Basin Modelling of Temperature and Heat Flow Distributions and Permafrost Evolution, Urengoy and Kuyumbinskaya Areas, Siberia.

ABSTRACT The thermal history and permafrost evolution in the Urengoy area of the West Siberian basin and in the Kuyumbinskaya area of the Siberian platform during the Pliocene-Quaternary were reconstructed numerically in a forward model from 3.4 Ma using the software package FROST, part of the basin modelling system GALO. Calculations suggest that variations in rock composition with depth strongly influenced permafrost evolution. Rock temperatures decreased by 15-20°C within the upper 1500 m of the sedimentary sequence because of climate cooling in the Pliocene-Holocene. The effect of cooling is greater in the Kuyumbinskaya area, which has a thinner sedimentary cover, than in the more northern Urengoy area. The model estimates permafrost depth and the stability zone of methane gas hydrate. An increase in salt content in porewater from 1 to 30 g/l lowers the melting temperature of ice by 2°С and decreases permafrost thickness by almost 100 m. The change in shape of the unfrozen water curve W(T), dependent upon the lithological composition of sedimentary rocks, strongly influences the numerical estimations of permafrost depth. The modelling demonstrates that permafrost thickness and temperature and heat flow distributions with depth in the basins calculated with climate variations of the last 50 ka differ significantly from the more accurate values obtained with climate variations during the last 200 ka, 1 Ma or 3.4 Ma. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]