Influence of Climate Variations on Rock Temperature and Heat Flow

Abstract

This chapter considers application the software package FROST as a part of the GALO system for basin modeling to reconstruction of thermal history and permafrost evolution during the Pliocene-Quaternary in the intra-continental and shelf sedimentary basins. The chapter examines as regions with modern areas of permafrost (Urengoy field in the West Siberian Basin and Kuyumba field in the Siberian Platform) as the basins where permafrost degraded 10–12 thousand years ago (in the South Urals region and Barents and Sakhalin shelf). The calculations confirm the significant role of variations in rock composition with depth in permafrost evolution. Repeated formation and degradation of permafrost in the Pliocene-Holocene results in considerable decrease of rock temperatures within the upper 1500 m of sedimentary section of Siberia. The model allows an estimate of permafrost depth and stability zone of methane gas hydrate in sedimentary section of basin. It is shown that an increase in salt content in porous water and change in shape of the unfrozen water curve, W(T), depending upon lithological composition of sedimentary rocks, can influence considerably the numerical estimations of permafrost depth. The modeling suggests that a changes in heat flow or temperature gradient at depths of less than 2–2.5 km in sedimentary sections of basins can be considerable even in the regions where permafrost has degraded. The modeling in the Barents Sea shelf suggests rather rigorous climate of the last 70–50 thousand years while in the North-East Sakhalin shelf it assumes that the sea smoothed over the climatic jumps of the mean annual temperature during the greater part of the last 2.5 My and here the influence of the Pliocene-Holocene climate fluctuations in the depth profile of temperature is limited.