Stratigraphy of Late Cenozoic sediments of the western Chukchi Sea: New results from shallow drilling and seismic-reflection profiling

Abstract

The Quaternary history of Beringia and of the Arctic-Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14 C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution.

Source, Origin, and Spatial Distribution of Shallow Sediment Methane in the Chukchi Sea

“…We suggest that the reflector is relict seafloor permafrost that formed when sea level was much lower juxtaposed on a more modern layer of non-permafrost marine sediment. According to seismo-stratigraphic data reported in Gusev et al (2009), a similar seismic reflector was identified south of Wrangel Island and offshore the Chukotka Peninsula. This reflector is interpreted to be the Pleistocene-Holocene boundary on the basis of radiocarbon dating and borehole lithostratigraphy.…”

“…Study of sediment cores and seismic stratigraphy provide deposition patterns and sedimentation rates for the Chukchi Sea (Gusev et al, 2009(Gusev et al, , 2014. For the western part of this sea, Gusev et al (2009) report relatively high early Holocene sedimentation rates of several meters per thousand years, which are common for the early stages of flooding on the Arctic shelf (e.g., Stein et al, 2004).…”

“…For the western part of this sea, Gusev et al (2009) report relatively high early Holocene sedimentation rates of several meters per thousand years, which are common for the early stages of flooding on the Arctic shelf (e.g., Stein et al, 2004). Subsequently, deposition was greatly reduced to about one meter in ~9,000 years.…”

Toward a standard stratigraphical classification practice for the Baltic Sea sediments: the CUAL approach

“…), and Chukchi Sea (Gusev et al . ). Sediment units defined by unconformities are called unconformity‐bounded units in the International Stratigraphic Guide (Salvador ) and Lithuanian Stratigraphic Guide (Grigelis et al .…”

Mineralogy and geochemistry of ferromanganese oxide deposits from the Chukchi Sea in the Arctic Ocean

“…Chukchi Sea receives many sediment loads from the peripheral continental rivers, the Pacific inflow, and sea ice transport (Viscosi-Shirley, Pisias, and Mammone 2003;Eicken et al 2005). The thickness of sediments can reach 20 to 22 km (Gusev et al 2009). These geomorphic features are controlled by the graben rift system that started in the Mesozoic (Shipilov 1989;Shipilov and Senin 1992).…”