| In this study, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and conventional TEM (CTEM) of Pt-C replicas are used to characterize both synthetic and natural 2:1 clay minerals from a variety of geological environments.;The major objective of manuscript 2 is to test whether oxalate catalyzes the crystallization of saponite at low temperatures and pressures. Additionally, the experiments of this study allow the investigation of the expansion behaviour and the structure of newly formed saponite crystals after exchange with n-alkylammonium cations in HRTEM lattice-fringe images. As these clay minerals are interpreted to replicate by template-catalyzed polymerization and transmit the charge distribution from layer to layer, the formation of 2:1 layer silicates with a variable layer-charge has significant implications for the abiotic origin of life. The finding that polar organic molecules such as oxalic acid catalyze clay-mineral formation in the laboratory is of great relevance to what processes may have occurred on carbonaceous chondrites and on the primitive, outgassing Earth that finally led to the evolution of life.;In manuscript 3, I investigated the role of oxalate in promoting the nucleation of 2:1 silicate layers of saponite within the low-charge, smectite-like interlayers of rectorite. This study was aimed to test the intercalating hypothesis of Weiss et al. (1969) and Weiss (1981), who claimed to have successfully proven the synthesis of new smectite layers from a solution within the low-charge interlayers of rectorite. Lattice-fringe images show that the oxalate-promoted formation of the new 2:1 layer silicates from the silica gel leads to the alteration and destruction of the rectorite structure. The saponite layers grow independently of any crystallographic orientation given by the rectorite layers.;In manuscript 4, XRD, HRTEM and CTEM were used to characterize the clay-mineral separates (2.0-0.5, 0.5-0.1, and <0.1 mum) from argillaceous rocks taken at increasing depth from two wells, North Ben Nevis (NBN) P-93 (2025 m, 2730 m) and Adolphus (AD) D-50 (2035 m, 3135 m) in the Jeanne d'Arc Basin, offshore Newfoundland, in order to understand the diagenetic changes of the 2:1 clay minerals that constitute the smectite to illite (S→I) reaction during progressive burial. Lattice-fringe images of clay minerals in ultrathin sections treated with nC=18 cations show the multiphase nature of the clay-mineral assemblages (e.g., smectite-group minerals, expandable and non-expandable illite, vermiculite) in all size fractions. Conventional TEM images of Pt-C replicas show a change in particle morphology with increasing depth of burial. Irregular, flake-like particles dominate in NBN P-93 at 2025 m and AD D-50 at 2035 m, whereas at greater depths (NBN P-93 at 2730 m and AD D-50 at 3135 m), a larger proportion of lath-like or equidimensional particles are observed. The diagenetic evolution of S→I in the investigated depth interval of the Jeanne d'Arc Basin should be considered as a sequence of multiple discrete 2:1 clay-mineral phases that dissolve and crystallize from solution in overlapping zones of burial depth and not as a single, continuous and progressive reaction-series, as conventionally assumed.;In manuscript 1, reference samples of illite and expandable 2:1 clay minerals (i.e., smectite-group minerals, vermiculite and rectorite) varying in interlayer charge were investigated to characterize their interlayer expansion after treatment with octadecylammonium (nC=18) cations. The results of this study show that the treatment of ultrathin sections of 2:1 clay minerals with nC=18 cations and their subsequent investigation under the HRTEM provide information on the distribution of layer charges and layer-charge heterogeneities that cannot be obtained with conventional techniques of sample preparation. |
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