The Al Rose Formation is a geologic formation located in

Inyo County Inyo County () is a county in the eastern central part of the U.S. state of California, located between the Sierra Nevada and the state of Nevada. In the 2020 census, the population was 19,016. The county seat is Independence. Inyo County is ...

, California. It is notable for preserving fossils from the

Cambrian Period The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

, offering insights into early Paleozoic life and environments.

Stratigraphy

The formation is primarily composed of

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

, with interbedded

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

layers, indicating a range of depositional environments. These rocks were deposited in a marine setting, as evidenced by their fossil content and sedimentary structures. The formation is stratigraphically positioned within the Great Basin region, an area renowned for its well-preserved Cambrian stratigraphy.

Fossil Content

Fossils recovered from the formation include a variety of

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s, and

archaeocyathid Archaeocyatha (), 'ancient cups') is a taxon of extinct, sessile, reef-building marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha origin is now locat ...

s, providing critical data on the diversity of life during the Cambrian explosion. These fossils help paleontologists reconstruct ancient ecosystems and understand evolutionary dynamics during the Cambrian.

Regional Significance

The formation is a key part of the Cambrian stratigraphy in California. Its correlation with other Cambrian formations in the Great Basin, such as the Carrara Formation and the

Bonanza King Formation The Bonanza King Formation is a geologic formation in Nevada. It preserves fossils dating back to the Cambrian period. See also * List of fossiliferous stratigraphic units in Nevada * Paleontology in Nevada Paleontology in Nevada refers to pa ...

, aids geologists in understanding the geological history of the region and broader paleoenvironmental changes.Barnes, H., & Palmer, A. R. (1961). Cambrian stratigraphy and trilobites of the Al Rose Formation, California. ''Geological Society of America Bulletin'', 72(2), 157-175. https://doi.org/10.1130/0016-7606(1961)72 57:CSAOTR.0.CO;2

References

{{ref-list Ordovician California Ordovician southern paleotropical deposits Siltstone formations of the United States Mudstone formations of the United States Shale formations of the United States Chert formations Geologic formations of California