Site U1620. Proceedings of the International Ocean Discovery Program

The Svyatogor Ridge is a northwest–southeast elongated contouritic sediment drift lying on a young (<10 Ma) oceanic crust. This sediment drift is 46 km long and 5 km wide (Johnson et al., 2015; Waghorn et al., 2018) and is located ~130 km from the western margin of Svalbard on the northwestern flank of the ultraslow spreading Knipovich Ridge, south of the Molloy Transform Fault (MTF) (Figure F1). The sediment record at Svyatogor has been influenced by multiple factors: the locally complex tectonic history, the evolution of the West Spitsbergen Current (WSC), the regional ice sheet history, and the presence and migration of methane gas with likely biotic and abiotic sources (Waghorn et al., 2020). It has been hypothesized that the Svyatogor and Vestnesa Ridge sediment drifts had once been contiguous and similarly northwest–southeast oriented, with sedimentation controlled by the main branch of the WSC and additionally controlled by tectonic-related (MTF) bathymetry (Johnson et al., 2015). As posited by Johnson et al. (2015), sediment drift buildup at the Svyatogor Ridge south of the MTF was delayed compared to the Vestnesa Ridge and only started when sediment delivery increased with the intensification of the Northern Hemisphere glaciation and shelf-edge glaciation of the paleo-Svalbard–Barents Sea Ice Sheet (SBSIS). Over the past 2 My, tectonic offset along the MTF separated the Svyatogor and Vestnesa sediment drifts (Johnson et al., 2015). It was believed that the sediment cover across the Svyatogor Ridge once again became limited compared to Vestnesa because displacement along the MTF has moved the ridge farther away from the main north/northwestern path of the WSC (Johnson et al., 2015), which is controlling the sedimentation today. The MTF right-lateral offset also impacted the geometry of the Vestnesa Ridge by turning its main axes westward. According to Eiken and Hinz (1993), three main stratigraphic units provide the chronological constraints on the northwestern margin of Svalbard. Unit YP-1 is the oldest, and it is composed of syn- and postrift sediments lying directly on the oceanic crust after the opening of the Fram Strait occurred, at the earliest, during the Early Miocene (~17 Ma; Jakobsson et al., 2007; Ehlers and Jokat, 2013) or Late Miocene, at the latest (~10 Ma; Engen et al., 2008), creating an environment favorable for the onset of contour currents (Eiken and Hinz, 1993; Gebhardt et al., 2014). Unit YP2 contains the sedimentation associated with contour current deposition having a basal age between ~7 and 10 Ma (Eiken and Hinz 1993; Gebhardt et al, 2014), whereas Unit YP-3 comprises the deposition associated with the onset of glacially transported sediments like glaciomarine deposits and debris flows. Correlation with the cores drilled during Ocean Drilling Program (ODP) Leg 151 indicate a boundary age between Units YP-2 and YP-3 of ~2.7 Ma, corresponding to the intensification of the North Hemisphere glaciation (Geissler et al., 2011, Mattingsdal et al., 2014). Based on the supposition that the Svyatogor Ridge experienced its initial growth as a south-