The Cambrian trilobite fauna from the Shian (Saybang) section, Pin Valley (Spiti) and its biostratigraphic significance

Abstract

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 (5.4m), 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 1160m of the Cambrian strata (deposited within about 2Ma, i.e., 509 to 507Ma) further eroded prior to the deposition of the Thango Formation.