Poleta Formation

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Poleta Formation
Stratigraphic range: Cambrian Series 2
~519–518 Ma
PrimaryFine siliciclastics
LocationWestern 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.[1]


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,[1] it outcrops in Esmeralda County in western Nevada.[1]

Depositional setting[edit]

The formation was deposited on an offshore shelf, and experienced storm-related pulses of siliciclastic sediment input.[1] 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.[1]


The fossil preservation is markedly similar to that in Utah Lagerstätten, 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]


Archeocyathids from the Death Valley area

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 1 millimetre (0.039 in) into the sediment.[1]


  1. ^ a b c d e f g h i j 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.
  2. ^ 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.