No abstract

Onset of rifting, andflooding by marine waters, occurred in the late Oligocene in the G u y of Aden and southern Red Sea. The northern part o f t h e Red Sea may have been a largely continental rift at this initial stage, but continued rifting established marine conditions throughout the system by the early Miocene. Episodic isolation of the Red Sea system, leading to evaporite deposition in some basins, commenced in the mid-Miocene and over two kilometres of salt had accumulated in most Red Sea basins by the end ofthe Miocene.Re-esta blish men t of persistentlym arin e conditions occurred in the Pliocene, and m arin e recharge is now sufficiently high to permit vigorous carbonate build-ups in shallow-water areas.elastic sediment textures suggest that marginal escarpments, which jirst developed during the onset ofrifting, were strongly uplifted in the Pliocene-to-Recent period. Subsidence of basin floors seems to have been particularly rapid during the period dominated by salt deposition. I f eruption of sea-floor basalts in the axial r$ areas is excluded, volumetrically important volcanism is centred on the present Afar triangle area, and is confined to the Oligocene and early Miocene. The amount of contemporary volcanic dkbris in the sandstones is consequently not particularly high. Some sandstones in northern Ethiopia, Sudan and Egypt do contain abundant acidic volcanic clasts, but these are derived from the Proterozoic basement and cause less diagenetic reservoir damage than contemporary glassy volcanic ash.Sandstones deposited in freely-drained alluvial fan settings are characterised by early diagenetic kaolinite, whereas those of sabkha and marginal-marine settings tend to show relatively early diagenetic chlorite. Those alluvial fan sandstones which were subsequently invaded by reduced pore waters espelled~from the basin axis, and those in the basin axis, ojen developed later diagmetic chlorite.

<p>IODP Expedition 379 to the Amundsen Sea continental rise recovered latest Miocene-Holocene sediments from two sites on a drift in water depths >3900m. Sediments are dominated by clay and silty clay with coarser-grained intervals and ice-rafted detritus (IRD) (Gohl et al. 2021, doi:10.14379/iodp.proc.379.2021). Cobble-sized dropstones appear as fall-in, in cores recovered from sediments >5.3 Ma.  We consider that abundant IRD and the sparse dropstones melted out of icebergs formed due to Antarctic ice-sheet calving events. We are using petrological and age characteristics of the clasts from the Exp379 sites to fingerprint their bedrock provenance. The results may aid in reconstruction of past changes in icesheet extent and extend knowledge of subglacial bedrock.</p><p>Mapped onshore geology shows pronounced distinctions in bedrock age between tectonic provinces of West or East Antarctica (e.g. Cox et al. 2020, doi:10.21420/7SH7-6K05; Jordan et al. 2020, doi.org/10.1038/s43017-019-0013-6). This allows us to use geochronology and thermochronology of rock clasts and minerals for tracing their provenance, and ascertain whether IRD deposited at IODP379 drillsites originated from proximal or distal Antarctic sources. We here report zircon and apatite U-Pb dates from four sand samples and five dropstones taken from latest Miocene, early Pliocene, and Plio-Pleistocene-boundary sediments. Additional Hf isotope data, and apatite fission track and <sup>40</sup>Ar/<sup>39</sup>Ar Kfeldspar ages for some of the same samples help to strengthen provenance interpretations.</p><p>The study revealed three distinct zircon age populations at ca. 100, 175, and 250 Ma. Using Kolmogorov-Smirnov (K-S) statistical tests to compare our new igneous and detrital zircon (DZ) U-Pb results with previously published data, we found strong similarities to West Antarctic bedrock, but low correspondence to prospective sources in East Antarctica, implying a role for icebergs calved from the West Antarctic Ice Sheet (WAIS). The ~100 Ma age resembles plutonic ages from Marie Byrd Land and islands in Pine Island Bay.  The ~250 and 175 Ma populations match published mineral dates from shelf sediments in the eastern Amundsen Sea Embayment as well as granite ages from the Antarctic Peninsula and the Ellsworth-Whitmore Mountains (EWM). The different derivation of coarse sediment sources requires changes in iceberg origin through the latest Miocene, early Pliocene, and Plio/Pleistocene, likely the result of changes in WAIS extent.</p><p>One unique dropstone recovered from Exp379 Site U1533B is green quartz arenite, which yielded mostly 500-625 Ma detrital zircons. In visual appearance and dominant U-Pb age population, it resembles a sandstone dropstone recovered from Exp382 Site U1536 in the Scotia Sea (Hemming et al. 2020, https://gsa.confex.com/gsa/2020AM/meetingapp.cgi/Paper/357276). K-S tests yield high values (P ≥ 0.6), suggesting a common provenance for both dropstones recovered from late Miocene to Pliocene sediments, despite the 3270 km distance separating the sites. Comparisons to published data, in progress, narrow the group of potential on-land sources to exposures in the EWM or isolated ranges at far south latitudes in the Antarctic interior.  If both dropstones originated from the same source area, they could signify dramatic shifts in the WAIS grounding line position, and the possibility of the periodic opening of a seaway connecting the Amundsen and Weddell Seas.</p>

International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea's "Iceberg Alley" recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well-resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. In this presentation, we discuss the alternation of warmer (diatom-rich) versus cooler (silty clays) Dove Basin lithologies in comparison to the LR04 benthic δ 18 O stack using an ensemble of possible age models constrained by the magnetic reversals. To account for limitation in the age model resolution, we begin by comparing the amplitude modulation of the eccentricity, obliquity, and precession frequency bands for different age-depth model possibilities. Then we compare the position of the magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ 18 O at North Atlantic IODP Site U1308. Finally, to establish a higher resolution age model in the latest Pliocene and early Pleistocene, we explore the possibility of interhemispheric stratigraphic correlation between North Atlantic IODP sites and Dove Basin using Relative Paleointensity (RPI). We demonstrate Dove Basin facies change at different times than benthic δ 18 O during intervals between ~3-1 Ma. These differences are consistent with precession phase shifts and suggests climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession variations not captured in benthic δ 18 O during the 41-kyr world.