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Based on complex study, including seismoacoustic profiling,
paleomagnetic, lithological, biostratigraphic, radiocarbon and organo-geochemical
investigations, the reconstruction of Late Cenozoic sedimentation of the
Chukchi
Sea
shelf was implemented. VNIIOkeangeologia carried out shallow drill coring southern the
Wrangel Island
in 2006. According to
seismoacoustic and lithology-mineralogy data could be marked out two
seismostratigraphic units - Upper Pleistocene – Holocene and
Eopleistocene – Pliocene, with a distinct unconformity between. Upper
Pleistocene – Holocene is represented by fine marine silts and clays
with mollusk shells and rare small pebbles. The Eopleistocene – Pliocene
complex is built of sand and sandy silt with pebble and gravel and
numerous fragments of burnt lumber. Paleomagnetic study confirms
two-layer structure of sediment core. We refer upper part to the Brunhes
epoch, the lower one (a reverse magnetization zone) likely corresponds
to the Matuyama orthozone. Spore and pollen spectra from boreholes show
that the upper part of the profile was formed when a forest-tundra and
tundra vegetation occupied the considered territory. The lower part of
the profile is believed to have formed, when the deposition area was
occupied by relatively warm-loving coniferous and broadleaf species. The
microfauna analysis of samples from Upper Pleistocene – Holocene
deposits show the predominance of
Arctic
and Arctic-Boreal species, typical for modern Arctic seas, and redeposited
shells of extinct Neogene species. In Eopleistocene – Pliocene deposits
the fresh water microfauna is observed. The organic matter (
OM
) characteristics of the upper part of deposits profile corresponds to
background values for modern terrigenous-marine Holocene deposits of the
Arctic shelf (organic carbon – 0,5-0,9%, carbonate carbon <0,1%).
OM
soars up (organic carbon >3%) in the lower part of the profile, changes
it’s molecular and group composition. And the presence of hydrocarbon
biomarkers testifies to sedimentation in continental shallow basins with
considerable income of humus organics.
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