Young rifts are shaped by combined tectonic and surface processes and climate, yet few records exist to evaluate the interplay of these processes over an extended period of early rift-basin development. Here, we present the longest and highest resolution record of sediment flux and paleoenvironmental changes when a young rift connects to the global oceans. New results from International Ocean Discovery Program (IODP) Expedition 381 in the Corinth Rift show 10s–100s of kyr cyclic variations in basin paleoenvironment as eustatic sea level fluctuated with respect to sills bounding this semi-isolated basin, and reveal substantial corresponding changes in the volume and character of sediment delivered into the rift. During interglacials, when the basin was marine, sedimentation rates were lower (excepting the Holocene), and bioturbation and organic carbon concentration higher. During glacials, the basin was isolated from the ocean, and sedimentation rates were higher (~2–7 times those in interglacials). We infer that reduced vegetation cover during glacials drove higher sediment flux from the rift flanks. These orbital-timescale changes in rate and type of basin infill will likely influence early rift sedimentary and faulting processes, potentially including syn-rift stratigraphy, sediment burial rates, and organic carbon flux and preservation on deep continental margins worldwide.

This work is distributed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. Contents 1 Introduction and operations 5 Lithostratigraphy 9 Structural geology 13 Micropaleontology 16 Geochemistry 18 Physical properties 25 Paleomagnetism 26 Downhole measurements 30 Core-log-seismic integration 33 References

The Chicxulub impact caused a crash in export productivity in much of the world's oceans which contributed to the extinction of 75% of marine species. In the immediate aftermath of the extinction, local export productivity was highly variable, with some sites, including the Chicxulub crater, recording elevated export production. The long-term transition back to more stable export productivity regimes has been poorly documented. Here, we present elemental abundances, foraminifer and calcareous nannoplankton assemblage counts, total organic carbon, and stable carbon isotopes from the Chicxulub crater to reconstruct long-term changes of productivity over the first 3 Myr of the Paleocene. We show that export production was elevated for the first 320 kyr of the Paleocene and then declined over the next ~900 kyr, remaining low thereafter. This interval is associated with fluctuations in water column stratification and terrigenous flux, but these variables are uncorrelated to export productivity. Instead, we suggest that the turnover in the phytoplankton community from a post-extinction assemblage dominated by picoplankton (which promoted nutrient recycling in the euphotic zone) to a more normal Paleocene pelagic community dominated by calcareous nannoplankton (which more efficiently removed nutrients from surface waters and led to oligotrophy) is responsible for the decline in export production in the southern Gulf of Mexico.

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