David Van Rooij

The Arctic Ocean plays a pivotal role in global climate, yet its circulation under greenhouse conditions remains poorly constrained. Seismic, sedimentological, and drilling evidence from the Chukchi Shelf reveals large contourite drifts and bathyal carbonate mounds dated to the Campanian to Maastrichtian [~80 to 66 million years ago (Ma)], indicating persistent bottom currents and high productivity. These features point to the presence of a regionally sourced Boreal deep-water mass, likely driven by seasonal sea-ice formation and brine rejection. Bathyal carbonate mound development was sustained by tidal mixing, localized upwelling, and well-oxygenated conditions following Oceanic Anoxic Event 3. This vigorous circulation system collapsed at the Cretaceous-to-Paleogene boundary, coinciding with closure of the Western Interior Seaway and reorganization of global circulation. Our findings challenge the prevailing view of a sluggish, surface-dominated Late Cretaceous Arctic, demonstrating instead that it supported deep-water formation and localized carbonate factories, highlighting its key role in high-latitude climate dynamics under greenhouse conditions.

This work uses seismic records to document and classify contourite features around the Iberian continental margin to determine their implications for depositional systems and petroleum exploration. Contourites include depositional features (separated, sheeted, plastered and confined drifts), erosional features (abraded surfaces, channels, furrows and moats) and mixed features (contourite terraces). Drifts generally show high- to moderate-amplitude reflectors, which are cyclically intercalated with transparent layers. Transparent layers may represent finer-grained deposits, which can serve as seal rocks. High-amplitude reflectors (HARs) are likely to represent sandier layers, which could form hydrocarbon reservoirs. HARs occur on erosive features (moats and channels), and are clearly developed on contourite terraces and overflow features. Most of the contourite features described here are influenced by Mediterranean water masses throughout their Pliocene and Quaternary history. They specifically record Mediterranean Outflow Water, following its exit through the Gibraltar Strait. This work gives a detailed report on the variation of modern contourite deposits, which can help inform ancient contourite reservoir interpretation. Further research correlating 2D and 3D seismic anomalies with core and well-logging data is needed to develop better diagnostic criteria for contourites. This can help to clarify the role of contourites in petroleum systems.