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Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Basin subsidence analysis, employing the backstripping method, indicates that fundamentally two different basin-generating mechanisms controlled Tanqua depocentre development in SW Karoo Basin. The subsidence curves display initial dominantly decelerating subsidence, suggesting an extensional and thermal control possibly in a strikeslip setting during the depocentre formation; on the other hand, subsequent accelerating subsidence with time suggests that the dominant control on the depocentre formation in SW Karoo was flexure of the lithosphere. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion (~ 290 Ma) is therefore recognised as the first stage of Tanqua depocentre formation. Petrographic study show that most of the studied sandstones of the Tanqua depocentre at depth of ~ 7.5 Km were subjected to high pressure due to the overlying sediments. They are tightly-packed as a result of grains adjustment made under such pressure which led also to the development of sutured contacts. It is clear the high compaction i.e. grain deformation and pressure solution occurred on the sediments; leading to total intergranular porosity reduction of the quartz-rich sediments and dissolution of the mineral grains at intergranular contacts under non-hydrostatic stress and subsequent re-precipitation in pore spaces. Furthermore, siliciclastic cover in the Tanqua depocentre expanded from minimal values in the early Triassic (Early to Late Anisian) and to a maximum in the middle Permian (Wordian -Roadian); thereby accompanying a global falling trend in eustatic sea-level and favoured by a compressional phase involving a regional shortening due to orogenic thrusting and positive inflexions (denoting foreland basin formation). The estimate of sediment volume obtained in this study for the Permian Period to a maximum in the middle Permian is therefore consistent with published eustatic sea-level and stress regime data. In addition, this new data are consistent with a diachronous cessation of marine incursion and closure of Tanqua depocentre, related to a compressional stress regime in Gondwana interior during the late Palaeozoic. / AFRIKAANSE OPSOMMING: Die ontleding van komversakking met behulp van die terugstropingsmetode bring aan die lig dat die ontwikkeling van die Tankwa-afsettingsentrum in die Suidwes-Karoo-kom hoofsaaklik deur twee verskillende komvormende meganismes bepaal is. Die versakkingskurwes toon aanvanklike, hoofsaaklik verlangsaamde versakking, wat daarop dui dat ekstensie- en termiese beheer gedurende die vorming van die afsettingsentrum plaasgevind het, waarskynlik in strekkingwaartse opset. Aan die ander kant toon daaropvolgende versnellende versakking wat mettertyd plaasgevind het dat die vorming van die afsettingsentrum in die Suidwes-Karoo eerder oorwegend deur kromming van die litosfeer beheer is. Op grond van hierdie waarnemings met betrekking tot die versakkingskurwes, kan mens aflei dat die eerste stadium van positiewe infleksie (~ 290 Ma) dus as die eerste stadium van die vorming van die Tankwa-afsettingsentrum beskou kan word. Petrografiese studie toon dat die meeste van die sandsteen wat van die Tankwaafsettingsentrum bestudeer is, op diepte van ~ 7,5 Km aan hoë druk onderwerp was weens die oorliggende sedimente. Die sandsteen is dig opmekaar as gevolg van die korrelaanpassing wat onder sulke hoë druk plaasvind, wat op sy beurt ook tot die ontwikkeling van kartelnaatkontakte aanleiding gegee het. Dit is duidelik dat die sediment aan hoë verdigting, dit wil sê korrelvervorming en drukoplossing, onderwerp was, wat gelei het tot algehele afname in interkorrelporeusheid by die kwartsryke sedimente; die ontbinding van die mineraalkorrels in interkorrelkontaksones onder niehidrostatiese spanning, en daaropvolgende herpresipitasie in poreuse ruimtes. Voorts het silisiklastiese dekking in die Tankwa-afsettingsentrum toegeneem van minimale waardes in die vroeë Triassiese tydperk (vroeë tot laat Anisiaanse tydperk) tot hoogtepunt in die mid-Permiaanse tydperk (Wordiaans–Roadiaans). Dié ontwikkeling het gepaardgegaan met algemene dalingstendens in die eustatiese seevlak, en is verder aangehelp deur saamdrukkingsfase wat gekenmerk is deur regionale verkorting weens orogeniese druk en positiewe infleksies (wat met voorlandkomvorming saamhang). Die geraamde sedimentvolume wat in hierdie studie vir die Permiaanse tydperk bepaal is, met die hoogtepunt in die middel van dié tydperk, is dus in pas met gepubliseerde data oor die eustatiese seevlak en spanningstoestand. Daarbenewens strook hierdie nuwe data met diachroniese staking van mariene instroming en die afsluiting van die Tankwaafsettingsentrum wat met spanningstoestand in die Gondwana-binneland gedurende die laat Paleosoïkum verband hou.

Rico strata are recognised throughout the Four Corners region of southwestern Colorado, southeastern Utah, northeastern Arizona, and northwestern New Mexico. The term Rico has been applied to a group of strata which exhibit a lateral and vertical transition between two contrasting environments, the marine Hermosa and the non-marine Cutler. Two faunal provinces reflect these widely diverse conditions of sedimentation. However, few fossils of diagnostic value have been discovered despite the abundance of fossiliferous strata within the Rico. Rico strata are believed to range between Desmoinesian and Virgilian in age. Lithofacies data on the Rico were assembled from literature, outcrop sections, and various well logs. These data were then compiled on an isopach-lithofacies map. The isopach-lithofacies map shows the thickness trends and the lithologic variations of Rico strata throughout the region of study. The tectonic framework of the region is reconstructed from the isopach-lithofacies map and mechanical analyses of the elastic strata. Clastic material in the Rico increases in average grain size from west to east toward the Uncomphagre Uplift suggest that this area was actively positive during Rico time. The vertical variation of normal marine limestone and clastic red beds in the Rico reflect an alternately transgressing and regressing sea over much of the Four Corners region. This intricate intertonguing of normal marine limestone and clastic red beds probably resulted from deposition in a shallow basin on an unstable shelf. The occurrence of oil, gas, and cement quality limestone in the Rico is examined from an economic aspect. A. brief review of the general geology and geologic history of tile region is also included.

Includes bibliographical references.

At head of title: "NERDDC/SENRAC Research Project." / Three folded maps in pocket / Two microfiches in pocket / Bibliography: leaves 155-187 / 118, [70] leaves, [23] leaves of plates : ill. (chiefly col.), maps ; 30 cm. + 2 microfiches / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, National Centre for Petroleum Geology & Geophysics (NCPGG) /Dept. of Geology & Geophysics, 1993

The Karoo Basin of South Africa holds an estimated 906 billion to 11 trillion cubic meters of unconventional shale gas within the shales of the Whitehill and Collingham formations of the Ecca Group. Evaluation of this potential resource has been limited due to the lack of exploration and a scarcity of existing drill core data. In order to circumnavigate this problem this study was undertaken to evaluate the potential target horizons exposed in outcrops along the southern portion of the Karoo Basin, north of Grahamstown in the Eastern Cape Province. Detailed field logging was done on the exposed Whitehill and Collingham formations as well as a possible conventional sandstone (turbidite) reservoir, the Ripon Formation, along road cuttings of the Ecca Pass. Palaeocurrent data, jointing directions and fossil material were also documented. Samples were analysed for mineralogy, porosity, permeability, and total organic carbon content (TOC). The extensively weathered black shales of the Whitehill Formation contain a maximum TOC value of 0.9% and the Collingham Formation shales contain a maximum TOC value of 0.6%. The organic lithic arkose sandstones of the Ripon Formation are classified as ‘tight rock’ with an average porosity of 1% and an average permeability of 0.05 mD. The Whitehill Formation in the southern portion of the Karoo Basin has experienced organic matter loss due to low grade metamorphism as well as burial to extreme depths, thus reducing shale gas potential. The Ripon Formation is an unsuitable conventional reservoir along the southern basin boundary due to extensive cementation and filling of pore spaces.

Indiana University-Purdue University Indianapolis (IUPUI) / The Antler and Sonoma orogenies occurred along the southwest-trending passive Pacific margin of North America during the Paleozoic concluding with the accretion of the McCloud Arc. A southeast-trending sinistral transform fault truncated the continental margin in the Permian, becoming a locus for initiation of an east-dipping subduction zone creating the Sierran magmatic arc. Constrained in age between two early Triassic tuff layers, the volcanic clasts in the breccia of Frog Lakes represent one of the earliest records of mafic magmatism in the eastern Sierra Nevada. Tholeiitic rock clasts found in the breccia of Frog Lakes in the Saddlebag Lake pendant in the east central Sierra Nevada range in composition from 48% to 63% SiO2. Boninites produced by early volcanism of subduction initiation by spontaneous nucleation at the Izu-Bonin-Mariana arc are more depleted in trace element concentrations than the clasts while andesites from the northern volcanic zone of the Andes produced on crust 50 km thick have similar levels of enrichment and provide a better geochemical modern analogue. Textural analysis of the breccia of Frog Lakes suggest a subaqueous environment of deposition from a mature magmatic arc built on continental crust > 50 km thick during the Triassic. The monzodiorites of Saddlebag and Odell Lakes are temporal intrusive equivalents of the breccia of Frog Lakes and zircon geochemistry indicates a magmatic arc petrogenesis.