Palynology in stratigraphy of lesser Himalayan sedimentary sequences from Arunachal Pradesh, India

Abstract

Arunachal Pradesh has a distinct geological setup and significant data have been generated during the last decade both from Permian as well as Tertiary sediments. The palynoflora investigated from Lesser Himalayan Permian sediments of Arunachal Pradesh has been differentiated into five palynozones 1. Plicalipollenites stigmatus 2. Callumispora gretensis 3. Crucisaccites indicus 4. Pselldoreticulatispora baraknrensis and 5. Primuspollenites + Rhizomaspora: the oldest being Palynozone I (Rilu Member, Rangit Formation) representing Late Asselian whilc Palynozones 2-5 (Garu Formation) represent Early Sakmarian to Early Artinskian age.

The palynoassemblages recorded from Tertiary sediments in Arunachal Pradesh largely show the overwhelming presence of angiosperm pollen. viz. Lakiapollis. Neocouperipollis, Arecipites, Pellicieroipollis and Ctenolophonidites. Pteridophytic spores. viz., Todisporites. Cyathidites. Striatriletes and Crassoretitriletes shows similar age connotations. Broadly two distinct palynozones have been differentiatcd. viz., Lakiapollis ovatus and Striatriletes susannae assemblage zones. At some sections presence of dinoflagellate and acritarch indicate marine influence during Early Tertiary.

Permian spores also occur in reworked state within Early Tertiary sediments. Palynological investigations carried out along the thrust suggest that some thrust slices of Tertiary rocks arc wedged deep within the Permian outcrops. These evidences indicate severe post depositional tectonic effect in these regions. Palynological evidences along with faunal evidences. Wherever possible, have been summarised to decipher the stratigraphic resolutions, palaeogeography and palaeoenvironment of the region.