SoftSediment Deformation Structures of Neogene Related to Earthquake and Its Geological Significance in the Southwestern Margin of Qaidam Basin

Key words: 
• softsediment deformation /
• geological significance /
• Neogene /
• Qaidam Basin

Abstract: Based on studies of regional tectonic setting and observation of drilling cores, softsediment deformation structures of Neogene related to earthquake are recognized in the southwestern margin of the Qaidam Basin. The softsediment deformation structures consist of liquefied sandstone vein，water escape structures，load casts，flame structures，pillow structures，ball structures，pillow beds，microfaults, seismocracks，pinch and swell structures，seismofolds, mixed layers structures and seismic brecciated structures. There are five kinds of sand dikes, such as throatlike sand dikes, venationlike sand dikes, beltlike sand dikes, upward wedge sand dikes and vshape sand dikes. They are caused by shakingfluidization, shakingliquefactionpushing and after shakingpulling softsediments filling in cracks. The load casts，flame structures，pillow structures and ball structures are formed by sinking and instilling caused from oscillation of earthquake along the face between sandy and muddy beds. The seismocracks，microfaults and seismofolds are cracks, faults and folds formed directly by oscillation of earthquake. The pillow beds form by dehydration, sinking and deforming of the sandy beds during earthquake′s oscillation. The integrity of mixed layers structure depends on the magnitude and duration of earthquake. The seismic brecciated structures are made up of autoclastic breccias, plastic breccias and brittle breccias formed by the cracking of basal undisturbed laminate bed because of oscillation of earthquake. The discovery demonstrates that the movement of earthquake was violent on the time of Neogene in the north of Kunlun Orogenic Belt from sedimentology, and it provides a theoretical foundation for the tectonic evolution studies of the Qaidam Basin. Seismic events affect greatly on the physical properties of reservoirs, and the permeability of reservoirs can be improved obviously.