Yanjiahe Formation

Yanjiahe Formation
Stratigraphic range: Ediacaran - Fortunian ~542–529  Ma PreꞒ Ꞓ O S D C P T J K Pg N [1]
Type	Formation
Overlies	Dengying Formation
Lithology
Primary	Shale, limestone, dolomite
Other	Chert, phosphorite
Location
Coordinates	30°48′N111°18′E / 30.8°N 111.3°E / 30.8; 111.3
Approximate paleocoordinates	27°36′N160°12′E / 27.6°N 160.2°E / 27.6; 160.2
Region	Hubei
Country	China
Extent	Yangtze Gorges
Yanjiahe Formation (China) Show map of China Yanjiahe Formation (Hubei) Show map of Hubei

The Yanjiahe Formation is an Ediacaran to Cambrian fossiliferous geologic formation found in South China. ^{[2] [3]}

Dating

The Yanjiahe Formation has been dated through various methods. The top of the formation is dated at 526.5±1.1  Ma and 526.4±5.3  Ma using radiometric dating on ash beds within the area. Likewise, the base of the formation has been dated to between 542±0  Ma to 526±0  Ma through carbon isotopic correlations. ^[1]

Beds

The Yanjiahe Formation consists of 5 beds, listed below. Every bed within the formation contains fossil material. ^[4]

Listed by ascending age:

• Bed 1 is characterized by basal dolomitic conglomerates, with banded black cherts. ^[4]
• Bed 2 is mostly consists of siliceous phosphatic dolostone, with flat pebble conglomerates. ^[4]
• Bed 3 is characterized by various shales, with the presence of siliceous-phosphatic nodules. ^[4]
• Bed 4 is comprised of carbonaceous limestones. ^[4]
• Bed 5 is characterized by cherts and siliceous phosphatic dolostone, with flat pebble conglomerates. ^[4]

Paleobiota

The Yanjiahe Formation contains a wide range of unique organisms from the base of the Cambrian, from Yanjiahella to Beretella, alongside a lot of early molluscs, like Watsonella. ^[3]

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Cnidaria

Genus	Species	Notes	Images
Octapyrgites [5]	O. elongatus	Olivooid Medusozoan, larger than any known Olivooid.
Quadrapyrgites [6] [7]	O. quadratacris	Olivooid Medusozoan.
Olivooides [6] [7]	Olivooides sp. O. multisulcatus O. mirabilis	Olivooid Medusozoan.
Pseudooides [6] [7]	Pseudooides sp.	Medusozoan.
Septuconularia [8] [9]	S. yanjiaheensis S. crassiformis	Hexangulaconulariid Medusozoan.
Decimoconularia [10]	D. isofacialis	Hexangulaconulariid Medusozoan.
Carinachites [6] [7]	C. spinatus	Cnidarian sclerite, related to the conulariids.
Cambrorhytium [11]	C. major	Elongated cone-like cnidarian.

Chancelloriida

Genus	Species	Notes	Images
Chancelloria [7]	Chancelloria sp.	Sponge-like eumetazoan.

Deuterostome

Genus	Species	Notes	Images
Protohertzina [12] [7]	P. unguliformis P. anabarica P. robusta	Possibly a Protoconodont, Paraconodont, or a Chaetognath.
Tarimspira [6]	T. plana	Possible Paraconodont.
Yunnanodus [12] [1]	Yunnanodus sp. Y. yanjiahensis	Possible Paraconodont.
Yanjiahella [13]	Y. biscarpa	Possibly earliest stem group echinoderm.
Yuknessia [14]	Yuknessia sp.	Unbranched pterobranch.
Hertzina [12]	H. guizhouensis H. tenuis	Furnishinid Paraconodont.

Ecdysozoa

Genus	Species	Notes	Images
Beretella [15]	B. spinosa	Possibly adult or larval ecdysozoan.
Saccorhytus [6] [7]	Saccorhytus sp.	Possibly adult or larval ecdysozoan.

Lophotrochozoa

Genus	Species	Notes	Images
Conotheca [14] [12]	C. subcurvata C. obesa C. nana C. transulcata	Hyolith lophotrochozoan.
Hyolithellus [12]	H. tenuis? H. decorus	Annelid lophotrochozoan, previously thought to be a Hyolith.
Lapworthella [14]	Lapworthella sp.	Tommotid lophotrochozoan.
Spinulitheca [12]	S. billingsi	Hyolith lophotrochozoan.
Microcornus [12]	M. parvulus?	Hyolith lophotrochozoan.
Cupitheca [12]	C. mira	Hyolith lophotrochozoan.
Turcutheca [12]	T. crasseocochlia T. lubrica	Hyolith lophotrochozoan.
Lophotheca [12]	L. costellata	Hyolith lophotrochozoan.
Circotheca [12] [1]	C. longiconica C. longiconica	Circothecid Hyolith.
Aldanella [14] [12]	A. attleborensis A. yanjiaheensis	Mollusc with a coiled shell.
Eohalobia [16] [6] [1]	E. diadongensis Eohalobia sp.	Halkieriid mollusc.
Ocruranus [6] [16] [7] [1]	Ocruranus sp. O. trulliformis O. finial	Halkieriid mollusc.
Scenella [12]	S. jijiapoensis	Scenellid mollusc.
Siphogonuchites [12]	S. triangularis	Siphogonuchitid mollusc.
Xianfengella [12]	X. ovata X. prima	Mollusc.
Tuberoconus [6] [1]	T. paucipapillae	Mollusc.
Watsonella [17]	W. crosbyi	Mollusc.
Anabarella [17]	A. plana	Helcionelloid mollusc.
Igorella [12] [17]	I. emeiensis I. maidipingensis Igorella sp.	Helcionelloid mollusc.
Oelandiella [12] [1]	O. korobkovi	Helcionelloid mollusc.
Ceratoconus [6] [1]	C. bucers	Helcionelloid mollusc.

Porifera

Genus	Species	Notes	Images
Blastulospongia [18]	Blastulospongia sp.	Globular demosponge, previously postured to be a radiolarian.
Hexactinellid spicules [4]	???	A collection of monaxons, diaxons and triaxons.

incertae sedis

Genus	Species	Notes	Images
Anabarites [2] [12] [7]	A. trisulcatus A. tianzhushanensis A. gracilis A. ternarius	Anabaritid small shelly fossil.
Tiksitheca [12]	T. korobovi	Anabaritid small shelly fossil.
Cambrotubulus [6] [7]	C. decurvatus	Anabaritid small shelly fossil.
Protoconites [14]	P. minor	Curved conical organism, possible relations to Cnidaria.
Purella [14] [12]	P. antiqua P. lepidites	Small shelly fossil.
Emeiconus [14]	E. antiqua	Small shelly fossil.
Rugatotheca [7]	Rugatotheca sp.	Small shelly fossil.
Coleolella [6]	C. recta	Small shelly fossil.
Vendotaenid [14]	Vendotaenia sp.	Ribbon-like organism.
Torellella [1]	T. lentiformis	Tubicolous fossil.

Flora

Genus	Species	Notes	Images
Archaeophycus [2] [19] [7]	A. yunnanensis	Either a cyanobacteria or the early developmental stage of an alga.	(J)
Konglingiphyton [14]	Konglingiphyton sp.	Macroalgae.
Megathrix [2] [20] [19]	M. longus	Filamentous cyanobacterium.
Myxococcoides [19]	Myxococcoides spp.	Cyanobacteria.
Archaeooides [7]	A. granulates	Microalgae.

Microorganisms

Genus	Species	Notes	Images
Asteridium [20]	A. tornatum	Acritarch.
Comasphaeridium [2] [20]	C. annulare	Acritarch.
Heliosphaeridium [2] [20]	H. ampliatum	Acritarch.
Micrhystridium [14]	M. regulare	Acritarch.
Yurtusia [19]	Y. uniformis	Acritarch.
Dictyotidium [19]	Dictyotidium sp.?	Acritarch.

Undescribed

Genus	Species	Notes	Images
Unnamed probable cnidarian [11]	???	Curved tubular organism, possible affinities to cnidarians.

See also

• Ediacaran biota

References

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3. Yanjiahe Formation at Fossilworks.org
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Further reading

• P. Chen. 1984. Discovery of Lower Cambrian small shelly fossils from Jijiapo, Yichang, west Hubei and its significance. Professional Papers of Stratigraphy and Palaeontology 13:49-64