A.V. Khabuev

Distribution and morphology of mud volcanoes and other fluid flow-related lake-bed structures in Lake Baikal, Russia

New high-resolution multibeam bathymetry data recorded in 2009 in the deepest lake in the World, Lake Baikal, Siberia, enabled a better understanding of the morphology of ten known lake-bed structures—the Bolshoy, Malenki, Malyutka and Stari mud volcanoes in the South Baikal Basin, the K1–4 structures in the Selenga delta, and the Novosibirsk and St. Petersburg structures in the Central Baikal Basin—and also the discovery of 29 new lake-bed structures. These new structures are the S1, Tolstiy, mTSG and S2 in the South Baikal Basin, the P1–P4, P6–P19 and K5–K8 in the Selenga delta accommodation zone, and the C1, C3 and C4 edifices in the Central Baikal Basin. In all, 39 positive relief structures were identified and their large-scale distribution mapped. Based on their typical shape, the observation of high-reflectivity areas on side-scan sonar data records, and evidence of feeder channels on subsurface data, these structures can be classified as mud volcanoes. This has already been confirmed in other publications for the Bolshoy, Malenki and K2 structures, by the recovery of mud breccias in sediment cores. Most structures occur on or near faults and have orientations parallel with the major faults and main stress orientations in the basins, suggesting a strong structural control on the formation of the mud volcanoes. Their slopes are generally steeper than 5°, consistent with interpretation as mud cones formed by high-viscosity, stiff mud plugs. Only few structures appear to be characterised by a crater, in which case this apparent crater seems to be formed by the coalescence of several single cones, leaving a depression in the centre. Some structures have a moat, which has probably an erosional origin. Furthermore, three depressions have been found, named P5, P20 and C2, which are suggested to be pockmarks.

Sequentially sampled gas hydrate water, coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano, Lake Baikal: ambiguous deep-rooted source of hydrate-forming water

The isotopic and ionic composition of pure gas hydrate (GH) water was examined for GHs recovered in three gravity cores (165–193 cm length) from the Kukuy K-9 mud volcano (MV) in Lake Baikal. A massive GH sample from core St6GC4 (143–165 cm core depth interval) was dissociated progressively over 6 h in a closed glass chamber, and 11 sequentially collected fractions of dissociated GH water analyzed. Their hydrogen and oxygen isotopic compositions, and the concentrations of Cl– and HCO3– remained essentially constant over time, except that the fraction collected during the first 50 minutes deviated partly from this pattern. Fraction #1 had a substantially higher Cl– concentration, similar to that of pore water sampled immediately above (135–142 cm core depth) the main GH-bearing interval in that core. Like the subsequent fractions, however, the HCO3– concentration was markedly lower than that of pore water. For the GH water fractions #2 to #11, an essentially constant HCO3–/Cl– ratio of 305 differed markedly from downcore pore water HCO3–/Cl– ratios of 63–99. Evidently, contamination of the extracted GH water by ambient pore water probably adhered to the massive GH sample was satisfactorily restricted to the initial phase of GH dissociation. The hydrogen and oxygen isotopic composition of hydrate-forming water was estimated using the measured isotopic composition of extracted GH water combined with known isotopic fractionation factors between GH and GH-forming water. Estimated δD of −126 to −133‰ and δ18O of −15.7 to −16.7‰ differed partly from the corresponding signatures of ambient pore water (δD of −123‰, δ18O of −15.6‰) and of lake bottom water (δD of −121‰, δ18O of −15.8‰) at the St6GC4 coring site, suggesting that the GH was not formed from those waters. Observations of breccias in that core point to a possible deep-rooted water source, consistent with published thermal measurements for the neighboring Kukuy K-2 MV. By contrast, the pore waters of core St6GC4 and also of the neighboring cores GC2 and GC3 from the Kukuy K-9 MV show neither isotopic nor ionic evidence of such a source (e.g., elevated sulfate concentration). These findings constrain GH formation to earlier times, but a deep-rooted source of hydrate-forming water remains ambiguous. A possible long-term dampening of key deep-water source signatures deserves further attention, notably in terms of diffusion and/or advection, as well as anaerobic oxidation of methane.

Diversity of Archaea in Bottom Sediments of the Discharge Areas With Oil- and Gas-Bearing Fluids in Lake Baikal

ABSTRACT Using massively parallel sequencing (the Roche 454 platform) we have studied the diversity of archaeal 16S rRNA gene sequences in oxic and anoxic sediments at six sites in Lake Baikal with oil- and gas-bearing fluids discharge. Archaeal communities appeared to be represented mainly by five phyla: Euryarchaeota, Crenarchaeota, Thaumarchaeota, Bathyarchaeota (miscellaneous Crenarchaeotic group), and Woesearchaeota (deep sea hydrothermal vent group 6). Among them we detected sequences of methanogens of the orders Methanomicrobiales, Methanosarsinales, Methanococcales, as well as representatives of the following uncultured archaeal lineages: Group C3, Marine Benthic Group D, and Terrestrial Miscellaneous Group. We have also identified sequences of ammonia-oxidizing archaea of the phyla Crenarchaeota and Thaumarchaeota. Phylogenetic analysis showed the presence ANME-2d-related sequences. However, the analysis of mcrA genes libraries has not revealed typical representatives of ANME groups. Comparison of amplicon libraries 16S rRNA gene fragments from different samples proved the widespread presence of previously detected Baikal archaeal lineages, which are members of the phylum Crenarchaeota and Thaumarchaeota (formerly Group C3 of Crenarchaeota).

New Evidence on the Relief of the Southern Underwater Slope in the South Baikal Basin

A high-resolution bathymetric survey of the entire underwater slope in South Baikal was carried out for the first time by means of the multibeam echosounder. New elements were revealed in the underwater relief of the southern slope of the basin from the Kultuchnaya river to the Mysovka river, and a relevant regionalization was carried out into three areas according to the presence of ancient landforms and the intensity of the processes of their reworking, with the boundaries along the delta-front and the river fan of the Utulik and Pereemnaya. We reconstructed the formation process of the modern relief of this area of the underwater slope and determined a dominant role of the underwater-erosion processes in the formation of the modern relief, with the tectonic movements served as the “trigger” for them. The study revealed a direct correlation between the reworking of the ancient geomorphological surfaces and the occurrence of separate large underwater elevations or group ridges (remnants), canyons and linear depressions. It is determined that the pivotal role in the appearance of the modern relief of the underwater slope in the second area of extensive plano-convex (in section) and fan-shaped (in plan) delta-fronts of large rivers and debris fans enveloping the remnants. The existence of a steep underwater slope from the mouth of the Pereemnaya to the mouth of the Bol’shaya Tel’naya and of two large benches, and also the proximity of the maximum depths of the southern basin at the foot of this slope are explained by a more intense step-like lowering of this part of the lake when compared with the western part of the basin. This also accounts for the absence of large remnants in this part of the slope. The area of occurrence of lacustrine-fluvial and lacustrine-delta deposits of the Tankhoi paleobasin within the southern basin of Baikal is reconstructed. Four new hydrate-bearing structures associated with these deposits and morphologically pronounced in the vertex parts of the remnants were discovered. The morphological exploration indicators of the presence of new accumulations of gas hydrates on the underwater slopes of Baikal have been expanded.

AGE OF MUD BRECCIA FROM MUD VOLCANOES IN ACADEMICIAN RIDGE, LAKE BAIKAL

LakeBaikalis the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central LakeBaikalbasins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var. These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seismostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than310 m below the lake bottom. Озеро Байкал является единственным пресноводным водоемом, в донных отложениях которого обнаружены скопления газовых гидратов, часть из них связана с деятельностью грязевых вулканов. В настоящей работе представлена группа грязевых вулканов, обнаруженных с помощью съемки многолучевым эхолотом на склоне подводной возвышенности Академический хребет между средней и северной котловинами озера Байкал. Анализ скелетов диатомей в грязевой брекчии выявил в массе вымерший вид Cyclotella iris et var., который ранее был обнаружен в керне скважины BDP-98. При помощи биостратиграфической и сейсмостратиграфической корреляции было установлено, что материал, входящий в грязевую брекчию исследуемых грязевых вулканов, имеет возрастной интервал от позднего миоцена до раннего плиоцена (от 5.6 до 4.6 млн лет) и мог быть поднят с глубины не более310 м ниже дна.Lake Baikal is the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central Lake Baikal basins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var. These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seis-mostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than 310 m below the lake bottom.LakeBaikalis the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central LakeBaikalbasins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var . These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seismostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than310 m below the lake bottom.

Возраст грязевой брекчии грязев ых вулканов Академического хреб та озера Байка

LakeBaikalis the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central LakeBaikalbasins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var. These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seismostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than310 m below the lake bottom. Озеро Байкал является единственным пресноводным водоемом, в донных отложениях которого обнаружены скопления газовых гидратов, часть из них связана с деятельностью грязевых вулканов. В настоящей работе представлена группа грязевых вулканов, обнаруженных с помощью съемки многолучевым эхолотом на склоне подводной возвышенности Академический хребет между средней и северной котловинами озера Байкал. Анализ скелетов диатомей в грязевой брекчии выявил в массе вымерший вид Cyclotella iris et var., который ранее был обнаружен в керне скважины BDP-98. При помощи биостратиграфической и сейсмостратиграфической корреляции было установлено, что материал, входящий в грязевую брекчию исследуемых грязевых вулканов, имеет возрастной интервал от позднего миоцена до раннего плиоцена (от 5.6 до 4.6 млн лет) и мог быть поднят с глубины не более310 м ниже дна.Lake Baikal is the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central Lake Baikal basins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var. These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seis-mostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than 310 m below the lake bottom.LakeBaikalis the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central LakeBaikalbasins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var . These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seismostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than310 m below the lake bottom.