MICROFLORA AND GEOLOGICAL AGE OF THE BASAL PART OF THE LOWER HUIHUIPOU FORMATION OF THE CHIUCHAN BASIN,OF WESTERN KANSU
J.HS AND H.I.CHOW
In this paper the authors present the result of their palynological investiga-tion of the Lower Huihuipou Formation which,owing to lack of proper fossils,hasnot yet been definitely assigned to any geological age.From a bed of the lowermost part of this formation at Chinshankou,numerouspollen grains of gymnosperms are found.Of them,Brachyphyllum,Ginkgoales,Bennettitales,and Cycadales are extremely abundant,amounting to 78% of thetotal number of the microfossils;the rest being those of Cedrus,Pinus,Podocarpusand Taxodiaceae (? Taxodium). The most prominent feature of the flora as a whole is the admixture of thetypical Mesozoic forms along with those of the modern types.Considering thepresence of ?Mohria (or Aneimia) spores which are unknown in the Jurassic,theappearence of a large amount of Brachyphyllum pollen,and the absence of anyangiospermous elements,the authors suggest that the basal part of the Lower Hui-huipou Formation is of Lower Cretaceous age.In this flora there are a large number of tropical plants,such as Cibotium,Lygodium,Gleichenia,?Mohria(or Aneimia),Podocarpus,Cycadales,and Bennetti-tales,thus indicating that the climate of this region in early Cretaceous was ratherwarm and moist.Two new types of Cedrus pollen are described as follows:1.Cedrus-pollenttes brevisaccata sp.nov.(Pl.Ⅰ,fig.10)Pollen grains with 2 air-sacs.Total height about 36.1 μ,and total width about81.6 μ-Body oblate,36.1 μ high and 70.7 μ wide.Distal face smooth,occasionallywith loosely arranged granules.Sexine of proximal face developed into a distinctcap,about 4.7 μ thick,consisting of compactly arranged rod-like structure.Surfaceof cap granular or striate,with irregularly arranged granules.Air-sacs developedat two flanks of distal face,in the shape of a short tongue,about 28.3 μ high and43.9 μ wide.No interruption between cap and root of air-sacs.Surface of air-sacs almost smooth.subsaccate reticulum 4-6 sided;muri slightly undulate,with 2-4 granules developed in lannina of each reticulum.Type specimen:Slide No.1516.2.Cedrus-pollenites aurisaccata sp.nov.(Pl.Ⅱ,fig.36)Pollen grains with 2 air-sacs.Total height about 17.7 μ and total width about59.5 μ Body oblate,17.3 μ high and 43.9 μ wide.Thickness of cap about 3.14 μSurface of cap granular to vermicular.Air-sacs developed at two flanks of dis-tat face,short and auricular,about 26.1 μ high and 29 μ wide.No interruptionbetween cap and root of air-sacs.Surface of air-sacs smooth.Subsaccate reticulum4-6 sided;muri slightly undulate,iwth 3-5 granules developed in lamina of eachreticulum.Type specimen:Slide No.1488.