Initial results from a Trans-Amazon Drilling Project core from the Acre Basin of Brazil

The Trans-Amazon Drilling Project (TADP) is reconstructing the late Cenozoic history of Amazonian geology, climate, rivers, and forests. Drilling in the Acre Basin of western Brazil in 2023 recovered an 860 m drill core characterized by sediments that were deposited in a large paleo-river system. The overall sequence includes sandstones, siltstones, and mudstones that underwent varied degrees of weathering and pedogenesis. Here, we describe the ongoing geochronologic, geochemical, mineralogical, geophysical, and biotic analyses of the sedimentary record and present some preliminary inferences of the environmental history based on these initial results. Except for the uppermost ∼ 12 m, sediments from the drill core represent a single lithostratigraphic unit, assigned to the Solimões Formation, which is dominated by feldspar-rich sands of Andean origin. The pollen assemblage is quite different from Early to Middle Miocene floras that have been analyzed from a few sites elsewhere in the western Amazon. The novel pollen assemblage and new geochronological results suggest that the sequence may span the latest Miocene and all of the Pliocene Epoch, an interval that currently is not well represented in existing regional records and that is crucial for understanding the evolution of Amazonian biodiversity, as well as landscape transformations driven by Andean uplift and global climate change.