Cretaceous detrital zircons and related data from the Jiangcheng area in the southern Simao Basin, southeastern Tibetan Plateau

The Cretaceous drainage evolution of the southeastern Tibetan Plateau (SETP) remains contentious, largely due to insufficient chronological constraints. This study presents 1121 detrital zircon U-Pb ages obtained from a magnetostratigraphically dated sedimentary sequence (Jiangcheng section) in the Simao Basin, which spans from ~141.5 to 71 Ma. Our data revealed a pronounced stratigraphic variation in the detrital zircon age spectra. Samples from the upper Bazhulu, Jingxing and Mangang formations show clusters at 300-200 Ma, 490-400 Ma, 1000-750 Ma, 1950-1750 Ma and 2600-2400 Ma. A significant shift is observed within the middle-lower Mengyejing (MYJ) Formation, marked by the weakening of ancient peaks (1950-1750 Ma, 2600-2400 Ma) and the dominance of younger signatures (300-200 Ma, 490-400 Ma, 1000-750 Ma). These major peaks persisted into the upper MYJ Formation, but with a weakened 1000-750 Ma signal, a resurgence of older peaks, and a notable increase in 150-80 Ma zircon content. Based on an integrated analysis of new and published zircon provenance data, we reconstructed a three-stage Cretaceous paleo-drainage evolution history for the SETP. Stage I (~141-109 Ma): A transcontinental drainage system linked the Songpan-Ganzi, Sichuan Basin and Qiangtang to the Paleo-Pacific Ocean via the Simao and Khorat basins under a relatively humid condition; Stage II (~109-90 Ma): A saline lacustrine environment prevailed in the Simao Basin, coeval with a persistently diminished continental-scale fluvial network eastward, amidst widespread aridification; Stage III (~90-71 Ma): A Stage I-type transcontinental drainage was reestablished and moderately expanded, despite subdued fluvial activity under persistent arid climate. Overall, the Simao Basin provenance signatures reflect Cretaceous transcontinental drainage evolution from establishment, through contraction, to eventual partial recovery with modest expansion. Our results provide a refined model for Cretaceous drainage reorganization in the SETP, which was fundamentally controlled by the interplay of global/regional tectonics and paleoclimatic forcing.

青藏高原东南部（southeastern Tibetan Plateau, SETP）的白垩纪水系演化长期存在学术争议，这主要受制于年代学约束的不足。本研究采自思茅盆地（Simao Basin）江城剖面（Jiangcheng section）的一套经古地磁定年的沉积序列，其年代跨度约为141.5 Ma至71 Ma，本研究从中获取了1121件碎屑锆石U-Pb年龄（detrital zircon U-Pb ages）数据。研究发现碎屑锆石年龄谱存在显著的地层分异特征：巴朱鲁组（Bazhulu Formation）、景星组（Jingxing Formation）与芒岗组（Mangang Formation）的样品，其年龄峰簇集中于300~200 Ma、490~400 Ma、1000~750 Ma、1950~1750 Ma以及2600~2400 Ma区间。在勐野井组（Mengyejing Formation, MYJ）中下段，观测到显著的年龄谱转变：古老年龄峰（1950~1750 Ma、2600~2400 Ma）的信号减弱，年轻年龄组分（300~200 Ma、490~400 Ma、1000~750 Ma）占据主导。上述主要年龄峰延续至勐野井组上段，但1000~750 Ma区间的信号有所削弱，古老年龄峰再度显现，同时150~80 Ma的锆石含量显著升高。

结合本次新获得与已发表的锆石物源数据，本研究重建了青藏高原东南部白垩纪三期古水系演化历史：第一阶段（约141~109 Ma）：在相对湿润的气候背景下，一套跨大陆水系通过思茅盆地与呵叻盆地（Khorat basins），将松潘-甘孜地块（Songpan-Ganzi）、四川盆地（Sichuan Basin）与羌塘地块（Qiangtang）连通至古太平洋（Paleo-Pacific Ocean）；第二阶段（约109~90 Ma）：思茅盆地发育咸水湖相环境（saline lacustrine environment），同期区域广泛干旱化（aridification），向东延伸的大陆尺度河网持续萎缩；第三阶段（约90~71 Ma）：尽管持续干旱气候下河流活动（fluvial activity）有所减弱，但第一阶段型的跨大陆水系得以重建并适度扩张。

整体而言，思茅盆地的物源特征反映了白垩纪跨大陆水系从形成、收缩到最终部分恢复并小幅扩张的完整演化过程。本研究提出了青藏高原东南部白垩纪水系重组的精细化模型，该演化过程本质上受全球与区域构造作用及古气候强迫的共同调控。