OS23B-2019
Tectonic Controls on Gas Hydrate Distribution off SW Taiwan
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Christian Berndt1, Wu-Cheng Chi2, Marion D Jegen1, Sina Muff1, Sebastian Hölz1, Elodie Lebas1, Malte Sommer1, Saulwood Lin3, Char-Shine Liu3, Andrew T Lin4, Ingo Klaucke1, Dirk Klaeschen5, Liwen Chen6, Pascal Kunath1, Kirk D McIntosh7 and Tomas Feseker8, (1)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (2)Academia Sinica, Taipei, Taiwan, (3)NTU National Taiwan University, Taipei, Taiwan, (4)NCU National Central University of Taiwan, Jhongli, Taiwan, (5)Geomar Helmholtz Centre for Ocean Research, Kiel, Germany, (6)National Taiwan University, Taipei, Taiwan, (7)Univ of Tx-Austin-Geosciences, Austin, TX, United States, (8)University of Bremen, Bremen, Germany
Abstract:
The northern part of the South China Sea is characterized by wide-spread occurrence of bottom simulating reflectors (BSR), indicating the presence of marine gas hydrates. Because the area covers both the tectonically inactive passive margin and the northern termination of the Manila Trench subduction zone while sediment input is broadly similar, this area provides an excellent opportunity to study the influence of tectonic processes on the dynamics of gas hydrate systems. Long-offset multi-channel seismic data show that movement along thrust faults and blind thrust faults caused anticlinal ridges on the active margin, while faults are absent on the passive margin. This coincides with high-hydrate saturations derived from ocean bottom seismometer data and controlled source electromagnetic data, and conspicuous high-amplitude reflections in P-Cable 3D seismic data above the BSR in the anticlinal ridges of the active margin. On the contrary, all geophysical evidence for the passive margin points to normal- to low-hydrate saturations. Geochemical analysis of gas samples collected at seep sites on the active margin show methane with heavy δ13C isotope composition, while gas collected on the passive margin shows highly depleted (light) carbon isotope composition. Thus, we interpret the passive margin as a typical gas hydrate province fuelled by biogenic production of methane and the active margin gas hydrate system as a system that is fuelled not only by biogenic gas production but also by additional advection of thermogenic methane from the subduction system. The location of the highest gas hydrate saturations in the hanging wall next to the thrust faults suggests that the thrust faults represent pathways for the migration of methane. Our findings suggest that the most promising gas hydrate occurrences for exploitation of gas hydrate as an energy source may be found in the core of the active margin roll over anticlines immediately above the BSR and that high-amplitude reflections in the seismic reflection data may be a good proxy for these targets.
