Tempesitites in Lower Submember of Member 8 of Shihezi Formation (Middle Permain) in Ordos Basin

Key words: 
• Ordos Basin /
• Middle Permian /
• Xiashihezi Formation /
• Tempesitite

Abstract: Lower submember of the 8th of middle Permain Shihezi Formation is quartz sandstone and lithic quartzsandstone with higher compositional and textural maturity and light greywhite color, and is one of the main reservoirs in the basin with the thickness generally 15~40 m, tempesitites frequently occur in some well cores. According to thickness of single tempesitite bed, grain size, fragment contents of external land carbonaceous mudstone and coal, profile feature, especially the scale of hummocky crossbedding and pot cast, and more or less of the stacked tempesitites and so on, three ended type tempesitites could be divided approximately by varying degrees of energy stone wave current in cores. (1) The tempesitite generated by higher energy storm wave current appeared large scale pot cast cute into the top of underlying quartz sandstone or lithic quartzsandstone, the super stratum tempesitite consists of flaky conglomerate of carbonous and light yellow grey mudstones, mixed with some quartz and coal clastics, thickness of single bed the same as 20~50 cm, some are too thick, graded bedding, and frequently show the stacked secession. (2)The tempesitites generated by the middle energy storm wave current show the integrated or nonintegrated tempesitite sequence, with developed hummocky cross bedding, and contain more or less some carbonous mudstone and coal clastics, the thickness of single bed is always 10~40 cm, and stacked sequence often occurred. (3) The tempesitite generated by lower energy storm wave current appeared the thickness about 5~10 cm, only develops the hummocky and swaley cross stratification, not only is single bed, but also stacked by several beds. Tempesitites frequently occur in quartzitic sandstones of Lower submember of the 8th is questioned to viewpoint of fluvial facies.