Возраст грязевой брекчии грязев ых вулканов Академического хреб та озера Байка

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

The lake floor morphology of the Southern Baikal rift basin as a result of holocene and Late Pleistocene seismogenic and gravitational processes

Based on an extensive bathymetric data set obtained using modern high-precision swath bathyrnetry instruments, a Digital Terrain Model (DTM) of the lake floor of the Southern Baikal Basin has been created. In this work we present the morphological analysis based on this DTM. We were able to determine that tectonic activity was directly or indirectly involved in the formation of the main characteristics of the lake floor morphology. Modern tectonic processes are fixed by tectogenic scarps and paleoseismic dislocations that strongly affected the slope surfaces of the depression with detached blocks in the friable strata of the ancient delta front of the Selenga River and landslides on the southeastern shore of the basin. Underwater gravitational processes developed on the slope surfaces and the formation of canyons are also directly related to the tectonic movements. The Miocene-Pliocene sedimentary surface of the Tankhoy field, the bulk of which is below the lake level, currently experiences tectonic uplifts near the shoreline. These uplifts initiated significant underwater erosion, and underwater gravitational processes, which led to the formation of the modern delta fronts of the largest Lake Baikal tributaries and associated canyons

Active hydrate destabilization in Lake Baikal, Siberia?

In this paper, we present new seismic and heat-flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper-than-normal and regions of shallower-than-normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift-basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre-existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present-day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature

Shallow-rooted mud volcanism in Lake Baikal

Lake Baikal is the only freshwater basin containing sediments with gas hydrate accumulations, some of which are associated with mud volcano activity. Twenty-two mud volcanoes have already been identified in different areas of Lake Baikal, but the formation process and source depth remained unknown due to a lack of conclusive evidences. Here we discuss a set of geological and geophysical data to report the discovery of the hydrate bearing Akadem mud volcanic complex (AMVC) on the Academician Ridge in central Lake Baikal. The obtained results allowed for the first time to concretely estimate the source depth of the mobilized fluids and sediments. Analysis of diatom skeletons present in the mud breccia revealed that the oldest diatom specimen is Cyclotella Iris et var. This species is characteristic for a short age interval ranging between 4.8 and 5.6 Ma. The same diatom was also detected between 230 and 310 m below the lake floor (mblf) in the borehole BDP-98 drilled near the AMVC. Combining biostratigraphic correlation and seismostratigraphy, it is estimated that the same interval is located at 200-300 mblf below the mud volcanic field. The elevated heat flow measured at AMVC indicates that the original base of gas hydrate stability (regionally located at similar to 212 mblf) is currently shifted upwards of similar to 100 m. The acquired data are consistent with a scenario envisaging the rise of warm fluids throughout the mud volcano complex zone. We suggest that migration of deep fluids could have initiated the gas hydrate dissociation and, in turn, rapidly generated overpressured shallow mud chambers. The ultimate piercing and triggering of the mud volcanoes activity resulted in the eruption of mud breccia and formation of densely packed crater sites in the study area. The depicted scenario can be applied to many mud volcanoes in Lake Baikal where similar anomalous heat flow conditions have been measured. These findings also emphasize that the genetic association between gas hydrate dissociation and the initiation of eruptive activity explains numerous peculiarities of the "Baikal" sedimentary volcanism (e.g. lack of lithified rocks among mud breccia clasts, gas hydrates, moderately elevated heat flow). This type of mud volcanism differentiates from the typically deeply rooted piercements observed worldwide in mature (marine) sedimentary basins. Ultimately our findings open a new prospective for mud volcano research worldwide, emphasizing that gas hydrates are not just one of the common features for sedimentary volcanism, but may have an active role as a triggering mechanism for the process itself