3d Seismic Imaging Of Submarine Stratovolcanic And Salt Structures Beneath The Taranaki Basin New Zealand And The Gulf Of Mexico

"The relationship of submarine stratovolcanic and salt structures with overlying sediments creates a significant role in the petroleum system due to the emplacement and burial of volcano and salt. This study characterizes the spatial and temporal distribution of structural and stratigraphic features associated with submarine stratovolcano and salt body to provide insights for elements and processes of petroleum geology related to regional tectonics. The stratovolcanic and salt structures are clearly identified on seismic sections. However, distortion of ray paths passing through the salt and turning seismic waves prevents accurate identification of steep flanks of salt. The seismic response to a surface of contact between the volcanic/salt structure and surrounding strata is interpreted as an unconformity. Adjacent younger layers onlap volcanic and salt structures. Magmatic intrusion thermally affects the maturity of source rocks, and oil migrates from the source rocks to volcaniclastic rocks along the major fault-2. Hydrocarbons migrate up to the shallow depth due to the fault and lack of impermeable seal rocks, and that causes gas chimneys and bright spots to be observed on seismic sections. Stratigraphic interpretation reveals features such as gullies, canyons, incised valleys, dendritic drainages, and seamount-edge fans. Seismic stratigraphy of volcano and enclosing formations shows seven dominant seismic facies. Petrophysical analysis indicates 21% porosity and 86.24 mD permeability for the Miocene Volcanics. Similar results are obtained in the interpretation of salt structures. Seismic interpretation focused on the seafloor shows stratigraphic and structural configuration affected by salt body in shallow depths. The high-amplitude seafloor reflectivity area represents the seafloor mound associated with hydrocarbon migration along growth faults, which were created by the salt body. Chaotic and attenuated reflections at shallow depths and negative reflection below the seafloor mound show the presence of gas"--Abstract, page iii.

The Taranaki Basin was formed as a consequence of multiple geologic events. From the Cretaceous period until present, it went through rifted margin, passive margin, foreland basin, and back-arc phases. A dominantly sandy unit, the Moki Formation, was deposited during the Middle Miocene within the Taranaki Basin offshore the west coast of the North Island of New Zealand. The study area covers about 1600 km2 of the southern part of the north Taranaki graben, an area covered by a 3D seismic volume. The Moki Formation is interpreted as a basin floor fan deposit that accumulated during basinward migration of the shelf edge with supplied sediments sourced from the SSE. Seismic profiles revealed that the mound-shape reflectors of Moki fan deposits situated between continuous reflectors of underlying Oligocene carbonates and hemipelagic muds of the overlying Manganui Formation. The reflections of the Moki sandy fan deposits locally grade laterally into interlobal deposits of hemipelagic muds. Correlation between wells Witiora-1, Taimana-1, and Arawa-1 verified the seismic interpretation, which shows an overall thickness variation of fan deposits that range from a greater thickness in the middle part of the sand lobe accumulation towards diminished thicknesses on the flanks. Gamma ray facies show clear progradation then aggradation motif that confirm the results from the seismic analyses. Depending on seismic attribute maps, paleochannels associated with the sand bodies sharing a SE to NW flow direction can be distinguished. Due to the volcanic activity in the eastern mobile belt, no paleochannels or significant stratigraphic features were recognized within the studied interval of the seismic data. Generally, in the study area, the fan deposits represent sand rich deposits that developed and prograded from south to north with variations in lateral extent driven by three major shifts in sediment pathways as the feeder channel orientations changed.

The Chandeleur Slide is a large submarine landslide on the Gulf of Mexico seafloor in approximately 1100 meters of water, 200 km southeast of New Orleans, LA. This part of the Mississippi Fan received high sedimentation throughout the Pleistocene, causing high pore fluid pressure and abundant slope failures, though few as large as the Chandeleur. Given its proximity to major coastal cities, oil and gas infrastructure, and its large size, I examine the Chandeleur Slide to: (1) map the location and thickness of the displaced sediment, (2) understand what led to the initial slope failure, (3) decipher if this was a fast-moving or slow-moving event, and (4) consider potential hazard implications a slide like the Chandeleur represents for seafloor infrastructures and tsunami risks to coastal communities surrounding the Gulf of Mexico. I interpreted publicly available 2D and 3D multichannel seismic surveys and high-resolution bathymetry data to reveal several flow paths generally due south/southeast, and a slow-moving sediment mass with a translational-rotational behavior. The Chandeleur Slide includes extensional faulting in the headscarp area and compressional structures in the northern-most toe confined by a natural ramp-like structure. Beneath the Chandeleur Slide, I observe an upward-migrating salt body that has compressed a regional sand-rich unit (the Blue Unit). I interpret that the upward-migrating salt led to overpressure within Blue Unit sand layers, facilitating the initial failure of the Chandeleur. After failure, the Chandeleur Slide transported a large volume of sediment southward but was blocked by antecedent topographic highs that deflected much of the sediment to the south/southwest. The initial failure was followed by retrogressive headwall retreat northward, which created the prominent scarp on the seafloor. In total, the Chandeleur Slide comprises an area just over 1000 km2 and contains about 300 km3 of failed sediment.

Multiple submarine landslides have been previously documented on the north flank of the Santa Barbara Channel, and such failures are considered to be capable of generating local tsunamis hazards to the Santa Barbara region. 2D seismic-reflection datasets provide a general view of regional framework geology, including faulting and folding associated with north-south compression. However, better understanding of the relationships between faults, folds, stratigraphic architecture, and submarine landslides can be obtained with 3D seismic datasets. In this study we use an industry 3D seismic-reflection volume that encompasses the slope and shelfbreak surrounding the Gaviota submarine landslide (3.8 km2) to investigate structural and stratigraphic controls on slope failure in this region. The depth-migrated seismic volume shows a network of stacked thrust faults, backthrusts, and splays that result in both broad and local zones of compression, folding, and uplift along the slope and shelf. One localized zone of enhanced folding and uplift associated with small-scale thrust faults is located directly beneath the Gaviota landslide, while another zone is located directly below the westernmost extent of a seafloor fissure inferred to represent incipient failure. In addition, 3D seismic attribute analysis provides insight into the shallow sedimentary section of the failed and non-failed sedimentary packages. Calculation of RMS amplitude within a windowed region below the seafloor horizon delineates an apparent zone of gas-charged strata that onlaps onto older folded sediments. The up-dip limit of these gas-charged sediments appears to align with the location of seafloor fissures and the Gaviota landslide headwall. The slope gradient surrounding the Gaviota slide is only 4°, which is significantly lower than the internal friction angle for fine-grained marine sediments. It is therefore proposed that the combination of active 8 deformation and fluid charging acted to pre-condition and trigger the failure of the Gaviota landslide through a reduction in shear strength. These conditions are also present in intact sections of the slope adjacent to the Gaviota landslide, which should be considered prone to future landslides.

Submarine mass movements represent major offshore geohazards due to their destructive and tsunami-generation potential. This potential poses a threat to human life as well as to coastal, nearshore and offshore engineering structures. Recent examples of catastrophic submarine landslide events that affected human populations (including tsunamis) are numerous; e.g., Nice airport in 1979, Papua-New Guinea in 1998, Stromboli in 2002, Finneidfjord in 1996, and the 2006 and 2009 failures in the submarine cable network around Taiwan. The Great East Japan Earthquake in March 2011 also generated submarine landslides that may have amplified effects of the devastating tsunami. Given that 30% of the World’s population live within 60 km of the coast, the hazard posed by submarine landslides is expected to grow as global sea level rises. This elevated awareness of the need for better understanding of submarine landslides is coupled with great advances in submarine mapping, sampling and monitoring technologies. Laboratory analogue and numerical modeling capabilities have also developed significantly of late. Multibeam sonar, 3D seismic reflection, and remote and autonomous underwater vehicle technologies provide hitherto unparalleled imagery of the geology beneath the oceans, permitting investigation of submarine landslide deposits in great detail. Increased and new access to drilling, coring, in situ measurements and monitoring devices allows for ground-thruth of geophysical data and provides access to samples for geotechnical laboratory experiments and information on in situ strength and effective stress conditions of underwater slopes susceptible to fail. Great advances in numerical simulation techniques of submarine landslide kinematics and tsunami propagation, particularly since the 2004 Sumatra tsunami, have also lead to increased understanding and predictability of submarine landslide consequences. This volume consists of the latest scientific research by international experts in geological, geophysical, engineering and environmental aspects of submarine mass failure, focused on understanding the full spectrum of challenges presented by submarine mass movements and their consequences.

Understanding submarine fans and turbidite systems has been a major quest of earth scientists. Although these deep water features have been historically important as petroleum reservoirs, recent advances in seismic reflection technology have dramatically improved our ability to image their internal character, making them increasingly more important exploration targets. However, the proliferation of many types of data has made it difficult for geoscientists to examine and integrate all aspects of these important depositional systems. Weimer and Link have addressed this problem by compiling twenty-three key papers that discuss current techniques and concepts and review important geological and geophysical characteristics of both ancient and modern submarine fans and turbidite systems.

The Rumble II (R2) seamounts are a geographical pair of major Quaternary submarine volcanic structures towards the southern end of the Tonga-Kermadec arc; a stratovolcano to the east and a silicic caldera to the west. The R2 seamounts are part of an actively widening arc-backarc complex driven predominantly by the Pacific-Australian plate convergence. The arc-backarc complex is bounded by the Kemadec and Colville Ridges, rifted apart through the opening of the Havre Trough at ca. 6 Ma. Hydrothermal vents have been detected by de Ronde et. al. (2001) at Rumble II West (R2W) but not at Rumble II East (R2E). Hydrothermal activity identified at any location of the Tonga-Kermadec arc is not completely understood. However, surveying to date indicates that silicic volcanoes are active but half of the strato-volcanoes appear inactive. It is therefore hypothesised that hydrothermal venting is related to the composition of the magmas and fluids produced at individual volcanoes, or the extent of magmatic replenishment. A comparison of data gathered during the KARMA voyage (May, 2010) including multiple geophysical disciplines such as seismic, backscatter and multi-beam is examined during this study. The near seafloor geology is used to examine and identify submarine volcanic features present to determine the volcanological history of these structures and to understand the mechanisms in place that drive active volcanism in submarine settings. The R2 seamounts has shown signs of recent activity based on seismic and multibeam features relating to mass flows, hydrothermal vents, feeders, sills and dykes near the surface of the southwest flanks of the R2 seamounts. These findings have aided our understanding of the distribution of economic deposits on seamounts and the likelihood of tsunami generation. Seismic features characteristic of buried hydrothermal vent structures are found in basin areas of the R2 area. The presence of buried hydrothermal vent structures suggests the potential for mineral deposits. Seismic and multibeam features relating to mass flow deposits have been identified in the R2 investigation area which may have resulted from an eruption or the overburdening of volcanic deposits on the flanks of R2E and R2W. However, the eventuation of seafloor instability is unlikely based on slope stability calculations where the threshold for slope failure through overburdening of deposits is not exceeded. The expression of volcanic activity within the R2 area is believed to be affected by the rate at which the Pacfic Plate subducts beneath the Australia plate. Based on the seismic and multibeam characteristics observed in the R2 area varying rates of subduction may have occurred resulting in overlapping volcanic structures. For example, linear expressions and elliptic cones with the longest axis oriented in the northeast to southwest direction is generally observed in the multibeam which trends in the same direction as the orientation of regional subduction and other volcanic features in the Kermadec area. The following volcanic expressions are categorised with varying rates of subduction: 1. Slow subduction and rifting continues in its present state over the western area of R2W, forming the slow accretion of volcanics at the surface and a building of a larger crustal thickness that becomes isostatic, influencing the distribution of magma at the subsurface. 2. Normal rate of subduction. There may be little or no volcanoes at the sediment accretion area adjacent the subduction trench. Regular volcanoes are formed and moved out gradually. 3. Rapid subduction. Smaller volcanoes are formed and thin new crust is present in the area of rifting.

We are poised to embark on a new era of discovery in the study of geomorphology. The discipline has a long and illustrious history, but in recent years an entirely new way of studying landscapes and seascapes has been developed. It involves the use of 3D seismic data. Just as CAT scans allow medical staff to view our anatomy in 3D, seismic data now allows Earth scientists to do what the early geomorphologists could only dream of - view tens and hundreds of square kilometres of the Earth's subsurface in 3D and therefore see for the first time how landscapes have evolved through time. This volume demonstrates how Earth scientists are starting to use this relatively new tool to study the dynamic evolution of a range of sedimentary environments.

The Campos Basin, located on the southeastern Brazil passive margin, is one of the most productive basins in the western South Atlantic. The development of many siliciclastic turbidite reservoirs in the southeastern Brazilian margin provided a great interest in submarine channel systems of the Campos Basin for hydrocarbon exploration purposes. Prior research highlights the variation of sediment supply, sea-level fluctuations and tectonic activity as the most critical controls on channel development within the Campos Basin. The Campos Basin is structurally complex as a result of salt movement, and it is an ideal setting in which to investigate the influences of structural deformation on channel evolution and architecture. I investigated the interaction between development of a post-Miocene submarine channel system and structural deformation related to salt tectonics by using structural and stratigraphic analysis of 3D seismic-reflection data, which covers an area of approximately 1750 km2. I produced detailed maps and cross sections of the submarine channel system, and compared them to structural maps in order to interpret the control of structural deformation on evolution and architecture of the submarine channel system. I interpreted that a regionally mapped seismic-reflection horizon approximates the paleobathymetry at the time of channel formation and correlated with the trend of the channel system. The paleobathymetry mainly dictated the transport pathway of the submarine channel system, as channels within the system mainly stayed in salt-withdrawal basins and avoided salt-influenced structural highs. However, the submarine channel system was diverted to flow directly on the top of a salt diapir within the southeastern part of the study area, rather than staying within salt-withdrawal basins. I explained this anomaly by two uplift stages of the salt diapir. Aggradation smoothed out much of the paleobathymetry associated with the first growth stage of the salt diapir, and the salt-influenced structural high was not able to divert the submarine channel system. The basal surfaces of channels within the system are deformed as a result of the growth of the salt diapir, which suggests that the salt diapir became active again when the submarine channel system started to develop.