| Poleta Formation | |
| Period: | Cambrian stage 3 |
| Age: | Cambrian Series 2 ~ |
| Underlies: | Harkless Formation[1] |
| Overlies: | Campito Formation[2] |
| Prilithology: | Fine siliciclastics |
| 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, located in eastern California and Nevada.[3]
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.[3] It outcrops in Esmeralda County in western Nevada.[3]
The formation was deposited on an offshore shelf, and experienced storm-related pulses of siliciclastic sediment input.[3] 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.[3]
The fossil preservation is markedly similar to that in Utah Lagerstätten, particularly the Spence Shale.[3] 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.[3]
Most of the fauna is biomineralized, including brachiopods, hyolithids, trilobites, archeocyathids,[4] and helicoplacoids, which are often articulated.[3] Non-mineralized components of these fossils are also preserved, as are sponges, anomalocaridid parts, and a range of algae and cyanobacteria.[3]
Trace fossils, mainly Planolites, are also common; ichnofossils generally lie on the bedding plane and very few penetrate more than 1mm into the sediment.[3]