The new key sections of the Last Interglacial transgression in the Eurasian Arctic (Eastern White Sea): paleoenvironmental reconstructions and interregional correlations

Abstract

New stratigraphic, micropaleontological and geochronometric (optically stimulated luminescence, OSL) data for the basal sediment units of the six sections around the periphery of the Kuloi Plateau (Zimnii Coast and Soyana-Kuloi River valley) assign them to the end of MIS 6 – MIS 5 Boreal (Eemian) transgression in the eastern White Sea Region. Most of the studied Boreal marine beds are composed of two units, with the dark grey fossiliferous silty clay overlain by beige and light grey loose (sand and gravel) variously bedded material. Presumably high sedimentation rates due to the proximity to the Kuloi Plateau resulted in the low total abundance of microfossils and their relatively monotonous taxonomic composition. Benthic foraminifers display almost equal proportions and coexistence of ecologically different groups occurring in the Arctic shelf seas, from shallow inner shelf inhabitants to relatively deep-water ones. Rare ostracods are represented by typical dwellers of the Arctic mid-outer shelf areas. Similar to benthic foraminifers, dinocysts show a mixture of heterotrophic, including cryophilic, and autotrophic forms. The constant presence of freshwater green algae points to river runoff influence. Findings of rare polar and subpolar planktonic foraminifers together with benthic foraminifer species Cassidulina neoteretis allow assuming periodical inflows of subsurface Atlantic-derived water. Altogether, this gives evidence for an Arctic-type marine basin likely corresponding to the early stage of the transgression probably including the local highstand prior to regression. The age assignment of these beds is supported by OSL dates from overlying sandy layers generally ranging between 140 and 87 ka, with possibly older (MIS 7) age in one of the Zimnii Coast sections.

The cross-correlation through the Northern Eurasia enables us to state that the common characteristic of the Last Interglacial (LIG) marine sedimentary succession is its two-unit structure. The lower unit corresponds to the early stage of inundation, the upper indicates the littoral sedimentary setting during the stillstand and regressive stage. The substantial range of available dates from 160 to 80 ka, encompassing the end of the MIS 6 glaciation, its degradation, and part of the MIS 5 stage, precludes precise determination of the duration of the Boreal transgression.

The “gap” in the occurrence of the LIG marine deposits in the northeastern Eurasia along the Laptev and western East Siberian coasts might be related to the formation and existence of the glacioisostatic forebulge at the periphery of the MIS 6 ice sheets in combination with local neotectonic movements.