J Integr Plant Biol. ›› 1974, Vol. 16 ›› Issue (4): -.

• Research Articles •    

Sporo-pollen Assemblage and Geological Age of the Lower Xinminbu Formation of Chiuchuan, Kansu

Hsü Jen, Chiang Te-chin and Young Hui-chiu   

Abstract: The Lower Xinminbu Formation is a lacustrine deposit which consists mainly of black papery shales intercalated with greyish green thick-layered sandstones and grey thin-layered marls. There are greyish white and reddish brown thick-layered conglomerates in the basal part. The total thickness of this formation sums up to 1135 metres. The black shales are rich in fossil pollen and spores. One hundred and sixty-two rock samples collected from six natural sections and two bore-holes of the above-mentioned deposit at Hongliuxia, Xinminbu, Hanxia, etc. have been treated. A lot of fossil pollen grains and spores have been found from 33 samples of them. Twenty species (or forms) of pollen and spores referred to 19 genera are described in this paper. Two species are described as new. The sporo-pollen assemblage of the Lower Xinminbu Formation is characterized by the absolute predominance of the pollen grains of gymnosperms, by the diminution of the spores of fern, and by the presence of the pollen grains of angiosperms. The pollen of gymnosperms amount to 93.3% of the total number of the microflora. The spores of fern merely amount to 5.9% of the total number. Although the pollen of angiosperms arc rarely found, they play an important role in the microflora. The prominent characteristics of this microflora are the predominance of the pollen grains of Coniferae, the abundance of the spores of Schizaeaceae and the presence of the pollen grains of the angiosperms. Based on the palynological investigation, the authors consider that the Lower Xinminbu Formation should belong to Early Cretaceous in age, because the Early Cretaceous floras both in the Eurasian Continent and in the northern American Continent possess ordinarily the above-mentioned characteristics. According to the flora reflected by the present sporo-pollen assemblage, it may be supposed that the climate of the Chiuchuan Basin in the Early Cretaceous period was certainly rather warm and wet. It may be referred to subtropical type similar to that of southern China at the present time. Description of new species Schizaeoisporites zizyphinus sp. nov. (pl. 1, fig. 11; pl.2, fig. 1) 1962 Schizaea sp. 2 Chang p. 259, pl. 2, fig. 8a-c. Holotype: No. 593 (pl. 2, fig. 1) Diagnosis: Spores zizyphus-shaped, 33.06–43.50 μ × 13.92–20.88 μ, monolete. Exine about 1 μ thick, and thicker at both ends. Surface with 14 ± ribs which are parallel to the long axis, straight or slightly curved, convergent or non-convergent at both ends. Ribs about 0.5–1.2 μ thick, and about 2 μ distant. Comparison: This kind of spores is similar to Cicatricososporites pseudodoro- gensis (R. Pot.) Pf. et Th. from Cretaceous of Quedlinburg (Weyland et Greifeld, 1953, p. 43, pl. 11, figs. 48–50, 53), but the latter is rounder, with non-parallel ribs, which are not convergent at both ends. Cingulatisporites ruginosus sp. nov. (pl. 2, figs. 2, 3, 3a) Holotype: No. 608 (pl. 2, fig. 3) Diagnosis: Spore rounded-triangular in polar view. Diameter 35.08–52.20μ. Triradiate suture long, stretched up to the equator. Cingulum 3 to 8 μ wide, with wrinkles in layers. Exine at the angles of the spore thicker than that of the other parts. Surface with granular sculpture.

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