| Poleta formation Stratigraphic range: Cambrian stage 3 |
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| Location | Western Nevada and Eastern California, USA |
The Poleta formation is a geological unit known for the exceptional fossil preservation in the Indian Springs Lagerstätte.[1]
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The formation dates to the third stage of the yet-to-be-ratified Cambrian series 2; the lower portion base of the formation and the youngest lagerstatte 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.[1] It outcrops in Esmerelda county in western Nevada.[1]
The formation was deposited on an offshore shelf, and experienced storm-related pulses of siliciclastic sediment input.[1] Like many other Burgess Shale-type lagerstatten, this unit was deposited on the Cordilleran margin of the Laurentian continent; it is among the oldest of the lagerstatten from this region.[1]
The fossil preservation is markedly similar to that in Utah lagerstatten, particularly the Spence Shale.[1] 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.[1]
Most of the fauna is biomineralized, including brachiopods, hyolithids, trilobites, archeocyathids,[2] and helicoplacoids, which are often articulated.[1] Non-mineralized components of these fossils are also preserved, as are sponges, anomalocaridid parts, and a range of algae and cyanobacteria.[1]
Trace fossils, mainly Planolites, are also common; ichnofossils generally lie on the bedding plane and very few penetrate more than a millimeter into the sediment.[1]
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