Orbital and sea-level controls on long-term sediment deposition in the Amazon Fan

The Amazon Fan, one of the largest deep-sea fans on Earth, is a vital archive of the Amazon Basin's long-term climate and tectonic evolution. However, the factors driving sediment deposition patterns during the Neogene remain poorly understood. Here, we present an astronomical age model for a 4800 m-long sedimentary record (BP-3 well), spanning the past ∼24 million years, a key interval encompassing the Amazon River's evolution into a transcontinental system. Gamma-ray (GR) data reveal strong Milankovitch cyclicity, highlighting the fan's sensitivity to orbital climate variability and enabling correlations with global mean sea level (GMSL). Our analysis shows persistently low sedimentation rates (∼5–13 cm/kyr) during the late Miocene, despite Andean uplift and increased precipitation, likely due to sediment trapping by mega-wetlands in Western Amazonia. A marked increase in sedimentation (∼50 cm/kyr) during the Early Pliocene (5.1–4.8 ± 1.78 Ma) reflects the collapse of these barriers, facilitating sediment transport to the Atlantic despite high GMSL. The GR record also captures the transition from obliquity- to eccentricity-dominated glacial-interglacial cycles during the mid-Pleistocene Transition (∼1.3 Ma). These findings align with GMSL and benthic δ¹⁸O data, supporting a minimal tuning approach and emphasizing the Amazon Fan's sensitivity to global climate changes. Our revised chronology provides a robust framework for understanding the Neogene evolution of the Amazon River and its links to Andean tectonics and climate variability.