Geophysical methods can be used to identify the frequency and spatial distribution of plant debris, as well as for the study of the development of such accumulations in recent depositional settings. Side-scan sonar and a sub-bottom profiler were used to generate acoustic images of plant macroremains along a 16.9 km stretch of the meandering course of the Preto River in the municipality of Itanhaém, São Paulo, Brazil. Numerous inclined heterolithic stratification (IHS) deposits with plant debris constitute point bars, while sand dunes mark the migration of the channel along the straighter portions of the river. A large concentration of methane gas was found associated with older organic sediments in the river. The acoustically generated results were confirmed by the analysis of cores with all data integrated into the geographic information system (GIS) environment. The present study is one of the first to apply the methods of geotechnology to taphonomic research.