古龙凹陷青山口组页岩中黄铁矿脉与凝灰岩脉特征及成因机制OA

[Objective]By studying the geometric characteristics and formation mechanism of pyrite and tuff dikes in shales of the Qingshankou Formation in Gulong Sag,this paper discusses their formation time,sedimentary environ-ment,sedimentary process,sediment state and diagenetic environment,and estimates the diagenetic compaction rate of shale,which provides reference for the formation mechanism and significance of the same type of dikes.[Methods]Based on detailed core observation,thin section analysis and dynamic calculation of dike formation,pyrite and tuff dikes are found in the Gulong shale,and their genetic mechanism and geological significance are explored.[Results]The pyrite and tuff dikes in shales of the Qingshankou Formation in Gulong Sag are small in scale,and pyrite dikes can be divided into two types according to their scale.One is the thick pyrite dikes with a width of 1-4 mm and a length of several centimeters;The other is a thin pyrite dike,which is less than 1 mm wide and several millimeters to several centimeters long.Tuff dikes are mostly less than 1 mm in width and several millime-ters to several centimeters in length,and most of them are strongly bent into ptygmatite,erect,inclined or horizontally produced.It is speculated that gravity subsidence may be caused by density inversion,and the dynamic formation model of pyrite and tuff dike is established by calculation.[Conclusions]The shape of pyrite dike in shale oil reser-voir of the Qingshankou Formation in Gulong Sag is very complex,which is formed by gravity subsidence sand dike after late pyritization,that is,there are silt dikes first and then pyrite dikes formation.The tuff formed by volcanic eruption settling on unconsolidated mud of lake,and then tuff dike formed due to gravity subsidence caused by density inversion,rather than overpressure filling from bottom to top caused by seismic liquefaction.The oblique py-rite dike and tuff dike are symmetrical at a distance of 180 degrees,which are subjected to bedding shear action.There are many silt-grade mud debris and large flame-like mud debris in the interior dikes,which are formed by the sand dike and tuff dike sinking into the unconsolidated or even muddy mud at the lower part and being captured.