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The Xiaowa Formation is a Carnian-age geological formation found in southern China. It is a sequence of limestone and marls from the Carnian stage of the Triassic. Its lower section was previously known as the Wayao Formation or Wayao Member of the Falang Formation (a nomenclature still used by some authors). In 2002, the Wayao Member was renamed and raised to the Xiaowa Formation to prevent confusion with an Eocene unit of the same name. Crinoids and marine reptiles are abundant in the Xiaowa Formation, forming a lagerstätte known as the Guanling biota. Ammonoids and conodonts found in the formation constrain its age to the early Carnian. Reptiles of the Guanling biota include ichthyosaurs, thalattosaurs, placodonts, and Odontochelys (an early relative of turtles). Sedimentary events within this formation have been tied to the Carnian Pluvial Event.

Geology

The Xiaowa Formation has three members. The lower member is relatively thin but is also very fossiliferous. It begins with thick-bedded grey biomicrite (fine-grained fossiliferous limestone) interbedded with greenish shale. Bivalves and crinoid fragments are the most common fossils in the biomicrite layers, which sometimes grade upwards to dark grey laminated marls. The lower section of the lower member represents a relatively well-oxygenated pelagic environment. The lower member then transitions to a section of darker and more clastic layers indicative of anoxic conditions and reduced reef activity. Most of the articulated crinoids and vertebrate fossils of the Guanling biota hail from a dark grey micrite at the base of the lower member's upper section. This is followed by dark grey marls and black shale rich in bivalves, ammonoids, and slightly radioactive clay minerals. The lower member concludes with a sequence of dark grey laminated marls incorporating conodont fossils and silty quartz grains.

The middle member of the Xiaowa Formation is by far the thickest unit and includes thick-bedded grey limestone and marl layers interbedding with each other. Sediment deformation is characteristic of layers in this member, while fossils are represented mainly by occasional bivalves and ammonoids. The middle member represents a deep-water environment influenced by tectonic events which disturb sediment layers and create distant turbidites that periodically supply increased clastic material. The upper member is mostly dominated by laminated limestone. Though marl interbedding and fossils are practically absent, silty to sandy quartz grains are common and dominate the last few meters of the formation. This member represents a shallower ocean environment (likely raised by tectonic uplift) supplied with dust from terrestrial areas

Paleobiota

The Xiaowa Formation encompasses several biostratigraphic zones. The Protrachyceras costulatum ammonoid zone of the upper Zhuganpo Formation continues into the first few meters of the Xiaowa Formation's lower member. However, the rest of the lower member (including the Guanling biota) belongs to the Trachyceras multituberculatum ammonoid zone. This unit has also been called the Austrotrachyceras triadicum zone, and is likely equivalent to the T. aon or T. aonoides zone of the western Tethys (Europe). The middle member of the Xiaowa Formation belongs to the Sirenites cf. senticosus ammonoid zone.

Bivalves

Brachiopods

Cephalopods

Conodonts

Echinoderms

Fish

Reptiles

References

1. ^ Xiaofeng, Wang; Bachmann, Gerhard H.; Hagdorn, Hans; Sander, P. Martin; Cuny, Gilles; Xiaohong, Chen; Chuanshang, Wang; Lide, Chen; Long, Cheng; Fansong, Meng; Guanghong, Xu (2008). "The Late Triassic Black Shales of the Guanling Area, Guizhou Province, South-West China: A Unique Marine Reptile and Pelagic Crinoid Fossil Lagerstätte". Palaeontology. 51 (1): 27–61. Bibcode:2008Palgy..51...27X. doi:10.1111/j.1475-4983.2007.00735.x. ISSN 1475-4983.
2. ^ Hao Weicheng, Sun Yuanlin, Jiang Dayong, Yang Shouren, Wang Xinping (2003). "Cephalopods of the "Falang Formation" (Triassic) from Guanling and Zhenfeng Counties, Guizhou Province, China". Acta Geologica Sinica - English Edition. 77 (4): 430–439. Bibcode:2003AcGlS..77..430H. doi:10.1111/j.1755-6724.2003.tb00124.x. ISSN 1755-6724. S2CID 129859010.{{cite journal}}: CS1 maint: multiple names: authors list (link)
3. ^ Yan Li, Zuoyu Sun, Yuan-Lin Sun, Dayong Jiang, Weicheng Hao (May 2013). "Carnian (Late Triassic) ammonoid biostratigraphy in Luoping County, eastern Yunnan Province, China". Acta Scientiarum Naturalium Universitatis Pekinensis (in Chinese and English). 49 (3): 471–479.{{cite journal}}: CS1 maint: multiple names: authors list (link)
4. ^ Benton, Michael J.; Zhang, Qiyue; Hu, Shixue; Chen, Zhong-Qiang; Wen, Wen; Liu, Jun; Huang, Jinyuan; Zhou, Changyong; Xie, Tao; Tong, Jinnan; Choo, Brian (2013-10-01). "Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo-Triassic mass extinction". Earth-Science Reviews. 125: 199–243. Bibcode:2013ESRv..125..199B. doi:10.1016/j.earscirev.2013.05.014. ISSN 0012-8252.
5. ^ Sun, Zuoyu; Jiang, Dayong; Ji, Cheng; Hao, Weicheng (2016-03-15). "Integrated biochronology for Triassic marine vertebrate faunas of Guizhou Province, South China". Journal of Asian Earth Sciences. 118: 101–110. Bibcode:2016JAESc.118..101S. doi:10.1016/j.jseaes.2016.01.004. ISSN 1367-9120.
6. Sun, Y. D.; Wignall, P. B.; Joachimski, M. M.; Bond, D. P. G.; Grasby, S. E.; Lai, X. L.; Wang, L. N.; Zhang, Z. T.; Sun, S. (2016-06-15). "Climate warming, euxinia and carbon isotope perturbations during the Carnian (Triassic) Crisis in South China". Earth and Planetary Science Letters. 444: 88–100. Bibcode:2016E&PSL.444...88S. doi:10.1016/j.epsl.2016.03.037. ISSN 0012-821X.
7. Zhang, Yang; Li, Mingsong; Ogg, James G.; Montgomery, Paul; Huang, Chunju; Chen, Zhong-Qiang; Shi, Zhiqiang; Enos, Paul; Lehrmann, Daniel J. (2015-10-15). "Cycle-calibrated magnetostratigraphy of middle Carnian from South China: Implications for Late Triassic time scale and termination of the Yangtze Platform". Palaeogeography, Palaeoclimatology, Palaeoecology. 436: 135–166. Bibcode:2015PPP...436..135Z. doi:10.1016/j.palaeo.2015.05.033. ISSN 0031-0182.
8. Yin, Hongfu; Peng, Yuanqiao (2000-01-01), Yin, Hongfu; Dickins, J. M.; Shi, G. R.; Tong, Jinnan (eds.), "The Triassic of China and its interregional correlation", Developments in Palaeontology and Stratigraphy, Permian-Triassic Evolution of Tethys and Western Circum-Pacific, vol. 18, Elsevier, pp. 197–220, doi:10.1016/S0920-5446(00)80012-6, ISBN 9780444501547, retrieved 2020-07-17
9. Mao, Kainan; Yang, Wei; Huang, Yongling; Ma, Zhiheng (4 Aug 2024). "A new ammonite genus of the Xiaowa Formation from Guanling Counties, Guizhou Province, China". Historical Biology: 1–5. doi:10.1080/08912963.2024.2382230.
10. ^ Zhang, Z. T.; Sun, Y. D.; Wignall, P. B.; Fu, J. L.; Li, H. X.; Wang, M. Y.; Lai, X. L. (2018-11-01). "Conodont size reduction and diversity losses during the Carnian Humid Episode in SW China". Journal of the Geological Society. 175 (6): 1027–1031. Bibcode:2018JGSoc.175.1027Z. doi:10.1144/jgs2018-002. ISSN 0016-7649. S2CID 134077252.
11. ^ Sun Zuoyu, Hao Weicheng, Jiang Dayong (2003). "Conodont stratigraphic evidence for the age of the Guanling fauna, Guizhou Province, China". Acta Scientiarum Naturalium Universitatis Pekinensis (in Chinese and English). 39 (1): 118–125.{{cite journal}}: CS1 maint: multiple names: authors list (link)
12. ^ Zhang, Z. T.; Sun, Y. D.; Lai, X. L.; Joachimski, M. M.; Wignall, P. B. (2017-11-15). "Early Carnian conodont fauna at Yongyue, Zhenfeng area and its implication for Ladinian-Carnian subdivision in Guizhou, South China". Palaeogeography, Palaeoclimatology, Palaeoecology. The Palaeozoic-Mesozoic Transition in South China: Oceanic Environments and Life from Late Permian to Late Triassic. 486: 142–157. Bibcode:2017PPP...486..142Z. doi:10.1016/j.palaeo.2017.02.011. ISSN 0031-0182.
13. ^ Wang, H.M. (2000). "Discussion on the age of Guanling Fauna by conodonts". Guizhou Geology (in Chinese and English). 17: 219–225.
14. Zhang, Zaitian; Sun, Yadong; Lai, Xulong; Wignall, Paul B. (2018). "Carnian (Late Triassic) conodont faunas from south-western China and their implications". Papers in Palaeontology. 4 (4): 513–535. Bibcode:2018PPal....4..513Z. doi:10.1002/spp2.1116. ISSN 2056-2802. S2CID 135356888.
15. Fang, G.-Y.; Sun, Y.-L.; Ji, C.; Wu, F.-X. (2022). "First record of Saurichthys (Actinopterygii: Saurichthyidae) from the Late Triassic of eastern Paleo-Tethys". Vertebrata PalAsiatica. 61 (1): 1–16. doi:10.19615/j.cnki.2096-9899.221013.
16. Cheng Ji, Da-Yong Jiang, Ryosuke Motani, Olivier Rieppel, Wei-Cheng Hao, and Zuo-Yu Sun (2016). "Phylogeny of the Ichthyopterygia Incorporating Recent Discoveries from South China". Journal of Vertebrate Paleontology. 36 (1): e1025956. Bibcode:2016JVPal..36E5956J. doi:10.1080/02724634.2015.1025956. S2CID 85621052.{{cite journal}}: CS1 maint: multiple names: authors list (link)
17. Liu, J.; Zhao, L. J.; Li, C.; He, T. (2013). "Osteology of Concavispina biseridens (Reptilia, Thalattosauria) from the Xiaowa Formation (Carnian), Guanling, Guizhou, China". Journal of Paleontology. 87 (2): 341. Bibcode:2013JPal...87..341L. doi:10.1666/12-059R1.1.
18. Wang, Wei; Li, Chun; Scheyer, Torsten M.; Zhao, Lijun (2019-09-02). "A new species of Cyamodus (Placodontia, Sauropterygia) from the early Late Triassic of south-west China". Journal of Systematic Palaeontology. 17 (17): 1457–1476. Bibcode:2019JSPal..17.1457W. doi:10.1080/14772019.2018.1535455. ISSN 1477-2019. S2CID 91579582.
19. ^ Li, Chun; Fraser, Nicholas C.; Rieppel, Olivier; Wu, Xiao-Chun (2018). "A Triassic stem turtle with an edentulous beak". Nature. 560 (7719): 476–479. Bibcode:2018Natur.560..476L. doi:10.1038/s41586-018-0419-1. PMID 30135526. S2CID 52067286.
20. ^ Wu, Xiao-Chun; Cheng, Yen-Nien; Sato, Tamaki; Shan, Hsi-Yin (2009). "Miodentosaurus brevis Cheng et al. 2007 (Diapsida: Thalattosauria): Its postcranial skeleton and phylogenetic relationships". Vertebrata PalAsiatica. 47 (1): 1–20.
21. Li, Chun; Wu, Xiao-Chun; Rieppel, Olivier; Wang, Li-Ting; Zhao, Li-Jun (27 November 2008). "An ancestral turtle from the Late Triassic of southwestern China". Nature. 456 (7221): 497–501. Bibcode:2008Natur.456..497L. doi:10.1038/nature07533. PMID 19037315. S2CID 4405644.
22. Liu, J. (2013). "On the taxonomy of Xinpusaurus (Reptilia: Thalattosauria)" (PDF). Vertebrata PalAsiatica. 51 (1): 17–23.
23. ^ Maisch, Michael W. (2014). "On the morphology and taxonomic status of Xinpusaurus kohi JIANG et al., 2004 (Diapsida: Thalattosauria) from the Upper Triassic of China" (PDF). Palaeodiversity. 7: 47–59.

• Geologic formations of China
• Triassic System of Asia
• Triassic China
• Carnian Stage
• Paleontology in Guizhou