Earth:Poleta Formation

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Poleta Formation
Stratigraphic range: Cambrian Series 2
~519–518 Ma
↓
The Poleta Folds area, the locality after which the formation is named.
TypeFormation
Sub-unitsSee: Members
UnderliesHarkless Formation
OverliesCampito Formation
Thickness0–1,900 ft (0–579 m)[1]
Lithology
PrimaryFine siliciclastics
OtherLimestone, Quartzite, Siltstone
Location
RegionCalifornia, Nevada
CountryUnited States
Type section
Named forPoleta Folds

Template:CEXNAV The Poleta Formation is a geological unit known for the exceptional fossil preservation in the Indian Springs Lagerstätte, located in eastern California and Nevada.[2]

Occurrence

The formation dates to the Stage 3 of the yet-to-be-ratified Cambrian Series 2; the lower portion base of the formation and the youngest Lagerstätte beds date to the Nevadella trilobite zone (= Laurentian Montezuman stage), with higher beds dating to the Olenellus trilobite zone (= Laurentian Dyeran stage), making the formation the same age as the Sirius Passet and just younger than the Chengjiang.[2] It outcrops in Esmeralda County in western Nevada.[2]

Geology

The Poleta Formation is mainly composed of limestone rocks within its lower and upper sections, with its middle section containing siltstone, quartzite, and some limestone.[1]

Members

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

  • Lower Member: This member is the thickest of the three, getting up to 1,000 ft (300 m) thick. It is primarily composed of medium to light-gray oolitic limestone, containing an abundance of archeocyathid reefs.[3] The limestone mostly well-bedded, although it is occasionally thin to very thin-bedded. There is also a single inter-stratified layer of greenish-gray or olive-gray siltstone, getting up to 100 ft (30 m) thick.[1]
  • Middle Member: This member in some areas gets up to 600 ft (180 m) thick. It is dominated by siltstones, limestones, and sandstones or quartzites. The siltstone layers are made up of grayish-olive, pale-olive, and locally pale-yellowish-brown or light-brown siltstone, shale, and phylitic silstone, which are composed of subangular silt-sized grains of quartz, embedded in a fine-textured matrix of muscovite or mica clay, and chlorite. The limestone layers are composed of medium-gray to grayish-orange or mottled-gray to light-brown aphanitic to medium crystalline limestone, which is inter-stratified with occasional siltstone. The sandstone or quartzite layers are primarily pale-brown, light-brown and very-pale-orange, very fine to fine grained and commonly evenly laminated. In some areas, these layers can grade into a coarse siltstone. They also contain quartz and feldspars.[1]
  • Upper Member: This member is the thinnest, only getting up to 100 ft (30 m) thick. It is mostly composed of medium-gray limestone, which is very thin to thin-bedded. It also contains a few archaeocyathid fossils.[1]

Depositional setting

The formation was deposited on an offshore shelf between the wave base and storm base, and experienced storm-related pulses of siliciclastic sediment input. Like many other Burgess Shale-type Lagerstätten, this unit was deposited on the Cordilleran margin of the Laurentian continent; it is among the oldest of the Lagerstätten from this region.[2]

Taphonomy

The modes of preservation of the non-biomineralised material found within the Indian Springs Lagerstätte has been noted to be either clay-mineral replacement, and pyrite or iron oxide staining. This is similar to the modes of preservation seen in the Chengjiang Lagerstätte. The Lagerstätte is also an example of a obrution-type deposition, which is a rapid burial of organisms, with some helicoplacoids being buried alive, still in their upright position. This form of deposition will have also obscured the buried specimens from scavengers.[2]

Paleobiota

Archeocyathids from the Death Valley area

Most of the fauna is biomineralized, including brachiopods, hyolithids, trilobites,[4] archeocyathids from the Gold Point Reef locality,[5][3] and helicoplacoids, which are often articulated.[2] Non-mineralized components of these fossils are also preserved, as are sponges, anomalocaridid parts, and a range of algae and cyanobacteria.[2]

Trace fossils, mainly Planolites, are also common; ichnofossils generally lie on the bedding plane and very few penetrate more than 1 millimetre (0.039 in) into the sediment. The biota of this formation has been noted to be similar to the Utah Lagerstätten, more so to the Spence Shale.[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.

Arthropoda

Genus Species Notes Images
Mesonacis
  • M. fremonti
 Olenellid trilobite, originally described as Fremonita.[6]
Laudonia[1][6]
  • Laudonia sp.
 Olenellid trilobite.
Olenellus[6]
  • O. clarki
 Olenellid trilobite.
Elliptocephala[7]
  • E. praenuntius
 Olenellid trilobite.
Teresellus[7]
  • Teresellus sp.
  • T. goldfieldensis
 Olenellid rilobite.
Nevadella[1][6][2]
  • N. eucharis
 Nevadid trilobite.
Nevadia[2]
  • N. parvoconica
 Nevadid trilobite.
Judomia (?)[1]
  • Judomia (?) sp.
 Nevadid trilobite.
Holmiella[4]
  • H. falx
 Holmiid trilobite.
Holmia[1]
  • Holmia sp.
 Holmiid trilobite.
Palmettaspis[4]
  • P. consorta
  • P. lidensis
 Holmiid trilobite.
Grandinasus[4]
  • Grandinasus sp.
  • G. argentus
  • G. auricampus
 Holmiid trilobite.
Holmidd (?)[4]
  • ???
 Undetermined holmiid trilobite.
Keeleaspis (?)[7]
  • K. (?) terhaari
 Corynexochid trilobite.
Polliaxis[7]
  • P. hanseni
 Corynexochid trilobite.
Geraldinella[2]
  • Geraldinella sp.
 Fallotaspidoid trilobite.
Anomalocarididae[2]
  • ???
 Anomalocaridid sclerites and fragments.

Lophotrochozoa

Genus Species Notes Images
Microcornus[8]
  • Microcornus sp.
 Lophotrochozoan hyolith.
Hyolithellus (?)[8]
  • Hyolithellus (?) sp.
 Lophotrochozoan hyolith.
Obolella[9]
  • Obolellasp.
 Obelellid brachiopod.
Kutorgina[9]
  • K. perugata
 Kutorginid brachiopod.
Lingulella[9]
  • Lingulella spp.
 Obolid brachiopod.
Spinulothele[9]
  • S. dubia
 Acrotheloid brachiopod.
Pompeckium (?)[9]
  • P. argenteum (?)
 Eoorthid brachiopod.
Mickwitzia[2]
  • M. occidens
 Mickwitziid brachiopod.
Swantonia[9]
  • S. weeksi
 Brachiopod of uncertain affinities.
Lingulid[2]
  • ???
 Lingulid brachiopod.
Obollelid[2]
  • ???
 Obollelid brachiopod, muscle scars preserved.
Hyolithes[6]
  • H. princeps
 Lophotrochozoan hyolith.
Hyolithellus[3]
  • Hyolithellus (?) sp.
  • H. insolitus
 Lophotrochozoan hyolith.
Hyolithid[2]
  • ???
 Lophotrochozoan hyolithids, too poorly preserved for taxonomic placement.
Orthothecida[10]
  • ???
 Orthothecid hyoliths, too poorly preserved for taxonomic placement.
Lapworthella (?)[11]
  • Lapworthella (?) sp.
 Lophotrochozoan tommotid.

Chancelloriidae

Genus Species Notes Images
Allonia[8]
  • Allonia sp.
 Chancelloriid organism.
Chancelloria[8]
  • Chancelloria sp.
 Chancelloriid organism.
Chancelloriid[2]
  • ???
 Chancelloriid spicules.

Cnidaria

Genus Species Notes Images
Paiutitubulites[12]
  • P. variabilis
  • P. durhami
 Anthozoan cnidarian.
Cambrotubulites[12]
  • Cambrotubulites sp.
  • C. trisepta
 Anthozoan cnidarian.
Sphenothallus[3]
  • Sphenothallus sp.
 Cnidarian conulariid.
Genus A[12]
  • Genus A sp.
 Anthozoan cnidarian, similar interior to Cambrotubulites and Paiutitubulites, though differs in having five septa.

Porifera (Sponges)

Genus Species Notes Images
Archaeocyathus[3]
  • A. arborensis
 Archeocyathid sponge.
Claruscoscinus[3]
  • Claruscoscinus sp.
 Archeocyathid sponge.
Protopharetra[3]
  • P. junensis
 Archeocyathid sponge.
Gatagacyathus[3]
  • Gatagacyathus sp.
 Archeocyathid sponge.
Ethmophyllum[3]
  • E. whitneyi
 Archeocyathid sponge.
Williamicyathus[3]
  • W. colvillensis
 Archeocyathid sponge.
Robustocyathellus[3]
  • Robustocyathellus sp.
 Archeocyathid sponge.
Paranacyathus[13]
  • Paranacyathus sp.
 Archeocyathid sponge.
Protopharetra[13]
  • Protopharetra sp.
 Archeocyathid sponge.
Metacyathellus (?)[3]
  • Metacyathellus (?) sp.
 Archeocyathid sponge.
Cordilleracyathus (?)[3]
  • Cordilleracyathus (?) sp.
 Archeocyathid sponge.
Wapkia (?)[2]
  • Wapkia (?) sp.
 Wapkiid demosponge.

Echniodermata

Genus Species Notes Images
Helicoplacus[1][6][14][2]
  • Helicoplacus sp.
  • H. gilberti
 Oblong echinoderm.
Eocystites[14]
  • Eocystites sp.
 Echinoderm.

Foraminifera

Genus Species Notes Images
Platysolenites[15]
  • P. antiquissimus
 Agglutinated hyperamminid foraminiferan.
Problematicum A[15]
  • ???
 Platysolenites-like tubular test, may be a taphonomic variant of Platysolenites. Also shows a resemblance to Spirosolenites spiralis, Although it differs to much in other ways when compared to Platysolenites and Spirosolenites.

Petalonamae

Genus Species Notes Images
Swartpuntia[16]
  • Swartpuntia sp.
 Sessile frondose organism, although assignment has been questioned based on the possibility that known specimens could be referred to other known Cambrian frondose organisms.[17]

incertae sedis

Genus Species Notes Images
Onuphionella[18]
  • O. claytonensis
 Tubular fossil.
Salterella[19]
  • Salterella sp.
 Tubular salterellid fossil.
Westgardia[20]
  • W. gigantea
 Valve-shaped fossil. Noted to be a mold of the shell, and poor preservation hinders taxonomic placement, although general morphology suggests it to be a mollusc.

Flora

Genus Species Notes Images
Cyanobacteria (?)[7]
  • ???
 Calcareous cyanobacteria.
Renalcis[13]
  • Renalcis sp.
 Cyanophyte cyanobacteria.

Ichnogenera

Genus Species Notes Images
Cruziana[14]
  • Cruziana sp.
 Trails.
Planolites[14][2]
  • Planolites sp.
 Burrows.
Scolicia[14]
  • Scolicia sp.
 Burrows.
Rusophycus[14]
  • Rusophycus sp.
 Resting trace of trilobites.
Bergaueria[14]
  • Bergaueria sp.
 Resting trace of cnidarians.
Laevicyclus[14]
  • Laevicyclus sp.
 Traces.
Psammichnites (?)[14]
  • Psammichnites (?) sp.
 Burrows.
Monocraterion[14]
  • Monocraterion sp.
 Burrows.
Skolithos[1][14]
  • Skolithos sp.
 Burrows.

See also

  • List of fossiliferous stratigraphic units in Nevada
  • Paleontology in Nevada

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Stewart, J. H.. "Upper Precambrian and Lower Cambrian Strata, in the Southern Great Basin California and Nevada". Geological Survey Professional. https://pubs.usgs.gov/pp/0620/report.pdf. 
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 English, Adam M.; Babcock, Loren E. (2010). "Census of the Indian Springs Lagerstätte, Poleta Formation (Cambrian), western Nevada, USA". Palaeogeography, Palaeoclimatology, Palaeoecology 295 (1–2): 236. doi:10.1016/j.palaeo.2010.05.041. 
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 Pruss, Sara B.; Slaymaker, Martha L.; Smith, Emily F.; Zhuravlev, Andrey Yu.; Fike, David A. (April 2021). "Cambrian reefs in the lower Poleta Formation: a new occurrence of a thick archaeocyathan reef near Gold Point, Nevada, USA". Facies 67 (2). doi:10.1007/s10347-021-00623-2. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Hollingsworth, J. Stewart (2006). "Holmiidae (Trilobita: Olenellina) of the Montezuman Stage (Early Cambrian) in Western Nevada". Journal of Paleontology 80 (2): 309–332. ISSN 0022-3360. https://www.jstor.org/stable/4095128. 
  5. ↑ McKee, E. H.; Gangloff, R. A. (1969). "Stratigraphic Distribution of Archaeocyathids in the Silver Peak Range and the White and Inyo Mountains, Western Nevada and Eastern California". Journal of Paleontology 43 (3): 716–726. 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Firby, Jean B.; Durham, J. Wyatt (1974). "Molluscan Radula from Earliest Cambrian". Journal of Paleontology 48 (6): 1109–1119. ISSN 0022-3360. https://www.jstor.org/stable/1303389. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Hollingsworth, J. Stewart (June 2005). "A trilobite fauna in a storm bed in the Poleta Formation (Dyeran, Lower Cambrian), western Nevada, U.S.A.". Geosciences Journal 9 (2): 129–143. doi:10.1007/BF02910575. 
  8. ↑ 8.0 8.1 8.2 8.3 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. https://www.jstor.org/stable/48572351. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Rowell, A. J. (1977). "Early Cambrian Brachiopods from the Southwestern Great Basin of California and Nevada". Journal of Paleontology 51 (1): 68–85. ISSN 0022-3360. https://www.jstor.org/stable/1303464. 
  10. ↑ 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. 
  11. ↑ Skovsted, Christian B.; Balthasar, Uwe; Vinther, Jakob; Sperling, Erik A. (May 2021). "Small shelly fossils and carbon isotopes from the early Cambrian (Stages 3–4) Mural Formation of western Laurentia". Papers in Palaeontology 7 (2): 951–983. doi:10.1002/spp2.1313. 
  12. ↑ 12.0 12.1 12.2 Tynan, Mark C. (1983). "Coral-like Microfossils from the Lower Cambrian of California". Journal of Paleontology 57 (6): 1188–1211. ISSN 0022-3360. https://www.jstor.org/stable/1304810. 
  13. ↑ 13.0 13.1 13.2 Manzuk, Ryan A.; Maloof, Adam C.; Kaandorp, Jaap A.; Webster, Mark (January 2023). "Branching archaeocyaths as ecosystem engineers during the Cambrian radiation". Geobiology 21 (1): 66–85. doi:10.1111/gbi.12521. 
  14. ↑ 14.00 14.01 14.02 14.03 14.04 14.05 14.06 14.07 14.08 14.09 14.10 Alpert, Stephen P. (1976). "Trilobite and Star-like Trace Fossils from the White-Inyo Mountains, California". Journal of Paleontology 50 (2): 226–239. ISSN 0022-3360. https://www.jstor.org/stable/1303490. 
  15. ↑ 15.0 15.1 Streng, M.; Babcock, L. E.; Hollingsworth, J. S. (November 2005). "AGGLUTINATED PROTISTS FROM THE LOWER CAMBRIAN OF NEVADA". Journal of Paleontology 79 (6): 1214–1218. doi:10.1666/0022-3360(2005)079[1214:APFTLC2.0.CO;2]. 
  16. ↑ Hagadorn, James W.; Fedo, Christopher M.; Waggoner, Ben M. (2000). "Early Cambrian Ediacaran-Type Fossils from California". Journal of Paleontology 74 (4): 731–740. doi:10.1666/0022-3360(2000)074<0731:ECETFF>2.0.CO;2. ISSN 0022-3360. 
  17. ↑ Runnegar, Bruce; Gehling, James G.; Jensen, Sören; Saltzman, Matthew R. (October 2024). "Ediacaran paleobiology and biostratigraphy of the Nama Group, Namibia, with emphasis on the erniettomorphs, tubular and trace fossils, and a new sponge, Arimasia germsi n. gen. n. sp.". Journal of Paleontology 98 (S94): 1–59. doi:10.1017/jpa.2023.81. Bibcode: 2024JPal...98S...1R. 
  18. ↑ Signor, Philip W.; Mcmenamin, Mark A. S. (March 1988). "The Early Cambrian worm tube Onuphionella from California and Nevada". Journal of Paleontology 62 (2): 233–240. doi:10.1017/S0022336000029863. 
  19. ↑ Pruss, Sara B.; Smith, Emily F.; Zhuravlev, Andrey Yu; Nolan, Rhiannon Z.; McGann, Tessa C. (June 2025). "Rise and fall of archaeocyath reefs shaped early Cambrian skeletal animal abundance". Palaeogeography, Palaeoclimatology, Palaeoecology 667. doi:10.1016/j.palaeo.2025.112852. 
  20. ↑ Rowland, Stephen M.; Carlson, Sandra J. (1983). "Westgardia gigantea, a New Lower Cambrian Fossil from Eastern California". Journal of Paleontology 57 (6): 1317–1320. https://www.jstor.org/stable/1304817. 

Template:Burgess shale type preservation



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