Early Cambrian (Stage 4) brachiopods from the Shipai Formation in the Three Gorges area of South China

Diverse and abundant fossil taxa have been described in the lower Cambrian Shipai Formation in the Three Gorges area of Hubei Province, South China, but the taxonomy and diversity of the co-occurring brachiopod fauna are still far from clear. Here we describe the brachiopod fauna recovered from the Shipai Formation in the Three Gorges area of South China, including representatives of the subphylum Linguliformea: linguloids (Lingulellotreta ergalievi, Eoobolus malongensis, and Neobolidae gen. indet. sp. indet.), and an acrotretoid (Linnarssonia sapushanensis); and representatives from the subphylum Rhynchonelliformea: the calcareous-shelled Kutorginates (Kutorgina sinensis, Kutorgina sp., and Nisusia liantuoensis). This brachiopod assemblage and the first occurrence of Linnarssonia sapushanensis shell beds permit correlation of the Shipai Formation in the Three Gorges area of Hubei Province with the Stage 4 Wulongqing Formation in the Wuding area of eastern Yunnan. This correlation is further strengthened by the first appearance datum (FAD) of the rhynchonelliform brachiopod Nisusia in the upper silty mudstone of both the Shipai and Wulongqing formations. The new well-preserved material, derived from siliciclastic rocks, also gives critical new insights into the fine shell structure of L. sapushanensis. Microstructural studies on micromorphic acrotretoids (like Linnarssonia) have previously been restricted to fossils that were acid-etched from limestones. This is the first study to carry out detailed comparative ultrastructural studies on acrotretoid shells preserved in siliciclastic rocks. This work reveals a hollow tube and solid column microstructure in the acrotretoid shells from the Shipai Formation, which is likely to be equivalent of traditional column and central canal observed in shells dissolved from limestones.

Formation Mechanism for Upland Low-Relief Surface Landscapes in the Three Gorges Region, China

Extensive areas with low-relief surfaces that are almost flat surfaces high in the mountain ranges constitute the dominant geomorphic feature of the Three Gorges area. However, their origin remains a matter of debate, and has been interpreted previously as the result of fluvial erosion after peneplain uplift. Here, a new formation mechanism for these low-relief surface landscapes has been proposed, based on the analyses of low-relief surface distribution, swath profiles, χ mapping, river capture landform characteristics, and a numerical analytical model. The results showed that the low-relief surfaces in the Three Gorges area could be divided into higher elevation and lower elevation surfaces, distributed mainly in the highlands between the Yangtze River and Qingjiang River. The analyses also showed that the rivers on both sides of the drainage divide have not yet reached equilibrium, with actively migrating drainage divides and river basins in the process of reorganizing. It was concluded that the low-relief surfaces in the Three Gorges area did not share a common uplift history, and neither were they peneplain relicts, but rather that the effect of “area-loss feedback” caused by river capture has promoted the formation of upland low-relief surface landscapes. A future work aims to present the contribution of accurate dating of low-relief surface landscapes.

Landslide Monitoring by Integrating Multi-Sensor InSAR Time Series Datasets and Corner Reflectors in the Three Gorges Area

<p>Landslide is one of the major geohazards in the Three Gorges area as a result of steep valley-side slopes and environmental conditions, e.g., high precipitation. To monitor and detect the landslides and rock falls at a regional scale as Three Gorges area, the differential Synthetic Aperture Radar Interferometry (D-InSAR) technology could be more effective and efficient than other conventional geological and geodetic measurements that can be performed only at a few sites with proper accessibility and conditions.</p><p>Over the past few decades, InSAR technology and advanced SAR Interferometry techniques such as Persistent Scatterer Interferometry (PSI) and Small Baseline Subsets (SBAS) have been developed to derive ground displacement over large areas with high-resolution measurement points and acceptable accuracy (cm to mm level). Both PSI and SBAS methods are based on a network of coherent pixels, including natural persistent scatterer (NPS) and artificial corner reflector (CR). NPSs can be easily found in urban areas or rocky regions. However, for landslide monitoring, the NPSs are usually difficult to be identified due to the steepness, vegetated and vulnerable moisture content among the high-risk locations. In this work, multiple SAR datasets including C-band Sentinel-1, L-band ALOS-2 and X-band TerraSAR-X (TSX) are exploited for landslide monitoring along the Yangtze River in the Three Gorges area in China.  Both PSI and SBAS methods are utilized. Besides, stable artificial CRs are deployed on selected sites to evaluate their performance in deriving landslide kinematics. Results are presented and discussed for a better assessment of landslide hazards in the Three Gorges region.</p>