Seismic reflection surveys on the Lomonosov Ridge in regard to IODP Leg 377

Abstract

We present a regional seismic data set across the southeastern Lomonosov Ridge (LR) serving as pre-site survey for the upcoming drilling project IODP-377 (ArcOP). The overall goal of this drilling campaign is to recover a com¬plete stratigraphic sedimentary record of the southern ridge to meet the highest priority paleoceanographic objective, the continuous long-term Cenozoic climate history of the central Arctic Ocean. The seismic surveys provide basic information for the drilling, as the identification of undisturbed strata, location of slumps or hiatuses, depth-calculations of target reflectors, age estimations, and suggestions on the type of sedimentary rocks inferred from interval velocities of seismic units. On the LR the seismic lines confirm the presence of 1600 m thick, undisturbed, parallel sedimentary layers. 10 drilling locations can be proposed to recover the entire Miocene sedimentary sequence or even down to sediments of Lower Eocene age at about 900 mbsf. A prominent high-amplitude-reflector sequence (HARS) within the strata can be used to directly correlate to previous seismostratigraphic models for the eastern Arctic Ocean. Four major seismic units were identified which provide constraints on the coupled evolution of tectonic processes, palaeoceanography, and glaciation history of the Arctic Ocean. First, Mesozoic strata on the LR, its faulted flanks and the initial Amundsen Basin were covered with syn-rift sediments of Paleocene to early Eocene age. Numerous vertical faults indicate differential compaction of possibly anoxic sediments deposited in the young, still isolated Eurasian Basin. The second stage, as indicated by a prominent high-amplitude-reflector sequence covering the ridge, was a time of widespread changes in deposition conditions, likely controlled by the ongoing subsidence of the LR and gradual opening of the Fram Strait. Episodic incursions of water masses from the North Atlantic probably were the consequences and led to the deposition of thin sedimentary layers of different lithology. The third stage is marked by continuous deposition since the early Miocene. At that time, the ridge no longer posed an obstacle between the Amerasia and Eurasia Basins and pelagic sedimentation was established. Drift bodies, sediment waves, and erosional structures indicate the onset of circulation. Lastly, a sequence of high-amplitude reflectors marks the transition to the early Pliocene large-scale Northern Hemisphere glaciations. In a future step, the link of drilling data to the seismic net via synthetic seismograms shall enable a spatial extrapolation of findings, and serve to improve the seismostratigraphic models