西秦岭洮河盆地上三叠统窄陆架型海底扇发育特征与输运机制

Developmental characteristics and transport mechanisms of the Upper Triassic submarine fans controlled by narrow shelf in the Taohe Basin， West Qinling Orogenic Belt

谈明轩 袁赛赛 陈绵培 孙浩南 马宏霞 章诚诚

Mingxuan TAN Saisai YUAN Mianpei CHEN Haonan SUN Hongxia MA Chengcheng ZHANG

西秦岭洮河盆地上三叠统出露一系列窄陆架控制的海底扇体系，是古特提斯洋东北缘最后一期深海相沉积记录。通过临潭-卓尼地区上三叠统纳鲁组典型露头野外与室内精细沉积学解剖，明确该海底扇的沉积组合、沉积单元和成因机制。研究表明，研究区上三叠统海底扇发育多种类型重力流沉积，具有低密度与高密度浊流沉积、混合事件层、异重岩和反射型浊流沉积等4种沉积组合。目前大部分深水露头反映了海底扇中-远端沉积面貌，以海底扇朵体内部沉积单元（如朵叶体水道、轴部、离轴和边缘等）为特征，而海底扇主水道与天然堤单元不甚发育。洮河盆地上三叠统窄陆架型海底扇的形成并不是由单一输运机制主导。斜坡失稳与陆架沿岸流改造为间接供源，异重流输运为直接供源。这两种机制交互主导与陆架特征和海平面高频变化密切相关。窄陆架地形背景与洮河盆地半封闭构造格局密切相关，而海底滑坡频发则提升了海底地形粗糙度。在白龙江隆起持续隆升影响下，促使洮河盆地上三叠统海底扇远端沉积受到反射流局部改造，形成了具有双重成因特征、部分限制性海底扇沉积。

The Taohe Basin， located in the West Qinling Orogenic Belt （WQOB）， exhibits a series of exposed Upper Triassic submarine fan systems controlled by narrow shelf， which records the last-stage deep-marine deposition along the northeastern margin of the Paleo-Tethys Ocean. Using field and laboratory sedimentological analyses of typical outcrops， we determine the sedimentary assemblages， sedimentary units， and genetic mechanisms of submarine fans in the Upper Triassic Nalu Formation in the Lintan-Zhuoni areas. The results indicate that the Upper Triassic submarine fans in the study area contain various gravity flow deposits， which show four sedimentary assemblages： low- and high-density turbidites， hybrid event beds， hyperpycnites， and reflected turbidites. Presently， most studied outcrops of deep-water deposits exhibit the mid-to-distal sedimentary features of submarine fans， with the dominance of various sedimentary units in the lobes （e.g.， lobe channels， axial and off-axis units of lobes， and lobe fringes）. The major feeder channels and natural levees， however， are largely absent in the submarine fans. The narrow shelf-controlled submarine fans of the Upper Triassic in the Taohe Basin are developed by multiple transport mechanisms. Specifically， slope instability and sediment reworking via littoral currents on the shelf are subject to indirect sediment supply， whereas hyperpycnal flows act as a direct sediment source. The alternation between both mechanisms is intimately associated with the shelf characteristics and high-frequency sea-level functuations. The narrow-shelf setting is closely related to the semi-closed tectonic framework of the Taohe Basin， while frequent submarine landslides have enhanced the ruggedness of the submarine topography. Influenced by the continuous uplift of the Bailongjiang Uplift， the distal deposits of the Upper Triassic submarine fans in the Taohe Basin are locally transformed by reflected currents， leading to the formation of the partially restricted submarine fan deposits with dual genetic characteristics.

10.11743/ogg20250313