Abstract:
The main purpose of this study is to reveal the sedimentary enviroments based on
sediment characteristics and relative sedimentation rates. The obtained data are all based on
analysis results of core samples taken from the Dumai Coastal Waters located off the north
coast of Dumai City Indonesia.
Bottom sediment samples were collected at 7 stations in the waters using gravity corer
in March 2011. The samples were used for mechanical grain size analysis, ignition loss
method, and bulk chemical analysis. In addition, the topmost one centimeter of core samples,
which approximately 10 cc of wet sediments, was utilized for benthic foraminiferal study,
namely, the study of of L/Tl values to infer the relative sedimentation rates.
The Dumai Coastal Waters, Riau Province Indonesia is subdivided into three areas
based on the general trend of sediment characteristics and relative sedimentation rates as
following: 1) the central part of the waters is characterized by coarse-grained sediments, high
relative sedimentation rates and dominantly terrigeneous sediments which under influence of
rather strong tidal currents, 2) the eastern and western parts of the waters are characterized by
relatively coarse-grained sediments, rather high relative sedimentation rates and relatively
high biogeneous sediments which are influenced by longshore currents, and 3) the area off
the coast (central part) is characterized by fine-grained sediments, the highest relative
sedimentation rates. The area correspond to the boundary between the waters masses derived
from Rupat Strait and of from Dumai Waters and is under influence of weak tidal current
The distribution of crude oil content in sediments indicate that study area under influence
of tidal and longshore currents. Judging from the distribution pattern of crude oil content in
sediments, sediments polluted by crude oil were transported northwestward and northeastward by
longshore currents and spread toward north by tidal currents, of the Dumai Coastal Waters.
Key words : sedimentary enviroments, relative sedimentation rates, Dumai Coastal Waters
