attached
Quaternary sediment deposits are well exposed along the
eastern coastal margin of Sri Lanka. Systematic trace fossil studies
along with sediment characteristics have been carried out for the
first time to interpret the paleoenvironment that prevailed during
Quaternary sedimentation in eastern Sri Lanka. The trace fossils
Thalassinoides, Skolithos and Polykladichnus have been recognized
about 5m above the present mean sea level. Features of the major
trace fossil, Thalassinoides, indicate that it was formed by
Thalassinidean shrimp Calianassa. Isolated, vertical to steeply
inclined, cylindrical to sub cylindrical tubes with thin internal wall
lining and inner wall striations of Skolithos and Polykladichnus
show that they were formed by polychaetes. The typical
characteristic of Polykladichnusis Y-shaped branching with slight
enlargement at junctions. Morphology and association of burrows
as well as mineralogy, grain size and roundness of sediments
indicate that the environment prevailed was marine soft grounds
of the intertidal zone. Presence of preserved fine-scale features of
burrows indicate that the bioturbated sandy tidal flat was suddenly
exposed to the tropical environment due to sea level regression in
Quaternary periods. Due to the microbial activities of wall linings,
burrows were preserved and it was supported by other microbial
activities that produced secondary iron bearing minerals that
suffered subsequent oxidation. The bio-origination of red sediments
of eastern coastal area of the present study can be used to interpret
the debatable origin of the red beds found in northwestern and
southeastern coastal areas of the island.
