Emigrant Formation

Not to be confused with the Emigrant Springs Formation, a different formation of a similar age.
Emigrant Formation
Stratigraphic range:
TypeFormation
Sub-unitsSee: Members
UnderliesPalmetto Formation
OverliesMule Spring Limestone
Lithology
PrimaryShale
OtherMudstone, Limestone, Chert, Sandstone
Location
RegionNevada
CountryUnited States
Type section
Named forEmigrant Pass

The Emigrant Formation is a Cambrian to Ordovician geologic formation in Nevada. It preserves fossils dating back to the Cambrian period, as well as the Ordovician period.

Geology

The Emigrant Formation is dominated by shales, with limestone common at the base and top of the formation.[1]

Members

The formation contains three members, which are as follows, in ascending age:

  • Limestone & Siltstone Member: This member is the thinnest of the three, only getting up to 150 m (490 ft) thick in some areas, and is dominated by lime mudstone. At the base of the member, it is entirely composed of shale, which gives way to calcareous sandstone, and then the common lime mudstones above that. Within these lime mudstones, there are occasional layers of more shale and chert.[1]
  • Shale Member: This member can get up to 250 m (820 ft) thick in some areas, and is, as the name suggests, entirely dominated by shale, which may be faulted and repeated in many places.[1]
  • Limestone & Chert Member: This member is the thickest of the three, getting up to 300 m (980 ft) thick in some areas, and contains a mixture of ribbon limestone, inter-bedded shales, as well as mega-breccia.[1]

The Emigrant Formation also contains lower Ordovician aged rocks above the Limestone & Chert Member, informally known as the "Platy Limestone Unit". This unit is primarily composed of fine-grained, platy limestone, which are inter-bedded with pale-red siltstone. The very top of the unit is not preserved, and contacts the overlying Palmetto Formation at a fault, and the unit itself is also difficult to age, although a lower Ordovician age is suggested, though more evidence will be needed to pinpoint the exact age of the unit. It has also been noted that this unit may represent a transitional bed between the Emigrant and Palmetto Formations.[2]

Paleobiota

The biota of the Emigrant Formation is mainly composed of trilobites like Olenellus and Bathyuriscus,[3] as well as some small shelly fauna in the form of Pelagiella and Microcornus.[4] It also contains a sparse collection of fossils from a lower Ordovician unit right at the top of the formation, containing the chelicerate Esmeraldacaris, as well as some graptolite fauna.[2]

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.

Cambrian

This section details all the fossils from the Cambrian sections of the Emigrant formation.

Arthropoda

Arthropoda
Genus Species Notes Images
Amecephalus[3]
  • Amecephalus (?) sp.
  • A. arrojosensis
 Ptychoparid trilobite.
Mexicella[3]
  • M. robusta
 Ptychoparid trilobite.
Paraantagmus[3]
  • P. latus
 Ptychoparid trilobite.
Onchocephalites[3]
  • Onchocephalites sp.
  • O. claytonensis
  • O. runcinatus
 Ptychoparid trilobite.
Tonopahella[3]
  • T. goldfieldensis
 Ptychoparid trilobite.
Syspacephalus[3][5]
  • S. variosus
  • S. laticeps
  • S. mccollumorum
 Ptychoparid trilobite.
Achlysopsis[5]
  • A. brighamensis
  • A. liokata
 Ptychoparid trilobite.
Eokochaspis[3]
  • E. nodosa
  • E. delamarensis (?)
  • E. piochensis (?)
  • E. longspina (?)
 Ptychoparid trilobite.
Chancia[5]
  • C. maladensis
 Ptychoparid trilobite.
Kistocare[5]
  • Kistocare sp.
 Ptychoparid trilobite.
Elrathia[5]
  • E. marginalis
 Ptychoparid trilobite.
Alokistocare[5]
  • A. paranotatum
 Ptychoparid trilobite.
Meteoraspis[5]
  • Meteoraspis sp.
 Ptychoparid trilobite.
Coosella[5]
  • Coosella sp.
 Ptychoparid trilobite.
Coosia[5]
  • Coosia sp.
 Ptychoparid trilobite.
Crepicephalus[5]
  • Crepicephalus sp.
 Ptychoparid trilobite.
Tricrepicephalusalus[5]
  • Tricrepicephalus sp.
 Ptychoparid trilobite.
Cedaria[5]
  • Cedaria sp. 1
  • Cedaria sp. 2
  • C. selwyni
  • C. brevifrons
 Ptychoparid trilobite.
Utia (?)[5]
  • U. curio (?)
 Ptychoparid trilobite.
Kochaspid (?)[3]
  • Kochaspid (?) sp.
 Ptychoparid trilobite.
Ptychoparioid[3][5]
  • Ptychoparioid sp. A
  • Ptychoparioid sp. B
 Ptychoparid trilobites.
Oryctocephalus[3][5]
  • Oryctocephalus sp. A
  • O. americanus
  • O. minor
  • O. orientalus
  • O. indicus
  • O. maior
  • O. reynoldsi
 Corynexochid trilobite.
Euarthricocephalus[5]
  • E. nevadensis
  • E. (?) wheelera
 Corynexochid trilobite.
Ovatoryctocara[3][5]
  • O. sinensis
  • Oryctocephalus (?) sp.
 Corynexochid trilobite.
Glossopleura[5]
  • G. walcotti
 Corynexochid trilobite.
Zacanthoides[5]
  • Zacanthoides sp.
  • Z. longipgus
  • Z. divergens
 Corynexochid trilobite.
Thoracocare[5]
  • T. minuta
 Corynexochid trilobite.
Parkaspis[5]
  • P. drumensis
 Corynexochid trilobite.
Kootenia (?)[5]
  • Kootenia (?) sp.
 Corynexochid trilobite.
Pseudagnostus[1][5]
  • P. josepha
  • P. brighamensis
  • P. bonnerensis
 Agnostid trilobite.
Pagetia[5]
  • P. aspinosa
  • P. rugosa
  • P. claytonensis
  • P. fossula
 Agnostid trilobite.
Agnostoid[5]
  • Agnostoid sp. 1
  • Agnostoid sp. 2
 Agnostid trilobite.
Bathyuriscus[3][5]
  • Bathyuriscus sp.
  • B. terranovensis
 Biceratopsid trilobite. Previously described as Wenkchemnia walcotti and W. sulcata.
Bolbolenellus[3]
  • B. brevispinus
 Biceratopsid trilobite.
Olenellus[3][5]
  • Olenellus sp.
  • O. puertoblancoensis (?)
 Olenellid trilobite.
Wujiajiania[1]
  • W. sutherlandi
 Olenellid trilobite.
Oryctocara[5]
  • Oryctocara sp.
 Oryctocarid trilobite.
Oryctocarella[5]
  • Oryctocarella sp.
 Oryctocarid trilobite.
Labiostria[1]
  • L. westropi
 Aphelaspid trilobite.
Crassifimbra[3]
  • C. walcotti
 Trilobite, family unknown.
Quasimodaspis[2]
  • O. brentsae
 Tremaglaspidid artiopod.

Lophotrochozoa

Genus Species Notes Images
Microcornus[4]
  • Microcornus sp.
 Lophotrochozoan hyolith.
Parkula[6][4]
  • P. esmeraldina
 Lophotrochozoan hyolith.
Haplophrentis[7]
  • H. carinatus
 Lophotrochozoan hyolith.
Hyolithellus (?)[4]
  • Hyolithellus (?) sp.
 Lophotrochozoan hyolith. May possibly be an annelid.[8]
Hyolithides[7]
  • ???
 Undetermined lophotrochozoan hyoliths, are either preserved as molds, or are too poorly preserved for identification.
Anabarella[6][4]
  • A. chelata
 Helcionellid mollusc.
Pelagiella[4]
  • P. subangulata
 Pelagiellid mollusc.
Costipelagiella[6][4]
  • C. nevadense
 Pelagiellid mollusc.

Chancelloriidae

Genus Species Notes Images
Allonia[4]
  • Allonia sp.
 Chancelloriid.
Chancelloria[6][4]
  • Chancelloria sp.
 Chancelloriid.

Echinodermata

Genus Species Notes Images
Echinoderm Ossicles[6][4]
  • ???
 Calcareous element that makes up the endoskeleton of echinoderms.

Porifera (Sponges)

Genus Species Notes Images
Hexactinellid spicules[6]
  • ???
 Sponge skeleton, with six rays.

Flora

Genus Species Notes Images
Archaeooides[4]
  • A. granulatus
 Microalgae.
Girvanella[6]
  • Girvanella sp.
 Cyanobacteria structures.

Ordovician

This section details all the fossils from the Ordovician unit at the top of the Emigrant Formation.

Arthropoda

Arthropoda
Genus Species Notes Images
Esmeraldacaris[2]
  • E. richardsonae
 Mollisonid chelicerate.
Caryocaris[2]
  • Caryocaris sp.
 Caryocarid arthropod.

Lophotrochozoa

Genus Species Notes Images
Inarticulate brachiopods[2]
  • ???
 Lophotrochozoan brachiopods, poor preservation hinders full identification.

Hemichordata

Genus Species Notes Images
Dictyonema[2]
  • Dictyonema sp.
 Dendroid graptolite.
Clonograptus[2]
  • Clonograptus sp.
 Graptolites.

Porifera (Sponges)

Genus Species Notes Images
Hexactinellid spicules[2]
  • ???
 Sponge skeleton.
Tetractinellid spicules[2]
  • ???
 Sponge skeleton.

Ichnogenera

Genus Species Notes Images
Branching Trace Fossils[2]
  • ???
 Branching traces.

See also

References

  1. ^ a b c d e f g Sundberg, Frederick A.; Kurkewicz, Richard; Rooks, Dustin L. (July 2007). "WUJIAJIANIA SUTHERLANDI FAUNA (ELVINIA BIOZONE, PAIBIAN STAGE, FURONGIAN SERIES—"UPPER" CAMBRIAN) FROM THE EMIGRANT FORMATION, NEVADA". Journal of Paleontology. 81 (4): 794–796. doi:10.1666/pleo0022-3360(2007)081[0794:WSFEBP]2.0.CO;2.
  2. ^ a b c d e f g h i j k Waggoner, Ben (2003). "Non-Trilobite Arthropods from the Silver Peak Range, Nevada". Journal of Paleontology. 77 (4): 706–720. ISSN 0022-3360.
  3. ^ a b c d e f g h i j k l m n o p Sundberg, Frederick A.; McCollum, Linda B. (September 2003). "Early and Mid Cambrian trilobites from the outer‐shelf deposits of Nevada and California, USA". Palaeontology. 46 (5): 945–986. doi:10.1111/1475-4983.00328.
  4. ^ a b c d e f g h i j k Wotte, Thomas; Sundberg, Frederick A. (2017). "Small shelly fossils from the Montezuman–Delamaran of the Great Basin in Nevada and California". Journal of Paleontology. 91 (5): 883–901. ISSN 0022-3360.
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac Sundberg, Frederick A. (May 2018). "Trilobite biostratigraphy of the Cambrian 5 and Drumian stages, Series 3 (Laurentian Delamaran, Topazan, and Marjuman stages, Lincolnian Series) of the lower Emigrant Formation at Clayton Ridge, Esmeralda County, Nevada". Journal of Paleontology. 92 (S76): 1–44. doi:10.1017/jpa.2017.130.
  6. ^ a b c d e f g Skovsted, Christian B (1 April 2006). "Small shelly fossils from the basal Emigrant Formation (Cambrian, uppermost Dyeran Stage) of Split Mountain, Nevada". Canadian Journal of Earth Sciences. 43 (4): 487–496. doi:10.1139/e05-119.
  7. ^ a b Sun, Haijing; Babcock, Loren E.; Peng, Jin; Kastigar, Jessica M. (2 January 2017). "Systematics and palaeobiology of some Cambrian hyoliths from Guizhou, China, and Nevada, USA". Alcheringa: An Australasian Journal of Palaeontology. 41 (1): 79–100. doi:10.1080/03115518.2016.1184426.
  8. ^ Skovsted, Christian B.; Peel, John S. (January 2011). "Hyolithellus in life position from the Lower Cambrian of North Greenland". Journal of Paleontology. 85 (1): 37–47. doi:10.1666/10-065.1.
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