The Sedimentary Petrographic Association and Palaeoenvironment of Zhuanchengzi Layer of Lower Cretaceous Yixian Formation in Yingwoshan Area, Yixian Basin

Key words: 
• turbidite division /
• sedimentary facies /
• Zhuanchengzi layer /
• Yixian Formation /
• Yingwoshan area

Abstract: In western Liaoning province, the Yixian Basin is thought as the subdepression of Cretaceous FuxinYixian Basin, the intrabasin Yixian Formation section is cropped out in MashenmiaoDaobadiSanbailongJingangshan, strikingly from east to west. As the middle part of Yixian Formation, Zhuanchengzi layer consists of lacustrine sediments in Yingwoshan area. These sedimentary piles are divided into three subdivisions. The lower part comprises coarser turbidites(T, Ta1, Ta2)and finer turbidites(Tb1, Tb2), the former is made up of bentonitic gritstone, mottle gompholite, grayishgreen tuffaceous conglomerate, earthy granular conglomerate, the latter is grayishgreen bentonitic siltsone, containing carbonized debris, sedimentary tuffite and mudstone. Influenced by turbidity and regional tectonic processes, the water column becomes shallower, the coarser and finer turbidites divisions (Ta3Ta6, Tb3Tb6)were formed around lake margin and thinbedded silicified dolomite deposits on the finer turbidite divisions. The middle part of Zhuangchengzi layer consists of silicified dolomite, containing chert nodules, dolomitic limestone, laminae dolomite and slumping dolomitic limestone. The upper part of Zhuangchengzi layer is characterized by hemi to deep and hemi to shallow lacustrine facies, the rock assemblage is of tuffaceous calcarenite, bentonitic marl, dolomite, bentonite and greyblack shale. The sedimentary rock association indicates that there were marginal turbidity processes, lacustrineplat environment, dolomitic limestone formed around lacustrine ramp, laminae dolomiteshale formed in deep lacustine facies, and a lot of volcanic and terrestrial clastic debris filled the basin.