After the research of our research group (Wang Yuanqing, Li Xi, Tong Yongsheng, etc. ), the main progress is to select the candidate stratotype profile of Lingcha period; The collection sequence of mammals in the order was initially established; The carbon isotope test has achieved good results, accumulated rich and important data for Lingcha period, and greatly improved its maturity.
(1) Location of candidate section of Lingcha stage boundary stratum
When naming Lingcha stage, the stratotype section is defined as Fukuitang-Lingcha section in Hengdong County, Hunan Province. After investigation by the research group (Wang Yuanqing, Li Xi, Tong Yongsheng, etc. ), it is suggested that the stratotype section of the boundary line of Lingcha Stage be selected next to the northeast Lingcha-Liu Xia Highway in Chengjiachong Village, Hengdong County, Hunan Province, with the geographical coordinates of 27 0 1.425' N,1249.949' e (. According to the carbon isotope test, the negative drift trend of carbon isotope is obtained at the bottom of the profile, which is completely consistent with the characteristics of the international Eocene/Paleocene boundary "Golden Nail" profile.
Figure 106 Location Map of Candidate Profile of Lingcha Stage Boundary Strata
(II) Description of stratum profile of Lingcha stage boundary line
On this profile, the representative stratum of Lingcha Stage is Lingcha Formation, but its top is not completely exposed, and its bottom is in integral contact with the underlying Limuping Formation. The layered lithologic characteristics of this profile are as follows:
Progress and Achievements of Major Dating Strata Research Projects in China (200 1 ~ 2009)
Progress and Achievements of Major Dating Strata Research Projects in China (200 1 ~ 2009)
The underlying stratum is the interbedded siltstone and mudstone of Paleocene Limuping Formation, and the top is paleosol stratum.
(3) The sequence of biological assemblage in Lingcha period.
Based on the comprehensive analysis of the research results of our research group and predecessors, the Lingcha period (stage) includes three mammal fauna from bottom to top, namely Lingcha fauna, Wutu fauna and Yuhuangding fauna. At the candidate section of boundary stratotype, because the upper and middle strata of Lingcha stage are not completely exposed, the mammalian fossils obtained from this section only belong to Lingcha fauna. At present, the composition of these three fauna is as follows:
Lingcha fauna
At present, it includes the following species: Hsiangolestes youngi, a male elephant predator, Matutinia nitidulus, Hapalodectes hetangensis, a Tseng's double-pointed China beast Dissacus zengi and an Asian crested beast. Asiocoryphodon？ Species Teihardina asatica, an Asian German monkey; Camellia mouse Cocomys lingchaensis hengdong oriental horse-the original Hengyang thick-toothed horse; An unexpected Hunan animal.
Wutu fauna
At present, it includes Dawson Monkey, Middle-legged Monkey, China Golden Monkey, Long-tailed Monkey, Asian Young Monkey and Oriental Spiny Monkey. Late-born senior monkeys Chronolestes simul, MICROTUS fortis, MICROTUS sinensis, and Acritoparamys, a Chinese peninsula mouse? Wutui, mount tai Changle rat, rodents. Asian chiropractor Asian partridge, ancestor of five pictures, Wutu tapir, Lushi Ampullaria, Millennium tapir, etc.
Yuhuangding fauna
At present, it includes: Hunan-like animal (undetermined species) Cf. Hunanictis sp., Mongolian gerbil in Turpan (similar species), Hubei rat Hohomys lii of Li, Hubei strange rat Advenimus hubeiensis, Asian crested animal asiocuryph-odon conicus, heterodentate animal Heterocoryphodon and Yang's heterodentate animal. Allosaurus? (mantedong) sp. Compare H. youngi, like rhinoceros, and the unidentified species compare the seven-toothed elephant species. , ice, Danjiangkou beast, Danjiangkou, etc.
Lingcha fauna is the lowest among the early Eocene fauna found in China. Among them, there are primitive rodents, primates (Teilhardina) and comb-toed rats (Cocomys), which are very similar to mammals in other continents in the early Eocene. There are a large number of primitive rodent fossils such as the comb-toed mouse (Zhong Jian mouse) and the relatively primitive wide-mortar beast (Chen Guang beast) in this fauna, which is similar to the Benben fauna found in Mongolia in the early Eocene and shows a relatively dry environment.
The Yuhuangding fauna is dominated by rodents, which reflects that the fauna also lives in a relatively dry environment. Among them, there are abundant wide-mortar animals (rhomboid animals) and many primitive comb-toed rats (Hohomys and Advenimus). Seven-toothed dragon also appeared in this fauna, which indicates that the age of Yuhuangding fauna is relatively late, because such animals are usually distributed in the middle and late Vasa in North America. Fauna similar to Yuhuangding Fauna is widely distributed in many areas of China, such as Youping Fauna in Fangxian County, Hubei Province, Ningjiashan Fauna in Shui Yuan Basin, Shisanfang Fauna in Turpan Basin, Xinjiang, Ira Fossil Site in Sardo, Niu Shan Fossil Site in Shandong Province, Huahua Fossil Site in Feng 'an, Anhui Province, Yanquan Fossil Site in Tao Chang Basin, Hunan Province, etc.
Wutu fauna, obviously different from the above two fauna, represents the fauna living in a relatively humid environment and contains a large number of insect-eating fossils. Rodents are mainly rodents, and there are many kinds. Homogalax appeared in this fauna, indicating that its age is later than Lingcha fauna and earlier than Yuhuangding fauna, which may be equivalent to Graybullian subfacies of Wasatchian period in North America.
(4) The chemical and magnetic stratigraphic characteristics of Lingcha period.
In 2000, Chinese and American scientists cooperated to sample and analyze the carbon isotopes and paleomagnetism of Limuping, Fukuitang-Lingcha and Tianzhifen-Jixian Bay in Lingcha area. Carbon isotope drift appears in Fukuitang-Lingcha section and Tianzhifen-Jixian Bay section respectively. The δ 13cv-PDB values in the paleosoil of the underlying Limuping Formation are-7 ‰ ~-8 ‰ in the Tianzhifen-Jixian Bay profile (the stratotype candidate profile selected by our research group). There is no paleosol layer in the coarse sandstone of Lingcha Formation 1 layer, but a paleosol layer appears in the 238m profile (the second layer of stratotype candidate profile), and the carbon isotope begins to drift negatively, with the δ 13cv-PDB value of-8.6 ‰ ~10.5 ‰; Upward, the maximum negative drift of carbon isotope appears in the sixth layer of the profile, and the δ 13cv-PDB value of individual samples reaches-13.0 ‰.
According to the paleomagnetic test results, the upper strata (Lingcha Formation) of the profile are C24r reverse polarity deposits, while the lower strata (Limuping Formation) are C25n and C25r polarity deposits, indicating that the upper strata (Lingcha Formation) should be Eocene and the lower strata (Limuping Formation) should be Paleocene.
(5) The definition and bottom boundary of Ling tea grade.
Since Lingcha period is the lowest stage of Eocene, its bottom boundary is also the boundary between Eocene and Paleocene. According to the international definition of Eocene/Paleocene boundary, it marks the negative drift of carbon isotope, and the results of carbon isotope test in Lingcha period are basically consistent with this. However, in the stratotype profile, because the Lingcha Formation 1 layer is grayish yellow coarse sandstone without paleosol layer, no carbon isotope drift phenomenon is detected, and the second layer of brownish red silty sandstone begins to drift negatively, so it is difficult to determine its accurate demarcation point in the field. Moreover, the negative drift of carbon isotope is not necessarily in the second layer. If there is a suitable interlayer, the same result may be obtained in the 1 layer. Moreover, the coarse sandstone of 1 layer is relatively stable in the local area, and its bottom boundary should be a good natural interface. Therefore, the research team suggested that the bottom boundary of Lingcha Stage should be located at the bottom of grayish yellow coarse sandstone of Lingcha Formation 1 layer, which is beneficial to stratotype profile.
For the Lingcha period, the following mammalian fossils can also be used as identification marks. The earliest and endemic mammals in the Ridge Tea Period are Portulaca, Gerbil (animal kingdom), Coconut, Advenimus (Rodent), Hapalodontidae, Asio-coryphodon, Hyopsodus (Diptera), Orientolophus, Homogalax and Hepto-. In addition, the middle-toothed beast (Polyodontidae), the golden-toothed beast (Archeodontidae), the tiger-toothed beast (odontidae), the long-toothed beast (Lepidoptera), the fine-toothed beast (Microodontidae) and the spotted-toothed beast (primate) also appeared for the first time in the Lingcha period. Asioplesiadapis, Carpocristes, Chronolestes (more like a monkey suborder), Gomphos (pika), Alagomys, Bandaomys, Hohomys, Hannanomys, Acritoparamys? As well as Tarzan zokor (Rodent), Neozokor (Miocene zokor) (Carnivora), Narrow-toothed Bat, Narrow-toothed Bat (Pseudoodontidae),? ? ? ? Genus, axe-footed bat and danjiang bat (Chiroptera).
(6) Regional comparison of Ling tea grades.
According to the negative drift characteristics of mammalian fossils and carbon isotopes at the bottom of Lingcha stage, it can be compared with the "golden nail" profile of ypres stage in the international stratigraphic table-Dababulia profile near Luxor; Mammals in Lingcha period can be compared with Wasacz period in North America and Ipsos period in Europe.
According to the comparison of bio-fossils, the lithostratigraphic units that are roughly in the same period as the Lingcha period in China are: Lingcha Formation in Hengyang Basin, Hunan Province, Wutu Formation in Changle Area, Shandong Province, Yuhuangding Formation in the border area between Danjiang River in Hubei Province and Xichuan in Henan Province, Zhang Shan Formation in Lu 'an Area, Anhui Province, Lower Member of Xinyu Formation in Xinyu Area, Jiangxi Province, and Thirteen Fangjian Formation in Turpan Basin, Xinjiang; Upper Oujiang Formation and Northern Jiangsu Dai Nan Formation in the East China Sea Shelf Basin.