Ubiquitous onshore Cenozoic basins of the southern margin of the South China Block (SCB) systematically show a stratigraphic hiatus in the sedimentary succession. The absence of strata between the residual Paleogene and the overlying Quaternary in the onshore basin is a serious obstacle to reconstruct their evolutionary history and completely understand the tectonic evolution of the southern SCB margin. Using multiple independent methods, this study reconstructs the entire tectonic subsidence and uplift history in the Sanshui Basin. To do so, we first constrain the eroded thickness and initial erosion time between the Quaternary strata and the residual Huayong Formation (∼41 Ma). The results show that the erosion thickness at the unconformity in the northwestern Sanshui Basin was approximately 2200 m, and the erosion event lasted from approximately 29 Ma to the early Quaternary. The tectonic evolution of the Sanshui Basin during the Paleogene to early Quaternary was characterized by four successive tectonic episodes, three rifting events, and one uplift stage. The first rifting episode lasted from ca. 66–48 Ma, during which approximately 1000 m of tectonic subsidence accommodated the deposition of the Xinzhuangcun (66–59 Ma), Buxin (59–53 Ma), and Baoyue (53–48 Ma) formations. This was followed by the second and third rifting episodes from ca. 48–29 Ma, during which the average tectonic subsidence was approximately 650–850 m, and the residual Huayong Formation (ca. 48–41 Ma) and eroded strata (ca. 41–29 Ma) accumulated. From 29 Ma to the early Quaternary, a tectonic uplift of approximately 1150 m occurred, with a rate of 43 m/Myr, which triggered the erosion of most sediments deposited during the second and third rifting episodes. Our results strongly suggest that although the main depocenters were located offshore since the second rifting episode, rifting in the Sanshui Basin continued until the occurrence of the late Cenozoic erosion event. The differential evolution between uplift (and erosion) onshore and subsidence offshore since the late Paleogene is probably related to the coastward attenuation of southeastern extrusion caused by the Indo–Asian plate collision.

中文翻译：

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华南区块南缘三水盆地晚古近纪侵蚀事件及其构造意义


华南区块 （SCB） 南缘无处不在的陆上新生代盆地系统地显示了沉积演替中的地层中断。陆上盆地残余古近纪和上覆第四纪之间缺乏地层，这是重建其演化历史和完全理解南部 SCB 边缘构造演化的严重障碍。本研究采用多种独立方法，重建了三水盆地整个构造沉降和隆升历史。为此，我们首先约束第四纪地层和残余华永组（∼41 马）之间的侵蚀厚度和初始侵蚀时间。结果表明：西北三水盆地不整合面处的侵蚀厚度约为2200 m，侵蚀事件从约29 马持续到第四纪早期。古近纪至第四纪早期三水盆地的构造演化表现为4个连续的构造事件、3个裂谷事件和1个隆起阶段。第一次裂谷事件持续了大约 66-48 马，在此期间大约 1000 m 的构造沉降容纳了新庄村（66-59 马）、布心（59-53 马）和宝岳（53-48 马）地层的沉积。紧随其后的是约 48-29 马 的第二次和第三次裂谷事件，在此期间，平均构造沉降约为 650-850 m，残余的华永组（约 48-41 马）和侵蚀地层（约 41-29 马）积累。从 29 马 到第四纪早期，发生了大约 1150 m 的构造隆起，速率为 43 m/Myr，这引发了第二次和第三次裂谷期间沉积的大多数沉积物的侵蚀。 我们的研究结果强烈表明，尽管自第二次裂谷事件以来主要沉积中心位于近海，但三水盆地的裂谷一直持续到新生代晚期侵蚀事件的发生。自晚古近纪以来，陆上隆起（和侵蚀）与近海沉降之间的差异演变可能与印亚板块碰撞引起的东南挤压向海岸衰减有关。