Browsing by Subject "Shatsky Rise"
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Item Application of the 2-D Continuous Wavelet Transforms for Characterization of Geological and Geophysical Data(2014-05-05) Vuong, Au KShatsky Rise, located in the northwest Pacific Ocean, is one of the largest oceanic plateaus. The origin and evolution of the oceanic plateaus are unclear because these features are remote and poorly imaged with geophysical data. Recently, marine multi-channel seismic (MCS) data were collected over Shatsky Rise to image its upper crustal structure. These data have the potential to improve understanding of the processes of basaltic volcanism and the formation and evolution of oceanic plateaus by providing direct insights into the geometry and distribution of igneous eruptions. In contrast to sedimentary settings, it is often difficult to interpret deeper layers within basaltic crust because of rugged layering and scattering. Reflections in igneous crust are characterized by poor lateral continuity compared with marine sediments and often with weak impedance contrasts, resulting in lower signal-to-noise ratio and more challenging interpretation. In this dissertation, we apply the 2-D anisotropic continuous wavelet transform (CWT) method to improve interpretations of MCS data from the Shatsky Rise oceanic plateau. Applying the transform to the time-domain MCS profiles with appropriate values of wavelength and period produces new images with enhanced continuity of reflectors and reduced amplitudes of incoherent noise at different periods. The analysis of the results obtained by using 2-D CWT on the MCS data over the Tamu Massif part of the Shatsky Rise also helps reveal features such as dome-like bulges possibly associated with lava intrusion and faults in the deeper part of the crust associated with volcanic rock. These were not readily seen in the original seismic images, but the suppression of random noise and other signal with low coherence makes their interpretation possible. These and similar results provide new insights into the complexity of the igneous processes forming Tamu Massif. The other research topic is to apply the CWT analysis to characterize and mea- sure the roughness of mineral surfaces to understand the effects of geochemical re- actions on the surface of the mineral. The effects of the geochemical and environ- mental reactions process are strongly related to the surface roughness. Because a rough surface has a large number of molecules exposed with unfilled bonds, these molecules have greater energy and react more readily. A thorough knowledge of the surface roughness could lead to better understanding of geochemical reactions and environmental effects on the mineral surface. We apply the 2-D CWT to character- ize the surface of two samples of Fe_(2)O_(3) and three samples of calcite. For a fresh surface of the calcite mineral, a cleavage plane exposed by fracturing, the surface measurements show discrete jumps in height because of the limited resolution of measurements. These stair-step-like features have been detected by using 2-D CWT with wavelength of 32.2 ? . Two other samples of calcite and two samples of Fe_(2)O_(3) show erosion effects and are much rougher. In these cases, the application of 2-D CWT analysis helps to localize the rough features at certain wavelengths of the wavelet, providing better understanding of the characterization of surface roughness. These locations are asso- ciated with the high energy surface where we expect the geochemical and weathering reaction initially occur. In the future work, one could implement the 2-D CWT in- version, allowing for the reconstruction of the surface of the mineral at selected wave- lengths. Therefore we could observe directly the relationship between the roughness and the wavelength.Item Estimation of Impedance Using Seismic Reflection Data Based on Transdimensional Inversion(2014-04-23) Dadi, SireeshDeterministic seismic inversion can obtain optimal results when there is a linear relationship between data and model parameters during local optimization (single optimum solution). For nonlinear geophysical problems and in the presence of multiple local minima for a cost function, global optimization techniques are necessary to characterize the global minimum solution. Stochastic, model-based seismic inversion is a widely used global optimization technique and Markov Chain Monte Carlo (MCMC) method is a natural choice to sample model parameters during the random walk. In this dissertation, I apply a sampling technique called reversible jump Markov Chain Monte Carlo (rjMCMC) to traverse the model space. A key property of this approach is that it automatically changes the layer thicknesses and number of layers, thereby predicting the optimum number of model parameters during inversion. The method applies Bayesian inversion, with rjMCMC sampling, so that it also quantifies the uncertainty in model parameters based on an ensemble of models. I apply Bayesian inversion with rjMCMC sampling for two applications. In the first application, I define upscaling velocity logs as an inversion problem to obtain optimal models and quantify uncertainty of upscaled models at the well location. The upscaled velocity at the well locations can be subsequently used to stabilize velocity inversion during Full waveform Inversion (FWI) for seismic imaging purposes. In the second application, I perform post-stack seismic inversion to obtain shallow impedance structure of the TAMU and Ori volcanoes at the Shatsky Rise oceanic plateau. Since impedance is a rock property, it is used to discriminate basalt rock types, which gives insight into the late-stage evolution of both the volcanoes.Item Oceanic and atmospheric response to climate change over varying geologic timescales(2012-07-16) Woodard, Stella C.Global climate is controlled by two factors, the amount of heat energy received from the sun (solar insolation) and the way that heat is distributed Earth's surface. Solar insolation varies on timescales of 10s to 100s of thousands of years due to changes in the path of Earth's orbit about the sun (Milankovitch cycles). Earth's internal boundary conditions, such as paleogeography, the presence/absence of polar icecaps, atmospheric/oceanic chemistry and sea level, provide distribution and feedback mechanisms for the incoming heat. Variations in these internal boundary conditions may happen abruptly or, as in the case of plate tectonics, take millions of years. We use geochemical and sedimentological techniques to investigate the response of ocean chemistry, regional aridity and atmospheric and oceanic circulation patterns to climate change during both greenhouse and icehouse climates. To explore the connection between orbitally-forced changes in solar insolation, continental aridity and wind, we generated a high-resolution dust record for ~58 Myr old deep-sea sediments from Shatsky Rise. Our data provide the first evidence of a correlation between dust flux to the deep sea and orbital cycles during the Early Paleogene, indicating dust supply (regional aridity) responded to orbital forcing during the last major interval of greenhouse climate. The change in dust flux was comparable to that during icehouse climates implying subtle variations in solar insolation have a similar impact on climate during intervals of over-all warmth as they do during glacial-interglacial states. The Carboniferous Period (359-299 Ma) marks a critical time in Earth's history when a series of tectonic and biological events caused a shift in the mean climate state from a global "greenhouse" to an "icehouse". Geochemical records extracted from sedimentary rocks deposited in shallow epicontinental seaways are increasingly being used to infer relationships between tectonism, carbon cycling and climate and therefore are assumed to reflect global ocean processes. We analyzed radiogenic isotopes in biogenic apatite along a North American transect to constrain the degree of geochemical coupling between the epicontinental seas and the open ocean. Our results argue strongly for decoupling of North American seaways from the open ocean by latest Mississippian time.Item Paleomagnetism of Igenous Rocks from Shatsky Rise(2013-04-24) Pueringer, MargaretShatsky Rise is oceanic plateau in the northwest part of the Pacific Ocean, and the formation of Shatsky Rise is poorly known. To get a better understanding of the formation Integrated Ocean Drilling Program (IODP) Expedition 324 drilled five sites: Sites U1347 and U1348 on Tamu Massif, Site U1349 and U1350 on Ori Massif, and Site U1346. Paleomagnetic measurements of the basaltic flows recovered can give insight into the timing and paleolatitude of each site. Relating the change in principle component inclination over depth at each site to the paleosecular variation of the geomagnetic field can better constrain the timing of the eruptions. Measurements were carried out by different sources during IODP Expedition 324 and after. This study is an amalgamation of the results from Sites U1346, U1347, U1349, and U1350. Samples from each site were divided into half and demagnetized using alternating field (AF) demagnetization and thermal (TH) demagnetization. After the drilling overprint was removed most samples displayed univectorial decay in the orthogonal vector plot. AF demagnetized samples displayed a low median destructive field (MDF) behavior, <10 mT, and a moderate MDF behavior, >10-20 mT. Thermal demagnetized samples displayed three behaviors: a rapid decline in magnetic intensity after moderate temperature steps behavior, a linear decline in magnetic intensity behavior, and some samples displayed a small segment of self-reversal at 300?-350?. Using the Cox and Gordon (1984) method Sites U1346, U1347, and U1349 displayed very little variation in principal component inclinations over depth, implying a relatively rapid lava emplacement of 10^2-10^3 years. Site U1350 display more variation, implying a longer eruptive time frame of 10^4-10^5years. With the assumption of a normal polarity the paleolatitude estimates are -11.0? +22.2?/-21.4? for Site U1346, 11.3? 27.4?/-28.5? for Site U1347, -5.0? +20.8?/-20.6? for Site U1349 and 1.6? ?7.7 ? for Site U1350. The site paleolatitudes imply that Ori Massif (Sites U1350 and U1349) formed at the equator and Tamu Massif (Site U1347) and Shirshov Massif (Site U1346) formed slightly north and south of the equator respectively. All results are consistent with the interpretation that Shatsky Rise formed near the equator.Item Structural and Morphologic Study of Shatsky Rise Oceanic Plateau in the Northwest Pacific Ocean from 2D Multichannel Seismic Reflection and Bathymetry Data and Implications for Oceanic Plateau Evolution(2014-04-10) Zhang, JinchangShatsky Rise is one of the largest oceanic plateaus, a class of volcanic features whose formation is poorly understood. It is also a plateau that was formed near spreading ridges, but the connection is unclear. The geologic structure and morphology of Shatsky Rise oceanic plateau provides key observations that can help understand its formation. Deep penetrating 2D multichannel seismic (MCS) reflection profiles and high-resolution multi-beam sonar data were acquired over the southern half of Shatsky Rise on R/V Marcus G. Langseth during two cruises. The MCS profiles allow us to image Shatsky Rise's upper crustal structure and Moho structure with unprecedented detail, and the multi-beam bathymetry data allow us to produce an improved bathymetric map of the plateau. MCS profiles and bathymetry data show that two of the volcanic massifs within Shatsky Rise are immense central volcanoes. Tamu Massif, the largest (~450 ? 650 km) and oldest (~145 Ma) volcano, is a single central volcano with rounded shape and shallow flank slopes (<0.5o-1.5o), characterized by lava flows emanating from the volcano center and extending hundreds of kilometers down smooth, shallow flanks to the surrounding seafloor. Ori Massif is another large volcano that is similar, but smaller in size than Tamu Massif. The morphology of the massifs implies formation by extensive and far ranging lava flows emplaced at small slope angles. The relatively smooth flanks of the massifs imply that the volcanoes were not greatly affected by rifting due to spreading ridge tectonics. Several down-to-basin faults observed on the flanks of the massifs are not parallel to magnetic lineations, suggesting that they were not formed by seafloor spreading. The Moho of Shatsky Rise starts shallow (~6-7 km) beneath normal crust at the distal flanks and dips (~3o-5o) towards the center of plateau massifs, reaching maximum thickness of ~ 30 km. Shatsky Rise crustal structure is consistent with the Moho topography of isostatically compensated crustal structures, which is why the plateau exhibits a small free-air gravity anomaly signature. Shatsky Rise was built on young oceanic lithosphere with little rigidity, so the plateau formed in isostatic equilibrium with a deep crustal root.