Changes in sediment source areas to the Amerasia Basin, Arctic Ocean, over the past 5.5 million years based on radiogenic isotopes (Sr, Nd, Pb) of detritus from ferromanganese crusts

Ferromanganese (FeMn) crusts provide a useful paleoenvironmental archive for studying the poorly understood climatic, oceanographic, and geologic evolution of the Arctic Ocean. This study is based on the identification and temporal reconstruction of sources and inferred transport pathways of terrigenous material in FeMn crusts collected from several sites across the Amerasia Basin. Samples from the Alpha Ridge (AR), Mendeleev Ridge (MR), and Chukchi Borderland (CB) have similar chemical compositions and high detrital contents. Sr, Nd, and Pb isotopic compositions of the terrigenous detritus extracted from the FeMn crust layers show spatial and temporal variability due to the variable proportions of inputs from the North American and East Siberian margins and local submarine outcrops. The temporal resolution is restricted by macroscopic crust layers, which represent times of significant changes in the depositional environment and are used to study first-order environmental changes. During the period of ca. 4.4 to 3.8 Myr ago, detritus in the MR area was derived mostly from the Laptev Sea. Then, until about 1.3 Myr ago, FeMn crusts from MR received a higher volcanic component sourced from the East Siberian Sea, with mixing of detritus from the Okhotsk-Chukotka volcanic belt (OCVB) area and possibly weathering of local MR outcrops, which is mostly High Arctic Large Igneous Province (HALIP) rocks. The period from about 1.3 Myr ago to the present reflects enhanced contributions of detritus from the Canadian Shield, approximately equal to the East Siberian contribution for the MR area. CB crusts show three main periods of distinct detrital input. During the period ca. 5.5–5.0 Myr ago, CB detritus was sourced from local submarine outcrops of the Jurassic-Cretaceous HALIP rocks and possibly from northeast Siberia, including OCVB rocks, while during the period from about 5.0 to 3.6 Myr ago, the CB FeMn crusts had a much greater input of detritus from the North American margin. After 3.6 Myr ago, the CB detritus shows a mixed composition predominantly sourced from North America with some material transported from the Bering Sea and smaller contributions from northeast Siberia. The AR crust was influenced mostly by detritus sourced from the Canadian Shield.