Poleta Formation
{{Short description|Geological unit located in eastern California and Nevada}}
{{infobox rockunit
| name = Poleta Formation
| period = Cambrian stage 3
| age = Cambrian Series 2
~{{fossil range|519|518}}
| underlies = Harkless Formation{{Cite Q|Q57805921|page=H10}}
| overlies = Campito Formation{{Cite Q|Q57805921|page=H7}}
| prilithology = Fine siliciclastics
| location = Western Nevada and Eastern California, USA
}}
{{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.{{cite journal | title = Census of the Indian Springs Lagerstätte, Poleta Formation (Cambrian), western Nevada, USA| journal = Palaeogeography, Palaeoclimatology, Palaeoecology| volume = 295 | issue = 1–2 | pages = 236| year = 2010| doi = 10.1016/j.palaeo.2010.05.041| author = English, Adam M. | author2 = Babcock, Loren E. }}
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. It outcrops in Esmeralda County in western Nevada.
Depositional setting
The formation was deposited on an offshore shelf, 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.
Taphonomy
The fossil preservation is markedly similar to that in Utah Lagerstätten, particularly the Spence Shale. The quality of preservation was obtained by the rapid burial of organisms in obrution events, which buried them out of reach of would-be scavengers.
Fauna
File:Archeocyathids.JPGs from the Death Valley area]]
Most of the fauna is biomineralized, including brachiopods, hyolithids, trilobites, archeocyathids,{{Cite journal| jstor = 1302466| pages = 716–726| title = Stratigraphic Distribution of Archaeocyathids in the Silver Peak Range and the White and Inyo Mountains, Western Nevada and Eastern California| journal = Journal of Paleontology| volume = 43| issue = 3| year = 1969| author1 = McKee | first1 = E. H.| author2 = Gangloff | first2 = R. A.}} and helicoplacoids, which are often articulated. Non-mineralized components of these fossils are also preserved, as are sponges, anomalocaridid parts, and a range of algae and cyanobacteria.
Trace fossils, mainly Planolites, are also common; ichnofossils generally lie on the bedding plane and very few penetrate more than {{convert|1|mm|in}} into the sediment.
See also
{{Portal|Earth sciences|United States|Paleontology}}
{{commons category|Poleta Formation}}
References
{{reflist}}
{{Burgess_shale_type_preservation}}
Category:Geologic formations of California
Category:Geologic formations of Nevada
Category:Cambrian System of North America