甘肃武都龙家沟盆地地层时代及发育特征

FEATURES AND GEOLOGIC AGE OF STRATIGRAPHY IN LONGJIAGOU BASIN, WUDU, GANSU PROVINCE

根据化石组合，龙家沟盆地的地层可划分为中侏罗统龙家沟组，上白垩统及上中新统保德组。龙家沟组是盆地的主体沉积，含有多层煤层及油页岩。保德组中发现有我国著名的“龙家沟三趾马动物群”．是保德期庙梁亚期的主要代表动物群之一。

Longjiagou basin is at the Northwest part of Wudu county in South Gansu. The basin is an inter moulltain one about 6. 5 km in north and south 1 2. 5 km in east and west. Around it there are all limestone of Carboniferous and Permian. The strata of Mesozoic and Cenozoic in the basin can be divided into three parts, Middle Jurassic (Longjiagou Formation ), Lower Cretaceous and Upper Miocene (Baode Formation ). The contact between foundation and Mesozoic as well as beds are angular uncomformity.Longjiagou Formation is the main sediment in the basin, consisting of gray-black, graygreen mudstone, siltstone and reddish-brown conglomerate, also contain thin-bedded coals and oil shale. An abunclant and diversity fossils of plant, bivalves ostracoda, charophyta were found in it. It is assigned to the Middle Jurassic on the basis of their correlation with Upper Lufen Formatioll etc. and fossils its containing.The Upper CretaceoLls is a set of white and red conglomerate, and nonfossils found.The Baode Formation is represented by a series of red-brown mudstone, fine sandy mudstone. Lower parts are brown sandy conglomerate, containing a lot of mammalian fossils, Adcrocuta. Hipparion, Acerorhinus, Eostyloceras etc., The total study about the Longjiagou Hippurion fauna is being carried on gradually. From the present classified of the fossils it shows that most elements of tile fauna are typical animals of Baodeian. So its geologic age is Baodeian undoubtedly. Some of the elements appeared later, for example, Gazella of. blacki found after Gaozhuangian tip to now. Hipparion platyodus, a hipparionine fossil in the fauna is more progress than other Hipparion in Turolian distribution in other part of China. The age of Baode Formation in Longjiagou basin may be later stage of Baodeian.