Seismoacoustic Study of the Shallow Gas Transport and ... - E-LIB

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Chapter 1 which have documented active gas seeps. The biotechnology industry can find new ‘resources’ in the microbes of chemosynthetic communities of vents and seeps (Querellou, 2003). 1.2.2 Related seabed features 1.2.2.1 Gas seeps Gas seeps belong to natural springs where liquid and gaseous hydrocarbons leak out of the seafloor. While freshwater springs are fed by underground water, gas seeps are fed by natural subsurface reservoirs of oil and natural gas. Gas seeps are generated by focused upward fluid migration (e.g. Judd, 2003), and the composition of gas seep fluids is dominated by methane. Based on the proportion of methane and the different nature of the accompanying fluids, methane seeps could be divided into four groups: (1) those dominated by microbial methane; (2) those dominated by thermogenic methane; (3) seeps associated with gas hydrates from a thermogenicmethane source; and (4) those associated with gas hydrates with a microbial-methane source (Judd and Hovland, 2007). Generally, gas seeps are related to shallow gas/gas hydrate accumulations or deeper hydrocarbon deposits (Kvenvolden, 1993; Buffet, 2000). They are globally distributed (Fig. 3), especially in the marine sediment of modern continental margins (Dimitrov, 2002b; Judd, 2003). However, the exact number and distribution of seep sites have so far not been clarified due to the fact that most of the world's seas and oceans have not been studied sufficiently (Judd, 2003). Figure 6 Gas bubble plumes from the Batumi seep area, Black Sea during ROV observations in spring 2007 (from Pape et al., 2011). Unique endemic ecosystems of marine organisms could be supported by gas seeps, containing chemoautotrophic clams, tubeworms and bacterial mats, which use the hydrogen sulphide and methane as energy source at the seafloor surface (Hovland et al., 1985; Suess et al., 1985). Aharon (1994), Roberts and Carney (1997), and Olu et al. (1997) suggested that the locations of seeps and the rate, spatial variability and longevity of the flow can be indicated by the cold seep communities. 11
Chapter 1 If methane and other gases are to escape through the seabed into the water column, the flux rate must exceed the microbial utilization rate. At high flux rates, dense bubble plumes (Fig. 6) are generated by large quantities of methane (Michaelis et al., 2002). Gas bubbles rising from the seabed can be detected directly by video observation or as gas flares (Fig. 7) by high-frequency acoustic systems such as echosounders, side scan sonar, and shallow subbottom profiles (Judd and Hovland, 2007). Rising velocities of gas bubbles can also be determined based on visual investigations and hydroacoustic measurements. For example velocities of 19-22 cm/s near the seafloor and 12-14 cm/s at the top of flares are observed at the Dvurechenskiy mud volcano in the Sorokin Trough, Black Sea (Greinert et al., 2006). Figure 7 Numerous methane seeps in the Dnepr paleo-delta, northwestern Black Sea, at water depths of 66 to 825 m (from Naudts et al., 2006). An abundant presence of methane seeps has been observed at the margins of the Black Sea, such as in the Dnepr paleo-delta, northwestern Black Sea (Fig. 7; Naudts et al., 2006). Gas seeps may occur with or without the formation of pockmarks and mud volcanoes. These morphological features can be easily recognized in bathymetric, side scan sonar and seismic data (e.g. Hovland and Judd, 1988). Gas seeps without apparent morphological features can be detected in backscatter data. High backscatter signatures except those caused by high topographic gradients are thought to correspond to authigenic carbonates, free gas and gas hydrates close to the seafloor or the seep-related chemosynthetic communities, such as tubeworms, mussels and even corals. The high backscatter responses are often characterized by circular or flow-like shape (Anderson and Bryant, 1990; Sager et al., 2003). Shallow gas accumulation or columns of focused 12
Page 1: Seismoacoustic Study of the Shallow
Page 4 and 5: Table of contents Table of contents
Page 6 and 7: Abstract Abstract In recent years,
Page 8 and 9: Outline of the Dissertation Outline
Page 10 and 11: Chapter 1 Chapter 1. Introduction 1
Page 12 and 13: Chapter 1 reflections, interpreted
Page 14 and 15: Chapter 1 Submarine gas seeps, pock
Page 18 and 19: Chapter 1 fluid migration related t
Page 20 and 21: Chapter 1 Evidence of gas seepage
Page 22 and 23: Chapter 1 The three main different
Page 24 and 25: Chapter 1 from deeper sources in th
Page 26 and 27: Chapter 1 numerous countries such a
Page 28 and 29: Chapter 1 1.5 Geological setting of
Page 30 and 31: Chapter 1 main sequences consist of
Page 32 and 33: Chapter 1 craterlike depressions wi
Page 34 and 35: Chapter 1 Jurassic - Paleogene, Upp
Page 36 and 37: Chapter 1 respectively, and one wat
Page 38 and 39: Chapter 1 During the seismic data p
Page 40 and 41: Chapter 1 1.6.2 The Parasound sedim
Page 42 and 43: Chapter 1 Caress, D.W., and Chayes,
Page 44 and 45: Chapter 1 Hovland, M., Gardner, J.V
Page 46 and 47: Chapter 1 Luo, X.R. and Vasseur, G.
Page 48 and 49: Chapter 1 Schroot, B.M., Klaver, G.
Page 50 and 51: Chapter 2 Chapter 2. Shallow Gas Tr
Page 52 and 53: Chapter 2 times. Seismically imaged
Page 54 and 55: Chapter 2 spike noise were marked a
Page 56 and 57: Chapter 2 The 2D high resolution se
Page 58 and 59: Chapter 2 Figure 4 A close-up of se
Page 60 and 61: Chapter 2 within the upper sediment
Page 62 and 63: Chapter 2 volcanoes between 66 and
Page 64 and 65: Chapter 2 Figure 7 Geo-seismic sect
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Chapter 2 In the study area, many b
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Chapter 2 volcanism could be calcul
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Chapter 2 along the feeder channel
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Chapter 2 Evpatoriya). Soviet Geol
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Chapter 3 Chapter 3. Sedimentary Ev
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Chapter 3 South (Fig. 2). The water
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Chapter 3 Figure 3 (a) Uninterprete
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Chapter 3 Seven seismic facies type
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Chapter 3 Seismic Unit 5 ranges in
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Chapter 3 3.4.3.5. Seismic Unit 2 A
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Chapter 3 Figure 11 (a) Uninterpret
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Chapter 3 Figure 13 (a) Uninterpret
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Chapter 3 boundary between the Plio
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Chapter 3 Seismic Unit 6 belongs to
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Chapter 3 subsidence was coincident
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Chapter 3 Acknowledgements We thank
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Chapter 3 Tugolesov, D.A., Gorshkov
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Chapter 4 study area at ~900 m wate
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Chapter 4 Figure 2 Bathymetry of th
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Chapter 4 University of Bremen). At
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Chapter 4 and Ridge R2 (GeoB07-139)
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Chapter 4 flares location. Anticlin
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Chapter 4 GeoB07-145. Green arrows
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Chapter 4 4.4.3.2.3. Other anomalou
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Chapter 4 Slope fan deposits with f
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Chapter 4 Figure 12 Possible locati
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Chapter 4 bulk hydrate or even high
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Chapter 4 may add to gas accumulati
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Chapter 4 The narrow-beam Parasound
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Chapter 4 River fan deposits. Being
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Chapter 4 Klaucke, I., Sahling, H.,
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Chapter 4 Wagner-Friedrichs, M., 20
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Chapter 5 deposited; during lowstan
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Chapter 5 accumulations. An acousti
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Acknowledgements Acknowledgements I
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