Early Permian macroinvertebrate assemblages from the Siang and Subansiri districts, Arunachal Pradesh: Implications on the regional stratigraphy, palaeoenvironment, palaeoecology, and palaeobiogeography

The Early Permian marine strata exposed at the Siang and Subansiri districts, Arunachal Pradesh are known for brachiopod and molluscan fossils. A stratigraphic review and palaeoenvironmental, palaeoecological, and palaeobiogeographic interpretation of these Early Permian fossils have been dealt here on the basis of additional fossil and rock materials. Our study confirms the following: (1) the brachiopod-dominated assemblage represents Early Permian, most likely the Sakmarian and younger, age; (2) all marine fossils were suspension feeding groups, representing normal marine condition. Based on the associated sediments and ecologies of taxa, the autecology of the assemblage represents an oxic, soft substrate condition, typical of shallow shelf environment; the plant remains of the upper Khelong/Bhareli Formation, however, indicate a coastal environment; (3) the depositional paleoenvironment indicates the waning phase of a marine glacial episode; and (4) this Early Permian bivalve-brachiopod assemblage show Gondwanan affinity, having strong faunal similarity with the East and West Australia, Nepal and North India (Kashmir) which were part of the Indoralian Province.