在宁夏六盘山盆地数条露头剖面原划归侏罗系延安组的含煤地层中新发现了晚三叠世孢粉、植物和双壳类化石 ,证明这一含煤地层中下段的地质时代应归晚三叠世 ,暂定为延长组 ,上部仍归延安组 The late Triassic sporopollen, plant and bivalve fossils have been newly discovered in the coal-bearing strata of the Yan’an Formation in the Jurassic in the outcrop of several outcrops of the Liupanshan Basin in Ningxia. This proved that the geological epoch of the middle and lower parts of this coal-bearing formation Should be late Triassic, tentatively scheduled to extend the group, the upper part of the return to Yan’an