The palynoflora and palynodebris content have been studied of a 3800 in dee
p well situated in the oil producing Tinali area in the Upper Assam basin o
f the Brahmaputra Valley, India. The well penetrated through Dhekiajuli For
mation, Namsang Formation, Tipam, Surma and Barail Groups (Oligocene-Pleist
ocene). Microfloral change from Barail Group to Surma Group is distinct and
indicates a more rich deltaic swamp vegetation during deposition of Barail
Group than overlying sediments. The fluviatile Neogene sediments are poor
in microfossils and indicative of comparatively drier conditions. Three inf
ormal zones have been proposed based on occurrance or abundance of palynofo
ssils. Amorphous organic matter is dominant in the Barail Group and is grad
ually replaced by biodegraded terrestrial and black debris in the post-Bara
il sediments. Reworked Palaeozoic and Mesozoic palynofossils occur through
out the sequence. Moreover, reworked Palaeocene and Eocene palynotaxa are a
lso recovered from the post-Barail sediments. This phenomenon is related wi
th the Himalayan orogenic movements. (C) Editions scientifiques et medicale
s Elsevier SAS.