Abstract Sedimentary models that apply to the Middle Miocene succession in Amazonia are controversial. Although tidally-influenced sedimentary deposits have been described from several locations, the identification of brackish-water or marine facies has been hampered by limited outcrop exposure. Also, ichnological data largely have been ignored. This study focuses on ichnological and sedimentological relationships observed in outcropping strata of the Solimoes Formation (Middle Miocene) along the Acre River in western Brazil and northern Bolivia. The studied strata comprise a fine-grained lower unit that is sharply overlain by dipping, interbedded sands and muds, known as inclined heterolithic stratification (IHS). The IHS is present throughout the length of the outcrop, about 80m. The outcropping strata are interpreted to represent two depositional subenvironments: (1) A lower unit that resulted from sediment accumulation in a shallow, restricted, subaqueous depositional environment. The deposit ultimate...