J. Klerkx

Sublacustrine mud volcanoes and methane seeps caused by dissociation of gas hydrates in Lake Baikal

Four lake-floor seeps have been studied in the gas-hydrate area in Lake Baikals South Basin by using side-scan sonar, detailed bathymetry, measurements of near-bottom water properties, heat-flow measurements, and selected seismic profiles in relation to results from geochemical pore-water analysis. The seeps at the lake floor are identified as methane seeps and occur in an area of high heat flow, where the base of the gas-hydrate layer shallows rapidly toward the vent sites from ;400 m to ;150 m below the lake floor. At the site of the seep, a vertical fluid conduit disrupts the sedimentary stratification from the base of the hydrate layer to the lake floor. The seeps are interpreted to result from local destabilization of gas-hydrate caused by a pulse of hydrothermal fluid flow along an active fault segment. This is the first time that methane seeps and/or mud volcanoes as- sociated with gas-hydrate destabilization have been observed in a sublacustrine setting. The finding demonstrates the potential of tectonically controlled gas-hydrate destabiliza- tion to cause extreme pore-fluid overpressure and short-lived mud volcanism.

Atypical heat-flow near gas hydrate irregularities and cold seeps in the Baikal Rift Zone

Abstract In this paper, we address the irregular behaviour and geometry of the gas hydrate stability zone (HSZ) inferred from reflection seismic data in relation to heat-flow measurements. The study area lies in the hanging wall of the Posolsky fault in the Southern Baikal Basin (SBB). Side-scan sonar imagery already revealed an undulating antithetic active fault structure and several isolated active vent structures. Remarkably, these fluid discharge structures occur only where the base of the hydrate stability zone (BHSZ), as inferred from seismic reflection profiles, is fluctuating and discontinuous, independent of lake floor morphology. The correlation between the interpreted BHSZ and heat-flow data across the Malenki seep is reasonable. On a seismic profile south of the fluid escape features, the BHSZ is expressed as an oscillatory, but continuous reflection, and shows poor correlation with heat-flow measurements. In nearly all cases, measured heat-flow exceeds inferred heat-flow. Additionally, the local inferred minima are anomalously low compared to the expected background values in the SBB. These observations suggest that the present-day hydrate accumulation and its (meta-)stability are more complicated than originally suspected. The limited area of these anomalies, their amplitudes and their occurrence in the immediate vicinity of faults and fluid escape features suggest that fluid convection cells disturb local gas hydrate stability conditions.

Bathymetry and Sedimentary Environments of Lake Issyk-Kul, Kyrgyz Republic (Central Asia): A Large, High-Altitude, Tectonic Lake

Lake Issyk-Kul, located in the northern Tien Shan of the Kyrgyz Republic, in the heart of Central Asia, is one of the deepest and largest lakes in the world. Although Kyrgyz and Russian scientists have studied the lake quite intensively since the 1850’s, not much of the scientific literature has found its way to the international community. It is only recently that Lake Issyk-Kul has also started to attract international attention, and this is essentially thanks to the fact that the area occupies a potentially interesting location for paleoclimate research as well as for geodynamic studies.

TECTONICALLY CONTROLLED METHANE ESCAPE IN LAKE BAIKAL

Methane, which is at least partly stored in the bottom sediments of Lake Baikal as gas hydrates, is released on the lake floor in the deeper parts of the basin along major faults, forming venting structures similar to small mud volcanoes. The CH4 venting structures are considered to be the surface expression of escape pathways for excess CH4 generated by the dissociation of pre-existing hydrates. The existence of a local heat flow anomaly associated with the seep area is most likely due to a heat pulse causing the dissociation of the underlying gas hydrates. The heat pulse may be caused by upward flow of geothermal fluids along segments of active faults, possibly accelerated by seismic pumping. It is assumed that this fluid flow is tectonically triggered, considering that left-lateral strike-slip movements along the border faults act as a major factor in fluid accumulation: even a reduced lateral displacement is able to generate fluid flow in the compressional direction, resulting in fluid escape along faults directed along the main direction of extension. The tectonic effect may be coupled to the sediment compaction due to a high sedimentation rate in the area of mud volcanism. Both processes may generate a large-scale convective fluid loop within the basin-fill sediments which advects deeper gases and fluids to the shallow sub-surface. Even in the extensional tectonic environment of Lake Baikal, local compressional forces related to a strike-slip component, may play a role in fluid flow, accumulation and gas escape along active faults. The mechanisms that result in the expulsion of the CH4 in the Lake Baikal sediments are considered as an analogue of what could happen during CO2 sequestration in a similar tectonic environment.

Recent Paleoenvironmental Evolution of Lake Issyk-Kul

Closed lakes located in arid and semi-arid environments are highly sensitive to climate oscillations since small variations in their environmental conditions induce dramatic changes within the lake [1]. The sensivity of these lakes is higher if they are located in the border of biomes, as Lake Issyk-Kul, located between the steppic and high mountains environments [2]. These facts make Lake Issyk-Kul an important ecosystem in order to study its adaptability under the environmental changes occurred in the Central Asia region.