Thesis (M.S.)--Ohio University, June, 2004. / Includes bibliographical references (p. 66-77).

Thesis (M.S.)--Ohio University, June, 2004. / Title from PDF t.p. Includes bibliographical references (p. 66-77)

No description available.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 45-49). Also available via the World Wide Web.

Fracture distribution in a fold and thrust belt is commonly thought to vary depending on structural position, strain, lithology and mechanical stratigraphy. The distribution, geometry, orientation, intensity, connectivity and fill of fractures in a reservoir are all important influences on fractured reservoir quality. The presence of fractures is particularly beneficial in reservoirs that contain little matrix porosity or permeability, for example tight sandstones. In these examples fractures provide essential secondary porosity and permeability that enhance reservoir production. To predict how reservoir quality may fluctuate spatially, it is important to understand how fracture attributes may vary, and what controls them. This research aims to investigate the influence of structural position on fracture attribute variations. Detailed fracture data collection is undertaken on folded sandstone outcrops. 2D forward modelling and 3D model restorations are used to predict strain distribution in the fold-and-thrust belt. Relationships between fracture attributes and predicted strain are determined. Discrete Fracture Network (DFN) modelling is then undertaken to predict fracture attribute variations. DFN modelling results are compared with field fracture data to determine how well fractured reservoir quality can be predicted. Field data suggests strain is a major controlling factor on fracture formation. Fractures become more organised and predictable as strain increases. For example in high strain forelimb regions, fracture intensity and connectivity are high, and fracture orientations are consistent. In lower strain regions, fracture attributes are much more variable and unpredictable. Fracture variations often do not correspond to strain fluctuations, and correlations can be seen between fracture intensity and lithology. Reservoir quality is likely to be much more variable in low strain regions than high strain regions. DFN modelling is also challenging because fracture attribute variations in low strain regions do not correspond to strain, and therefore cannot be predicted.

abstract / Earth Sciences / Master / Master of Philosophy

Thesis (Ph. D.)--University of Alberta, 2010. / Title from pdf file main screen (viewed on June 28, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geophysics, Department of Physics, University of Alberta. Includes bibliographical references.

Scotland is one of the most valuable regions available for geologic study, as it has been a breeding ground for the discovery and development of many fundamental concepts from the earliest studies in the field through today. Scotland has traditionally been viewed, in a broad sense, as the amalgamation of two components: the eroded remnants of the Caledonide Orogen north of the Highland Boundary Fault (HBF), and the post-Caledonian Old Red Sandstone (ORS) to the south. Studies based in the Scottish Caledonides and the ORS have provided a host of concepts that we now deem fundamental, but much of that has been the byproduct of effort to understand how they were juxtaposed along the HBF. The metamorphosed strata of the Grampian Terrane (GT) lie against pillow basalts and minor sediments associated with the Highland Border Complex (HBC), and undeformed fluvial deposits of the ORS near the Highland Border. The incompatibility of lithologies, but also palaeontologic and radiometric ages, on either side of the fault was seemingly inexplicable, and coined the term “the Highland Border Paradox”. The Highland Border Paradox was used to describe the conflicting idea of continuity between the GT and HBC, despite incompatible lithologies and ages within the section. Several tectonic models have been suggested as a solution to the core of the issue, but a widely accepted solution has so far been elusive. The 40Ar/39Ar method is well-poised to investigate when the Scottish Caledonides were active, and when the ORS was deposited; each valuable in their own dimension but combined represent the best opportunity to understand the Highland Border Paradox to date. Two models exist: one which considers the Midland Valley Terrane (MVT; predominately ORS) to be relatively autochthonous relative to the northern terranes, and another that suggests the MVT is mostly allochthonous, or exotic. This dissertation is designed as a multi-pronged approach to offer an overarching understanding of the relationship between the Scottish Caledonides and the ORS, but with the intention that each chapter is a standalone contribution. We first investigate the relationship between the Grampian Terrane and the Old Red Sandstone by studying the contact that bounds them, which is along the Highland Boundary Fault. The base of the ORS is only reported to be exposed at five localities along the northern margin of the Midland Valley, but the basal unconformity is only found at Stonehaven. Outcrop exposure is not ideal in Scotland, such that the exposure of the contact between the GT and MVT is only exposed at those few localities, and physically tracing contacts between those localities is not possible. Chapter 1 is focused on exposure of the contact from the locality near Stonehaven, where we were surprised to find that no unconformity exists, and that the base of the ORS is a fault. A new age 40Ar/39Ar age of 438 Ma from biotite separated from a dike that crosscuts the Cowie Formation is over 20 Myr older than previous estimates, pushing the base of the ORS well into the Silurian. Fossils of Pneumodesmus Newmani found there, the earliest documented terrestrial and air-breathing fauna in the geologic record, must also be as old as 438 Ma. This pushes back both the timing of when air-breathing animals emerged from land, but also reinstates Stonehaven as the ideal locality to study the earliest life on land. This chapter was designed to be a manuscript for submission to Geology, or a similar journal, as it is a famous locality pertinent to a host of Caledonian studies, is commonly used for teaching, and has broad interest to the scientific community with respect to Pneumodesmus Newmani. Chapter 2 is focused on studying the physical contact between the GT and MVT at its other reported localities: Edzell (North Esk River), Callander, and Balmaha. Detailed field mapping and observations were made for each, also supplemented petrographic details from thin sections as needed. One of the most surprising findings is that, combined with observations from Stonehaven, the base of the ORS is either faulted or not exposed; there is effectively no evidence for a basal ORS unconformity. This releases the constraints that the ORS was deposited strictly after the Caledonian Orogeny, and that the ORS was deposited above the GT/HBC stack as we see it today. In addition, at each of these localities, we identify considerable evidence of faulting in the area between the GT and MVT; most affected is the intervening HBC. This is hard to reconcile with previous interpretations proposed for those localities by proponents of the autochthonous model, as it is based largely on proposed continuity at those localities. It is also difficult to reconcile with the suggestion, in that view, that the HBF only modestly displaces geology, and not responsible for the juxtaposition of the GT and MVT. Evidence at each locality for undeformed units directly juxtaposed with highly deformed rocks implies a significant amount of vertical displacement that has not previously been appreciated, in any previous account. A significant amount of vertical displacement is a characteristic of major strike-slip faults, yet previous strike-slip models for the HBF have invoked movements in a purely lateral sense. Chapter 3 aims to constraint when the GT, Northern Highland Terrane (NHT), and Hebridean Terrane (HT) were exhumed during the Caledonian Orogeny, with a particular focus on the southern region of the GT near the HBF. We employed single-step 40Ar/39Ar analysis of muscovite separated from bedrock exposed throughout the terranes north of the HBF, complementing a similar work by Dewey and Pankhurst (1970). Throughout all the terranes, these ages range from 500-420 Ma, with a concentration of ages ca. 470 Ma. Combined with previous data sets, the NHT appears to have had a younger exhumation, but if our dataset is considered alone that distinction is unclear. The second portion of Chapter 3 presents the results of step-heating 40Ar/39Ar analysis of muscovite separated from metamorphosed GT strata, sampled in transects spanning across the metamorphic zones of the GT. The purpose of the transects is to evaluate when the portion of the GT immediately against the MVT was active. The step-heating analyses range between 471-461 Ma at Stonehaven, 468-453 Ma at North Esk, and 459-447 Ma at Balmaha (combined with Callander). These ages indicate that the Caledonian Orogeny was active at least from ca. 471-447 Ma, whereas the Caledonian Orogeny was previously proposed to be unusually short (10 Myr). As these ages likely capture the latest stage of orogenesis, the actual duration is likely considerably longer, and this is also suggested by the wider range of single-step ages. It is also now difficult to envision a scenario in which the GT was a passive margin through Ordovician times, which is a widely accepted notion. Chapter 4 is designed to investigate the time at which the Midland Valley ORS was deposited, and where its sediments originated from. We obtained three ages from volcanic units interleaved throughout the ORS, including a result of 438 Ma near the base (from Stonehaven), a result of 431 Ma from the Lintrathen Porphyry near mid-section, and a result of 400 Ma at the top of the ORS near Oban. We sampled over ten volcanic units interleaved within the ORS, but most ultimately were unsuitable for age analysis. Despite only obtaining three ages, it is now clear that at least the onset of ORS sedimentation is significantly older than previous estimates, now as far back as 438 Ma, whereas it was previously considered to be mostly Devonian. Considering that the age from Lintrathen at midsection is only 6 Myr younger, and still Silurian, it is possible that a majority of the Midland Valley LORS is Silurian, and deposited within a much more narrow timeframe than previously suggested. The result of 399 Ma from Oban confirms the previous suspicion that the ORS near Oban is unrelated to the ORS in the Midland Valley. Detrital analyses from the Midland Valley ORS indicate a source that ranges in age from mainly 480-420 Ma, which effectively overlaps the Scottish source ages obtained in Chapter 3. This is at odds with a previous hypothesis that suggested the ORS was sourced from large river systems from Scandinavia (including the Western Gneiss Region), analogous to the Himalayan drainages today. In combination, the depositional ages (437 and 431 Ma) and range of detrital ages (480-420 Ma), suggest that the ORS was locally related to the Scottish Caledonides, rather than an exotic origin. So, while it is now clear that displacement along the HBF is more substantial than previously conceived, that displacement was not significant enough to isolate the ORS from a Scottish source.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

The Trans-North China Orogen (TNCO) has been recognized as a continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form the North China Craton. However, controversy has surrounded the timing and tectonic processes involved in the collision between the two blocks, ranging from the westward-directed subduction with final collision at ~2.5 Ga, through the west-dipping subduction with two collisional events at ~2.1 Ga and ~1.85 Ga, to the eastward-directed subduction with final collision at ~1.85 Ga. This project aims to present detailed lithostratigraphic, geochronological and isotopic data for the low-grade supracrustal successions in the TNCO to examine current models and to establish a reasonable scenario for the tectonic evolution of the TNCO in the Paleoproterozoic. The low-grade supracrustal successions include the Hutuo and Yejishan Groups in the middle sector of the TNCO and the Songjiashan, Lower Zhongtiao, Upper Zhongtiao, Danshanshi and Songshan Groups in the southern sector. Lithostratigraphic data indicate that the Songjiashan, Lower Zhongtiao Groups and lower parts of the Hutuo and Yejishan Groups are composed of metaclastic rocks, carbonates and metavolcanic rocks, interpreted as back-arc basin deposits, whereas the Upper Zhongtiao, Danshanshi, Songshan Groups and the upper parts of the Hutuo and Yejishan Groups consist only of metaconglomerates and metasandstones, interpreted as foreland basin deposits. To constrain the provenance and maximum depositional ages for these low-grade supracrustal successions, the LA-MC-ICP-MS technique was applied to analyze U-Pb and Hf isotopic compositions for detrital zircons from them. For the Hutuo and Yejishan Groups, we found major age peaks at ~2.5 and ~2.2 Ga and minor amounts of 2.8-2.6 Ga detrital zircons, which are consistent with ages of the lithological units in the middle sector of the TNCO. On the other hand, for the Songjiashan, Lower Zhongtiao, Upper Zhongtiao, Danshanshi and Songshan Groups, detrital zircons from them have the major age population of 2.85-1.95 Ma and the minor age population of 3.6-3.1 Ga, of which the former is comparable with ages of the lithological units in the southern sector of the TNCO and the latter was derived from the Paleoarchean and Mesoarchean crust of the Eastern Block. The maximum depositional ages of the low-grade supracrustal successions have also been well constrained in this study. For the back-arc basin deposits, their maximum depositional ages were constrained between ~2.15 and ~2.10 Ga. For the foreland basin deposits, the presence of ~1.85 Ga detrital zircons indicates that they were deposited after this time. Taken together, we present a brief scenario for the evolution of the sedimentary basins in the TNCO. At 2.15-2.10 Ga, a series of back-arc basins developed behind an “Andean-type” arc that were subsequently incorporated into the TNCO during the collision of the Eastern and Western Blocks. At ~1.85 Ga, the two blocks collided along the TNCO, resulting in the crustal thickening followed by rapid exhumation/uplift, which shifted the back-arc basins to foreland basins. Such a shift in the late Paleoproterozoic supports the model that the collision between the Eastern and Western Blocks occurred at ~1.85 Ga. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy