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Holocene sediments from intertidal and shallow subtidal zones in Bahia la Choya, Mexico exhibit significant differences based on their mineralogical content, constituent composition, textural parameters, and foraminiferal assemblages. The intertidal sediments are characterized by low calcium carbonate content, being dominated by quartz, and are moderately well sorted and coarse skewed with a fine mean grain size {Mz = 2.73 phi}. Total numbers {living and dead} of benthonic Foraminifera per ml of sediment are relatively low (12/ml) in the intertidal zones. In contrast, the subtidal sediments are characterized by high calcium carbonate content, being dominated by molluscan shell fragments, and are poorly sorted and nearly symmetrically skewed with a medium mean grain size {Mz = 1.41 phi}. Total numbers of benthonic Foraminifera per ml of sediment are relatively high (52/ml) in the subtidal zone. The analysis of bioerosion intensity indicates that differences in susceptibility to bioerosion exist not only at the subordinal level but also at the generic level of Foraminifera. Overall rates of test destruction are rapid, apparently due to the combination of biological, chemical, and physical processes. The experimental determination of test characteristics which correlate with settling or entrainment enables the delineation of foraminiferal morphotypes which are most likely to be transported. Test settling velocity is mostly affected by test size and weight. Movement threshold velocity is, also, mostly affected by test size, weight, and shape, in addition to the nature of the substrates and initial test orientation. Foraminifera from siliciclastic environments exhibit relatively low settling and movement threshold velocities. Thus, taxa from siliciclastic settings are more likely to be transported by currents than are those from carbonate environments, which show a wide range of settling and movement threshold velocities. Such information may be utilized to distinguish between autochthonous and allochthonous microfossil assemblages in the stratigraphic record.

Les propriétés pétrophysiques des réservoirs silicoclastiques sont influencées par de nombreux facteurs sédimentaires et diagénétiques. Les principaux phénomènes diagénétiques affectant les réservoirs sont généralement la cimentation de quartz et les compactions mécanique et chimique. Des réservoirs gréseux ayant des contextes géologiques différents ont été considérés dans cette étude ; les réservoirs carbonifères d’origine deltaïque-marine du bassin des Palmyrides-Sud en Syrie et les réservoirs cambro-ordoviciens du bassin de Sbaa en Algérie. Cette thèse consiste à établir l’histoire diagénétique, déterminer les contrôles sédimentaires et structuraux influençant l’évolution des phénomènes diagénétiques, caractériser l’habitus des cristaux authigènes de quartz formés autour les grains détritiques et aussi mettre en relation les différentes contrôles sédimentaires et diagénétiques sur les caractéristiques des pores et ainsi que sur la variation de la perméabilité. L’histoire diagénétique entre le réservoir du bassin de Sbaa se caractérise par une forte cimentation de quartz composée de trois phases Q1, Q2 /et Q3, par tapissage illitique et ainsi par une importante compaction chimique liée à certains faciès glaciaires et également une cimentation d’argiles principalement en illite mais surtout dans les champs d’Oued Zine et de Bou Hadid. A l’exception du champ de Hassi Ilatou, où une faible cimentation de quartz composée de Q1 a eu lieu. Alors que la diagenèse des réservoirs gréseux du bassin des Palmyrides-Sud est représentée par une faible cimentation de quartz composée d’une seule phase Q1, une absence de compaction chimique, ainsi qu’une cimentation d’argiles dominée par la chlorite et les kaolins. Les analyses microthermométriques des inclusions fluides dans les surcroissances de quartz mettent en évidence une silicification se déroulant principalement entre 100 et 160°C dans les deux bassins. D’après la reconstitution de l’histoire thermique de bassin, cet intervalle de température a été atteint entre le Viséen et la fin du Namurien dans le bassin de Sbaa et au Crétacé supérieur-Paléocène dans le bassin des Palmyrides-Sud. Les analyses isotopiques indiquent une eau originelle météorique et marine, progressivement réchauffée lors de l’enfouissement, et s’enrichissant au fur et à mesure en ¹⁸O dans les pores intergranulaires et des fluides évolués et chauds à l’origine des filonnets. L’habitus des cristaux authigènes de quartz et la forme de croissance montrent une relation avec les phases de ciment de quartz, son taux et la présence/absence de gaz. En effet, des cristaux à prisme court, tronqués par des facettes additionnelles, et des cristaux trapus caractérisent les grès cimentés par une seule phase de quartz authigène, et une fréquence importante des cristaux de quartz à multiples nucléas est constatée dans ces grès. Des cristaux à prisme développé et rarement des cristaux à prisme court caractérisent les grès contenant deux phases du ciment de quartz. Des cristaux peu développés et limités à quelques faces sont présents dans les grès cimentés par trois phases du ciment de quartz dans la paléozone à eau du réservoir dans le champ ODZ. Une forme de croissance en escalier est présente uniquement dans ces derniers grès. La présence des inclusions à hydrocarbures dans les surcroissances de quartz dans la partie supérieure du réservoir ordovicien du champ de Oued Zine indique que la mise en place des hydrocarbures dans le réservoir a été contemporaine à la cimentation de quartz à des températures 100-140°C en raison de la paléostructure anticlinale dans ce champ. Un deuxième épisode a eu lieu suite à la fracturation hercynienne à des températures comprises entre 117-185°C qui augmente vers le nord-ouest du bassin. La composition du gaz dans les inclusions monophasées (92 ± 5 mole %) est comparable à la composition actuelle du gaz dans le réservoir. / Petrophysic properties of siliciclastic reservoirs are influenced by many sedimentary and diagenetic factors. The main diagenetic processes affecting the reservoir quality are quartz cementation and mechanical and chemical compaction. The cementing of quartz plays a role in reducing the porosity as it precipitates occupying intergranular porosity. However, its influence on the evolution of permeability is not well known because the morphology of authigenic quartz crystals and controls responsible for this morphology remain poorly understood. Sandstone reservoirs with different geological settings were considered in this study; Carboniferous reservoirs of deltaic-marine Palmyrides South Basin (fields: Arak, Debayate South, and Sukhneh) in Syria and the Cambro-Ordovician reservoirs Sbaa Basin (fields : Hassi Ilatou , Hassi Ilatou NE, Bou Hadid, Oued Zine, and Bou Hadid W) in Algeria. They have widely varying porosities both laterally and vertically and permeabilities. Thus, this thesis is to establish the diagenetic history, determine the sedimentary and structural controls influencing the evolution of diagenesis, characterize crystallographic habits of authigenic quartz formed around the detrital grains and to relate the different sedimentary controls and diagenetic on pore characteristics and as well as the variation of the permeability. In the Sbaa Basin, the presence of inclusions hydrocarbons allowed to reconstruct the history of gas migration. The diagenetic history of the Sbaa Basin is characterized by strong cementing quartz composed of three phases Q1, Q2 / Q3, illite coatings, significant chemical compaction, and also by illite cements, especially in the fields of Oued Zine and Bou Hadid. However, Hassi Ilatou field shows low quartz cementation (Q1). In addition, reservoir sandstones of the Palmyrides-South Basin show low quartz cementation composed of a single phase Q1, an absence of chemical compaction, as well as clay cementation dominated by chlorite and kaolin characterize the diagenesis history. Microthermometric analyzes of fluid inclusions located in quartz overgrowths show that the silicification occurred mainly between 100 and 160 °C in both basins. According to the reconstruction of the thermal history, these temperatures have been reached between the end of the Visean and Namurian for the Sbaa Basin and Upper Cretaceous-Paéocène for the Palmyrides-South Basin. Isotope analyzes indicate marine/meteoric water gradually heated during burial, and enriched in ¹⁸O in intergranular pores and evolved hot fluids are responsible for vein precipitation. The habits of quartz overgrowth crystals and growth forms observed in the studied sandstones show a relation with the number of quartz cement phases. Effectively, crystals with short prisms, truncated by supplementary faces, and large crystals characterize one-phased (Q1) cemented sandstones. In addition, quartz crystals of multiple nucleations are frequent in these sandstones. However, crystals with long prisms and rarely crystals with short prisms characterize two-phased (Q1 and Q2) cemented sandstones. Crystals of poorly developed faces are present in three-phased (Q1, Q2, and Q3) cemented sandstones. Step-like striation present only in these sandstones. Methane inclusions in the quartz overgrowths of the upper part of Ordovician reservoir of Oued Zine indicate that the gas emplacement into the reservoir occurred synchronically with early quartz cementation in the sandstones located near the contact with the Silurian gas-source rocks at 100-140°C during the Late Carboniferous period and the late Hercynian episode fracturing at temperatures between 117 and 185°C. Microthermometric data on gas inclusions reveal the presence of an average of 92 ± 5 mole % of CH4, which is similar to the present-day gas composition in the reservoirs.

Este trabalho foi desenvolvido utilizando-se rochas reservatório siliciclásticas provenientes de afloramentos brasileiros, pertencentes ao Grupo Guaritas (Caçapava do Sul e Pinheiro Machado - RS) e à Formação Pirambóia (Rio Claro - SP), com o objetivo de se obter suas características petrofísicas. As amostras são provenientes de diferentes fácies eólicas e pluviais, com características semelhantes a reservatórios de água e hidrocarbonetos. Foram utilizados experimentos de Ressonância Magnética Nuclear (RMN), intrusão de mercúrio, susceptibilidade magnética, análise de lâmina petrográfica e Espectroscopia de Fluorescência de Energia Dispersiva de Raios-X (EDX) para a análise das amostras. Apesar de serem provenientes de sistemas deposicionais similares, a correlação entre os resultados demonstrou que a diagênese tem importante papel no desenvolvimento dos reservatórios, influenciando na porosidade e permeabilidade das amostras. Foi demonstrado que a susceptibilidade magnética possui correlação com as quantidades de Fe 203, Al 203 e SiO2, onde o Al 203 está relacionado com a quantidade de argila das amostras (aluminossilicatos). Através dos resultados de RMN foi possível estimar a susceptibilidade magnética das amostras através da largura de linha espectral em baixo campo. As estimativas de porosidade e tamanhos de poros via RMN demonstraram compatibilidade com as análises das lâminas e experimentos de intrusão de mercúrio. Com os experimentos de RMN bidimensionais T1xT2, foi mostrado que há uniformidade na relaxação, devido aos mapas de correlação serem aproximadamente paralelos à diagonal dos mapas 2D. Nos experimentos DxT2 há a correlação entre a distribuição de tempos de relaxação e coeficientes de difusão, demonstrando que, em muitos casos, há restrição de difusão translacional das moléculas do fluido. Para estimar a permeabilidade das rochas foi utilizado o modelo desenvolvido por pesquisadores da Schlumberger Doll Research (SDR), amplamente aplicado na previsão da permeabilidade através de resultados obtidos pela RMN. Aplicando-o de maneira clássica, os resultados não foram plenamente satisfatórios, em função das características magnéticas das rochas estudadas. O coeficiente relaxatividade superficial foi calculado pela convolução entre a distribuição de tamanhos de poros da intrusão de mercúrio e a distribuição de tempos de relaxação transversal. Este parâmetro foi utilizado como correção ao modelo SDR, entretanto, os resultados obtidos continuaram não satisfatórios. Foi proposta então a correção através da susceptibilidade magnética, tanto medida pelo susceptômetro quanto estimada pela RMN. As utilizações dessas duas informações culminaram em melhores resultados para o valor das permeabilidades, com destaque para a RMN, desta maneira, propondo um novo método para estimar esse importante parâmetro das rochas reservatório. Com estes resultados podemos verificar a coesão entre os aspectos geológicos das amostras e a RMN, porém, as técnicas de RMN existentes empregadas ao estudo devem ainda ser aperfeiçoadas e novas devem ser desenvolvidas para o estudo de rochas reservatório que apresentam alta susceptibilidade magnética, um problema comum encontrado no estudo de rochas sedimentares por RMN. / The petrophysical characterization of siliciclastic reservoir rocks from Brazilian outcrops was the objective of this work. The samples were obtainded from different eolian and pluvial facies of the Guaritas Group (Caçapava do Sul and Pinheiro Machado - RS) and Pirambóia Formation (Rio Claro -SP). Different methods were applied in order to study these samples: Nuclear Magnetic Resonance (NMR), mercury injection, magnetic susceptibility, petrographic thin sections analysis and Energy Dispersive X-ray Fluorescence Spectroscopy (EDX). Despite the depositional similarities, the results indicate that permeability and porosity are affected by diagenetic processes which show that the diagenesis plays an important role at the development of these reservoirs. It was shown the correlation between magnetic susceptibility and the amounts of Fe 2O3 , Al 203 and Si0 2 were the amount of Al 203 is related with the quantity of clay (aluminosilicates). Magnetic susceptibilities were estimated using the linewidth obtained from NMR spectra (by FFTs of the FIDs) measured at low and homogeneous magnetic fields, obtaining good agreement with the bulk magnetic susceptibility. Porosity and pore size distributions determined by NMR, mercury injection and petrographic analysis were compatible. In the two-dimensional NMR experiment T 1xT2 a diagonal behavior of relaxation time distributions was observed, indicating uniformity of relaxation mechanisms inside the samples. With DxT 2 measurements, the transverse relaxation times were correlated with diffusion coefficients showing restricted diffusion in most samples. In order to predict permeability the model proposed by researchers from Schlumberger Doll Research (SDR), which uses NMR parameters, was applied. With the classical permeability SDR predictor the obtained results were not fully satisfactory, as consequence of the magnetic characteristics of the samples. In order to correct this predictor, surface relaxivity coefficients were determined by the superposition of T2 and mercury injection pore diameter distributions nevertheless, these results were again unsatisfactory. Thus, a new correction method for the SDR permeability predictor was proposed using NMR and bulk magnetic susceptibilities. This approach improved considerably the permeability prediction, especially when using NMR-derived magnetic susceptibilities. The consistency between NMR and geological properties of the samples was verified nevertheless, the used NMR techniques still need to be improved and new ones must be developed, in order to allow the study of reservoir rocks with high magnetic susceptibility.

Temperate mixed carbonate-siliciclastic sediments and authigenic minerals are the current surficial deposits at shelf and slope depths (30-1015 m water depth) on the north Kaipara continental margin (NKCM) in northern New Zealand. This is the first detailed study of these NKCM deposits which are described and mapped from the analysis of 54 surficial sediment samples collected along seven shorenormal transects and from three short piston cores. Five surficial sediment facies are defined from the textural and compositional characteristics of this sediment involving relict, modern or mixed relict-modern components. Facies 1 (siliciclastic sand) forms a modern sand prism that extends out to outer shelf depths and contains three subfacies. Subfacies 1a (quartzofeldspathic sand) is an extensive North Island volcanic and basement rock derived sand deposit that occurs at less than 100-200 m water depth across the entire NKCM. Subfacies 1b (heavy mineral sand) occurs at less than 50 m water depth along only two transects and consists of predominantly local basaltic to basaltic andesite derived heavy mineral rich (gt30%) deposits. Subfacies 1c (mica rich sand) occurs at one sample site at 300 m water depth and contains 20-30% mica grains, probably sourced from South Island schists and granites. Facies 2 (glauconitic sand) comprises medium to fine sand with over 30% and up to 95% authigenic glauconite grains occurring in areas of low sedimentation on the outer shelf and upper slope (150-400 m water depth) in central NKCM. Facies 3 (mixed bryozoan-siliciclastic sand) consists of greater than 40% bryozoan skeletal material and occurs only in the northern half of the NKCM. Facies 4 (pelletal mud) occurs on the mid shelf (100-150 m water depth) in northern NKCM and comprises muddy sediment dominated by greater than c. 30% mixed carbonatesiliciclastic pellets. Facies 5 (foraminiferal mud and sand) contains at least 30% foraminifera tests and comprises two subfacies. Subfacies 5a consists of at least 50% mud sized sediment and occurs at gt400 m water depth in southern NKCM while subfacies 5b comprises gt70% sand sized sediment and occurs at mid to outer shelf and slope depths in the northern NKCM. vi A number of environmental controls affect the composition and distribution of NKCM sediments and these include: (1) variable sediment inputs to the NKCM dominated by inshore bedload sources from the south; (2) northerly directed nearshore littoral and combined storm-current sediment transport on the beach and shelf, respectively; (3) offshore suspended sediment bypassing allowing deposition of authigenic minerals and skeletal grains; (4) exchange between the beach and shelf producing similar compositions and grain sizes at less than 150 m water depth; and (5) the episodic rise of sea level since the Last Glaciation maximum approximately 20 000 years ago which has resulted in much sediment being left stranded at greater depths than would otherwise be anticipated. Sedimentation models developed from other wave-dominated shelves generally do not appear to apply to the NKCM sediments due to their overall relative coarseness and their mosaic textural characteristics. In particular, the NKCM sediments do not show the expected fining offshore trends of most wavedominated shelf models. Consequently, sandy sediments (both siliciclastic and authigenic) are most typical with mud becoming a dominant component in southern NKCM sediments only at greater than 400 m water depth, over 350 m deeper than most models suggest, a situation accentuated by the very low mud sediment supply to the NKCM from the bordering Northland landmass.

<p>Development of a predictive model for the distribution of diagenetic alterations and related evolution of reservoir quality of sandstones was achieved by integrating the knowledge of diagenesis to sequence stratigraphy. This approach allows a better elucidation of the distribution of eogenetic alterations within sequence stratigraphy, because changes in the relative sea level induce changes to: (i) pore water chemistry, (ii) residence time of sediments under certain near-surface geochemical conditions, (iii) variations in the detrital composition, and (iv) amounts and type of organic matter.</p><p>This thesis revealed that eogenetic alterations, which are linked to sequence stratigraphy and have an impact on reservoir quality evolution, include formation of: (i) pseudomatrix and mechanically infiltrated clays in fluvial sandstones of the lowstand and highstand systems tracts (LST and HST, respectively), (ii) kaolinite in tide-dominated deltaic and foreshore-shoreface sandstones of HST, Gilbert-type deltaic sandstones of LST and fluvial deltaic sandstones of LST, (iii) kaolinite and mechanically infiltrated clays in sandstones lying below sequence boundary, (iv) K-feldspar overgrowths in fluvial deltaic LST, (v) glaucony towards the top of fluvial deltaic LST immediately below and at transgressive surface (TS) and in foreshore and shoreface transgressive systems tracts (TST) below parasequence boundaries (PB) and maximum flooding surface (MFS), (vi) framboidal pyrite and extensive cementation by calcite and dolomite in foreshore and shoreface and tide-dominated deltaic TST, and shoreface and tidal flat HST bioclastic-rich arenites particularly in the vicinity of PB, TS and MFS, (vii) pervasive cementation by iron oxide in shoreface-offshore and shoreface sandstones of TST immediately below the MFS, (viii) zeolites and palygroskite in shoreface sandstones of TST and HST, particularly above PB, and (ix) cementation by siderite in Gilbert-type deltaic sandstones of LST, tide-dominated deltaic and foreshore-shoreface sandstones of HST and in tide-dominated deltaic sandstones of TST, particularly at MFS. Moreover, this thesis revealed that the distribution of eogenetic alterations strongly control, and thus provide information for constraining the distribution patterns of mesogenetic alterations, such as illitization of mechanically infiltrated clays and dickitization of kaolinite, and hence of related reservoir quality evolution of sandstones during progressive burial.</p>

<p>This thesis constrains the distribution of diagenetic alterations and their impact on reservoir-quality and heterogeneity evolution pathways in relation to depositional environments and sequence stratigraphy (systems tracts and key sequence stratigraphic surfaces) of four selected paralic and shallow marine siliciclastic successions. </p><p>Typical eogenetic alterations encountered include the dissolution and kaolinitization of framework silicates, which are closely associated to shoreface facies of forced regressive systems tract (FRWST), lowstand systems tract (LST), upper part of the highstand systems tract (HST), and below the sequence boundary (SB). These alterations are attributed to incursion of meteoric water owing to rapid and considerable fall in the relative sea level. Extensive carbonate cementation is most evident below marine and maximum flooding surfaces (MFS), whereas dissolution of carbonate cement and detrital dolomite occur in LST, HST and below SB. Parameters controlling the patterns and texture (microcrystalline vs. poikilotopic) of calcite cement have been constrained within sequence stratigraphic framework of the sandstones. Coarse crystalline to poikilotopic calcite textures of meteoric water origin are thus closely linked to the FRWST, LST and upper part of the HST sandstones and occur mainly as stratabound concretions, whereas microcrystalline calcite, which was precipitated from marine porewaters, occurs as continuously cemented layers in the transgressive systems tract (TST) and lower part of the HST sandstones.</p><p>Eogenetic alterations impose, in turn, profound control on the distribution pattern of mesogenetic alterations, and hence on reservoir quality evolution (destruction vs. preservation) pathways of sandstones. Eogenetic infiltrated clays, which occur in the tidal estuarine TST and HST sandstones, have helped preserving porosity in deeply buried sandstone reservoirs (≈ 5 km) through inhibition of extensive cementation by quartz overgrowths. Other essential findings of this thesis include deciphering the control on the formation of authigenic illite and chlorite by ultra-thin (≤ 1 µm thick), grain-coating clay mineral substrate. </p>

This thesis constrains the distribution of diagenetic alterations and their impact on reservoir-quality and heterogeneity evolution pathways in relation to depositional environments and sequence stratigraphy (systems tracts and key sequence stratigraphic surfaces) of four selected paralic and shallow marine siliciclastic successions. Typical eogenetic alterations encountered include the dissolution and kaolinitization of framework silicates, which are closely associated to shoreface facies of forced regressive systems tract (FRWST), lowstand systems tract (LST), upper part of the highstand systems tract (HST), and below the sequence boundary (SB). These alterations are attributed to incursion of meteoric water owing to rapid and considerable fall in the relative sea level. Extensive carbonate cementation is most evident below marine and maximum flooding surfaces (MFS), whereas dissolution of carbonate cement and detrital dolomite occur in LST, HST and below SB. Parameters controlling the patterns and texture (microcrystalline vs. poikilotopic) of calcite cement have been constrained within sequence stratigraphic framework of the sandstones. Coarse crystalline to poikilotopic calcite textures of meteoric water origin are thus closely linked to the FRWST, LST and upper part of the HST sandstones and occur mainly as stratabound concretions, whereas microcrystalline calcite, which was precipitated from marine porewaters, occurs as continuously cemented layers in the transgressive systems tract (TST) and lower part of the HST sandstones. Eogenetic alterations impose, in turn, profound control on the distribution pattern of mesogenetic alterations, and hence on reservoir quality evolution (destruction vs. preservation) pathways of sandstones. Eogenetic infiltrated clays, which occur in the tidal estuarine TST and HST sandstones, have helped preserving porosity in deeply buried sandstone reservoirs (≈ 5 km) through inhibition of extensive cementation by quartz overgrowths. Other essential findings of this thesis include deciphering the control on the formation of authigenic illite and chlorite by ultra-thin (≤ 1 µm thick), grain-coating clay mineral substrate.

Development of a predictive model for the distribution of diagenetic alterations and related evolution of reservoir quality of sandstones was achieved by integrating the knowledge of diagenesis to sequence stratigraphy. This approach allows a better elucidation of the distribution of eogenetic alterations within sequence stratigraphy, because changes in the relative sea level induce changes to: (i) pore water chemistry, (ii) residence time of sediments under certain near-surface geochemical conditions, (iii) variations in the detrital composition, and (iv) amounts and type of organic matter. This thesis revealed that eogenetic alterations, which are linked to sequence stratigraphy and have an impact on reservoir quality evolution, include formation of: (i) pseudomatrix and mechanically infiltrated clays in fluvial sandstones of the lowstand and highstand systems tracts (LST and HST, respectively), (ii) kaolinite in tide-dominated deltaic and foreshore-shoreface sandstones of HST, Gilbert-type deltaic sandstones of LST and fluvial deltaic sandstones of LST, (iii) kaolinite and mechanically infiltrated clays in sandstones lying below sequence boundary, (iv) K-feldspar overgrowths in fluvial deltaic LST, (v) glaucony towards the top of fluvial deltaic LST immediately below and at transgressive surface (TS) and in foreshore and shoreface transgressive systems tracts (TST) below parasequence boundaries (PB) and maximum flooding surface (MFS), (vi) framboidal pyrite and extensive cementation by calcite and dolomite in foreshore and shoreface and tide-dominated deltaic TST, and shoreface and tidal flat HST bioclastic-rich arenites particularly in the vicinity of PB, TS and MFS, (vii) pervasive cementation by iron oxide in shoreface-offshore and shoreface sandstones of TST immediately below the MFS, (viii) zeolites and palygroskite in shoreface sandstones of TST and HST, particularly above PB, and (ix) cementation by siderite in Gilbert-type deltaic sandstones of LST, tide-dominated deltaic and foreshore-shoreface sandstones of HST and in tide-dominated deltaic sandstones of TST, particularly at MFS. Moreover, this thesis revealed that the distribution of eogenetic alterations strongly control, and thus provide information for constraining the distribution patterns of mesogenetic alterations, such as illitization of mechanically infiltrated clays and dickitization of kaolinite, and hence of related reservoir quality evolution of sandstones during progressive burial.

The mixed carbonate–siliciclastic Abrigo Formation of middle and late Cambrian age, which crops out in southeastern Arizona, was deposited during the Sauk transgression in the craton interior, landward of the passive margin of Laurentia. The Abrigo Formation consists of ten basic rock types: claystone, siltstone, sandstone, lime mudstone, wackestone, bioclastic grainstone, packstone, oolitic packstone, oncolitic packstone, and intraclastic conglomerate. These comprise fifteen lithofacies, which are grouped into eight facies associations. They represent an array of shallow-marine environments that were dominated by wave and storm activity. The interpreted paleoenvironments include lower offshore, upper offshore, offshore transition, and lower, middle and upper shoreface. One hundred eighty-two collections, yielding 940 trilobite remains have been found in the Abrigo Formation. They represent 69 species and 42 genera. Eight of the species are new. The fossil age ranges from early Marjuman to late Steptoean. Eight trilobite biofacies are defined from the generic relative abundance data: Ehmaniella, Olenoides–Bolaspidella, Blairella, Eldoradia, Modocia–Paracedaria, Cedaria, Coosella–Coosina, and Camaraspis. Trilobites collected and identified in this study are assigned to five biostratigraphic zones: Bolaspidella, Cedaria, Crepicephalus, Aphelaspis, and Elvinia zones. In addition, two subzones had been defined. Cedaria eurycheilos Subzone recognized in the upper part of Cedaria Zone and Coosella helena Subzone recognized in the upper part of Crepicephalus Zone. The stratigraphic succession was divided into six distinct phases associated with large-scale relative sea-level fluctuations. An initial flooding over the Bolsa Quartzite forming the transgressive systems tract was terminated by maximum flooding, and a subsequent highstand systems tract developed during Bolaspidella Biozone time. The second sequence starts with another transgressive systems tract, and is overlain by a final highstand systems tract during the Cedaria and Crepicephalus biozones. The uppermost part of the second sequence represents a falling stage systems tract that developed during Aphelaspis Biozone time. The presence of Elvinia Biozone trilobites near the base of the highest sandstone unit suggests that delivery and deposition of these sands took place during the lowstand that followed the protracted and widespread Sauk II–Sauk III hiatus. Sedimentary dynamics were controlled by storm-induced wave action and offshore flows. There are two carbonate factories that operated simultaneously in this Cambrian inner shelf region. Dominance of carbonate versus siliciclastic strata in the offshore transition setting is interpreted to reflect periods when siliciclastic input was depleted, such that increasing accommodation and reduction of clay and possibly nutrients promoted carbonate production. Clay and silt bypassed the nearshore carbonate-depositing zone. Siliciclastic sediment input and dispersal were not only restricted to the falls in sea level, but appear to have dominated the transgressive systems tract and late phase of the highstand. Thus, carbonate sedimentation does not dominate the entire highstand systems tract as is commonly held but, rather, only during the late phase of the transgressive and early highstand phase. The comparison of this Cambrian model with younger mixed carbonate-siliciclastic units will help reveal the subtleties of the carbonate factory and how it operated in response to biotic evolution.