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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Early Channel Evolution in the Middle Permian Brushy Canyon Formation, West Texas, USA

Gunderson, Spencer 2011 August 1900 (has links)
Submarine channels are important conduits for sediment in deep marine environments, and understanding their formation is critical to modeling basin fill processes. Most models describing channel evolution focus on turbidity currents as the erosive and constructive force in channel initiation. However, slope failure and slumping can be significant drivers of channelization, particularly in upper slope and ramp environments. Determining the relative roles of slumping and erosion by turbidity currents can provide important insight into the timing of channelization and the geometries of subsequent deposits. Samples were collected from Guadalupe Mountains National Park from two primary localities at Salt Flat Bench (Figure 2). Three vertical sections were measured at both locations. A total of 16 samples were collected for petrographic analysis and X-ray fluorescence (XRF) imaging. Spectacular outcrop quality makes the Middle Permian Brushy Canyon Formation in Guadalupe Mountains National Park an ideal location for the study of early channel evolution. A detailed facies analysis of fine-grained channel deposits was conducted in the Upper Brushy Canyon Formation in the Salt Flat Bench outcrops. After channelization, an interval of relative condensation dominated by hemipelagic settling of organic matter and silt was followed by an interval of incomplete sediment bypass by turbidity currents. This sequence of events suggests that sea level was at a relative highstand at the time of channel inception, whereas channel inception by turbidity currents is expected during a lowstand. Slumping rather than erosion by turbidity currents is the most likely mechanism to have initiated a channel at the study area. There is no evidence for the existence for high energy currents until after the interval of condensation. However, the action of weak contour currents during early channel evolution is observed in outcrop and microtextural features. Early carbonate cementation of channel-lining silts may have stabilized the slump surface with respect to erosion by later turbidity currents.
2

Sedimentology and basin context of the Numidian Flysch Formation; Sicily and Tunisia

Thomas, Myron January 2011 (has links)
The Numidian Flysch Formation is a regionally extensive series of deep marine sandstones and mudstones which crop out in Spain, Morocco, Algeria, Tunisia, Sicily, and southern mainland Italy. The formation is dated as Oligocene to mid Miocene and represents an approximately linear series of submarine fans characterised by a quartz rich petrofacies. Their unique regional extent is nearly twice the length of the Angolan margin although issues surrounding provenance and basin context have hampered understanding. The Numidian Flysch Formation was deposited into the Maghrebian Flysch Basin (MFB) which was a foreland basin remnant of the neo-Tethys ocean in the western portion of the present day Mediterranean Basin. The basin was bordered to the north by an active margin which consisted of a southward verging accretionary prism, underlain by European crustal blocks which rode above northwards subducting oceanic crust. To the south, the African margin formed a passive-margin to the basin.The huge amount of geophysical and outcrop data which is becoming increasingly available suggests that submarine slope systems are more complex than previously thought, including topographically complex slopes, a wide variety of density flow types, and flow transformations. This thesis aims to review the sedimentology of the Numidian Flysch Formation in Sicily and Tunisia in light of these developments. Constraining the provenance and basin context of the formation is therefore of paramount importance, and this is also addressed.Commonly used evidence for the provenance of Numidian Flysch sandstones include its quartz rich petrology, an Eburnian and Pan-African age detrital zircon suite, its structural position within the foreland fold and thrust belt, and complex palaeocurrent orientations. when reviewd in their entirety and placed in context of other basin successions, the Numidian Flysch is constrained to a depositional location in the south of the basin, with polycyclic sediment sourced from African basement. The Numidian Flysch Formation is therefore a 'passive margin' sequence as opposed to a flysch sensu stricto. The timing of Numidian Flysch deposition is also coincidental with uplift of the Atlas chain in North Africa, during a period of significantly wetter conditions. A switch from carbonate to clastic deposition results from these conditions, and the Numidian Flysch Formation is considered an offshore extension of this regional sedimentation.Characterisation of outcrops in Sicily and Tunisia shows remarkably similar lithofacies and depositional elements. Sinuous upper slope channel complexes are entrenched within slope deposits to a depth of 100 m and occur within channel systems up to 5.7 km in width. They are filled predominantly with massive ungraded sandstones interpreted to aggrade through quasi-steady turbidity currents, interbedded with normally graded turbidites. Channel elements are subseismic in scale, are nested within complexes and show sinuosity. Coupled with lateral offset stacking, this strongly affects the architecture and facies heterogeneity of channel complexes. When compared to globally reviewed data, the thickness of channel elements as shown through their frequency distribution also suggests a fundamental control upon the degree of slope incision which is as yet unconstrained.In lower slope settings, channel complexes stack aggradationally with a width of over 1000 m. They are also predominantly filled with massive sandstones in fining upwards cycles, and show heterogeneous margins and large scale slumping. In central Sicily, large channel complexes are overlain by a stacked lobe complex, in turn overlain by a channel lobe transition zone. This progression coupled with palaeocurrent variability suggests intraslope deformation strongly impacts transiting flows through changes in flow capacity. Salt tectonics, present in Algeria and Tunisia is a possible forcing mechanism.Taken in context, the sections in Sicily record a proximal to distal palaeogeographic trend which is reconstructed towards the north/northeast once well constrained tectonic rotations are taken into account. Given regional similarities, controls upon slope architecture are interpreted to be similar throughout the basin, and deposits in Sicily therefore provide a good analogue for the remainder of the basin. These results therefore allow for a better constrained fan architecture, along with the allogenic controls upon them. Given the continental extent of this formation, the Numidian Flysch Formation provides a unique opportunity to study controls upon fan architecture once provenance and intraslope topography is factored in.

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