Известия Томского политехнического университета: Инжиниринг георесурсов (Oct 2016)
Detailed stratigraphy and dynamics of Central Yamal khasyrey during the late holocene
Abstract
The relevance of the discussed issue is caused by insufficient knowledge of the stratigraphy and dynamics of peatland of the Western Siberia tundra zone and of the impact of permafrost conditions and climate. The main aim of the study is the detailed study of stratigraphic and reconstruction of the dynamics of plant communities, water regimes and geocryological conditions of Central Yamal khasyrey. The methods used in the study: detailed (1…3,5 cm) study of the macrofossils composition and physic-chemical properties of peat, radiocarbon dating (6 dates) peat deposit; reconstruction of phytoceanoses and water regimes by traditional paleoecological methods, reconstruction of paleogeocryological conditions according to paleophytocoenoses successions and peat secondary diagenesis; comparative analysis of the obtained data with the data of reconstructions of regional climate and functional state of mires to other zones and regions. The results. For the first time the authors have obtained the detailed stratigraphy of peat deposits, data on peat density and its organic substance. By the example of the khasyrey in the Lake Sokhonto area of Central Yamal the authors determined the impact of paleo-cryological conditions on increase of peat decomposition level and density. The y carried out the detailed reconstruction of khasyrey dynamics for the 1350-year period of its formation. Seven large stages and 15 stages with 6 substages of khasyrey formation of interdecadal and century scale were revealed. Water regimes and cryogenic conditions of these stages are in agreement with regional climate reconstructions data and the solar activity periods. The authors differentiated 2 periods in which khasyrey surface was wet: 952…843; 273 cal. yr. BP…2001 yr. The khasyrey surface was drained maximally during 4 periods: 1099…1065 and 1037…984; 719-652; 542…434 cal. yr. BP. The short-term formation of low permafrost mound during periods of 1099…1065; 1008…984 and 719…652 cal. yr. BP is of high probability. Formation of polygonal mire took place during 542…434 cal. yr. BP. Since 434 cal. yr. BP the depth of seasonal thawing increased, and since 330 cal. yr. BP of ice veins started melting, formation of mire with raised-centre polygons, caused by thermokarst and erosion. In 136...91 cal. yr. BP the depth of seasonal thawing decreased. Drainage of a khasyrey surface in a consequence of waters dumping of the khasyrey lake during the wet warm periods took place between 1153 and 1099, 869 and 843 cal. yr. BP; ca. 2003 and 2008 yrs. Thus, climate changes in the Western Siberia tundra were the main cause of pulsating nature of khasyreis in contrast to the more southern areas. Climate influence was direct, through the hydrothermal regime, and indirect, through cryogenic processes in peat deposit and the water table regime of the lake. Optimal conditions for palsa and polygonal mire formation were created with increasing continental climate and summer temperatures during periods of dry cooling.
