Thesis (M.S. - Geology)--University of Arizona. / Part of illustrative material in pocket. Bibliography: leaves 54-55.

Thesis (M.S. - Geology)--University of Arizona, 1968. / Includes bibliographical references. Includes bibliographical references (leaves 72-74).

Silica cemented pedogenic horizons known as duripans occur on relict landforms in climates having limited leaching potential. Under the influence of tephra, incipient silica cementation may also occur in late Quaternary soils. The source of silica for cementation in Holocene soils is rapidly weatherable volcanic glass. In response to wetting and drying cycles volcanic glass weathers to form sand-size composite particles composed of silt, clay and redeposited silica. A portion of the hydrolyzed silica is eluviated as monosilicic acid which accumulates as the wetting front evaporates. Illuvial silica augments existing composite particles eventually forming a continuously cemented duripan. In actively forming late Quaternary soils, the cementation process is a complex interaction between illuvial silica, clay and calcium carbonate and the soil matrix. Surface reactions between monosilicic acid and illuvial clay or soil matrix particles provide nucleation sites for polymerization of silica concentrated by evaporation. The resulting opaline silica bonds adjacent soil grains without necessarily plugging intervening pore spaces. In contrast, calcium carbonate preferentially precipitates in large pores and interped voids. Cementation occurs by the plugging of progressively smaller pores with relatively pure calcite rather than by heterogeneous bonding of mineral grains. In illuvial zones containing both silica and calcium carbonate, cementation may occur rapidly because the former holds small soil particles in place while the latter plugs large pores. The mineralogy of silica cement is determined by identification of varying amounts of crystal order using X-ray diffraction. Opal-A is recently polymerized, noncrystalline, highly hydrated silica gel. The more prevalent, partly crystalline opal-CT forms where surface reaction with clays create crystal orientation, where silica gel dehydrates or when silica precipitates from soil solutions having high concentrations.

Red-bed alluvial systems are becoming increasingly important as hydrocarbon plays in the UK Northern North Sea. Commonly such ephemeral systems are hard to define in terms of reservoir architecture, due to the difficulty in correlating such diverse and palaeontologically-barren sequences. This project aims to improve understanding of one such system, the Late Jurassic Cormorant Formation, of the Northern North Sea, through detailed sedimentological study of two outcrop analogues. The whole-rock trace element geochemical correlation technique in a variety of settings. The Lower Old Red Sandstone Moor Cliffs Formation of the Anglo-Welsh Basin provides ideal conditions for testing the whole-rock trace element geochemical correlation technique. The Moor Cliffs Formation is a low net:gross alluvial red bed suite, which by virtue of Variscan deformation, outcrops in a well-exposed, easily accessible cliff section at Priests Nose, near Manorbier, Pembrokeshire. A 100m section was sampled to determine variables that may affect whole-rock trace element geochemical correlation. The results prove that whole-rock trace element geochemical correlation can be applied to alluvial successions, despite pedogenic modification and deep burial. The Late Triassic Blomidon Formation of the Fundy Basin, Nova Scotia, provided a second outcrop example of an alluvial red-bed sequence, which was deposited in similar palaeo-climatic and tectonic conditions to the Northem North Sea Triassic. The Blomidon Formation contained a range of fluvial styles from confined channels to unconfined sheetfloods. Three sections were studied along the hanging-wall margin of the Fundy Basin, separated by up to 150km along strike. Each section provided a contrasting basinal setting, allowing comparison of facies along strike and down depositional dip. Sections were measured in detail to quantify bed geometries and facies variants, facilitating architectural analysis. Specific attention was paid to features that may be diagnostic in sub-surface cored sections of the Northern North Sea Triassic. Correlation was possible on a number of scales, using laterally continuous ephemeral marker beds within the Blomidon Formation. Detailed facies evaluation has allowed the division of the Blomidon Formation into four distinctive facies packages that vary considerably in sandstone net:gross. Each facies assemblage is defined by variations in fluvial style and occurrence of evaporite rich, ephemeral lacustrine and rare aeolian sediments. It was possible to produce a broad, basin-wide correlation scheme for the Blomidon Formation, based on these four facies packages. Detailed facies analysis of three cores from the Cormorant Formation, Tem Field, Northern North Sea allowed definition of reservoir architecture, based on models derived from outcrop analogues. The results suggest that correlation based on individual horizons and facies packages is possible in alluvial red-bed sequences through detailed sedimentological study. The whole-rock trace element geochemical correlation technique can also provide additional datasets to enhance correlation in the subsurface.

Thesis (Ph. D.)--University of Texas at Austin, 1997. / Vita. Includes bibliographical references (leaves 361-393). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Oregon State University, 2005. / Printout. Includes bibliographical references (leaves 196-205). Also available on the World Wide Web.

Note:

Thesis (Ph. D.)--Utrecht University, 2007. / One folded col. plate of geological sections in pocket. Vita. Includes bibliographical references.

Univ., Diss.--Utrecht, 2007.

Alluvial gold placers in Otago and northern Southland occur at several stratigraphic horizons within the Late Cretaceous - Recent sedimentary sequence. The gold is derived ultimately from primary sources in the Otago Schist. Poor correlation between the distribution of placers and that of the known primary deposits reflects repeated recycling of gold in the present drainage network and two precursor networks, each with substantially different architecture. The previous drainage networks were inundated and buried during marine or lacustrine transgression. There has been local addition of first cycle gold and immature detritus during each recycling phase. Most of the placer deposits are fluvial in origin but colluvial placers occur locally along the margins of several Central Otago ranges. Aeolian placers and marine placers are rare. Most of the gold in placers north of the Caples/Torlesse Terrane boundary is Au-Ag alloy, except in vicinity of the Hyde-Macraes Shear Zone, where α-Au-Ag-Hg alloy is also present. Conversely, α-Au-Ag-Hg alloy dominates in placers south of the Caples/Torlesse Terrane boundary, except those whose headwaters lie, or lay, in the Torlesse Terrane. These systems that cross the terrane boundary contain Au-Ag and Au-Ag-Hg alloys in the reach downstream of the boundary, and placers with their source in Aspiring Lithologic Association also contain both alloys. Textural and compositional maturity of the placer host generally increase with decreasing age, reach maxima at the Waipounamu Erosion Surface, and generally decrease in tandem with age above this surface. Exceptions occur in northern Southland, where quartz pebble conglomerate placers are actively forming. Fluvial quartz pebble conglomerate placers have not formed in a single sedimentary cycle. Instead, they have formed from precursor sediment where a high water table drives alteration of the labile component, and when uplift and erosion rates, topography and stream gradients are all sufficiently low to drive sedimentary recycling without significant input of low-grade basement detritus. The maturity of pre-marine examples (Taratu, Papakaio and Hogburn Formations) was enhanced by wave-reworking before final inundation during marine transgression. Colluvial placers in alluvial fans at the margins of Quaternary schist antiforms are repeatedly recycled into younger fan sediments during range growth. These ranges grow in width, as well as length and height, at the expense of the intervening basins, which become progressively narrower. The colluvial placers are ultimately reworked into a fluvial placer in an axial river between two ranges, which concentrates all of the colluvial gold into an incised channel once the widening ranges meet. Aeolian placers have formed from fluvial precursors in the semi-arid parts of the rain shadow east of the Southern Alps, particularly on the lower slope of ranges exposed to westerly winds. Silcrete and less common greywacke ventifacts are commonly associated with these placers. Progressive changes in gold particle shape by flattening during transport in fluvial systems has been the most important process in the concentration of gold in placers. Flattening changes the hydrodynamic behaviour of gold particles by increasing their surface area to volume ratio, thereby making them easier to entrain and enabling transport to lower energy parts of the fluvial system. Gold particle flatness determines whether transport or concentration occurs and there is a predictable relationship between particle flatness and transport distance. This relationship explains the typical occurrence of placers immediately downstream of terminal moraines, the confluence with steeper tributary streams and the mouth of incised gorges. In each case, gold with sub-critical flatness is deposited from a higher energy system or reach into a lower energy system or reach, and must be flattened to a critical state before further transport can occur. Chemical mobility of gold in groundwater occurs during uplift, commonly in association with sedimentary recycling. Secondary gold overgrowths are common in some placers and stitch or overgrow transport-induced features such as folds and abrasion marks. Chemical mobilisation and re-precipitation of gold is of minor importance, however, and results in volumetrically insignificant amounts of secondary gold. Increases in gold grain size upward through the section on both the local and the regional scale does not result from gold 'growth', but instead from preservation of progressively more proximal reaches of the host placers with decreasing age.