柴北缘全吉地区晚震旦世冰川沉积特征及地质意义

Glacial sedimentary characteristics of late Sinian in Quanji area in the northern margin of Qaidam Basin and its geological significance

通过对柴达木盆地北缘全吉山、石灰沟等野外剖面详细的勘察及实测,对新元古代全吉群红铁沟组冰川沉积事件进行研究,分析冰成岩发育特征,揭示各类冰川沉积现象的形成机制,建立冰成岩沉积模式,探讨冰川事件对柴北缘地区地层划分与板块对比的重要意义。结果表明:柴达木盆地北缘全吉地区红铁沟组发育新元古代冰川沉积事件,冰成岩发育位置与正常潮坪沉积一致;该地层序列中保留了冰底碛、消融碛以及冰海沉积物等不同的沉积物类型;该套冰成岩厚度横向变化大,可能为与弧后扩张有关的盆地伸展阶段的斜坡相沉积;红铁沟组下伏黑土坡组顶、底各存在一个区域不整合面,柴北缘地区新元古代末期至少发育两期大规模构造运动,研究区各剖面中黑土坡组、红铁沟组及皱节山组不同程度的剥蚀是新元古代末期柴北缘洋盆向北俯冲造成的挤压-剥蚀以及弧后伸展导致的盆地再次沉降—接受沉积转换的直接体现;红铁沟组冰成岩为震旦纪全球性冰川事件——Gaskiers冰期的产物,可与华北南缘罗圈组及塔里木汉格尔乔克组冰成岩层对比,认为塔里木、柴达木等地块在晚震旦世亲华北。

Based on the detailed investigation of field profiles in Quanjishan and Shihuigou in the northern margin of Qaidam Basin,a study of glacial events in Hongtiegou Formation of Quanji group was presented.The characteristics of glacial diagenesis were analyzed,the formation mechanism of various glacial deposition phenomena was revealed,the glacial diagenetic sedimentary model was established,and the significance of glacial events for stratigraphic division and plate correlation in the north margin of Qaidam Basin was discussed.The results show that Hongtiegou Formation experienced Neoproterozoic glaciation in Quanji area in the northern margin of Qaidam Basin,and the location of glacial diagenesis was consistent with that of normal tidal flat deposits.Its stratigraphic sequence retains glacial ground moraine,ablation moraine and proglacial tidal deposit.The formation thickness is characterized by great horizontal variations,and this glacial deposit may be the product of slop which formed under the background of basin extension during back-arc spreading.Furthermore,two unconformities are recognized on top and underneath Heitupo Formation,which represent two tectonic movements during Neoproterozoic.Moreover,the denudation of the Heitupo Formation,Hongtiegou Formation and Zhoujieshan Formation in the profiles of the study area is the direct reflection of compression-denudation caused by the northward subduction of the oceanic basin in the northern margin of the Qaidam Basin in the late Neoproterozoic era and the re-subsidence caused by the back-arc basin extension.This glacial deposit of Hongtiegou Formation was the product of Gaskiers glaciation during the global glacial period in Sinian.It can make a contrast with Luoquan Formation in southern margin of North China and Hangerqiaok Formation glacial event in Tarim.It is believed that the Tarim and Qaidam blocks are related to the North China plate in the late Sinian.