Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Abstract

Oscillations in ice sheet extent during early and middle Miocene are intermittently preserved in the sedimentary record from the Antarctic continental shelf, with widespread erosion occurring during major ice sheet advances, and open marine deposition during times of ice sheet retreat. Data from seismic reflection surveys and drill sites from Deep Sea Drilling Project Leg 28 and International Ocean Discovery Program Expedition 374, located across the present-day middle continental shelf of the central Ross Sea (Antarctica), indicate the presence of expanded early to middle Miocene sedimentary sections. These include the Miocene climate optimum (MCO ca. 17−14.6 Ma) and the middle Miocene climate transition (MMCT ca. 14.6−13.9 Ma). Here, we correlate drill core records, wireline logs and reflection seismic data to elucidate the depositional architecture of the continental shelf and reconstruct the evolution and variability of dynamic ice sheets in the Ross Sea during the Miocene. Drill-site data are used to constrain seismic isopach maps that document the evolution of different ice sheets and ice caps which influenced sedimentary processes in the Ross Sea through the early to middle Miocene. In the early Miocene, periods of localized advance of the ice margin are revealed by the formation of thick sediment wedges prograding into the basins. At this time, morainal bank complexes are distinguished along the basin margins suggesting sediment supply derived from marine-terminating glaciers. During the MCO, biosiliceous-bearing sediments are regionally mapped within the depocenters of the major sedimentary basin across the Ross Sea, indicative of widespread open marine deposition with reduced glacimarine influence. At the MMCT, a distinct erosive surface is interpreted as representing large-scale marine-based ice sheet advance over most of the Ross Sea paleo-continental shelf. The regional mapping of the seismic stratigraphic architecture and its correlation to drilling data indicate a regional transition through the Miocene from growth of ice caps and inland ice sheets with marine-terminating margins, to widespread marine-based ice sheets extending across the outer continental shelf in the Ross Sea.

A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude

“…Our data therefore reveal WAIS expansions across the Ross Sea continental shelf date back to at least 17.72 Ma, which is significantly earlier than previously suggested 12,13,23,24,39 . Advance of the WAIS into marine-based areas (i.e., regions grounded mainly below sea level) at 17.72-17.40 Ma is supported by a corresponding period of high sensitivity of the marine δ 18 O record to obliquity forcing (Fig.…”

“…Further evidence for WAIS expansion can be found in seismic data, which can trace the sediment package deposited at Site U1521 between 17.72 and 17.40 Ma (Sequence 2) across the Ross Sea continental shelf 23 . The sediment package, which is thicker towards the eastern Ross Sea (i.e., West Antarctica), contains glacial features including widespread progradational wedges and high relief morainal banks 20,21,23 . Coupled with the lithological and palynological evidence for ice proximity at Site U1521, this shows marine-terminating ice was present.…”

“…The mean erosion rate for the WAIS catchments draining to the Ross Sea between 17.72 and 17.40 Ma can be estimated using the volume of the corresponding seismic package east of Site U1521 23 .…”

“…However, ice proximal geological records have been hampered by poor recovery, unconformities, and/or influence from East Antarctica 9,10,11 . Seismic data suggest that significant volumes of lower Miocene glacimarine sediment exist around the West Antarctic margin 20,21,22,23 . However, seismic data require constraints from drilling to determine the age of the sediments, and to differentiate between detritus from continental-scale ice-sheet expansion and local ice caps on (paleo)topographic highs 22,23 .…”

Temperate Oligocene surface ocean conditions offshore of Cape Adare, Ross Sea, Antarctica

“…Samples with BIT index values >0.4 may be biased by soiland river-derived GDGTs (Bijl et al, 2013). However, we do note that the validity of this proxy for soil organic matter input is called into question now that it has become clear that branched GDGTs may also be produced in the marine realm (Peterse et al, 2009;Sinninghe Damsté, 2016) and in terrestrial ecosystems that contain crenarchaeol (Pearson et al, 2004). The methane index (Zhang et al, 2011) flags overprint by sedimentary methanogenic activity, the GDGT-2 / GDGT-3 ratio (Taylor et al, 2013) signals overprint by archaeal communities dwelling deeper into the water column, and the GDGT-0 / Crenarchaeol ratio (Blaga et al, 2009;Sinninghe Damsté et al, 2009;Taylor et al, 2013) flags overprint by in situ production of isoprenoidal GDGTs in lakes and rivers as well as contribution from Euryarchaeota.…”