vel do mar relativo no Holoceno para o Rio Grande do Norte, dispon?veis na literatura, e na correla??o aqui realizada entre os beachrocks costeiro e aqueles de zona costa-afora, foi poss?vel inferir que estes ?ltimos representam uma antiga linha de costa formada a idades relativas superiores a 7.000 anos A.P / Beachrocks s?o rochas sedimentares formadas pela cimenta??o de sedimentos praiais por carbonato de c?lcio em especial, calcita e/ou aragonita em zona de estir?ncio. A ocorr?ncia dessas rochas ? bastante comum em diversas partes do globo, sobretudo em regi?es com latitudes inferiores a 40?. O Rio Grande do Norte possui grande quantidade de beachrocks, os quais afloram tanto em regi?es costeiras quanto em zona costa-afora. Os dep?sitos de beachrocks de zona costeira do referido estado t?m sido estudados por diversos autores, os quais abordaram os mais variados temas desde o in?cio do s?culo XX. Por outro lado, os dep?sitos de zona costa-afora apesar de terem sido estudados por poucos autores t?m ganhado aten??o apenas nos ?ltimos anos. Por?m, nenhum trabalho at? o presente fez algum tipo de estudo comparativo de cunho geol?gico entre os corpos de beachrocks presentes em ambas as zonas: costeira e costa-afora. Sendo assim, a presente disserta??o teve o intuito de correlacionar os corpos de beachrocks que afloram em zona costeira aos que est?o atualmente dispostos em zona costa-afora, pr?ximo a is?bata de 25 m, levando em considera??o seus aspectos petrogr?ficos, diagen?ticos e sedimentol?gicos. Para isso, foram percorridos cerca de 260 km de litoral, correspondendo ao trecho entre os munic?pios de Extremoz e Tibau, em busca de afloramentos de beachrocks. Se??es colunares foram confeccionadas e amostras coletadas em esta??es de amostragem representativas da zona costeira, ao passo que da zona costa-afora apenas se??es delgadas foram analisadas. Trabalhos dispon?veis na literatura sobre o tema e ?rea em pauta tamb?m foram utilizados. A partir dos dados levantados, observou-se que os beachrocks s?o formados por diferentes camadas ao longo de um perfil vertical. Estas camadas s?o claramente identificadas em afloramento pela diferen?a existente na composi??o, textura e estruturas sedimentares peculiares a cada uma delas. Se??es delgadas foram confeccionadas e analisadas a partir de amostras coletadas nas diferentes camadas de diversos afloramentos. Um afloramento foi escolhido como afloramento modelo sendo este o de S?o Bento do Norte por apresentar a maior espessura de rocha aflorante (1,9 m). Este tem sido muito bem estudado tanto no corrente trabalho quanto em trabalhos de outros autores. A este foram comparados todos os outros afloramentos analisados. A partir da an?lise micropetrogr?fica, foram identificadas 03 microf?cies para os beachrocks do Rio Grande do Norte, sendo elas: Quartzaren?tica (< 2,9% de bioclastos), Quartzaren?tica Biocl?stica (entre 3 e 9,9% de bioclastos) e Bio-quartzaren?tica (> 10% de bioclastos). Associando essas microf?cies ?s an?lises sedimentol?gicas realizadas foi poss?vel propor que as microf?cies Quartzaren?tica e Bio-quartzaren?tica foram depositadas em zona de estir?ncio enquanto que a microf?cies Quartzaren?tica Biocl?stica foi depositada em zona de face litor?nea superior. A hist?ria diagen?tica dos beachrocks estudados ? marcada por quatro principais processos: compacta??o mec?nica, cimenta??o, dissolu??o e gera??o de porosidade secund?ria, e oxida??o. Dentre esses, o processo de cimenta??o ? o mais importante, sendo caracterizado por precipita??o de cimento de calcita rica em Mg sob cinco morfologias, a saber: cut?culas criptocristalinas, franjas prism?ticas is?pacas, calcita esp?tica microcristalina, calcita esp?tica equante e agregados pseudo-peloidais. Todas estas morfologias foram formadas durante o est?gio de eodiag?nese, nas zonas fre?tica marinha ativa ou fre?tica mete?rica ativa, corroborando assim com a id?ia de que beachrocks t?m sua litifica??o completa a pequenas profundidades. Associando as an?lises microfaciol?gicas ?s diagen?ticas foi poss?vel sugerir que a sucess?o vertical de camadas vista em alguns beachrocks costeiros representam registros de varia??es de mais alta frequ?ncia do n?vel do mar durante o Holoceno. A partir da?, baseando-se em informa??es obtidas atrav?s de curvas de varia??o do n?vel do mar relativo no Holoceno para o Rio Grande do Norte, dispon?veis na literatura, e na correla??o aqui realizada entre os beachrocks costeiro e aqueles de zona costa-afora, foi poss?vel inferir que estes ?ltimos representam uma antiga linha de costa formada a idades relativas superiores a 7.000 anos A.P

Ce travail s'inscrit dans une démarche visant à quantifier l'impact de la diagenèse sur les ratios élémentaires Sr/Ca, Mg/Ca et U/Ca caractéristiques de l'exosquelette (aragonite biogénique) de coraux Porites sp. Ces ratios élémentaires sont très utilisés comme paléo thermomètres en paléo climatologie tropicale pour reconstruire les paléo variables environnementales comme la température de surface de l'océan. On considère dans un premier temps un corail moderne prélevé in vivo et un corail fossile daté au 14C de l'Holocène Moyen (5445 ans BP). Les deux coraux ne présentent aucune trace d'altération diagénétique. On mesure Sr/Ca, Mg/Ca, U/Ca dans l'exosquelette par spectrométrie de masse couplée à un plasma inductif et à la microsonde de Castaing pour Sr/Ca. Les températures de l'océan du temps du vivant des coraux sont alors reconstruites à partir de la géochimie des échantillons et validées. L'approche est ensuite étendue à des coraux pléistocènes (~125000 ans BP) altérés par la diagénèse e.g., apparition de calcite au détriment de l'aragonite initiale sous l'action de l'eau douce percolant dans les récifs. Cette calcitisation affecte les ratios Sr/Ca et Mg/Ca originels et est susceptible d'entacher les reconstructions d'un biais qu'il est important de bien connaître. En s'appuyant sur la spectrométrie Raman et la microanalyse X, on confirme les tendances qualitatives rapportées dans la littérature sur l'impact de la calcite sur les proxies du climat : la présence de calcite diminue (resp. rehausse) le ratio Sr/Ca (resp. Mg/Ca) créant donc des artéfacts chauds dans les températures reconstruites. / This work is part of an approach aimed at quantifying the impact of diagenesis upon the Sr/Ca, Mg/Ca and U/Ca elemental ratios that typify the exoskeleton (biogenic aragonite) of Porites sp corals. These elemental ratios are indeed routinely used as paleothermometers in tropical paleoclimatology in order to reconstruct environmental paleovariables such as the Sea Surface Temperature (SST). In a first step, we analyze a modern coral collected in vivo and a fossil coral dated by 14C to mid-Holocene (5545 year BP). Both corals are in pristine state. The Sr/Ca, Mg/Ca and U/Ca ratios are measured by inductively coupled plasma mass spectrometry (ICP-MS) and with a Castaing microprobe for Sr/Ca. The SSTs at the time when the corals were alive are reconstructed from the geochemistry of the samples and validated against in situ measurements / previous work in the same area. Next, the approach is extended to Pleistocene fossil corals (~125000 year BP) that have been altered by diagenesis e.g., calcitization of the samples to the detriment of the original aragonite due to the fresh water that percolates through the coral reefs. Calcitization alters the original Sr/Ca and Mg/Ca. The reconstructed SSTs can therefore include nontrivial biases whose magnitude must be evaluated. Relying on Raman spectrometry, we confirm published qualitative trends on the impact of calcite upon the climate proxies : calcite lowers (resp. increases) the Sr/Ca (resp. Mg/Ca) ratio leading therefore to warm artifacts in the reconstructed SSTs.

Introduction : La détermination du délai postmortem dans les cas de découvertes de restes squelettisés est un élément clé de l’enquête judiciaire. Pour autant, face à la découverte de restes osseux, peu de méthodes sont applicables pour une estimation précise de ce délai. Cette étude taphonomique souhaitait s’inscrire dans une temporalité rejoignant les impératifs judiciaires appliqués en médecine légale. Ainsi, l’hypothèse principale de ce travail était constituée par une dégradation organique précoce de l’os en période postmortem, notamment sous la forme d’une dégradation collagénique. Celle ci a donc fait l’objet d’une évaluation prospective.Matériels et Méthodes : 6 dons de corps humains, sans pathologie osseuse connue ont été inclus et pour chaque sujet, le choix des os étudiés s’est orienté vers les côtes. Ces os ont été inclus dans un environnement de diagénèse et étudiés sur 2 ans. Une analyse macroscopique de perte de poids de l’os a été réalisée, et complétée par deux méthodes : l’une moléculaire (microspectrométrie Raman) et l’autre morphologique (histologie).Résultats : Ce travail, a permis de mettre en évidence certaines caractéristiques de l’altération temporelle des différentes phases osseuses via : une dessiccation mise en évidence par une perte de poids osseuse ; une diagénèse des fractions organiques et minérales. Ainsi, l’étude des paramètres physico-chimiques en microspectrométrie Raman a montré une tendance temporelle à la diminution des rapports phase minérale/phase organique ; la diminution de la carbonatation minérale ; l’augmentation de la cristallinité. L’analyse statistique multivariée des spectres Raman a permis : de distinguer des groupes temporels en les discriminant via leurs contributions organiques ; de construire l’ébauche d’un modèle statistique d’utilisation pratique. L’étude microscopique des prélèvements a montré l’absence de toute attaque microbienne en période postmortem précoce, mais un mécanisme d’altération organique collagénique de type hydrolyse chimique.Discussion : Notre travail, a permis d’identifier 3 paramètres fondamentaux du vieillissement osseux qui doivent être connus du praticien qualifié en anthropologie médico-légale, et cela même sur une période d’étude de 2 ans « courte » à l’échelle de l’anthropologie :- L’environnement influence fortement la diagénèse osseuse et doit être aussi bien étudié que l’os en lui même. En effet, l’étude de la perte de poids de l’os, a montré une altération de composition osseuse très précoce avec phénomène de dessiccation osseuse, comparable à la déshydratation globale du corps en période postmortem ;- La diagénèse osseuse est un phénomène global dans lequel les différentes altérations de phases minérales et organiques sont interdépendantes et peuvent être appréciées par la microspectrométrie Raman, qui outre son apport dans l’analyse de la dégradation chimique de l’os, permet par les outils statistiques qui y sont associés, d’identifier des classes temporelles de diagénèse. Ces classes, qui devront faire l’objet d’études supplémentaires, pourraient à terme être une aide pratique et servir de référence dans la datation précise d’un os ;- L’altération organique de l’os peut s’opérer selon des modes de dégradations chimiques ou bactériens en fonction de l’environnement et du délai postmortem. L’histologie peut permettre de faire ce distinguo. Sur ce délai d’étude, la dégradation collagénique de type chimique par hydrolyse est prédominante.Conclusion : Ces paramètres forment une unité structurelle indissociable qui est connue de longue date en anthropologie archéologique, et qui est parfaitement transposable en pratique médico-légale si des méthodologies adaptées sont développées. Les voies de recherche sur cette thématique ont un rôle essentiel à jouer pour que la médecine légale puisse répondre aux légitimes demandes exprimées par les victimes et leurs ayants-droits auprès de la justice. / Introduction: Determining the postmortem interval in cases of skeletonized remains is a key element of the judicial investigation. However, few methods are applicable for an accurate estimate of this period. This taphonomic study wanted to be performed in a temporality joining the legal requirements applied in forensics. Thus, the main hypothesis of this study was an early organic postmortem bone degradation, particularly a collagen degradation. The latter has been studied prospectively.Materials and Methods: 6 human bodies without known bone disease were included, and for each subject, the ribs were chosen. The bones were included in a diagenetic environment and studied over 2 years. Macroscopic analysis of bone weight loss was performed, and completed by two methods: one molecular (Raman microspectrometry) and the other morphological (histology).Results: This work has highlighted certain features of the temporary bone alteration on its different phases via: a desiccation highlighted by bone mass loss; a diagenesis of organic and mineral phases. Thus, the study of physicochemical parameters by Raman microspectrometry revealed a temporary trend of declining mineral / organic ratios; decreasing carbonation; increasing crystallinity. Multivariate analysis of Raman spectra allowed: to distinguish temporal groups by discriminating via their organic contributions; to design a statistical model of practical use. The microscopic study of the samples revealed no microbial attack in the early postmortem period, but an alteration of collagen by chemical hydrolysis.Discussion: Our study identified three basic parameters of bone diagenesis that must be known to the forensic anthropologist, even over a period of 2 years which is \\\"short\\\" on the scale of anthropology:- The environment strongly influences bone diagenesis and should be studied as well as the bone itself. Indeed, the study of weight loss of the bone, revealed a phenomenon of bone drying, similar to the overall dehydration of the body in the postmortem period;- Bone diagenesis is a global phenomenon in which the various alterations of inorganic and organic phases are interdependent and can be evaluated by Raman microspectrometry. Also its contribution in the analysis of the chemical degradation of the bone, Raman spectroscopy and statistical tools associated with it, allows the identification of diagenesis classes. These classes will require additional studies, eventually to be a practical support in dating a bone;- The organic alteration of the bone may be due to chemical or bacterial degradation, according to the environment and the postmortem period. Histology can make this distinction. On this period of study, the collagen degradation by chemical hydrolysis is predominant.Conclusion: These parameters form a structural unit, which is well known in archaeological anthropology, and is absolutely transposable in forensic practice if appropriate methodologies are developed. Research on this topic has an essential role as forensics can respond to legitimate requests from victims and their relatives towards justice.

Le but de ce travail est de comprendre les relations entre la déformation et la diagenèse dans les carbonates. Pour cela, l’échelle du m au dam est adéquate car elle permet de séparer les effets matriciels, des fractures et des failles. Celle-ci est sous la résolution de la sismique, donc peu de données géophysiques et diagénétiques spatiale et quantitatives sont disponibles, le plus souvent limitées aux données 1D de puit.Nous avons choisi 4 affleurements présentant des hétérogénéités et des intensités de déformation et de diagenèse diverses. Un protocole multi-échelle et multidisciplinaire a été développé, comprenant de la géophysique à l’échelle du cm au dam, de la diagenèse structurale et de la géochimie sur les ciments de fracture. Nous montrons un fort effet d’échelle entre les Vp en laboratoire et à l’affleurement dû à des hétérogénéités sédimentaire, d’enfouissement et structurale, qui conduisent à différents motifs géostatistiques.Les fractures ont l’effet le plus fort sur les Vp, modulé par leur cimentation, et qui peut entièrement effacer la signature initiale du faciès. La réactivation des fractures induit une anisotropie directionnelle de 10% due à des changements dans le remplissage des fractures, caractérisés par de multiples phases de cimentation, broyage et dissolution.Dans les zones de faille, l’anisotropie sismique est amplifiée, conduisant à un fort affaiblissement de la roche au cisaillement et à une diminution de Vp autour de la faille. Les données géochimiques tracent plusieurs flux de fluides diagénétiques et soulignent les fortes interactions entre l’évolution de la perméabilité, la diagenèse structurale et la signature géophysique des carbonates. / The aim of this work was to understand the relationships between deformations and diagenesis in carbonates. The relevant scale to study it may be the m to dkm scale which allows individualizing fracture, fault and matrix effects. This scale is under the seismic resolution, so few quantitative diagenetic and geophysical spatial data are available, mainly constrained to 1D borehole.Therefore, we selected 4 dkm scale outcrops displaying various heterogeneities and intensities of deformation and diagenesis. We developed a multidisciplinary/multiscale protocol including geophysics from cm to dkm scale along with structural diagenesis study and geochemical measurements on fractures cements. We found a strong scale effect between laboratory and outcrop Vp due to sedimentary, burial and structural heterogeneities that lead to different geostatistical patterns. Fractures have the strongest effect on Vp, being modulated by their cementation and can erase the initial facies acoustic signature. The fracture reactivation induce a 10% Vp directional anisotropy due to microscale changes in the fractures infillings characterized by multiple cementation, crushing and dissolution phases. In fault-zones the seismic anisotropy magnitude is amplified, leading to a strong directional rock shear weakening and a Vp decrease around the fault, caused by higher discontinuities aperture and brecciation. Geochemical data indicate that the Vp signature evolution is linked to different diagenetic fluids flow origins occurring during each deformation phase. This underlines the strong interplay between permeability evolution, structural diagenesis and geophysical signature in carbonates.