Charcteristics of sedimentary evolution of Early Cretaceous in Liupanshan Basin

Liupanshan Basin has geosynclinal-platform transitional nature,formed in early Yanshan Movement,and it is shear-extrusion basin of Qilianshan piedmont basin.Liupanshan group of Lower Cretaceous included Sanqiao formation,Heshangpu formation,Liwaxia formation,Madongshan and Naijiahe formation from bottom to top,developed argillaceous limestone press from clastic rocks,and a small amount of plaster layer on the top of the strata,sedimentary sequence is conglomerate-coarse sandstonefine sandstone-mudstone-marl and plaster,sediment color developed two brown-red to gray-black depositional cycles,reflecting two water inlet and retreat sedimentary cycles.Based on the color,rock type,sedimentary structures,Liupanshan group divided into four sedimentary facies types,such as alluvial fan,fan delta,braided river delta and lacustrine.