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We present low-diversity acritarch assemblages, including Alliumella baltica , Bavlinella faveolata , Brocholaminaria nigrita , Brocholaminaria sp., Eliasum sp., Leiosphaeridia minutissima , Leiosphaeridia spp., Lophosphaeridium sp., Pterospermella solida , Satka colonialica , Siphonophycus sp., and Synsphaeridium sp., as well as filamentous algae and cryptospore-like microfossils recorded from 45 rock samples around the Oryctocephalus indicus Zone (Cambrian Series 3) in the Cambrian Kunzam La (Parahio) Formation at the Kaltarbo locality in the Parahio valley, Northwest Himalaya. One new species Synsphaeridium parahioense was established. The acritarch assemblages at the basal part of the Cambrian Series 3 in the Kunzam La (Parahio) Formation were dependent on the local marine environment. The new discovery of cryptospore-like microfossils from the Cambrian Kunzam La (Parahio) Formation supports the extensive distribution of possible cryptospores in the Cambrian stratigraphic sequences.

Additional Cambrian Series 3, Stage 5, trilobite fauna comprising Peronopsis sp., Eosoptychoparia cf. Spinosa Gaotanaspis cf. pingzhaiensis and Gaotanaspis cf. transversa have been recorded just immediately above the known Oryctocephalus indicus biozone (Cambrian Series 3, Stage 5) in the Parahio valley section (Spiti region). The FAD of Peronopsis and LAD of Gaotanaspis are used to establish a Peronopsis–Gaotanaspis concurrent biozone immediately above the Oryctocephalus indicus biozone. The first records of Gaotanaspis cf. pingzhaiensis and G. transversa from the Cambrian of Spiti region and the other faunal elements are correlated with the Peronopsis taijiangensis biozone of the Kaili Formation (South China). The stratigraphic thickness from the base of the O. indicus biozone to the top of the Peronopsis–Gaotanaspis concurrent biozone in the Kunzam La (=Parahio) Formation and its comparison to the Kaili Formation (South China) indicate a possible stratigraphic condensation in the basal part of the Cambrian Series 3, Stage 5 of the Parahio valley (Spiti). Sedimentological and sequence stratigraphic analysis supports this contention.

The Cambrian trilobite fauna, illustrated for the first time from the Pin Valley (Spiti, Northwest Himalaya, India), comprises Oryctocephalus indicus, Pagetia significans, Kunmingaspis pervulgata, and Bhargavia prakritika and they ranges from the top part of the Cambrian Series 2 (Stage 4) to the basal most part of the Series 3 (Stage 5). On the basis of the trilobite fauna and their stratigraphic order of occurrence we recognize the Oryctocephalus indicus Zone (5.4 m), interval 1 of no zonation, and the Bhargavia prakritika Level (Cambrian Series 3, Stage 5). The Oryctocephalus indicus Zone is based on the FAD and LAD (local range) of the eponymous species in the Pin Valley section. The occurrence of fossiliferous section immediately below the Cambro-Ordovician angular unconformity in the Pin Valley indicates, in comparison to the Parahio Valley, nearly 1160 m of the Cambrian strata (deposited within about 2 Ma, i.e., 509 to 507 Ma) further eroded prior to the deposition of the Thango Formation.

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 14.61 m respectively, indicating 6.87 m 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 7.34 m predate the FAD of O. indicus 7.74 m. 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.