Sedimentary Environment And Tectonic Background Of Lingshan Island In Early Cretaceous

Lingshan Island, which is among the Sulu Orogenic Belt between the South China Block and North China Block, is situated in the nearshore water to the southeast of Huangdao district, Qingdao, Shandong Province, China. Lu Hongbo et al investigated the island and found the distal turbidites and interbedded slump deposits in the Mesozoic clastic rocks, which appealed much attention of many researcher inland. The author of this paper has carried a elementary study of Lingshan Island under the guide of my tutor in aspects of stratum, types of soft sedimentary deformations, their genetic mechanism, sedimentary environment and tectonic background etc.After field study, we found sequence of stratums is more complicated than former researcher decribed. The stratums roughly consist of Lingshandao formation(K1lsd), which is early Mesozoic flysch, Molasse, Rhyolite, volcanic breccia and agglomerate form the bottom to the top.There are abundant slump deposit beds found in this flysch, indicating frequent strong earthquake events happened in the Early Cretaceous. Different types of soft sediment deformation structures show their different deformation stages compared to the slump deposition events and can be classified into three groups according to their formation period: the structures developed before slump, including distorted fragments of sandstone and mudstone, and sole casts etc.; during the slump, including synsedimentary slump fold, synsedimentary boudinages, synsedimentary duplexes, synsedimentary stretching lineations, X-type conjugate thrust faults, sand blocks and balls, slump scarps etc.; and after the slump, including mini hosts and grabens. Among these structures, slump scarps can be the indicator of slump depletion zone. Some of the soft sediment deformation structures formed during the slump event can be used to identify the slump direction, whereas the structures developed before or during the slump, due to the long distance transportation and late reformation, cannot be used as the indicators of slump direction.According to the analysis of the feature of stratums and soft sedimentary deformation, Lingshandao formation deposited on bathyal or abyssal quake-prone continental rise. The attitude of some soft sedimentary structures revealed the major slump direction is SEâ†'NW and SWâ†'NE, which means slump deposit and sediment came from the SE and SW of remnant basin. At the same time, the remnant basin was in its late stage with water shallowing upward during the sedimentation time. The X-type shear jointing, normal to the sedimentary beds, indicates that the horizon was compressed in SE—NW direction. The asymmetric folding structures of the horizon suggest that the South China Plate was subducting toward northwest under the North China Plate after the slump beds settled down in the Mesozoic time. The early Cretaceous flysch and slump deposits found in Lingshan Island are valuable data for tectonic research on the evolution history in the east of the Sulu Orogenic Belt between South China Block and North China.