Rainfall magnitude and seasonality are primary determinants of African savannas today, governing essential aspects of biomass production, such as primary productivity and the amount of tree cover. It remains unclear to what extent past seasonality differed from today, potentially accounting for differences in habitats and faunal diversity. Stable isotopes along with trace elements of the growth layers in bivalve shells provide valuable insights into paleoenvironmental conditions, including rainfall, river productivity, and water temperature. In this study, we analyzed stable oxygen and carbon isotopes in 11 fossil and three modern Etheria elliptica shells collected from the middle Atbara River in eastern Sudan. The fossil specimens are from sediments dated by optically stimulated luminescence (OSL) to between ∼ 224 and ∼ 17 ka in age. The δ18O values of fossil and modern shells are broadly similar, although the fossils are more enriched (−2.4 ‰ to 5.9 ‰ for fossils vs. −6.4 ‰ to 1.5 ‰ for modern shells), possibly indicating more evaporative and drier conditions during the Pleistocene. However, the Atbara River is today altered by dams, which might also explain the more depleted isotopic values in modern shells. δ13C values are broadly similar in fossil and modern shells, ranging from −14.1 ‰ to 4.5 ‰ in fossils and −16.9 ‰ to −9.6 ‰ in modern shells but show significant changes over time. Enriched δ13C values in Pleistocene shells may reflect lower atmospheric CO2 levels, while depleted values in modern shells align with post-industrial increases in CO2, although changes in catchment vegetation, weathering processes, or biological factors might also play a role. We also reconstructed the Atbara local meteoric water line (ALMWL) from seven river water samples. Results suggested that the Atbara River experiences low relative humidity compared to the global MWL. Moisture sources inferred from the ALMWL likely include the Indian Ocean, the Atlantic Ocean, and recycled moisture from continental input. These may have also supplied moisture during the Pleistocene, as fossil and modern shells exhibit comparable isotopic ranges. Our results overall indicate that a strong precipitation seasonality pattern has likely persisted in eastern Sudan since at least ∼ 200 ka.
The quality of the numerical age estimates used to establish the eruption chronology of a volcanic field is a critical control on the dependability of temporal hazard assessments. However, researchers involved in hazard assessment and modelling may be unfamiliar with dating methods and their complexities, which are needed to assess the quality of published ages. This paper aims to increase the awareness regarding the quality of geochronological data by providing brief introductions to the principles and applications of the dating methods applicable to Quaternary volcanism. The numerical dating methods included in this review are as follows: 40K / 40Ar and 40Ar / 39Ar dating, radiocarbon dating, uranium-series-related dating, cosmogenic nuclide exposure dating, and luminescence dating, as well as tephrostratigraphy and annual layer counting. First, the physical phenomena utilised by each method to provide age estimates are presented and then concerns related to the application of these methods are discussed, including necessary calibration steps and possible sources of error. This is followed by examples of the application of each of the methods.
The postglacial geological evolution of the southwestern Baltic Sea is marked by dynamic water level developments, accompanied by pronounced coastline displacements and associated changes in coastal geomorphological features. This study describes preserved remnants of paleo-landscapes in northeastern Mecklenburg Bay, dating to the period from the Baltic Ice Lake to the regression following the Ancylus Lake stage. The Late Pleistocene to Early Holocene geologic development of the area is reconstructed based on multibeam echo sounder, sidescan-sonar, and sediment echo sounder data; sediment core analysis; and visual seafloor imagery. The spatial distribution of Baltic Ice Lake deposits suggests a coastline at depths of 20 m below present sea level at the northeastern margin of Mecklenburg Bay during the Baltic Ice Lake's initial transgressive phase. The deposits are truncated by a regional erosional unconformity associated with the final regression following the Baltic Ice Lake highstand that marks the onset of lowstand conditions in the study area. A developing terrestrial environment was subsequently flooded by the Ancylus Lake. The Ancylus Lake highstand is constrained by peat and fine-grained limnic deposits in water depths of 19 m below present sea level. The acoustic data reveal a lacustrine environment throughout the Ancylus Lake stage until at least 10.2 ka cal BP. The regression at the end of the Ancylus Lake period is preserved by a northward-draining channel system cutting into Ancylus Lake sediments. The geometry of these channels suggests a water level drop of 6–7 m in northeastern Mecklenburg Bay, supporting a minor Ancylus Lake regression west of the Darss Sill. The findings provide insights into the water level development of a key threshold area in the southwestern Baltic Sea and therefore contribute to the reconstruction of the postglacial evolution of the entire Baltic Sea.
Sediments preserved in glacially overdeepened structures can provide a record of the regional Pleistocene glacial dynamics beyond the last glaciation. In order to unravel the glacial dynamics of the Isar-Loisach paleo-glacier, a cored sedimentary succession (ICDP-DOVE 5068_3_A) from an overdeepened basin near Schäftlarn, south of Munich, Germany, and an outcrop in its northern foreland (“Münchner Klettergarten” near Baierbrunn, on the southern margin of the Munich gravel plain, the “Münchner Schotterebene”) were investigated with a multi-method approach. This approach focused on single-grain feldspar luminescence dating to establish a chronological framework and on a comprehensive geophysical survey to better understand the morphology of the overdeepened basin. The Schäftlarn core is generally divided into a fine-grained basal section and a coarse-grained top section. The filling of the fine-grained basal section started in early Marine Isotope Stage (MIS) 8. The basal part of the overlying coarse-grained sediment can be attributed to late MIS 8. The “Münchner Klettergarten” outcrop to the north exhibited a similar depositional age dating to late MIS 8 and therefore corresponding to the basal part of the coarse-grained sediment in Schäftlarn. The geophysical survey revealed two cross-cutting glacial basins, with the MIS 8 basin being cut by a younger basin of undetermined age. Based on the luminescence dating results and the geophysical survey, a mid-Pleistocene landscape development model of the Isar-Loisach paleo-glacier region is presented.
Three phases of archaeological investigations have been conducted in the area of the City Museum of Novi Sad at the Petrovaradin Fortress. In this study, we summarize the results of geoarchaeological research carried out during the third phase of excavations inside the museum building. The investigated area covered 27 m2. The approximately 0.60 m thick loessic sequence offers a unique opportunity to reconstruct the environmental evolution of this area during the last glacial period. In sectors inside of the City Museum of Novi Sad, artefacts from the Upper Palaeolithic (Gravettian) were discovered. The analysed paleoenvironmental proxies (magnetic, geochemical, and colour proxies) largely indicate similarities with the uppermost three units of previously studied sections and with the Late Pleniglacial loess unit in nearby loess profiles in Petrovaradin and Mišeluk. This chronostratigraphic interpretation, suggesting that the profile most likely formed during the Marine Isotope Stage (MIS) 2 and possibly the youngest part of MIS 3, is supported by one radiocarbon date. The identified mollusc assemblages indicate relatively humid and cold environmental conditions in the upper part of the section. These results suggest that the northern slopes of Fruška Gora Mountain played an important environmental role during the Late Pleistocene. Up to 12 different mollusc species per sample were identified, favouring both steppe and forest-like vegetation. This environmental diversity, combined with favourable strategic factors, may have influenced the human occupation in the area.
