Characteristics of Tempestite of Ediacaran Dengying Formation,in the Eastern Yangtze Gorges Area and Its Geological Significance

Tempestite of the Ediacaran Dengying Formation has been discovered for the first time in the Eastern Yangtze Gorges area.The outcrop sections and our observation helped recognize many depositional characteristics of storm deposits,such as hummocky cross stratifications,scouring-filling structures,graded bedding and convolute bedding.Four types of storm deposits have been recognized.TypeⅠis characterized by stranded gravel deposition,hummocky cross stratifications,and scouring base,which was formed in the vicinity of the fair weather wave base.TypeⅡis characterized by the intraclastic limestones,hummocky cross stratifications and convolute bedding,which was formed in the upper ramp environment.TypeⅢis characterized by the limestones with gutter cast and hummocky cross stratifications,which were deposited at the places between storm and fine weather wave base.Type Ⅳis represented by the thin bedded silty micrites formed by distal storm turbidity currents below storm wave base.Study of the storm deposits indicates that the tempestites carry important paleoclimate information and frequent occurrences of storms responded to climate changes during the Dengying Period,in which relatively strong tectonic activity and complicated submarine topography was responsible for the formation of tempestites.Therefore,the characteristics of tempestites are of great significance in understanding of stratigraphic comparison study.