New recognitions to genesis and exploitation of the Xuxi River in Jiangsu Province

Along the north bank of the Xuxi River, the sand-intercalated-muddy gravel layer from -3.7 - -5.8 m in the borehole 7508 at the East Dam and the middle, coarse and fine sand layer with a thickness of 4.5 m at the lower part of the borehole 8179 between the East Dam and the West Dam indicate that a large natural river was here before the Kingdom of Wu excavated the Xuxi Canal. The existence of Neolithic sites such as Xuecheng, Chaoduntou and Xiajiadang along the Xuxi River and the silt layer with dozens of meters archived under the earth＇s surface within a range of 1 km along both banks are the even more important evidences for the existence of the ancient Zhongjiang River. The floodgate of the East Dam nowadays makes against the communication between the Shuiyangjiang River and the Taihu Lake. The authors suggest the canal between Wuhu and Taihu Lake should be excavated as soon as possible, namely, the navigation channel from Wuhu through Guchenghu Lake, Xuxi River, East Dam, Liyang, Yixing to Taihu Lake should be further widen and the deposits composed of slope wash on the watershed between Shuiyangjiang River and Taihu Lake should be dredged away. Then, the channel journey can be shortened, the boats in ship transportation on the Yangtze River can be shunted to ensure the security of shipping, the resources of sand and gravel in the old river channel can be exploited and the dike of the Yangtze River can be reinforced. So, the problems of irrigation, flood diversion, pollution abatement and drainage of flooded fields in the lower Yangtze River will be resolved. Then, the above methods can impel the sustainable development of the Xuxi River and Taihu Lake area.

From foredeep to orogenic wedge-top: The Cretaceous Songliao retroforeland basin, China

Songliao Basin,the largest Mesozoic intracontinental nonmarine basin in eastern China,initiated during the latest Jurassic as a backarc extensional basin;rifting failed and thermal cooling controlled subsidence through the early Late Cretaceous.Integrating 2-D and 3D reflection seismic and borehole data with regional geological studies,we interpret sedimentary sequence and structural patterns of the Coniacian-Maastrichtian fill of Songliao Basin as defining a retroforeland basin system developed after 88 Ma(marked by the T11 unconformity in the basin),including(1)significant increase in the thickness of the Nenjiang Formation eastward towards orogenic highlands of the Zhangguangcai Range and the convergent continental margin;(2)a shift of detrital provenance in the basin from north to southeast;and(3)propagation of E-W shortened structures,increasing eastward in amplitude,frequency,and degree of inversion toward the orogen.During latest Cretaceous,foreland basin fill progressively deformed,as the foredeep evolved to a wedge-top tectonic setting,marked by the basin-wide T04 unconformity within the upper Nenjiang Formation at 81.6 Ma.Much of the basin was brought into the orogenic wedge and eroded by the end of the Cretaceous.Late Jurassic/Early Cretaceous backarc rifting of uncratonized basement comprised of accreted terranes likely facilitated and localized the foreland.Synrift normal faults reactivated and extensively inverted as thrust faults are prominent in the eastern 1/3 of the basin,whereas folds developed above detachments in shaley early post-rift strata dominate the western 2/3 of the basin.Songliao foreland development likely was driven by changing plate dynamics and collision along the Pacific margin after 88 Ma.