Sedimentological Aspects and Relative Sedimentation Rates in the Dumai Coastal Waters, Riau Province Indonesia

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