Intense interest in uranium in the past decade has led to the discovery of new kinds of deposits of which the so-called unconformity-type are economically the most important. Presently known occurrences are restricted to Australia and Canada where they are characterized chiefly by their spatial relationship to Lower-Middle Proterozoic unconformities. Other common features include similar host-rock assemblages, structural controls, alteration, mineralogy, age relationships and fluid-inclusion data. Similar characteristics in other vein-type deposits, including those of the Beaverlodge district in Canada, deposits in France and Portugal, and the Schwartzwalder mine in the United States, suggest that they may also be of the unconformity-type. Various interpretations of the geological relationships of unconformity-type deposits have resulted in a number of genetic hypotheses, which require different exploration philosophies. Nearsurface supergene processes are considered to be most important although other mechanisms may have played contributing roles in the concentration of uranium. There is considerable potential for further discoveries of unconformity-type uranium deposits throughout the world. No such deposits are yet known in southern Africa although several favourable Precambrian unconformities are present.

The Knox unconformity in the central and southern Appalachians is developed on Lower to early Middle Ordovician Knox/Beekmantown carbonates. The unconformity marks the transition from Cambro-Ordovician shelf carbonate deposition on a passive margin to carbonate and clastic deposition in a foreland basin associated with a convergent margin, possibly during a time of global sea-level lowering. Erosional relief on the unconformity decreases from over 140 m in southwest Virginia to 20 m or less in northern Virginia. This corresponds with a marked decrease in stratigraphic relief in the same direction. Paleokarst features that formed on the unconformity include topographic highs that extend up to 30 m into overlying Middle Ordovician peritidal carbonates, sinkholes and caves that extend down to 65 m below the unconformity and are filled with detritus from the unconformity and breccia from host carbonates, and sub-unconformity dolomite breccia bodies that formed by collapse after dissolution of limestone interbeds. Coarse detritus on the unconformity surface formed thin to thick veneers of regolith; locally this material was reworked by fluvial and marine processes. Much fine dolomite detritus was reworked and deposited as alluvial fan and playa mud-flat sediments in lows on the unconformity surface. The unconformity influenced the regional distribution, composition and thickness of some post-unconformity peritidal carbonates. This is evidenced by lithoclastic supratidal sheets that cap cycles in these beds up to 100 m above the unconformity. Unconformity highs also may have controlled later Middle Ordovician buildup distribution in Virginia. Development of regional unconformities on shelf sequences of passive margins immediately beneath foreland basin sequences is common in other orogens, reflecting gentle warping of the shelf prior to foundering beneath synorogenic clastics. Such unconformities may localize hydrocarbons and base metal deposits (Pb-Zn), by controlling the distribution of permeable horizons adjacent to the unconformity. / Master of Science

The Jurassic J-2 surface is one of the more extensive unconformities of the Western Interior (U.S.A.). Stratigraphic relationships show that this is an angular unconformity, which developed first in the north and progressively moved south. An examination of features associated with the J-2 surface reveals detrital and diagenetic chert grains, ventifacts, polygonal fracture patterns, oscillation ripples, and paleotopographic relief. Some of these features indicate that the J-2 unconformity was a hot, dry, deflationary surface, and that the level of deflation on this surface was controlled, at times, by the height of the water table. The ventifacts are a lag deposit of the overlying Gypsum Spring Formation. Three possible variables involved in the formation of the J-2 surface are fluctuations in water table, disruption of sediment supply, and tectonic activity. For the Early-Middle Jurassic, these variables can be associated with increased rifting rates in the Atlantic Ocean. The increase in rifting rate raised eustatic sea level, which resulted in a larger area for deposition of marine sediments and a rise in continental water table. A higher water table would have trapped sediment that was previously available for sand sea (erg) formation. Furthermore, a higher sea level might have changed sediment supply and transportation routes. As the increase in rifting continued, tectonic movement and tilting of the North American plate occurred. This tilting caused the uplift and erosion of some deposits, and influenced the sites available for sediment preservation. / text

Thesis (M. Sc.)--University of Adelaide, Petroleum Geology and Geophysics, 1989. / Typescript (Photocopy). Three maps, folded, in back cover pocket. Includes bibliographical references (leaves [22-24]).

Thesis (Ph.D.)--University of Adelaide, Dept. of Geology, 2000? / At head of title: National Centre for Petroleum Geology and Geophysics. CD-ROM contains Appendices (1-10) in PDF. Includes copies of papers co-authored by the author. Includes bibliographical references (leaves [471]-499 in vol. 2).

Thesis (M.S.)--Ohio University, August, 2004. / Includes bibliographical references (p. 152-159).

Thesis (M.S.)--Ohio University, August, 2004. / Title from PDF t.p. Includes bibliographical references (p. 152-159)

Thesis (Ph. D.)--University of Montana, 2007. / Title from title screen. Description based on contents viewed Oct. 10, 2007. Includes bibliographical references.

Typescript (Photocopy) Three maps, folded, in back cover pocket. Includes bibliography: leaves [22-24]

At head of title: National Centre for Petroleum Geology and Geophysics. / CD-ROM contains Appendices (1-10) in PDF. / Includes copies of papers co-authored by the author. / Includes bibliographical references (leaves [471]-499 in vol. 2) / System requirements for accompanying CD-ROM: Macintosh or IBM compatible computer with Windows NT. Other requirements: Adobe Acrobat Reader. / 2 v. (various pagings) : ill. (some col.), maps, ports. ; 30 cm. + 1 CD-ROM (4 3/4 in.) / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Studies the provenance and diagenesis of the Merrimelia Formation in South Australia and Queensland; a complex mosaic of glacial facies in which the Tirrawarra Sandstone and Merrimelia Formation exhibit an interfingering relationship, and defines the relationship further. Indicates that the Tirrawarra Sandstone should be included in the Merrimelia Formation as a "facies type" as both the Merrimelia and Tirrawarra sediments form an integrated suite of sediments. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology, 2000?