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Poleta Formation

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Geological unit located in eastern California and Nevada
Poleta Formation
Stratigraphic range: Cambrian Series 2
~519–518 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
UnderliesHarkless Formation
OverliesCampito Formation
Lithology
PrimaryFine siliciclastics
Location
LocationWestern Nevada and Eastern California, USA
Part of a series on
The Cambrian explosion
Fossil localities
Key organisms
Ediacaran biota
Burgess-type
Small shelly fauna
Evolutionary concepts
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Themes

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

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

Archeocyathids from the Death Valley area

Most of the fauna is biomineralized, including brachiopods, hyolithids, trilobites, archeocyathids, 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 1 millimetre (0.039 in) into the sediment.

See also

References

  1. Edwin H. McKee (1968). "Geology of the Magruder Mountain area, Nevada-California" (PDF). U.S. Geological Survey Bulletin: H10. doi:10.3133/B1251H. ISSN 8755-531X. Wikidata Q57805921.
  2. Edwin H. McKee (1968). "Geology of the Magruder Mountain area, Nevada-California" (PDF). U.S. Geological Survey Bulletin: H7. doi:10.3133/B1251H. ISSN 8755-531X. Wikidata Q57805921.
  3. ^ 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.
  4. 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. JSTOR 1302466.
Burgess Shale-type preservation
Cambrian localities
Ordovician localities
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