Middle-upper quaternary deposits of the northern sector of the Patagonian continental slope contourite system (Southwestern Atlantic)

Lithological and micropaleontological (planktonic and benthic foraminifers, diatoms) studies in four sediment cores revealed major patterns of lithostratigraphy and biostratigraphy of contourites and gravitites in the uppermost sediment layer within the depth range 3500–4300 m of the northern sector of the Patagonian continental slope contourite system. It is ascertained that in conditions of low terrigenous material supply from the land and high, although variable bottom contour current velocities of waters of Antarctic origin, hemipelagic calcareous nanno-foraminiferal ooze deposited in the Holocene over middleupper Pleistocene contourites in the southern part of the study area (cores AI–2609, AI–2610). The Holocene calcareous surface layer is absent in the northern part of the study area (cores AI–2611, AI–2612). Middle-Upper contourites and gravitites are unevenly enriched in diatoms and radiolarians here, up to formation of slightly siliceous-terrigenous diatomaceous mud. Reworked Neogene foraminifers and diatoms evidence for erosion of Neogene deposits bottom currents and gravity flows.

Reliability of foraminiferal Na/Ca as a direct paleo-salinity proxy in various planktonic species from the eastern tropical North Atlantic

<p><span>Foraminiferal Na/Ca in planktonic and benthic foraminifers is a promising new method to assess directly past seawater salinities, which complements existing approaches (e.g., paired shell Mg/Ca and δ</span><sup><span>18</span></sup><span>O, shell Ba/Ca). Recent culture and field calibration studies have shown a significant positive relationship of Na incorporation into foraminiferal calcite shells with increasing salinity [1, 2], as confirmed by our culture study of <em>Trilobatus sacculifer </em>[3]. However, we note that the sensitivity of Na/Ca in response to salinity changes is species-specific and regional dependent, whereas temperature could be excluded as a secondary influencing factor [2, 3, 5]. Na/Ca values vary from 1–3 mmol/mol for the same salinity within and between foraminiferal species, suggesting a dominant biological control. </span></p><p><span>To further evaluate the robustness of Na/Ca for its application as a reliable proxy, we here examine possible secondary controls on foraminiferal Na/Ca with new data for commonly used species for paleoreconstructions (<em>Globigerinoides elongatus</em>, <em>G. ruber </em>(pink), <em>Orbulina universa</em>, <em>Globigerina bulloides</em>, <em>Neogloboquadrina dutertrei</em>) collected by plankton tows in the eastern tropical North Atlantic during R/V Meteor cruise M140. We performed laser ablation ICP-MS measurements on single foraminiferal shells from depth-resolved plankton tows in 20 m net-intervals from locations where salinity was essentially constant, </span>while seawater <span>pH and total alkalinity differed</span> by ~0.5 and 100 µmol/kg, respectively. Plankton tow samples <span>provide new insights </span>in<span>to </span>the <span>possible effects of </span>natural variations in <span>carbonate system parameters on Na incorporation into calcite tests with increasing water depth. The comparison of living foraminifers to sedimentary shells gives further information about the preservation state of Na/Ca in calcite shells over time, whereas fossil shells have mostly undergone gametogenesis during their life-time, or were affected post mortem by early diagenesis (sedimentation) processes. Those foraminifers were collected from surface sediments (M65-1) located in proximity to plankton tows. Our results show that all measured species, either from plankton tows or buried in the sediment, are within the Na/Ca range of previous studies [1-5], which increases the confidence for a robust Na/Ca to salinity proxy. However, the offset of ~2-5 mmol/mol between living foraminifers collected in surface waters (0-20 m) and fossil assemblages of the same species could be related to spine loss at the end of a foraminiferal life cycle [4]. In addition, the usage of inconsistent test sizes could further influence the foraminiferal Na/Ca signal. Our results reveal significant (R = </span><span>-</span><span>0.97, <em>p</em><0.03</span><span>) decreasing Na/Ca values with increasing test sizes between </span><span>180-250 µm </span><span>for <em>G. ruber </em>(pink, white), <em>N. dutertei </em>and <em>T. sacculifer</em>, whereas values increase again with larger size classes >355 µm (R = 0.87, <em>p</em><0.02).</span><span> </span></p><p><span>[1] Wit et al. (2013) Biogeosciences <strong>10</strong>, 6375-6387. [2] Mezger et al. (2016) Paleoceanography <strong>31</strong>, 1562-1582. [3] Bertlich et al. (2018) Biogeosciences </span><strong>15</strong>, 5991–6018.<span>[4] Mezger et al. (2019) Biogeosciences <strong>16</strong>, 1147-1165, 2019. [5] Allen et al. (2016) Geochim. Cosmochim. Acta <strong>193</strong>, 197-221.</span></p>

Biostratigraphy and paleoecology of the Burdigalian-Serravallian sediments in Wadi Sudr (Gulf of Suez, Egypt): comparison with the Central Paratethys evolution

Biostratigraphy and paleoecology of the Burdigalian-Serravallian sediments in Wadi Sudr (Gulf of Suez, Egypt): comparison with the Central Paratethys evolutionTwo main Miocene facies were recorded in the Gulf of Suez area: a deep marine and a coastal facies. The analysed sections in the Wadi Sudr area belong to the marine facies. The Lower Miocene (Burdigalian) is represented by coastal, shallow marine sediments, rich in coral, algae, gastropods and large pectinids followed by Langhian open marine sediments and Serravallian lagoonal carbonates. The open marine sediments contain well preserved planktonic and benthic foraminifers and abundant ostracods. The parts of the sections containing foraminifers have been correlated with three planktonic foraminiferal zones (Praeorbulina glomerosa Zone, Orbulina ZoneandGloborotalia praemenardii-Globorotalia peripherorondaZone). Two benthic ecozones were defined (Heterolepa dutemplei-Laevidentalina elegans ZoneandBolivina compressa-Elphidiumspp. Zone). Two cycles of sea-level changes can be distinguished and correlated with global sea-level cycles Bur5/Lan1 and Ser1. The first (Langhian) cycle culminated in open marine sublittoral to upper bathyal well aerated sediments. The second (Serravallian) cycle was shallower, littoral suboxic sediments were overlaid by euryhaline carbonates. The studied foraminifera-bearing sediments can be correlated with the lower and Middle Badenian of the Central Paratethys. Though the area of the Gulf of Suez and the Central Paratethys were situated in different climatic zones, and influenced by different tectonic events, the main paleoenvironmental events (sea-level changes, oxygen decrease, salinity changes) are comparable. This correspondence shows that the decisive factors triggering these events were global climatic events.