海拉尔盆地介形类化石的发现及其地层意义

DISCOVERY OF OSTRACODS FROM THE HAILAR BASIN AND ITS STRATIGRAPHIC SIGNIFICANCE

海拉尔盆地发现了较丰富的介形类化石,主要分布在青元岗组和大磨拐河组。建立了2个介形类化石组合,Talicypridea组合和Limnocypridea组合。描记了3个新种Talicypridea hailarensis sp.nov.,T.qingyuangangensis sp.nov.,T.,subranaformis sp.nov.。对盆地中白垩纪沉积进行了元素含量分析,根据元素分析结果,讨论了各组地层的沉积环境。

Altnoug geological research work in the Hailar Basin has a long history, the geological exploration of petroleum was started only in 1984. Up to now, nearly twenty exploratory wells have been drilled, and several thousand samples have been analyzed, resulting in the discovery of great amounts of fossils, and the establishment of stratigraphic sequence Which is divided in descending order into the Qingyuangang, Hulun, Yimin, Damogttaihe and Beir Formations. With the exception of the Qingyuangang Formation belongin; to Late Cretaceous, all the others belong to Early Cretaceous.The ostracod fossils in the Hailar Basin are mainly distributed within the Qingyuangang and Damoguaihe Formations. According to their composition and morphological characteristics, they can be divided into two fossil assemblages as follows8:1. Talicypridea assemblage This assemblage is developed in the Qingyuangang Formation, with such important elements as Talicypridea aff. amoana, Cypridea apiculata, Cypridea aff. cavernosa, Cypridea gigantea,Harbinia hapta. Based on their composition, the ostracods from Qingyuangang can be compared with those from the 4th—5th members of the Nenjiang Formation, and the Sifangtai and Mingshui Formations in the songliao Basin.2. Limnocypridea assemblage This assemblage is distributed within the Damoguaihe Formation, with such important elements as Lirnnocypridea grammi, Limnocypridea abscondida and Djungarica sP., Cypridea sp., Lycopterocypris sp., etc. in association with abundant fossil phycophytes, bivalves, gastropods, etc. For the first time great amounts of ostracods have been found in the Damoguaihe Formation with their main elements also observed within the middle Zhunbayin Formation in the Tugelige district in Mongolia. In China, they are also deveioped in the middle-upper Jiufotang Formation in western Liaoning, and the upper Saihan Tal Formation of the Bayanhua Group in the Erlian Basin. All of them are common elements in the Early Cretaceous.In the Hailar Basin, the characteristics of element distribution display an obvious regularity in variation with depth. Based on results from systematic element spectrum research on the common elements contained in Wu Well-6, such as Fe_2O_3, MnO_2, TiO_2, CaO, SiO_2, Al_2O_3, MgO, Na_2O, etc. and the trace elements such as Ba, Mo, Sr, Rb, Ga, Zn, Cu, Ni, Cr, V, etc., the element contents are higher in the Qingyuangang Formation, but lower in the Hulun Formation with a relatively graudual change in the Yimin Formation; there is a considerable fluctuation in the Damoguaihe Formation with a relatively gradual change in the Beir Formation. Based on element distribution it is suggested that the Qiagyuangang Formation might have been deposited in a lakeshore and shallow water environment, the Hulun Formation may be fluvial, the Yimin Formation may be of lakeshore marsh facies alternating with fluvial facies, the Damoguaihe Formation may be controlled by fluviel facies alternating with lakeshore and marsh facies in the upper part and intercalated with deep lake facies deposits in the lower part, while the Beir Formation was mainly deposited in a fluvial environment, and intercalated with a small amount of lacustrine facies deposits.Description of New SpeciesFamily Cyprididae Baird, 1845Genus Talicypridea Khand, 1977Talicyprldea qingyuangangensis Ye sp. nov.(P1.Ⅱ, figs.3, 4 )Description Carapace small, elongate—oblong in lateral view. Anterior end higher than posterior end; both ends rounded. Dorsal margin nearly straight, sloping to the posterior; ventral margin somewhat concave medially. Lower part of right valve bearing a cristate protuberance. Left valve larger than the right one, overlapping the latter along the dorsal and ventral margins, with a shallow compression near the dorsal margin of the anterior one-third. Anterion part inflated and posterior end bluntly rounded in dorsal view. Greatest thickness at posterior one-fourth; greatest height at anterior one-third. Surface ornamented with irregularly curved ridge-like striation.Remarks This species differs from Ta