The Fenxiang Formation (also spelled Fenhshiang) is a geological formation and Konservat-Lagerstätte in the Hubei Province of China. It is notable for its exceptional preservation of sessile fauna like black corals, hydroids, and the possible pterobranch Crinisdendrum, as well as preserving pyritized pedicles of the lingulid Leontiella, a Markuelia-like scalidophoran embryo, and nematode trace fossils.
Geology The Fenxiang Formation is located in the Yangtze Platform that covers the area around the Yangtze River in South China. The Paleozoic sequences are exposed around the Huangling Anticline (convex geologic fold that exposes the oldest beds at its core) in the Three Gorges, Hubei. The lower part of the formation (the Lower Limestone Member) is mainly composed of poorly fossiliferous limestone containing allochems (grain-like elements found in carbonate rocks). The middle to upper part of the formation (the Upper Limestone Member) is composed of dark-grey to grey bioclastic (containing abundant fragments of skeletal fossils) and peloidal limestone intercalated with shale. In the west of the anticline, the Fenxiang Formation is approximately 20 m thick. It attains a thickness of 10 m in the Tianjialing section. In the east, it is approximately 40 to 50 m thick. The Fenxiang Formation was previously thought to date back to the late Tremadocian. However, the occurrence of the conodont Acodus triangularis suggests an early Floian age for the upper part of the formation.
Soft tissue preservation often occurs in shale of the Tianjialing section, the preserved soft parts appear reddish-yellow to brown. This results from pyritization, a process in which organic matter is broken down by sulfate reducing anaerobic bacteria to produce hydrogen sulfide. The sulfide can react with iron; which eventually creates pyrite. Some of the most important fossils of the Fenxiang Formation are linguloid brachiopods preserving exceptional soft parts, pyritized colony of hydroids and pyritized burrows made by nematodes.
Paleoenvironment The paleolatitude of the Fenxiang Formation was about 19°S, in tropical waters at the edge of the Yangtze carbonate platform. The Fenxiang Formation at Tianjialing was probably deposited in fairly deep-water basinal environments; however, several elements of the Tianjialing fauna were allochthonous and shallow-water in origin. These probably originated from reefs and were transported into deeper waters via ocean currents or heavy storms.
The Fenxiang Formation preserves reef buildups in the Chenjiahe and Huanghuachang sections. Reefs in the lower parts are composed of bioclastic packstones or grainstones, suggesting that they were deposited in turbulent, shallow-water (possibly less than 10 meters deep) carbonate platforms where early cementation of the sands provided substrate for bryozoan larvae to settle. Shale becomes more abundant in the upper parts, signaling a shift into a deeper-water subtidal setting.
The reefs in the Fenxiang Formation are dominated by lithistid and stromatoporoid sponges, the bryozoan Nekhorosheviella (previously identified as Batostoma jinhongshanense), Calathium, pelmatozoan echinoderms, and the calcimicrobe Girvanella. These reefs can be divided into several different communities based on their constituent organisms:
+ Communities in the Fenxiang Formation Communities according to Xi et al. 2011 (Huanghuachang section) Communities according to Adachi et al. 2012 (Chenjiahe section) Biofacies Community Dominant organisms Communities Dominant organisms Shelly biofacies Tritoechia-Pelmatozoan Brachiopods (Tritoechia); Pelmatozoans Tritoechia-Pomatotrema Brachiopods (Tritoechia, Pomatotrema) Reef biofacies "Batostoma" Bryozoans (Nekhorosheviella); Brachiopods (Tritoechia) Lithistid sponge-bryozoan Bryozoans (Nekhorosheviella); Sponges (Archaeoscyphia) Pelmatozoan-"Batostoma" Pelmatozoans; Bryozoans (Nekhorosheviella) Bryozoan-pelmatozoan Pelmatozoans; Bryozoans (Nekhorosheviella) Calathium-Archaeoscyphia Calathium; Cyanobacteria; Sponges (Archaeoscyphia) Lithistid sponge-calcimicrobe Calcimicrobes (Girvanella); Sponges (Archaeoscyphia) Archaeoscyphia Sponges (Archaeoscyphia, Pulchrilamina) Lithistid sponge-stromatolite Stromatolites (incl. Girvanella); Sponges (Archaeoscyphia) Standing-water biofacies Acanthograptus-Dendrograptus Graptolites (Acanthograptus, Dendrograptus, Adelograptus, Kiaerograptus) Yichangopora Bryozoans (Yichangopora); Brachiopods (Nanorthis) Allochtonous biofacies Nanorthis-Psilocephalina Brachiopods (Nanorthis); Trilobites (Psilocephalina, Tungtzuella)
Fossil content
Ichnotaxa Ichnotaxa Genus Species Locality ImagesSinusoidal traces probably belonging to nematodes Huanghuachang, TianjialingLarge burrows
Receptaculitids Receptaculitidae Genus Species Locality ImagesCalathiumC. sp. Huanghuachang
Sponges Porifera Genus Species Class Order Locality ImagesHeteractinida indet. Calcarea? Heteractinida HuanghuachangArchaeoscyphiaA. chihliensisDemospongiaeLithistida HuanghuachangA. minganensis Yichang areaA. pulchra HuanghuachangPulchrilaminaP. spinosa Stromatoporoidea(?) Chenjiahe
Cnidarians Conulates Conulata Genus Species Clade Locality ImagesSphenothallusS. ruedemanniConulata indet. Huanghuachang, TianjialingConulariida indet.Conulariida Jiangjiafan
Black corals Antipatharia Genus Species Family Locality ImagesSinopathesS. reptansSinopathidae Huanghuachang, Tianjialing, Gudongkou, JiangjiafanS. sp. Huanghuachang, Tianjialing, Gudongkou, JiangjiafanSterictopathesS. radicatus Huanghuachang, Tianjialing, Gudongkou
Hydroids Hydrozoa Genus Species Family Locality ImagesSinobryonS. elongatumHaleciidae? Tianjialing
Conodonts Conodonta Genus Species Order Family Locality ImagesAcodusA. hamulosusPrioniodontidaAcodontidaeHuanghuachang, HuaqiaoA. proclinatusHuanghuachangA. suberectusHuanghuachang, HuaqiaoA. triangularisTianjialingAcontiodusA. rectusHuanghuachangA. staefferiHuanghuachangTriangulodusT. bicostatusHuanghuachang, HuaqiaoT. unicostatusHuanghuachangTropodusT. yichangensisHuanghuachangOistodusO. complanatusOistodontidaeHuanghuachangO. lanceolatusHuanghuachangO. robustusHuanghuachangProtoprioniodusP. sp.ParacordylodontidaeHuanghuachangProconodontusP? sp.ProconodontidaProconodontidaeHuanghuachangScalpellodusS. gracilisProtopanderodontidaAcanthodontidaeHuanghuachangClavohamulusC? sp.ClavohamulidaeHuanghuachangCornuodusC. longibasisCornuodontidaeHuanghuachangDrepanoistodusD. nanjinguanensisDrepanoistodontidaeHuanghuachangD. pitjantiHuanghuachang, HuaqiaoD. sp.Huanghuachang, TianjialingPaltodusP. brevicornisHuanghuachangP. deltiferHuanghuachangP. subaequalisHuanghuachangParoistodusP. concavusHuanghuachangP. mistusHuanghuachang, HuaqiaoTeridontusT? sp.OneotodontidaeHuanghuachangColaptoconusC. quadraplicatusProtopanderodontidaeHuanghuachang, HuaqiaoDrepanodusD. amoenusHuanghuachangD. arcuatusHuanghuachang, HuaqiaoD. latusHuanghuachangD. sp.Huaqiao, TianjialingProtopanderodusP. yichangensisHuanghuachangP? cf. rectusHuaqiaoScolopodusS? sp.HuanghuachangSerratognathusS. diversusSerratognathidaeHuanghuachang
Pterobranchs
Pterobranchia Genus Species Order Family Locality Images Crinisdendrum C. sinicum Pterobranchia indet. Huanghuachang, Tianjialing
Graptolites
Graptolithina Genus Species Order Family Locality ImagesHaplograptusH. huanghuaensisGraptolithina indet.HuanghuachangH. yichangensisHuanghuachang "Dictyonema" "D." asiaticum Dendroidea Dendroidea indet. Huanghuachang "D." cf. asiaticum Huanghuachang "D." sp. Huanghuachang Acanthograptus A. erectoramosus Acanthograptidae Huanghuachang, Huaqiao A. rigidus Huanghuachang A. sinensis Huanghuachang, Chenjiahe, Huaqiao, Tianjialing A. sp. Huanghuachang, Huaqiao Koremagraptus K. sp. Chenjiahe, TianjialingParacanthograptusP. sanxiaensisHuanghuachangDendrograptusD. yiniDendrograptidaeHuanghuachangD? muiChenjiaheD. sp.HuanghuachangMastigograptusM? sp.MastigograptidaeHuanghuachangAdelograptusA? orientalisGraptoloideaAnisograptidaeHuanghuachangA. sp.HuanghuachangKiaerograptusK. kiaeri yichangensisHuanghuachang
Arthropods Ostracods Ostracoda Genus Species Order Family Locality ImagesSinoprimitiaS. hemicircularisPalaeocopidaPalaeocopida indet. HuanghiachangS. quadrata HuanghuachangLeperditellaL. cf. aequilateraPlatycopidaLeperditellidae HuanghuachangL. hubeiensis HuanghuachangL. cf. mundula HuanghuachangL. subsymmetrica HuanghuachangPrimitiaP. ichangensisPrimitiidae Huaqiao
Trilobites Trilobita Genus Species Order Family Locality ImagesPsilocephalinaP. lataAsaphidaAsaphidae HuanghuachangP. lubrica Huanghuachang, HuaqiaoP. sinuata Huanghuachang, HuaqiaoAsaphopsoidesA. grandispiniger Hungaiidae Huanghuachang, HuaqiaoA. angustatus HuanghuachangA. changyangensis HuaqiaoDactylocephalus D. laevigatus D. transversusTungtzuellaT. elongataTaihungshaniidae HuanghuachangT. kweichouensis Huanghuachang, HuaqiaoT. recta HuanghuachangT. sinuata HuaqiaoT. szechuanensis Huanghuachang, HuaqiaoT. yunnanensis HuanghuachangChosenia C. divergens Corynexochida Leiostegiidae HuaqiaoC. quadrata HuaqiaoPseudocalymene LiujiachangSzechuanella S. granulata ParapilekiaP. inexpectaPhacopida Pilekiidae ProtopliomeropsP. changyangensis Pliomeridae HuaqiaoProtarchaeogonusP? huaqiaoensis Proetida Rorringtoniidae HuaqiaoGoniophrysG. subcylindricus Telephinidae Huaqiao
Bryozoans Bryozoa Genus Species Class Order Locality ImagesNematoporaN. ovalisStenolaemataCryptostomata ChenjiaheProphyllodictyaP. prisca DapingP. sp. ChenjiaheTreptocryptoporaT. sp. Chenjiahe VeroclemaV. sp. ChenjiaheAmsassiporaA. sp.Cystoporata ChenjiaheAnolotichiaA. sp. ChenjiaheCeramoporaC. sp. ChenjiaheFistuliporaF. sp. ChenjiaheHaplotrypaH. sp. ChenjiaheHennigoporaH. sp. ChenjiaheProfistuliporaP. sp. ChenjiaheNekhorosheviellaN. noduliferaEsthonioporata DapingN. semisphaerica Daping, Huanghuachang, LiujiachangDianulitesD. sp. ChenjiaheOrbiramusO. minusTrepostomata DapingO. normalis Daping, Huanghuachang, LiujiachangO. ovalis DapingBythoporaB. sp. ChenjiaheGoldfussitrypaG. sp. ChenjiaheMonotrypaM. sp. ChenjiaheOrbignyellaO. sp. ChenjiaheTrepostomata undet. Chenjiahe
Brachiopods Brachiopoda Genus Species Class Order Locality Images Eopunctata E. mamagouensis Brachiopoda indet. Huanghuachang, Huaqiao E. sp. Huanghuachang Leontiella L. sp. Lingulata LingulidaTianjialing LingulaL. sp. 2 LiujiachangL. sp. 3 Liujiachang Nanorthis N. hamburgensis Rhynchonellata Orthida Huanghuachang, HuaqiaoN. sp. 1 HuanghuachangSinorthisS. sp. 1 Liujiachang Martellia M. sp. 2 Strophomenata Billingsellida LiujiachangTritoechia T. lianghekouensis Huanghuachang T. mucronata Huanghuachang T. obesa Huanghuachang T. recta Huanghuachang T. subconis Huanghuachang, Huaqiao T. sp. 1 Liujiachang T. sp. 2 Huanghuachang T. sp. 3 Huanghuachang T. sp. 4 Huanghuachang Punctolira P. huanghuaensis Pentamerida Huanghuachang Syntrophinella S. sp. 1 Liujiachang Tetralobula T. fenxiangensis Huaqiao
Cephalopods Cephalopoda Genus Species Order Family Locality ImagesDaobaowanceroidesD. densum Cephalopoda indet. LiujiachangHopeiocerasH. yichangense Actinocerida Actinocerida indet. HuanghuachangRecurvocerasR. changyangensis Bisonocerida Manchuroceratidae HuaqiaoEllesmerocerasEllesmeroceras sp. 1 Ellesmerocerida Ellesmeroceratidae HuaqiaoEllesmeroceras sp. 2 HuaqiaoCyrtovaginocerasCyrtovaginoceras sp. 1Endocerida Cyrtovaginoceratidae LiujiachangPronajacerasP. eccentricumNajaceratidae HuanghuachangP. hubeiense HuanghuachangP. yichangense HuanghuachangProterocamerocerasP. orientale Proterocameroceratidae HuanghuachangP. yichangense Huanghuachang
See also
List of fossiliferous stratigraphic units in China
References