Early Cretaceous deep-water bedforms west of the Guinea Plateau revise the opening history of the Equatorial Atlantic Gateway

Abstract

The Equatorial Atlantic Gateway (EAG) was critical to Earth's climatic and oceanographic evolution during the Mesozoic, yet its early opening history remains enigmatic. Here, we present new 2D seismic reflection data and biostratigraphic ages from DSDP Site 367, integrated with tectonic reconstruction models, to constrain the sedimentary response to the evolution of the gateway. Seismic analysis reveals five stratigraphic units (U1 to U5) documenting tectonic and oceanographic changes in the Guinea Plateau margin. Morphosedimentary features identified in units U2 to U4, including sediment waves and contourite drifts, document changing current dynamics during EAG opening. We propose a two-stage model for the initial gateway opening: i) middle-late Aptian (∼117 to ∼113 Ma) formation of a marginal sea in the western EAG and overflow of Equatorial waters into the Central Atlantic, producing large sediment waves northwest of the gateway, and ii) latest Aptian-late Albian (from ∼113 Ma onwards) widening and deepening of the gateway, establishing more continuous water exchange and leading to the transition into contourite deposition. This direct sedimentary evidence shows the establishment of a marine connection started at around 117 Ma, significantly earlier than previous estimates, and coinciding with the onset of global climate cooling. These findings show the dynamic interplay between gateway opening, ocean circulation, and climate change during the middle Cretaceous, highlighting the pivotal role of ocean gateways in Earth's climate system.