The Characteristics Of Quaternary Deposits At Xingshan Near Siping And Its Response To Environmental Change

Geological records in Quaternary deposits and characteristics of Quaternary deposits provide valuable information about the past response of earth systems to global climatic and environmental changes; and thus contribute towards improved predictions of future environmental conditions. Environmental and climatic changes recorded from the characteristics of Quaternary deposits have been the subject of several studies during the last two decades. The Quaternary is the geological era extending back some 2,400,000 years. Its two main characteristics are the mobility and dynamism of its physical and biological processes. Mobility is revealed by changes in natural balances which are rapid on the geological time scale. The Quaternary is thus distinguished by variations in climate and consequently in ecosystems.Characteristics of grain size analysis, ESR dating, pollen grains analysis and magnetic susceptibility studies indicate that the Xingshan Quaternary deposits have undergone many oscillating cycles of climatic and environmental changes during the middle and late Pleistocene period. The Quaternary deposits at Xingshan lie unconformable on Cretaceous rocks made of siltstone, mudstone and sandstone. The average grain size is between 8.06 and 8.55Φ(0.0026-0.0037mm).The compositions of the grade are clay 63% and silt 37%. The Quaternary deposits at Xingshan mainly compose of very fine silt to clay. The clay size components are weathered debris transported and deposited by flowing water from the SE highlands or hills to the low-lying NW Xingshan plains whereas the silty components accumulated by aeolian process. The Quaternary deposits accumulated in the middle and late Pleistocene glacial and interglacial periods from (459.12±39.03) ka to (88.92±7.56) ka BP. The standard deviation ranged from 0.96 to 1.36Φ, indicating that the sediments are moderately to poorly sorted, Coefficient of skewness ranged from 0.16-0.31 with an average skewness of 0.218. Kurtosis values (0.84-1.05) from the grain size distribution and visual inspection of the frequency curves indicate platykurtic to mesokurtic curves and unimodal to bimodal grain-size distribution. The type of deposit formation is sand dune and the source is at a distal from its provenance. The calculated Y- values of the Xingshan Quaternary deposits are between -19.8426 and -24.4627 and this indicates that the primary origin of the deposit is Aeolian. The pebbles have no observable striations which indicate that glacial process is not involved in the transportation process of the Xingshan Quaternary deposits. Most of the pebbles have pits and dull surface textures which probably resulted from innumerable impacts of other grains being pushed against the surface of the pebbles during wind action. The pebbles in the study area are mostly brownish in color and irregularly scattered in the study area. The size of the pebbles ranged from 10mm to 60mm in diameter with an average of 45mmThe Xingshan Quaternary deposit is marked by the distribution of conifers, herbs and shrubs in the total pollen assemblage. Non-arboreal pollens (NAP) dominate over the arboreal pollen (AP) groups. The arboreal pollen groups are mainly dominated by Pinus ranging from 7.89% to 33.33% and Betula ranging from 8.33% to 28.57%. The Non–arboreal groups consist mainly of Artemisia, Gramineae, Chenopodiaceae and other accessory taxa. Zoning of the pollen assemblage indicates that the study area has undergone 9 oscillating periods of climatic and environmental changes during the middle and late Pleistocene. The area experienced generally cold/dry climatic and environmental conditions during the middle Pleistocene and it responded to the deposition of clay sediments transported by both wind and fluvial processes.Present studies at Xingshan show that the interglacial periods, 147.73±12.56 ka and 188.89±16.06 ka. B.P. contrast to the RISS glacial stages in the Alps and the SAALAIN glacial period in the Northern Europe-- O¹⁸/O¹⁶ isotopes stage 6 (OIS 6). Xingshan probably experienced warmer environmental conditions than the Alps and Northern Europe during147.73±12.56 ka and 188.89±16.06 ka. B.P The glacial period at Xingshan during 243.42±20.69 ka and 271.81±23.11 ka B.P contrast to MINDEL RISS interglacial stages in the Alps and Holsteinian interglacial periods in Northern Europe- Oxygen isotope stage 7 .Present research at Xingshan shows that layer 11-2 in section I deposited during the glacial period (88.92±7.56) which do not correlate with the global climate and environmental interglacial time period records such as GISP2, Vostok and SPECMAP records of Wurmian in the Alps, Weischselian in Europe and Wisconsinian in North America. This period do not correspond to O¹⁸/O¹⁶ isotopes sub-stage 5a (OIS 5a).The layer 1-1, accumulated during the interglacial period at 459.12±39.03 ka. B.P., which correlates well with the interglacial time period of MINDEL RISS interglacial stages in the Alps and Holsteinian interglacial periods in North Europe. The interglacial period, (459.12±39.03) ka B.P correlates well with oxygen isotope stage 11 (OIS 11).