Patricia Standring

The Loop Current is a key component of global circulation via the northward transport of warm, salty water, and an important influence on Gulf of Mexico hydrography. Understanding how the Loop Current will respond to ongoing anthropogenic warming is critically important, but the history of the Loop Current is poorly known. Here, we present the results of a high resolution (3–8 m) multichannel seismic survey of pelagic carbonate sediment drifts on the eastern Campeche Bank associated with the Loop Current. We identify three seismic megasequences: Megasequence A is a Lower Cretaceous carbonate platform, Megasequence B comprises Cretaceous to lower Cenozoic pelagic carbonates with weak/no contour current flow, and Megasequence C comprises a series of large (100s of m thick) contourite drifts representing the inception and history of the Loop Current. The base of the contourites is marked by a regionally mappable unconformity eroding underling strata, sometimes incising hundreds of meters. The drifts contain a succession of sequence sets separated from each other by regional unconformities and comprising plastered drifts and massive mounded drifts, which characterize modern deposition with active moats on the seafloor. A lack of sediment cores in the study area precludes age determination of these drifts, except for the youngest (Late Pleistocene). Comparison to legacy seismic lines across Deep Sea Drilling Project Site 95, outside our study area, implies that the base of Megasequence C is Oligocene in age, and that the Loop Current developed during the global reorganization of ocean circulation around the Eocene‐Oligocene Transition.