Original title: Early Triassic Nanzhang-Yuan'an fauna endowed with strata and biological combination characteristics
Source of "China Geological Survey Results Newsletter"
Abstract: Through field investigation, cross-sectional measurement and fossil excavation, it was found that the world's earliest Early Triassic Nanzhang-Yuan'an fauna was mainly vested in the veined layered limestone in the upper part of the second section of the Jialing River Formation, and the living environment was mainly a depression in the Lagoon environment. The fauna biological combination mainly includes hubei crocodiles, ichthyosaurs, archaeopteryx and dragon turtles, so far 11 species of 11 genera have been found, and three new types of predation methods have been preliminarily identified, showing the rich species diversity characteristics of the fauna, and providing an important basis for studying the biological recovery process after the mass extinction at the end of the Permian.
1. Project Overview
The topic "Characteristics of the Nanzhang-Yuan'an Fauna and Its Response to the Recovery of Triassic Organisms" belongs to the project "Geology and Mineral Survey of Shennongjia-Huayuan Area of the Mineralizing Belt of Western Hunan-Western Hubei", which is undertaken by the Wuhan Geological Survey Center of the China Geological Survey of the Ministry of Natural Resources. The working cycle is from 2016 to 2018. The main objective and task of this topic is to carry out research on the spatio-temporal distribution, biological combination characteristics and environmental background of the Nanzhang-Yuan'an fauna on the basis of field work such as 1:50,000 geological survey and fossil excavation, so as to provide important clues for the study of the origin of marine reptiles and the recovery process of Marine Life in the Triassic Period.
2. Brief introduction of results
(1) Nanzhang-Yuan'an fauna is endowed with stratigraphic characteristics. The Nanzhang-Yuan'an fauna refers specifically to the fauna of the Lower Triassic with the characteristics of early marine reptiles in the lower Triassic area distributed at the junction of Nanzhang County and Yuan'an County in Hubei Province. The work mainly measured 9 typical geological profiles of the Jialing River Formation strata in the Nanzhang-Yuan'an Fauna area, namely: the Zhangjiawan section of Yuan'an, the section of Fetal Ping, the section of Majiagou in Nanzhang, the section of Baihe Boat, the section of quarry, the section of Pine Gully and the section of Xiliuping, the section of Banqiao Ancient Well and the section of Xiaoyan Large Stone Slab (Figure 1). On this basis, the stratigraphic lattice of the Jialing River Formation under different sedimentary environments in the Nanzhang-Yuan'an area (Figure 2) was established, and the endowed stratigraphic characteristics of the Nanzhang-Yuan'an fauna were fully identified. It can be confirmed that the reported fossils of the Nanzhang-Yuan'an fauna were found in the upper stratified limestone of the second section of the Jialingjiang Formation, rather than some of the previously reported specimens from the earlier Daye Formation. The thickness of each section of the strata in this section is about 30 m, and the abundance and differentiation of fauna are the highest at the top of the strata of this section, and the lower strata are also found, but the abundance and differentiation are not as good as the upper strata. At present, we have not found a complete reptile fossil in the inspection of the Xiliuping section, only one skeleton was found, compared with other complete fossil profiles, the profile of the lithological dolomite content is slightly higher, the local development of bird's eye structure, and in its southwest direction of about 3 km of the large stone slab profile is completely devoid of fossils endowment layer of typical lithological stratum limestone production, so it is inferred that the Nanzhang-Yuan'an fauna of the late Triassic period may mainly live in a depression in the Lagoon environment at that time, of which the phase change is faster along the north, east and east. Below the fauna reservoir layer is mainly a set of slippery breccia and worm-like limestone, and above the reservoir layer is a set of gray-green or gray-yellow glass chip tuff layers, the thickness fluctuates in the range of 20 to 35 cm, but both are widely distributed in the Nanzhang-Yuan'an area, which can be used as a marker layer for stratigraphic comparison.
Figure 1 Traffic location map of the nanzhang-yuan'an fauna in western Hubei and the location of typical geological profiles
Figure 2 Stratigraphy comparison of the JialingJiang Formation in the typical geological profile of the Nanzhang-Yuan'an area in western Hubei
(2) Characteristics of the biological combination of nanzhang-yuan'an fauna. In addition to the abundant marine reptile fossils, only a small number of fossils such as algae and tooth-shaped stones have been found, so the biological combination characteristics here mainly guide the combined characteristics of marine reptiles in the Zhang-Yuan'an fauna. In the process of this fossil excavation, a total of 10 relatively complete marine reptile fossil specimens and more than 20 marine reptile bone fragments were found, and many new progress and new discoveries were made. Among them, the fossil of the dragon turtle Bian's tumor Spinosaurus was identified for the first time, which is not only the first dragon turtle found in the Nanzhang-Yuan'an fauna, but also the earliest record of the dragon turtle in the world; the first time in the fauna was found in the fauna, the marine reptile Hubei crocodile Calodong's fan paddle dragon with a similar predation method to the living platypus, which is the earliest fossil record of the blind induction (non-visual detection) predation method of quadrupeds (Figure 3). In addition, through the study of a marine reptile fossil specimen collected, it was found that it belonged to a new genus of the plesiosaurs, named Xiangchulong, which provided an important clue for the phylogenetic evolution of the finosaurs. So far, the marine reptile combination of the Nanzhang-Yuan'an fauna mainly includes four major categories of Hubei crocodiles, ichthyosaurs, archaeopternosaurs and dragon turtles, with a total of 11 genera and 11 species (Figure 4), of which 5 genera are Hubei crocodiles, namely Nanzhanghu crocodile, Sun's Nanzhanglong, slender Hubei crocodile, short-necked Hubei crocodile and Carlo Dong's fan paddle dragon; ichthyosaurs have only found Zhangjiawan nest lake dragon; ichthyosaurs have found only Zhangjiawan chaohu dragon; 4 genera of archaeoptera, namely Three Gorges Oulong, Hubei Hanjiang lizard, Yuan'an Guizhou dragon and Xiangchu dragon; and the dragon turtle is Bian's tumor spinosaurus. The face of the fauna is much higher than the diversity of marine reptiles in the Anhui Chaohu Dragon Fauna of the same period.
Figure 3 Ecological restoration of Carlo Dong's fan paddle dragon
Figure 4 The main marine reptile types of the early Triassic Nanzhang-Yuan'an fauna in the Nanzhang-Yuan'an area of Hubei Province
A- Nanzhang Hubei Crocodile; B - Slender Hubei Crocodile; C - Xiangchu Dragon; D- Carlo Dong's Fan Paddle Dragon; E- Sun's Nanzhang Dragon; F- Three Gorges Oulong; G- Zhangjiawan Chaohu Dragon; H, I- Hubei Hanjiang Lizard
3. The significance of the results
Through this special investigation work, it was confirmed that the reported fossils of the Nanzhang-Yuan'an fauna were from the upper strata of the second section of the Jialingjiang Formation, not some of the previously reported fossils from the upper part of the Daye Formation, and the comparison of the strata of the Jialingjiang Formation under different sedimentary environments in the region was completed. Through fossil excavation and restoration, the characteristics of marine reptile combinations in the Nanzhang-Yuan'an fauna have been identified, confirming that the species diversity or ecological diversity of marine reptiles in the late Early Triassic period has been highly developed, indicating that predators at the top of the vegetative structure have flourished in the Early Triassic, indicating that marine life may have fully recovered during this period after the Permian mass extinction.
(Courtesy of Yan Chunbo, Wuhan Geological Survey Center, China Geological Survey)