scholarly journals Geochemistry of the frost mound’s ice in the Sentsa River Valley (Oka plateau, East Sayan Mnt.)

2019 ◽  
Vol 98 ◽  
pp. 07002
Author(s):  
Sergey Alexeev ◽  
Ludmila Alexeeva
Keyword(s):  
Chemical Composition ◽  
Lacustrine Sediments ◽  
River Valley ◽  
Unconsolidated Sediments ◽  
Ground Ice ◽  
Rock Interaction ◽  
Formation History ◽  
History Of ◽  
Melt Texture ◽  
Eastern Sayan

The authors have studied the chemical composition of ground ice sampled from the frost mounds located in the unconsolidated sediments of the Sentsa River valley (Oka plateau, Eastern Sayan Mountains) to reconstruct the formation history of these cryogenic creations. Numerous frost mounds of various sizes are mainly composed of clayey silts with interlayers of heavy silts and ice lenses. It is found that the chemical composition of the melt ice sampled from lenses and layers within the frost mounds is HCO3 Ca, SO4-HCO3 Ca and NH4-HCO3 Ca with 6.5–15.6 mg/L salinity and pH = 5.6÷6.1. Whereas, the salinity of the melt texture-forming ice sampled from the ice with fractions of enclosing clayey silts was much higher: from 50 up to 792.5 mg/L. River and lake water is ultra-fresh HCO3 Ca with 99–132 mg/L salinity. The geochemical features of ground ice depend on a water-rock interaction, a presence of organic matter in the unconsolidated sediments and a repeated volcanic activity. The frost mounds are confined to a lacustrine sediments area in the backwater zone that was formed by the Late Pleistocene end moraine. The frost mounds have probably a mixed segregation-injection genesis.

scholarly journals Geochemistry of ice in frost mounds in the valley of the River Sentsa (Oka plateau, East Sayan)

2018 ◽  
Vol 58 (4) ◽  
pp. 524-536
Author(s):  
S. V. Alekseev ◽  
L. P. Alekseeva
Keyword(s):  
Chemical Composition ◽  
Late Pleistocene ◽  
Lacustrine Sediments ◽  
Unconsolidated Sediments ◽  
Geochemical Type ◽  
Rock Interaction ◽  
Terminal Moraine ◽  
Underground Waters ◽  
Injection Process ◽  
Eastern Sayan

Te authors examined the chemical composition of underground ice sampled from the frost mounds located in the loose (unconsolidated) sediments of the Sentsa River valley (Oka plateau, Eastern Sayan) with the purpose of reconstruction the formation history of these cryogenic creations. Numerous frost mounds of various sizes are mainly composed of alternating icy loams, sandy loams, and lenses of pure ice. Samples of underground ice taken in the outcrops of the river ledges and cores from wells together with samples of river and lake waters were analyzed by traditional hydrochemical techniques (methods) in the center "Geodynamics and geochronology" (Institute of the Earth's Crust of the Siberian branch of RAS, Irkutsk). It was found that the chemical composition of pure ice melts from lenses and layers of the frost mounds is hydrocarbonate calcium (HCO3 Ca, SO4-HCO3 Ca and NH4-HCO3 Ca) with mineralization of 6.5 – 15.6 mg/L, pH = 5.6÷6.1. Mineralization of melts of texture-forming ice, taken from icy ground (i.e. with fractions of enclosing loams) was much higher – from 50 to 792.5 mg/L. River and lake water is ultra-fresh with 99–132 mg/L salinity, and according to geochemical type it is hydrocarbonate calcium (HCO3 Ca). Te specifc features of chemical composition of the underground ice (high content of ammonium salts and sulfates) depend on a water-rock interaction, the presence of organic matter in the loose (unconsolidated) sediments and a repeated volcanic activity in the late Pleistocene–Holocene. Te frost mounds are confned to a lacustrine sediments area in the backwater zone that was formed by the Late Pleistocene terminal moraine. Teir formation in the Holocene took place as a result of segregational ice formation during freezing of water-saturated lake sediments, and, presumably, repeated injections of underground waters of the under-channel and floodplain aquifers hydraulically connected with river waters. Tus, the genesis of the studied frost mounds is probably a mixed segregation-injection process.

scholarly journals Chemical Composition of Cometary Ice and Grain, and Origin of Comets

1987 ◽  
Vol 120 ◽  
pp. 565-575
Author(s):  
Tetsuo Yamamoto
Keyword(s):  
Chemical Composition ◽  
Solar System ◽  
Solar Nebula ◽  
Cometary Nucleus ◽  
Elemental Abundances ◽  
Formation History ◽  
History Of

The chemical composition of the ice and grains in a cometary nucleus is discussed by applying the condensation theory. The equilibrium condensation theory of a gas having the elemental abundances in the solar system is briefly reviewed. The composition of solids predicted by the equilibrium condensation theory is compared with that of the ice and grains in the nucleus; the latter is inferred from the observations of cometary molecules and grains. On the basis of the results of this comparison, a scenario for the formation history of comets is proposed, and discussion is given on the temperature and region of the primordial solar nebula where comets formed.

EVIDENCE ABOUT THE FORMATION HISTORY OF NATURAL QUASICRYSTALS IN OUTER SPACE, AND THE OCCURRENCE OF STOLPERITE

2017 ◽  
Author(s):  
Lincoln S. Hollister ◽  
◽  
Chaney Lin ◽  
Glenn J. Macpherson ◽  
Luca Bindi ◽  
...  
Keyword(s):  
Outer Space ◽  
Formation History ◽  
History Of

The Star Formation History of the Local Group Dwarf Galaxy Leo I

1999 ◽  
Vol 118 (5) ◽  
pp. 2245-2261 ◽  
Author(s):  
Carme Gallart ◽  
Wendy L. Freedman ◽  
Antonio Aparicio ◽  
Giampaolo Bertelli ◽  
Cesare Chiosi
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Star Formation History ◽  
Formation History ◽  
History Of

scholarly journals Is there enough star formation in simulated protoclusters?

2020 ◽  
Vol 501 (2) ◽  
pp. 1803-1822
Author(s):  
Seunghwan Lim ◽  
Douglas Scott ◽  
Arif Babul ◽  
David J Barnes ◽  
Scott T Kay ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Star Formation History ◽  
Test Case ◽  
Numerical Resolution ◽  
Formation History ◽  
Order Of Magnitude ◽  
History Of ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT As progenitors of the most massive objects, protoclusters are key to tracing the evolution and star formation history of the Universe, and are responsible for ${\gtrsim }\, 20$ per cent of the cosmic star formation at $z\, {\gt }\, 2$. Using a combination of state-of-the-art hydrodynamical simulations and empirical models, we show that current galaxy formation models do not produce enough star formation in protoclusters to match observations. We find that the star formation rates (SFRs) predicted from the models are an order of magnitude lower than what is seen in observations, despite the relatively good agreement found for their mass-accretion histories, specifically that they lie on an evolutionary path to become Coma-like clusters at $z\, {\simeq }\, 0$. Using a well-studied protocluster core at $z\, {=}\, 4.3$ as a test case, we find that star formation efficiency of protocluster galaxies is higher than predicted by the models. We show that a large part of the discrepancy can be attributed to a dependence of SFR on the numerical resolution of the simulations, with a roughly factor of 3 drop in SFR when the spatial resolution decreases by a factor of 4. We also present predictions up to $z\, {\simeq }\, 7$. Compared to lower redshifts, we find that centrals (the most massive member galaxies) are more distinct from the other galaxies, while protocluster galaxies are less distinct from field galaxies. All these results suggest that, as a rare and extreme population at high z, protoclusters can help constrain galaxy formation models tuned to match the average population at $z\, {\simeq }\, 0$.

Sign in / Sign up

Export Citation Format

Share Document