Structural Controls on the Formation of Bottom-simulating Reflectors Offshore Southwestern Taiwan from a Dense Seismic Reflection Survey
Philippe Schnurle, Char-Shine Liu, 2009. "Structural Controls on the Formation of Bottom-simulating Reflectors Offshore Southwestern Taiwan from a Dense Seismic Reflection Survey", Natural Gas Hydrates—Energy Resource Potential and Associated Geologic Hazards, T. Collett, A. Johnson, C. Knapp, R. Boswell
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Adense seismic reflection survey with a 400-m (1312-ft) line spacing has been conducted in a 14- by 16-km (9- by 10-mi) area offshore southwestern Taiwan where bottom-simulating reflectors (BSRs) are highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north-south-trending thrust faults and northeast-southwest oblique ramps exist in this region, which impacts on the distribution and seismic characteristics of the BSR. A clear BSR is observed almost continuously in the southeastern half of the survey box, whereas BSRs either appear as small patches or are absent in the northwestern half. The reflection coefficient at the BSR presents abrupt lateral variations, with an average value of —0.094 or 32% of the reflection coefficient at the sea floor. A pattern of seismic blanking beneath the ridge crests overlying a high-amplitude BSR with bright reflections below the BSR in the slope basins reveals the significance of tectonics and sedimentation of the formation of BSRs. Local heat-flow values estimated from BSR subbottom depths show different ranges across the northeast-southwest-trending Yung-An lineament (YAL), with higher heat-flow values ranging from 55 to 70 mW/m2 in the southeastern half of the survey area, whereas the heat-flow values range from 45 to 55 mW/m2 to the northwest of the YAL. In the southeastern part of the survey area, an elongated diapiric feature deforms the sedimentary layers, BSRs occur shallower, and high heat-flow values are inferred. Furthermore, local dips of BSRs and sedimentary strata that crosscut the BSR at intersections of any two seismic profiles have been computed. A dominant N308° stratigraphic up dip direction characterizes the anticlinal ridges; stratal dips fan out toward N285° south of the ridges and toward N330° north of the ridges. The concentric patterns of steep stratigraphic dips constitute favorable migration paths for the upward transport of fluids with significant dissolved-gas content across the BSR, which correlate well with the high gas volumes sampled in this area.
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In September 2004, the American Association of Petroleum Geologists (AAPG) convened a Hedberg Research Conference in Vancouver, British Columbia, Canada titled "Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards." As a continuation of the Hedberg Research Conference in Vancouver, the conveners of the conference and the editors of this Memoir have worked with more than 150 authors and coauthors to prepare this Memoir on gas hydrates. This publication follows the goals of the Hedberg conference; however, the contents of this Memoir were expanded to include all aspects of gas hydrates in nature. This Memoir contains 39 individual contributions, ranging from long topical summaries to shorter focused research papers. This Memoir has been published in two parts, with digital versions of all the complete research papers included on the enclosed CD. The hardcopy portion of the Memoir includes abstracts and several key figures for each of the contributions along with a complete copy of a gas hydrate technical review. The digital portion of this Memoir has been organized into a series of topical sections consisting of review articles, marine gas hydrate papers, and gas hydrate laboratory and modeling studies. Because of the rapidly emerging worldwide interest in gas hydrates, this comprehensive treatise on the geology of gas hydrates will be valuable to both the gas hydrate research community and exploration/development geologists working in arctic and deep marine environments.