云南曲靖蔡家冲地区下第三系

NEW FINDS OF FOSSILS FROM PALEOGENE OF QUJING, YUNNAN

云南曲靖蔡家冲地区下第三系可分为两部分,上部蔡家冲组有三个含化石层,并含有小哺乳动物和鱼化石,进一步证实了它的时代为早渐新世,可与阿尔丁鄂博组比较。但与华南相邻盆地同时代的地层和动物群比较,却存在不同程度的差异。下部红层不整合伏于蔡家冲组之下,在其中第一次发现了脊椎动物化石,并建立了格浪河组。

Caijiachong (Tsaichiaehung) area, situated in the northmost part of Yuezhow Basin, has been well known since 1932, when Young first diseribed some mammalian fossils and considered the age of the beds as Pliocene based on the first discovered specimen preliminarily identified as Merycopatamus sp. This viewpoint was followed with slight modification by Colbert(1940). With additional new data Young and Bien(1939), and Bien (1940) divided the deposits into two parts: the lower Caijiachong(Tsaichiachong) subaerial sandstone overlain by an upper Caijiachong lacustrine beds. The age of the latter was assigned as Early Oligocene by presence of 'Cadurcodon'. In 1957 Chow reexamined the old collections found in Caijiachong Marls and reaffirmed the Oligocene age by recognition of Bothriodon among them. Concerning the lower part, views differ. According to the field work carried out by a IVPP team in 1980, the stratigraphic sequence could be summarized as follows. The early Tertiary sediments overlying unconforably on Permian limestone are monoclinal dipping from 3°—11° to the west and bordered by faulted block of Carboniferous limestone along the western margin of the basin. The total thickness is 218 m. The sediments can be divided into two units: the Gelanghe Formation and the Caijiachong Formation. The Caijiachong Formation, used to be called Tsaichiachung upper lacustrine beds or Tsaiehiachung marls, is composed of light coloured marls mudstone and siltstone. In 1980 some more mammalian fossils, especially micro-mammalian fossils, were collected from three different layers. The lower layer consists of grey mudstone, where the fossil remains, such as Crocodylinae indet., Brontotheriidae indet., Prohyracodon sp. Cadurcodon sp. and cf. Indomeryx sp. etc. were collected. The middle layer is composed of light grey marls intercalated with varicoloured mudstone and siltstone, and contains Charophyta: Harrisichara vesiformis, H. dezhouensis, E. subleres, H. yunlongensis, Harrisichara sp. Rhabdochara cf. major, R., cauliculosa, R. stockmansi, R. langeri, R. kigyonensis, Rhabdochara sp. Sphaerochara inconpicua, Grambastichara sp. Charttes sp., Amblyochara subeiensis; Gastropoda: Bithynia (Pseudemmericia)? largicirca, B. (P.)? parvobliqua, Assiminea pressoopercula; Vertebrate: Barbinae, Leuciscinae., Abramidinae Cyprininae, Cyprinidae indet., ?Characidae indet., Crocodylidae indet., Erinaceidae indet., Plesiosminthus sp. Eucricetodon sp. Karakoromys sp. Lagomorpha indet., Carnivora indet., Brontotheriidae indet., Amynodontidae indet., Prohyracodon sp., Miomeryx sp. Lophiomeryx sp., cf. Indomeryx sp. etc. The upper layer consists of greyish green marls, calcareous mudstone intercalated with mudstone and siltstone, and yields Charapbyta: Amblyochara subeinsis, A. wangguanensis, Maedlerisphaera chinenvis, Harrisichara subleres, Harrisichara sp., Rhaodochara major, Sphaerochara sp. ; Gastropoda: Bithynia (Pseudemmericia)? largivirca, B. (P.)? parvobliqua, Assiminea pressoopercula; Vertebrate: Crocodylinae indet., Emydidae indet., Rodentia indet., Brontotheriidae indet., Cadurcodon sp., Gigantamynodon sp., Amynodontidae indet., Rhinocerotidae indet., Entelodon sp., Bothriodon sp., Artiodactyla indet, etc. As can be seen from the list above, the whole Caijiachong mammalian fauna is essentially similar to the eaely Oligocene fauna of North Asia and can be closely comparable to the Ardyn Obo Fauna of the Mongolia People's Republic, but is quite different from the Gongkang Fauna in Baise Basin, Guangxi, which is also considered of Early Oligocene in age. Though the mammalian fossils of the Xiaotun Formation is comparable to that of the Caijiachong Formation, but the rock of the former is quite different from that of the latter. On the contrary the rock of the upper part of the Lumeiyi Formation is similar to that of the Caijiachong Formation. In addition the mammalian fossils of the upper part of the Lumeiyi Formation, such as Indricotherium and Dianatitan, indicate the early Oligocene age. May the upper part of the Lumeiyi Formation be considered contemporaneous with the Caijiachong Formation? This problem is to be solved in the future. The Gelanghe Formation lying uncomoforably under the Caijiachong Formation is series of red beds consisting of red mudstone, siltstone with calcareous concretions, sandstone, conglomerate and greenish streaks, and with basal breccia. No fossil had been found until 1980. At first it was considered as of Late Eocene in age and synchronous with the Lunan deposits by Bien in 1940. Sometimes it was called the Lunan Formation of Late Eocene or the Xiaotun Formation of Oligocene. Some others considered it as merely the lower part of the 'Caijiachong Formation', which represented the whole Lower Tertiary sediments in the area and was considered as of OligoceneEocene in age. Though some Vertebrate fossils, such as Primate, Rodentia indet. and Emydidae indet, were found in the lower 'Red beds' in 1980, it is still difficult to give a definit answer concerning the age of the lower 'Red beds' based on these fossils only. But since the 'Red beds' are overlain uncomforably by the Caijiachong Formation of Early Oligocene. It is quite possible that the 'Red beds' represents the sediments of the Late Eocene in age as was originally suggested by Young and Bien (1939) and Bien (1940). Since the Paleogene deposits which used to be called Lunan Formation was subdivided into two Formations, the Xiaotun Formation and the Lumeiyi Formation, by Zhen et al. in 1978, the age of the Xiaotun Formation is Early Oligocene and is later than that of the lower 'Red beds' in the Caijiachong area. The Lumeiyi Formation may be synchronous with the lower 'Red beds' in Caijiachong area, but the rock is different from the latter in detail. We prefer the new name, Gelanghe Formation, for the lower 'Red beds' to the Lunan Formation, or the Xiaotun Formation or the Lumeiyi Formation used in Lunan Basin.