Quartz grain microtextures illuminate Pliocene periglacial sand fluxes on the Antarctic continental margin

Abstract

On high‐latitude continental margins sediment is supplied from land to the deep sea through a variety of processes, including iceberg and sea‐ice rafting, and bottom current transport. The accurate reconstruction of sediment fluxes from these sources through time is important in palaeoclimate reconstructions. The goal of this study was to assess a shift in the intensity of glacial processes, iceberg and sea‐ice rafting during the Pliocene through an investigation of coarse sediment deposited at the AND‐2A site in the Ross Sea and at International Ocean Discovery Program Site U1359 on the Antarctic continental rise. Terrigenous particle‐size distributions and suites of quartz grain microtextures in the sand fraction of the deep‐sea sediments were compared to those from Antarctic glaciomarine diamictites as a baseline for proximal glacial sediment in its source area. Using images acquired through Scanning Electron Microscopy, and following a quantitative approach, fewer immature and potentially glacially transported grains were found in Pliocene deep‐sea sand fractions than in ice‐contact sediments. Specifically, in the lower Pliocene interval silt and fine sand percentages are elevated, and microtextures in at least half of the sand fraction are inconsistent with a primary glacial origin. Larger numbers of chemically altered and abraded grains in the deep‐sea sand fraction, along with microtextures that are diagnostic of periglacial environments, suggest a role for eolian sediment transport. These results highlight the anomalous nature of high‐latitude sediment fluxes during prolonged periods of ice retreat. Furthermore, the identification of a significant offshore sediment flux during Antarctic deglaciation has implications for estimated nutrient supply to the Southern Ocean and the potential for high‐latitude climate feedbacks under warmer climate states.

Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa

“…It would be exceptional if no grain from any diamicitite sampled showed evidence of glaciation. Surface microtextures can be different or change, if transported with water, in periglacial areas, or if all samples are from supraglacial/englacial sediments, but there was no evidence of such environments from surface microtextures or macrotextures in the Dwyka Group diamictites (Mahaney, 2002;Molén, 2014Molén, , 2017Kalińska-Nartiša et al, 2017;Kut et al, 2021;Passchier et al, 2021;Górska et al, 2022;Kalińska et al, 2022). All diamictite samples are compressed and they do not show geological features of any other environments than those that would be interpreted as tills or debrites.…”

A Comparison of Methods for Identifying and Quantifying Ice Rafted Debris on the Antarctic Margin

“…Another key uncertainty in this method is the assumption that %CS 125μm–2 mm does not require correction for other non‐IRD fraction. We discuss the possibility of other processes influencing this size fraction above, but volcanic ash, diagenetic minerals and other non‐IRD particles could be present, and independent methods will be required to determine if these are present in a sediment population (Passchier et al., 2021). It could be argued this is also the case for x‐radiograph based methods, although the 2 mm cut‐off for defining an IRD grain means visual examination of the core face is likely to be sufficient for a trained operator to identify diagenetic grains and particles delivered by volcanic eruptive processes.…”

“…However, this alone does not confirm that a grain is rafted by either an iceberg or sea ice to the site, as a glacial erosion signature is likely to be pervasive on the Antarctic continental margin as this is the predominant mechanism for physical weathering of sediment. Similarly, well‐rounded grain shapes have been used in some settings to distinguish grains that have been potentially wind‐blown onto sea ice and subsequently transported offshore (Passchier et al., 2021). However, such rounding could also be inherited from non‐glacial strata that have been eroded and deposited within sub‐glacially deposited diamictites.…”

Unraveling the Deep‐Sea Sedimentary Record of Ice Sheet History

“…Passchier et al. (2021) combined SEM quartz microtextures with grain size data to document a significant component of Pliocene sand collected at IODP Site U1359 off of the Wilkes Land margin included periglacial grains, suggesting eolian rather than a glacial source. Sand‐sized biogenic components such as foraminifera associated with IRD provided insight into the tidewater glacial cycle in the Gulf of Alaska (Cowan et al., 2020) and the opportunity to develop a high‐resolution chronology for the Antarctica Peninsula drifts (Hillenbrand et al., 2021).…”

“…For example, imaging of quartz sand grains in IRD with the scanning electron microscope (SEM) have shown distinctive characteristics indicative of sea ice rather than glacier transport (i.e., icebergs) in areas under sea ice influence (St John et al, 2015) or changes in ice sheet thickness in iceberg source regions (Cowan et al, 2008). Passchier et al (2021) combined SEM quartz microtextures with grain size data to document a significant component of Pliocene sand collected at IODP Site U1359 off of the Wilkes Land margin included periglacial grains, suggesting eolian rather than a glacial source. Sand-sized biogenic components such as foraminifera associated with IRD provided insight into the tidewater glacial cycle in the Gulf of Alaska (Cowan et al, 2020) and the opportunity to develop a high-resolution chronology for the Antarctica Peninsula drifts (Hillenbrand et al, 2021).…”