Vol 55, No 5 (2017)

It was shown that the history of the biosphere is closely related to processes caused by low solar luminosity. Solar radiation is insufficient to maintain the Earth’s surface temperature above the freezing point of water. Positive temperatures are kept owing to the presence of greenhouse gases in the atmosphere: CO₂, CH₄, and others. Certain stages in the development of the biosphere and climate are related to these effects. Methane was the main carbon-bearing gas in the primordial atmosphere. It compensated the low solar luminosity. Life originated under the reduced conditions of the early Earth. Methane-producing biota was formed. Methane remained to be the main greenhouse gas in the Archean. The release of molecular oxygen into the atmosphere 2.4 Ga ago resulted in the disruption of the established mechanism of the compensation of the low solar luminosity. Methane ceased to cause a significant greenhouse effect, and the content of carbon dioxide was insufficient to play this role. A global glaciation began and had lasted for approximately 200 million years. However, the increasing CO₂ content in the atmosphere reached eventually a level sufficient for the compensation for the low solar luminosity. The glaciation period came to an end. Simultaneously, a conflict arose between the role of CO₂ as a gas controlling the thermal regime of the planet and as an initial material for biota production. As long as the resource of biotic carbon was inferior to that of atmospheric CO₂, the uptake of atmospheric CO₂ related to sporadic increases in biologic production was insufficient for a significant change in the thermal regime. This was the reason for a long-term climate stabilization for 1.5 billion years. By 0.8 Ga, the resource of oceanic biota reached the level at which variations in the uptake of atmospheric CO₂ related to variations in the production of organic and carbonate carbon became comparable with the resource of atmospheric CO₂. Since then, an oscillatory equilibrium has been established between the intensity of biota development and climate-controlling CO₂ content in the atmosphere. Glaciation and warming periods have alternated. These changes were triggered by various geologic events: intensification or attenuation of volcanism; growth, breakup, or migration of continents; large-scale magmatism; etc. A new relation between atmospheric CO₂ and biotic carbon was established in response to the emergence of terrestrial biota and the appearance of massive buffers of organic carbon on land. The interrelation of the biosphere and climate changed.

A comparative analysis of Pleistocene pelagic sedimentation in the Pacific, Indian, and Atlantic oceans revealed the predominance of terrigenous sediments, while carbonate and siliceous sediments are second and third in abundance. During Pleistocene, the mass of terrigenous and siliceous sediments increased, while that of carbonates slightly decreased. The latter is related to the fact that the bottom waters aggressive to carbonates became increasingly generated at high latitudes, thus exceeding an increase in the productivity of plankton carbonate organisms. The peculiarities of accumulation of the main types of bottom sediments in the Pleistocene are considered. It is concluded that the Pleistocene geological history of continents, especially neotectonic uplift and continental glaciations, played an important role in pelagic sedimentation.

For better understanding of the fluid phase sources of carbonatites of Guli alkaline-ultrabasic intrusion (Maymecha-Kotuy complex) we have studied isotope composition of He and Ne in the carbonatites of different formation stages. The data definitely point to the subcontinental lithospheric mantle (SCLM) as a primary source of fluid phase of Guli carbonatites. The absence of plume signature in such a plume-like object (from petrological point of view) could be explained in terms that Guli carbonatites have been formed at the waning stage of plume magmatic activity with an essential input of SCLM components.

Vindhyan basin witnessed a widespread explosive type of felsic volcanism at Palaeo-Mesoproterozoic boundary which is manifested as Chopan porcellanite shale. This is exposed as a linear belt along the Son valley in Central India. Porcellanite shale is pyroclastics deposit comprising strongly welded to unwelded ignimbrites. CIA values coupled with A–CN–K systematics provide strong evidence regarding their igneous origin and proximity of the source. The pyroclastics are rhyodacitic to rhyolitic in nature. The enriched LREE, LILE, depleted HFSE and incompatible element ratios such as Nb/Th, La/Sm and Zr/Nb indicate contamination and mixing between mantle-derived rocks and the average continental crust. Five distinct phases of volcanic activity have been identified based on field observations and petrological evidences. Pyroclastics at various stratigraphic levels indicate repeated occurrences of intrabasinal felsic volcanism, pointing to episodic extension, rifting and eruption over a period of time. The present studies have suggested that volcanic activity in Son valley and pyroclastic detritus resulted from a common chamber due to the rejuvenation and activation of deep seated faults like Son-Narmada lineament.

Membrane filtration technique was applied to study the distribution of iodine and some other chemical elements (iron, manganese, aluminum, and silicon) in natural waters between different sized fractions (>0.45, 0.45–0.22, 0.22–0.1, and <0.1 μm). The paper presents analysis of factors able to modify the proportions of the adsorbed and dissolved species of the elements in waters. It is proved that up to 90% of the total amount of the iodine ion occurs in aquatic environments in the form of dissolved species (according to the current standard, in the fraction < 0.45 μm), with approximately 49% of the total concentration corresponding to the fraction of <0.10 μm. An increase in the acidity of the waters and their enrichment in finely divided organic and mineral material, and also an increase in Fe and Mn concentrations, may increase in the concentrations of the trace element in the particulate matter (up to 26% of the total iodide concentration). The greatest variations in iodine distribution between different fractions are found in the surface waters.