The Gydratny Fault zone of Lake Baikal

The Central basin of Lake Baikal is intersected by the North-East – South-West-oriented escarpment named the «Gydratny Fault zone». This laterally extensive structure runs subparallel to the North-Western shore of the lake. The Gydratny Fault zone has been investigated using geophysical techniques during 6 years of research in the framework of international expeditions of the Class@Baikal project. The acquired seismic data provided details of the structure of the upper part of the sedimentary section revealing a system of previously unknown faults. A new tectonic scheme of the South-Western deep-water part of the Central basin is presented. The Gydratny fault is accompanied by a system of numerous synthetic and antithetic normal faults that form a wide and extended faulted zone. These structures are unevenly distributed, and include modern and active faults as well as features buried under undeformed sedimentary units with different thickness. This parameter is used to constrain the patterns observed in several zones of the study area. The difference in the characteristics of faults and their manifestations on seismic data can be explained by complex and uneven distribution of active tectonic and sedimentary processes

Biogeochemical processes at the Krasniy Yar seepage area (Lake Baikal) and a comparison with oceanic seeps

The expulsion of sedimentary, methane-rich fluids to bottom waters is a widespread process in Lake Baikal (eastern Siberia), resulting in deep water cold seep systems comparable in size and frequency to those of oceanic, high-productivity continental margins. Little is known, however, about how biogeochemical processes in Baikal cold seeps compare with those of oceanic cold seeps. In this paper, we present new pore water chemistry data from the Krasniy Yar seepage area located on the slope near the Selenga river delta. We compare biogeochemical processes deduced from these pore water chemical profiles with processes prevalent at oceanic cold seeps of highly productive continental margins. This comparison allows to draw the following conclusions: (1) in sediments not affected by seepage the fresh water mass of Lake Baikal results in a very low relative importance of the nitrogenous and sulfidic geochemical zones compared to the ocean; (2) diagenetic processes involving silicate minerals are, however, similar in Lake Baikal and the ocean; (3) fluid advection rates in cold seep sediments are similar in Lake Baikal and ocean systems but (4) the deep methane flux of Baikal seeps is mitigated by reaction with O-2, and possibly Mn(IV) and Fe(III) oxides, whereas in oceanic sediments the main methane-consuming process is the anaerobic oxidation of methane with sulfate. Lake Baikal cold seep sediments are therefore nearly devoid of authigenic carbonate minerals and have a reduced capacity to decrease the deep methane flux

Model of formation of double structure gas hydrates in Lake Baikal based on isotopic data

International audienceWe measured the isotopic compositions of methane (C 1) and ethane (C 2) of hydrate-bound gas and of dissolved gas in pore water retrieved from bottom sediments in Lake Baikal. Both structure I (sI:3%C 2) and II (sII:14%C 2) gas hydrates are observed in the same sediment cores in Kukuy K-2 mud volcano. We found that C 2 dD of sI gas hydrate is larger than that of sII, whereas C 1 d 13 C, C 1 dD and C 2 d 13 C values are practically the same in both hydrate structures. d 13 C of C 1 and C 2 of hydrate-bound gas are several permil smaller than those in pore water, showing that the current pore water is not the source of gas hydrates. These findings lead to a new model where the sII gas hydrates were formed prior to the sI hydrates

Thermal anomalies associated with shallow gas hydrates in the K-2 mud volcano, Lake Baikal

Thermal measurements and hydrate mapping in the vicinity of the K-2 mud volcano in Lake Baikal have revealed a particular type of association of thermal anomalies (29-121 mW m(-2)) near hydrate-forming layers. Detailed coring within K-2 showed that hydrates are restricted to two distinct zones at sub-bottom depths exceeding 70-300 cm. Temperature data from stations with hydrate recovery and degassing features all display low thermal gradients. Otherwise, the thermal gradients within the mud volcano are generally increased. These findings imply a more complicated thermal regime than often assumed for mud volcanoes, with important roles for both fluids and hydrates. The coexistence of neighbouring low and high thermal anomalies is interpreted to result from discharging and recharging fluid activity, rather than hydrate thermodynamics. It is suggested that hydrates play a key role in controlling the fluid circulation pattern at an early stage. At a later stage, the inflow of undersaturated lake water would favour the dissolution of structure I hydrates and the formation of structure II hydrates, the latter having been observed on top of structure I hydrates in the K-2 mud volcano