Trilobite fauna of basal Cambrian Series 3 (Stage 5) from the Parahio Valley (Spiti), Northwest Himalaya, India and its biostratigraphic significance

Abstract

We precisely demarcate the Hayden level 2 in the Kunzam La (Parahio) Formation, exposed on a steep hill on the left bank of the Parahio River in Spiti (India), which brackets the (local) stratigraphic range of Oryctocephalus indicus, a key taxon for establishing the base of the Cambrian Series 3 (Stage 5) and perhaps the Cambrian Series 2–Series 3 boundary interval globally. The FAD and LAD of O. indicus are observed at 7.74 and 14.61m respectively, indicating 6.87m stratigraphic range of the taxon along the Parahio valley section. The O. indicus Zone is demarcated with precise stratigraphic range of the eponymous species. The FADs of Pagetia and Kunmingaspis together at 7.34m predate the FAD of O. indicus 7.74m. Pagetia ranges from the Cambrian Series 2 (Stage 4) to the Cambrian Series 3 (Stage 5) and its occurrence is consistent with the global occurrences. Eosoptychoparia (Danzhaina) sp. is recorded for the first time from the Indian Himalaya. The base of the Cambrian Series 3 is considered to be placed at the FAD of the O. indicus.