The organic matter determination, made by different areas, justified a comparison between methodologies to establish the point of result differences is acceptable. The present study aims to elucidate questions about organic matter elimination, under Oceanography view (through method of calcination and methods of chemical attack with Hydrogen Peroxide and Sodium Hypochlorite), making possible future and reliable mineralogic and granulometric analysis, especially in different regions dominated by fine-grained sediments (silts and clays) with high amount of organic matter, like Amapa’s Coastal Plain. Sucuriju River, localized in Amapa’s cost northeast, is characterized by fluvial-marine plain, composed Holocenic sediments, fixed predominantly by mangroves. To compare the methodologies, was used mineralogic analysis and sample losses quantify, aims to qualify effectiveness. Approximately 97% of tests indicate the organic matter content below 6%, while the highest values are associated with peat region (north of the mouth) and the village residents and/or channel and tributaries (within the river). The method of calcination obtained values between 0 and 10,5% with an average of 2%, while the methods of adding H2O2 and NaOCl were 0,19 and 0,01% (minimum) of 12,96% and 10,6% (maximum) with averages of 1,98 and 1,40%, respectively. The average obtained by Calcination is associated with loss of structural water, while the average obtained through addition of H2O2 is related of sample losses arising from the time of settled of clays. Comparing to mineral identification of the gross sample, the method of Calcination changed the mineralogical composition while the other methods did not indicate changes. The distribution of organic matter in bottom sediments of the river Sucuriju is conditioned by hydrodynamic forcing and the proximity of the source areas.
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