2006(4):498-513.
DOI: 1
CSTR:
Abstract:
The Liupanshan Group is widely distributed and well exposed in the bordering areas of Shaanxi, Gansu and Ningxia, or the western margin of the Shaanxi-Gansu-Ningxia Basin. A variety of spores and pollen are discovered during the present study of a section near Anguo Town, Pingliang, Gansu Province. Fifteen samples are found quite palyniferous from four of the five composing formations, e.g. the Sanqiao, Heshang- pu, Liwaxia, Madongshan and Naijiahe formations in ascending order with the basal one, Sanqiao Formation, as an exception. Gymnosperm pollen predominate the palynoassemblages except LD272, 271 and 206, in which fern spores prevail. The most abundant of this group is Classopollis, and others include Cycadopites, Ephedripites and Jugella. Saccate pollen of conifers is common but always in low percentages. Fern spores Cicatricosisporites is abundant and of high diversity, flourishing in a few samples. Schizaeoisporites acts in a similar way of Cicatricosisporites, but usually in lower percentages. Cyathidites and Lygodiumsporites are common in the assemblages. Compared with the assemblages discovered by Liu Zhaosheng (1983), which only refers to two formations of the Liupanshan Group, e.g. the Liwaxia Formation and the Naijiahe Formation, much more Cretaceous indicators are encountered in our study. They include Foraminisporis, Hsuisporites, Pilosisporites, Plicatella, Wulongspora, Yichangsporites, Coptospora, Jugella, Zhonghuapollis and Tricolpopollenites. Based on these taxa, especially the occurrence of angiosperm pollen Tricolpopollenites, a late Early Cretaceous age, e.g. Early to Middle Albian, is indicated though late Aptian may not be entirely ruled out. The xerophytic Schizaeoi- sporites, Classopollis, Ephedripites and Jugella occur abundantly and diversely in the palynoassemblages, especially in those of the Heshang- pu and Naijiahe formations. Thus an arid climate is indicated though semi- arid or periodic arid may be more likely for the Liwaxia and Madongshan formations. A comparison is made between the Liupanshan Group and the Zhidan Group deposited at the central Shaanxi-Gansu-Ningxia Basin. That is, the Heshangpu, Liwaxia, Madongshan, and Naijiahe formations are correlative to the Jingchuan Formation, and the Sanqiao Formation to the Luohandong Formation. It thus indicates that the early Early Cretaceous sediments are unproductive at the marginal region of the basin.
