Yanjiahe Formation

Yanjiahe Formation
Yanjiahe Formation
Stratigraphic range: Ediacaran - Fortunian; ~542–529 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	View of Yanjiahe River in Macheng, Huanggang, Hubei, the locality after which the formation is named.
Type	Formation
Sub-units	See: Beds
Overlies	Dengying Formation
Lithology
Primary	Shale, limestone, dolomite
Other	Chert, phosphorite
Location
Coordinates	30°48′N 111°18′E / 30.8°N 111.3°E
Approximate paleocoordinates	27°36′N 160°12′E / 27.6°N 160.2°E
Region	Hubei
Country	China
Extent	Yangtze Gorges
Type section
Named for	Yanjiahe River
	Yanjiahe Formation (China) Yanjiahe Formation (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 five beds. Every bed within the formation contains fossil material.^[4]

The beds are as follows, in ascending stratigraphic order (lowest to highest):

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 composed 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 the probable earliest stem group echinoderm Yanjiahella, to the ecdysozoan Beretella, alongside a large wealth of early molluscs, such as Watsonella and Scenella.^[3] The formation is also home to several large but incomplete ecdysozoan-like cuticles, exceeding the other fully complete ecdysozoans like Beretella and Saccorhytus in size. Despite their incompleteness, they still offer an insight into the already varied biodiversity of ecdysozoans during the early Cambrian.^[5]

Cnidaria

Genus	Species	Notes
Octapyrgites^[6]	O. elongatus	Olivooid Medusozoan, larger than any known Olivooid.
Quadrapyrgites^[7]^[8]	O. quadratacris	Olivooid Medusozoan.
Olivooides^[7]^[8]	Olivooides sp. O. multisulcatus O. mirabilis	Olivooid Medusozoan.
Pseudooides^[7]^[8]	Pseudooides sp.	Medusozoan.
Septuconularia^[9]^[10]	S. yanjiaheensis S. crassiformis	Hexangulaconulariid Medusozoan.
Decimoconularia^[11]	D. isofacialis	Hexangulaconulariid Medusozoan.
Carinachites^[7]^[8]	C. spinatus	Cnidarian sclerite, related to the conulariids.
Cambrorhytium^[12]	C. major	Elongated cone-like cnidarian.

Chancelloriida

Genus	Species	Notes	Images
Chancelloria^[8]	Chancelloria sp.	Sponge-like eumetazoan.

Deuterostome

Genus	Species	Notes
Protohertzina^[13]^[8]	P. unguliformis P. anabarica P. robusta	Possibly a Protoconodont, Paraconodont, or a Chaetognath.
Tarimspira^[7]	T. plana	Possible Paraconodont.
Yunnanodus^[13]^[1]	Yunnanodus sp. Y. yanjiahensis	Possible Paraconodont.
Yanjiahella^[14]	Y. biscarpa	Ambulacrarian; possibly earliest stem group echinoderm.
Yuknessia^[15]	Yuknessia sp.	Unbranched pterobranch.
Hertzina^[13]	H. guizhouensis H. tenuis	Furnishinid Paraconodont.

Ecdysozoa

Genus	Species	Notes	Images
Beretella^[16]	B. spinosa	Possibly adult or larval ecdysozoan.
Saccorhytus^[7]^[8]	Saccorhytus sp.	Possibly adult or larval ecdysozoan.

Lophotrochozoa

Genus	Species	Notes
Conotheca^[15]^[13]	C. subcurvata C. obesa C. nana C. transulcata	Hyolith lophotrochozoan.
Hyolithellus^[13]	H. tenuis? H. decorus	Annelid lophotrochozoan, previously thought to be a Hyolith.
Lapworthella^[15]	Lapworthella sp.	Tommotid lophotrochozoan.
Spinulitheca^[13]	S. billingsi	Hyolith lophotrochozoan.
Microcornus^[13]	M. parvulus?	Hyolith lophotrochozoan.
Cupitheca^[13]	C. mira	Hyolith lophotrochozoan.
Turcutheca^[13]	T. crasseocochlia T. lubrica	Hyolith lophotrochozoan.
Lophotheca^[13]	L. costellata	Hyolith lophotrochozoan.
Circotheca^[13]^[1]	C. longiconica C. longiconica	Circothecid Hyolith.
Aldanella^[15]^[13]	A. attleborensis A. yanjiaheensis	Mollusc with a coiled shell.
Eohalobia^[17]^[7]^[1]	E. diadongensis Eohalobia sp.	Halkieriid mollusc.
Ocruranus^[7]^[17]^[8]^[1]	Ocruranus sp. O. trulliformis O. finial	Halkieriid mollusc.
Scenella^[13]	S. jijiapoensis	Scenellid mollusc.
Siphogonuchites^[13]	S. triangularis	Siphogonuchitid mollusc.
Xianfengella^[13]	X. ovata X. prima	Mollusc.
Tuberoconus^[7]^[1]	T. paucipapillae	Mollusc.
Watsonella^[18]	W. crosbyi	Mollusc.
Anabarella^[18]	A. plana	Helcionelloid mollusc.
Igorella^[13]^[18]	I. emeiensis I. maidipingensis Igorella sp.	Helcionelloid mollusc.
Oelandiella^[13]^[1]	O. korobkovi	Helcionelloid mollusc.
Ceratoconus^[7]^[1]	C. bucers	Helcionelloid mollusc.

Porifera

Genus	Species	Notes	Images
Blastulospongia^[19]	Blastulospongia sp.	Globular demosponge, previously postured to be a radiolarian.

incertae sedis

Genus	Species	Notes
Anabarites^[2]^[13]^[8]	A. trisulcatus A. tianzhushanensis A. gracilis A. ternarius	Anabaritid small shelly fossil.
Tiksitheca^[13]	T. korobovi	Anabaritid small shelly fossil.
Cambrotubulus^[7]^[8]	C. decurvatus	Anabaritid small shelly fossil.
Protoconites^[15]	P. minor	Curved conical organism, possible relations to Cnidaria.
Purella^[15]^[13]	P. antiqua P. lepidites	Small shelly fossil.
Emeiconus^[15]	E. antiqua	Small shelly fossil.
Rugatotheca^[8]	Rugatotheca sp.	Small shelly fossil.
Coleolella^[7]	C. recta	Small shelly fossil.
Vendotaenid^[15]	Vendotaenia sp.	Ribbon-like organism.
Torellella^[1]	T. lentiformis	Tubicolous fossil.

Flora

Genus	Species	Notes	Images
Archaeophycus^[2]^[20]^[8]	A. yunnanensis	Either a cyanobacteria or the early developmental stage of an alga.	(J)
Konglingiphyton^[15]	Konglingiphyton sp.	Macroalgae.
Megathrix^[2]^[21]^[20]	M. longus	Filamentous cyanobacterium.
Myxococcoides^[20]	Myxococcoides spp.	Cyanobacteria.
Archaeooides^[8]	A. granulates	Microalgae.

Microorganisms

Genus	Species	Notes
Asteridium^[21]	A. tornatum	Acritarch.
Comasphaeridium^[2]^[21]	C. annulare	Acritarch.
Heliosphaeridium^[2]^[21]	H. ampliatum	Acritarch.
Micrhystridium^[15]	M. regulare	Acritarch.
Yurtusia^[20]	Y. uniformis	Acritarch.
Dictyotidium^[20]	Dictyotidium sp.?	Acritarch.

Undescribed

Genus	Species	Notes
Hexactinellid spicules^[4]	???	A collection of monaxons, diaxons and triaxons.
Unnamed probable cnidarian^[12]	???	Curved tubular organism, possible affinities to cnidarians.
Form A^[5]	???	Four specimens with a vermiform morphology that is annulated in appearance, maximum known length is 3.1 mm (0.1 in). Surface ornamentation noted to resemble that seen in the pancrustacean Yicaris from the Yu’anshan Formation, as well as the ecdysozoan Saccorhytus from this formation.
Form B^[5]	???	A singular specimen of a trunk segment covered in spines of varying sizes, maximum length of the specimen is 2.7 mm (0.1 in). Is comparable to various ecdysozoan groups, such as lobopods, and more so to the extant kinorhynchs. It is noted that if the latter interpretation is valid, the specimen would likely be placed as a crown-group kinorhynch, although more evidence is needed.
Form C^[5]	???	The most abundant, with seventeen specimens known, and found in two modes of preservation. Specimens are covered in fractured spines of varying shapes, and the maximum known length of this form being 4.3 mm (0.2 in). Is noted to be comparable to various small shelly fossils such as Protohertzina and Mongolodus, and several ecdysozoans such as Eokinorhynchus, Scalidodendron, and Saccorhytus.
Form D^[5]	???	Two specimens with a vermiform morphology, and is only known to attain a length of 1.8 mm (0.1 in), making it the smallest of the known forms. These specimens have been compared to the likes of Eopriapulites and Palaeoscolex.
Form E^[5]	???	Two specimens, which are evenly covered in small papillate knobs, and attain a maximum known length of 4.9 mm (0.2 in). They have been compared to a wide range of papillate knob-bearing acritarchs, embryos, algae-like forms, and tentative sponges, such as Bacatisphaera, Archaeooides, Shaanisphaera, and Aetholicopalla respectively.
Form F^[5]	???	Five specimens with a dense covering of short coniform to hook-like spines, and are the largest of the forms, attaining a maximum length of 8.9 mm (0.4 in). The five specimens are noted to bear a striking resemblance to Saccorhytus, although they are also notably much larger, suggesting that saccorhytids may have attained much larger sizes than currently known.

References

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