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Thesis advisor: Kenneth G. Galli / Thesis advisor: Noah P. Snyder / The Brushy Basin Member of the Morrison Formation records a time of increased volcanic activity in the North American Cordillera during the Late Jurassic. Sedimentological and petrographic observations in the Brushy Basin, in conjunction with findings of widespread plutonic intrusion in the source areas, point to a volcanic pulse within the Cordilleran magmatic arc. This study investigated the subjacent Salt Wash Member, for the purpose of better constraining the timing of the volcanic pulse. Petrographic and statistical analyses of the Salt Wash sandstone identified statistically significant upsection trends in volcanic rock fragment and plagioclase feldspar at one of the four study areas. The remaining three study areas showed no upsection trends in sandstone composition that would reflect a pulse in volcanism during Salt Wash Member time. It is more likely that the Salt Wash was deposited during a time of volcanic quiescence leading up to the post-Nevadan Orogeny volcanic reactivation. Sedimentology and cementation patterns of the Salt Wash Member were also studied. Cathodoluminescence indicates that the member was well-flushed with shallow formation waters, thus preventing any calcite optical zoning. Luminescence intensity suggests that the Salt Wash Member sediments were cemented at varying depths and within differing Eh-pH regimes. Field-based sedimentological observations support a model of braided stream channel deposition across a semi-arid landscape with streamflow entering the basin from both the south and west. / Thesis (MS) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Mount Etna, Europe's largest active volcano, shows a long history of changing structure and environment, culminating in the modern volcanic edifice with its observed slope instability and region of past collapse (the Valle del Bove). The structure and evolution of the volcano and, more importantly, the Valle del Bove are poorly understood but have major effects on its present day behaviour. Several geophysical techniques have been used in order to determine new models for the sub-surface structure of the volcano, concentrating on the Eastern Flank and the Valle del Bove. The Valle del Bove is an important feature on the Eastern Flank. It measures 5 by 7 km and is 1200m deep at its maximum. Its formation and evolution are poorly understood and represent the main thrust of this work. The primary work has been gravity and aeromagnetic surveys combined with 2.5-D and 3-D modelling to develop a better understanding of the sub-surface structures of the area. This work has identified several large gravity and magnetic anomalies indicating areas of contrasting geophysical properties. A 16mGal positive gravity anomaly over the Southern Wall of the Valle del Bove is interpreted as a large (volume = 38km3) high density (2950 kg m-3) body, related to the old Trifoglietto centre, possibly representing the ancient feeder system. A second high density body is seen under the present day summit region and is interpreted as an area of shallow level magma storage within the upper flanks of the volcano. A negative gravity anomaly of 10mGal towards the coast, over the Chiancone sedimentary fan deposit, is interpreted as reworked debris flow material, derived from the Valle del Bove. The shape of the anomaly is strongly asymmetrical relative to the geographical extent of the deposit, with the centre of the anomaly sitting over its Northern extent. The resultant model of this material gives a thickness of 700m, with the material being deposited within a fault controlled basin, open to the sea. Such a shape suggests that a sizeable volume of material may be deposited off-shore. Below the Etnean volcanics lie sedimentary layers which slope in an easterly direction, providing a surface over which the Eastern Flank. is free to slide. Finite element modelling of the stress fields within the volcanic edifice and basement shows that the effects of sea-level variations and glaciations may be of a sufficient magnitude to affect the volcanic system, however, the time over which these changes occur may be more significant than the changes themselves. Similarly the Valle del Bove is shown to have had a significant effect on the stress patterns, and has resulted in a self-reinforcing process whereby the tension caused by the removal of mass encourages further collapse. Palaeomagnetic measurements show that rotational failure has not been important in the formation of the Valle del Bove, and combined with the results of the other methods, show the Valle's formation to have been via a series of small piecemeal collapses, possibly relating to oversteepening of the walls following dyke emplacement. These results are combined together to show that the Valle del Bove has been developing over much of the history of Etna, and is not a recent addition to the volcano.

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No description available.

Rivers sourced in the Himalayan mountains support more than 10% of the global population, where the majority of these people live downstream of the mountain front on the alluvial Indo-Gangetic Plain. Many of these rivers however, are also the source of devastating floods. The tendency of these rivers to flood is directly related to their large-scale morphology. In general, rivers that drain the east Indo-Gangetic Plain have channels that are perched at a higher elevation relative to their floodplain, leading to more frequent channel avulsion and flooding. In contrast, those further west have channels that are incised into the floodplain and are historically less prone to flooding. Understanding the controls on these contrasting river forms is fundamental to determining the sensitivity of these systems to projected climate change and the growing water resource demands across the Plain. This thesis examines controls on river morphology across the central portion of the Indo-Gangetic Plain drained by the Ganga River (the Ganga Plain). Specifically, the relative roles of basin subsidence, sediment grain size and sediment flux have been explored in the context of large-scale alluvial river morphology over a range of timescales. Furthermore, this thesis has developed and tested techniques that can be utilised to help quantify these variables at catchment-wide scales. This analysis has been achieved through combining new sediment grain size, pebble lithology and cosmogenic radionuclide data with quantitative topographic and sedimentological analysis of the Ganga Plain. In the first part of this thesis, I examine the contrast in channel morphology between the east and west Ganga Plain. Using topographic analysis, basin subsidence rates and sediment grain size data, I propose that higher subsidence rates in the east Ganga Plain are responsible for a deeper basin, with perched low-gradient rivers systems that are relatively insensitive to climatically driven changes in base-level. In contrast, lower basin subsidence rates in the west are associated with a shallower basin with entrenched river systems that are capable of recording climatically induced lowering of river base-level during the Holocene. Through an analysis of fan geometry, sediment grain size and lithology, I then demonstrate that gravel flux from rivers draining the central Himalaya with contributing areas spanning three orders of magnitude is approximately constant. I show that the abrasion of gravel during fluvial transport can explain this observation, where gravel sourced from more than 100 km upstream is converted into sand by the time it reaches the Plain. I attribute the over-representation of quartzitic pebble lithologies in the Plain (relative to the proportion of the upstream catchment area likely to contribute quartzite pebbles) to the selective abrasion of weaker lithologies during transport in the mountainous catchment. This process places an upper limit on the amount of coarse sediment exported into the Indo-Gangetic Plain. Finally, I consider the use of cosmogenic 10Be derived erosion rates as a method to generate sediment flux estimates over timescales of 102-104 years. Cosmogenic radionuclide samples from modern channel and independently dated Holocene terrace and flood deposits in the Ganga River reveal a degree of natural variability in 10Be concentrations close to the mountain front. This is explored using a numerical analysis of processes which are likely to drive variability in catchment-averaged 10Be concentrations. I propose that the observed variability is explained by the nature of stochastic inputs of sediment (e.g. the dominant erosional process, surface production rates, depth of landsliding, degree of mixing), and secondly, by the evacuation timescales of individual sediment deposits which buffers their impact on catchment-averaged concentrations. In landscapes dominated by high topographic relief, spatially variable climate and multiple geomorphic process domains, the use of 10Be concentrations to generate sediment flux estimates may not be truly representative. The analysis presented here suggests that comparable mean catchment-averaged 10Be concentrations can be derived through different erosional processes. For a given 10Be concentration, volumetric sediment flux estimates may therefore differ.

The Ucayali Basin is a Peruvian sub-Andean basin that initially formed during the extensive tectonics of the Early Paleozoic. Originally, the Ucayali Basin was part of a larger basin that extended east of the current Andean chain along the Peruvian territory. Subsequently, this large basin was divided into many smaller sub-Basins during the Andean Orogeny. Today, the basin covers an area of about 140,000 km2, and it is morphologically defined by two well-differentiated structural features: the sub- Andean fold and thrust belt (SFTB) to the west and the Amazon plain and Brazilian shield to the east. It is limited to the north and south by the Contaya and Fitzcarrald Arches respectively, the Andes to the west and the Brazilian Shield to the east. These structural features acted as favorable elements to add sediments and to contribute to the structural development of this basin. The sedimentary section of the basin varies in thickness from 1 to 10 km, with ages of strata ranging from the Paleozoic to Quaternary. The strata were deposited in deep and shallow marine as well as transitional and fluvial continental environments. The most important phase of marine sedimentation was initiated with the transgression of the Cretaceous sea (Aptian –Albian) over the irregular paleogeography defined by morphologic highs and peneplains. Tectonic features of the basin show structural deformations parallel to the Andean front, where overturned structures are observed. These are commonly cut by thrusts and laterally displaced by strike-slip faults. To better understand the development of the Shira Mountains in the central part of the Ucayali Basin, the structural and stratigraphic relationships were mapped out using a dense grid of 2D seismic reflection data and well log control. Three regional EW cross sections were constructed and restored to the top of the Cretaceous to determine the nature of deformation and faulting during the Paleozoic and Mesozoic. The reconstructions show that Shira Mountains fault was initially a major normal fault bounding a half graben. The fault was reactivated by later compression as a thick-skinned thrust fault that detaches between 21 and 24 km depth. Reactivation occurred during Upper Miocene between 7.2 and 5.3 Ma, corresponding to the Quechua 3 compressive phase of Andean Orogeny. The shortening of the central Ucayali Basin determined by the reconstructed cross sections ranges between 3 and 5.5%.

The Ucayali Basin is a Peruvian sub-Andean basin that initially formed during the extensive tectonics of the Early Paleozoic. Originally, the Ucayali Basin was part of a larger basin that extended east of the current Andean chain along the Peruvian territory. Subsequently, this large basin was divided into many smaller sub-Basins during the Andean Orogeny. Today, the basin covers an area of about 140,000 km2, and it is morphologically defined by two well-differentiated structural features: the sub- Andean fold and thrust belt (SFTB) to the west and the Amazon plain and Brazilian shield to the east. It is limited to the north and south by the Contaya and Fitzcarrald Arches respectively, the Andes to the west and the Brazilian Shield to the east. These structural features acted as favorable elements to add sediments and to contribute to the structural development of this basin. The sedimentary section of the basin varies in thickness from 1 to 10 km, with ages of strata ranging from the Paleozoic to Quaternary. The strata were deposited in deep and shallow marine as well as transitional and fluvial continental environments. The most important phase of marine sedimentation was initiated with the transgression of the Cretaceous sea (Aptian - Albian) over the irregular paleogeography defined by morphologic highs and peneplains. Tectonic features of the basin show structural deformations parallel to the Andean front, where overturned structures are observed. These are commonly cut by thrusts and laterally displaced by strike-slip faults. To better understand the development of the Shira Mountains in the central part of the Ucayali Basin, the structural and stratigraphic relationships were mapped out using a dense grid of 2D seismic reflection data and well log control. Three regional EW cross sections were constructed and restored to the top of the Cretaceous to determine the nature of deformation and faulting during the Paleozoic and Mesozoic. The reconstructions show that Shira Mountains fault was initially a major normal fault bounding a half graben. The fault was reactivated by later compression as a thick-skinned thrust fault that detaches between 21 and 24 km depth. Reactivation occurred during Upper Miocene between 7.2 and 5.3 Ma, corresponding to the Quechua 3 compressive phase of Andean Orogeny. The shortening of the central Ucayali Basin determined by the reconstructed cross sections ranges between 3 and 5.5%.