Bedrock cores from 89° North: Implications for the geologic framework and Neogene paleoceanography of Lomonosov Ridge and a tie to the Barents shelf

Two piston cores from the Eurasian flank of Lomonosov Ridge near lat 88.9°N, long 140°E provide the first samples of bedrock from this high-standing trans-Arctic ridge. Core 94-PC27 sampled nonmarine siltstone similar in facies and age to uppermost Triassic to lower Lower Jurassic and mid– Lower Cretaceous beds in the 4 to > 5 km Mesozoic section on Franz Josef Land, on the outer Barents shelf. A ca. 250 Ma peak in the cumulative frequency curve of detrital zircons from the siltstone, dated by U- Th-Pb analysis, suggests a source in the post-tectonic syenites of northern Taymyr and nearby islands in the Kara Sea. Textural trends reported in the literature indicate that the Lower Jurassic nonmarine strata of Franz Josef Land coarsen to the southeast; this suggests the existence of a sedimentary system in which detrital zircons could be transported from the northern Taymyr Peninsula to the outer Barents shelf near the position of core 94-PC27 prior to opening of the Eurasia Basin. Correlation of the coaly siltstone in core 94-PC27 with part of the Mesozoic section on Franz Josef Land is compatible with the strong evidence from seafloor magnetic anomalies and bathymetry that Lomonosov Ridge is a continental fragment rifted from the Barents shelf during the Cenozoic. It also suggests that Lomonosov Ridge near the North Pole is underlain by a substantial section of unmetamorphosed Mesozoic marine and nonmarine sedimentary strata.

Core 94-PC29 sampled cyclical deposits containing ice-rafted debris (IRD) overlying weakly consolidated laminated olive-black anoxic Neogene siltstone and mudstone with an average total organic carbon (TOC) of 4.1 wt%. The high TOC content of the mudstone indicates that during the Neogene, prior to the introduction of IRD into the Arctic seas about 3.3 Ma (early late Pliocene), the shallow waters of the central Arctic Ocean supported significant primary photosynthetic organic production near the North Pole. These deposits also contain fine grains of siltstone that resemble the breccia-clast siltstone of core 94-PC27 and reworked Carboniferous, Cretaceous, and Tertiary palynomorphs that may have also originated in the bedrock of Lomonosov Ridge.