Molecular Geochemistry of the Dispersed Organic Matter in the Late Cenozoic Sediments of the Laptev Sea Continental Margin and Adjacent Part of the Arctic Ocean

––The main factors controlling the bulk sedimentation in the Siberian segment of the Lomonosov Ridge (axial part and western slope) and the Laptev Sea continental margin during the late Cenozoic were studied using a complex of geomorphological, lithological, and organic geochemical data. Samples for the study were collected during the cruises of R/V Akademik Fedorov in 2005 and 2007 and nuclear icebreaker Rossiya in 2007. Analysis of the group and molecular composition of the dispersed organic matter (DOM) in bottom sediments has shown that the input of terrigenous sediments enriched in the products of abrasion of lithified rocks determines sedimentation process on the continental slope of the Laptev Sea and in the Amundsen Basin. The individual characteristics of the DOM of the late Cenozoic sediments from the Lomonosov Ridge reflect the wide diversity of sedimentary sources and depositional environments. Subaqueous erosion of edaphogenic products and pre-Holocene sediments plays an important part in sedimentation together with terrigenous flow and ice transport.

On tectonic-geodynamic relationships of the Eurasian basin and the Lomonosov Ridge with the continental margin of Siberia according to new seismic data

Basing on the results of the interpretation of new seismic materials, the authors consider the structural features of the southern segments of the Eurasian Basin and the Lomonosov Ridge in the zone of junction with the continental margin of Siberia (the Laptev and East Siberian Seas). Interpretative analysis of the materials shows that the base of the sedimentary cover of the southern segment of the Eurasian Basin, where there are no regular linear magnetic anomalies, is predominantly represented by strongly stretched blocks of the continental basement. The formation the axial zone of spreading of the Gakkel Ridge here took place according to a three-stage development scheme: rifting in the Aptian-Alba and its telescoping development in the Late Cretaceous — Paleocene-Eocene, inherited valley formation in late neotectonic time. The development of the Severny Basin located in the zone of junction of the Lomonosov Ridge with the continental margin is similar to the scenario for the formation of pull-apart basins. Its formation was interconnected with the simultaneously opening adjacent extreme southeastern segment of the Amundsen Basin of the Eurasian Basin.

Late Paleocene–early Eocene Arctic Ocean sea surface temperatures: reassessing biomarker paleothermometry at Lomonosov Ridge

A series of papers published shortly after the Integrated Ocean Drilling Program Arctic Coring Expedition (ACEX, 2004) on Lomonosov Ridge indicated remarkably high early Eocene sea surface temperatures (SSTs; ca. 23 to 27 ∘C) and land air temperatures (ca. 17 to 25 ∘C) based on the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether (isoGDGT and brGDGT) lipids, respectively. Here, we revisit these results using recent analytical developments – which have led to improved temperature calibrations and the discovery of new temperature-sensitive glycerol monoalkyl glycerol tetraethers (GMGTs) – and currently available proxy constraints. The isoGDGT assemblages support temperature as the dominant variable controlling TEX86 values for most samples. However, contributions of isoGDGTs from land, which we characterize in detail, complicate TEX86 paleothermometry in the late Paleocene and part of the interval between the Paleocene–Eocene Thermal Maximum (PETM; ∼ 56 Ma) and the Eocene Thermal Maximum 2 (ETM2; ∼ 54 Ma). Background early Eocene SSTs generally exceeded 20 ∘C, with peak warmth during the PETM (∼ 26 ∘C) and ETM2 (∼ 27 ∘C). We find abundant branched GMGTs, likely dominantly marine in origin, and their distribution responds to environmental change. Further modern work is required to test to what extent temperature and other environmental factors determine their distribution. Published Arctic vegetation reconstructions indicate coldest-month mean continental air temperatures of 6–13 ∘C, which reinforces the question of whether TEX86-derived SSTs in the Paleogene Arctic are skewed towards the summer season. The exact meaning of TEX86 in the Paleogene Arctic thus remains a fundamental issue, and it is one that limits our assessment of the performance of fully coupled climate models under greenhouse conditions.