Continental shelves as detrital mixers: U–Pb and Lu–Hf detrital zircon provenance of the Pleistocene–Holocene Bering Sea and its margins

Abstract

Continental shelves serve as critical transfer zones in sediment routing systems, linking the terrestrial erosional and deep-water depositional domains. The degree to which clastic sediment is mixed and homogenised during transfer across broad shelves has important implications for understanding deep sea detrital records. Wide continental shelves are thought to act as capacitors characterised by transient sediment storage during sea-level rise and sediment remobilisation during sea-level fall. This study attempts to test the hypothesis that sea-level lowstand yields more efficient and direct sediment transfer from fluvial sources to deep sea sinks compared to highstand when sediment is sequestered and mixed on the shelf. This hypothesis is tested by evaluating U–Pb and Lu–Hf detrital zircon provenance trends along the vast Bering Sea shelf and deep-marine Beringian continental margin. Presented here are 5884 U–Pb ages and 402 Lu–Hf analyses from 30 samples to characterise the provenance of modern to Pleistocene sediment across the Bering Sea region. Both forward and inverse numerical mixture modelling was used to estimate the abundance of distinct fluvial sources in shelfal and deep-water deposits. These results demonstrate that sediment in the Bering Sea is derived from a mixture of regional fluvial sources, but that the Yukon River is the primary detrital source for sediment throughout the region. Although Yukon River signatures are abundant in all basin samples, the relative proportions of Yukon River versus other sources vary spatially across the shelf. A comparison of Holocene and surficial sediment with Pleistocene deposits shows that sediment across the shelf and in the deep sea remains well-mixed between climate states. Thus, detrital provenance signatures in deep-marine deposits outward of broad transfer zones are likely to represent mixtures of fluvial sources regardless of sea level.