可可西里盆地早渐新世雅西措群爬升沙纹层理及其沉积环境意义

可可西里盆地早渐新世雅西措群砂岩极其发育爬升沙纹层理,形成于沉积物来源供给太快太多而不能随流体一起迁移,从而产生向上的加积。雅西措群砂岩主要包括迎水坡侵蚀的A型和迎水坡沉积的B1型两种,其中,A型沙纹层理单个层系厚一般约为2cm,爬升角小于7°;B1型沙纹层单个层系厚一般为4cm,爬升角介于10o～20o之间。这两种爬升沙纹层形成于变速流、非稳定流或变速非稳定流,主要归于砂质碎屑流和底流,平均流速在11～60cm/s之间,堆积速度可以达到0.1g/cm2s,发育于浅湖环境的三角洲前缘沉积。雅西措群爬升沙纹层理发育于青藏高原的早渐新世快速隆升作用和全球变冷变干气候条件下。

Climbing-Ripple Cross-Lamination of the Early Oligocene Yaxicuo Group in the Hoh Xil Basin and Its Significance for Depositional Environment

The climbing ripple cross lamination is especially well developed and widely distributed in the early Oligocene Yaxicuo Group sandstone of the Hoh Xil Basin, northern Tibetan Plateau. The small scale cross lamination is formed from the upward movement of sediment, when the source quickly provides too much new sediment. Two types of climbing ripple cross lamination, i.e. erosional stoss Type A and depositional stoss Type B1, are included in the Yaxicuo Group sandstone. Among that, a single set of Type A is about 2 cm in thickness and less than 7° for its climb angle; but a single set of Type B1 is about 4 cm in thickness and around 10° 20° for its climb angle. Three kinds of flows including non uniform, unsteady, and non uniform unsteady flows, which belong to sandy clastic flow and bottom flow, contributed their formation. The mean fluid velocity is generally 11 60 cm/s and the sediment deposition rate may be up to 0.1 g/cm₂ s. The depositional environment is the delta front in shallow lake. The development of the Yaxicuo Group climbing ripple cross lamination could be under conditions of the early Oligocene uplift process of the Tibetan Plateau and global cooling and drying climate change.