Diancang Mountain Last Glaciation Geomorphic Features And Glacial Deposits Features And Its ESR Dating

Dali glaciation is synonymous with the Last Glaciation in China, and it is named after the glacier discovered in Diancang Mountain of Dali city. In this paper, the author studied the characteristics of the glacial landforms of Diancang Mountain, and applied Scanning Electron Microscopy(SEM) and grain size analysis on glacial sediments, to provided a reference to solve the controversy that whether Quaternary glaciations existed in east China. And the author applied Electron Spin Resonance(ESR) dating to the glacial sediments on the north flank of the Yuju peak. According to the dating results, the author discussed the mechanism of glaciations during MIS3 b on the Diancang Mountain, and the relation of the development of Dali glaciation with tectonic movement and climate system during the Last Glaciation.The author studied the characteristics of glacial erosional landforms and depositional landforms of Diancang Mountain, and using a flat index of F=a/2c and a length-width ratio G=a/b, to describe to the morphometry of typical glacial cirques on Diancang Mountain. The flat index isranged from 1.60-3.47, with its average of 2.10, and the length-width ratio is ranged from 0.82-2.94, with its average of 1.43.By using Scanning Electron Microscopy(SEM) on glacial sediments on Diancang Mountain, the author got the micro-textures and its frequency. In quartz grains shape, the glacial quartz grains are mainly subangular and angular with high relief, and with its edges shape of subangular. The mechanical features are mainly conchoidal fractures, V-shaped pits, parallel cleavage planes, striations, adhering particles, cracks. Chemical features are mainly amorphous precipitation, smooth silica veneer, solution etching surface, solution pits and crevasses. The features most related to glacial genesis are striations, with its frequency of 8%-32%; adhering particles, with its frequency of 16%-40%; cracks with its frequency of 12%-32%.Grain size analysis indicates that the glacial sediments are mainly composed by very fine sand, very coarse silt and coarse silt. The frequency distribution curves are of multi-peak form, with its main peak between 4~5φ, belonging to very coarse slit. The peak between 4~5φ is of typical glacial genesis that can be used to distinguish the unknown sediments’ environments. Grain size parameters are calculated using Folk &Ward method, the mean grain size are between 4.414~4.689φ, belonging to very coarse silt. The sorting is between 1.150~1.411, indicating that they are poorly sorted. The skewness is between 0.055~0.257, indicating that they are composed by more fine particles. The kurtosis are between 0.996~1.149, indicating a mesokurtic.ESR dating to the north flank of the Yuju peak are as 38ka(±10-15%), 10ka(±10-15%), 8ka(±10-15%). The ESR dating results indicate that there were Last Glaciation MIS3 period glacial advances, Last Glacial Maximum MIS2, and the early Holocene glacial remains. The extent of the glacier shrink and the snowline increased gradually. The largest glaciation on the Diancang Mountain appeared in the MIS3 period, instead of the Last Glacial Maximum. This phenomenon was caused by the cold and humid atmosphere during MIS3 b period, greatly promoted the development of glaciation. The development of Dali Glaciation on the Diancang Mountain is the result of uplift of the mountain after Gonghe Movement(0.15Ma) and the climate system of Last Glaciation.