祁连盆地木里坳陷上三叠统辫状三角洲沉积模式

The depositional models of braided delta of Upper Triassic in Muri depression of South Qilian basin, Qinghai province, China.

对青海祁连盆地木里坳陷上三叠统辫状三角洲进行剖析，从沉积学角度讨论了辫状三角洲的形成背景；从岩性、结构、构造、古生物、分布特征等方面总结了辫状三角洲的相标志及相层序；对辫状三角洲的亚相和微相进行了划分；提出了辫状三角洲的沉积模式；并对辫状三角洲砂体类型进行了探讨。辫状三角洲不具有重力流沉积特征，以牵引流沉积特征为主；由于辫状三角洲比三角洲更靠近物源，沉积物搬运距离短，沉积物粒度粗，成分成熟度和结构成熟度低；发育反映急水流的大型块状层理、平行层理和交错层理；主要发育辫状河道和水下辫状河道砂体；垂向为向上变粗层序；砂体类型对储集层物性有明显的控制作用。图３表２参１（邹冬平摘）

Based on the analysis of braided delta of Upper Triassic of Muri depression of Qiliian basin in Qinghai province, the formation background of braided delta was discussed from the view point of sedimentology. The facies marks and sequence of braided delta were summarized from a few aspects such as lithology, texture, sedimentary structure, paleontology and distribution. In this paper, the subfacies and microfacies of braided delta were divided, the sedimentary models of braided delta were established, and the sandbody type of braided delta was studied as well. It is considered that the sedimentary characters are between those of delta and fan delta, and the main sedimentary feature was formed by tractional current, and no turbidite was developed in braided delta. Because the braided delta is much near to the sediment source than delta, so the transportation distance of sediments is very short and the grain size is coarse, and the maturity of composition and texture is low. The large scale block bedding, parallel bedding and cross bedding that are formed in upper flow regime were well developed; while distributary channel, natural bank, inter channel bay were not developed, but braided channel, sub water braided channel sandbody were much developed. The vertical sequence is coarsening upward sequence; and the reservoir character is obviously controlled by the sandbody type.