Deglaciation and volcano-seismic activity in Northern Iceland: Holocene and early Eemian

The North Volcanic Zone of Iceland was unglaciated during most interglacials. Subsequently, the region was covered by the Weichselian ice cap. A widespread interglacial complex, the Sy?ra Formation, has been mapped in this zone. It covers probably O.I.S.5e, 5d and 5c. Its formation and preservation are discussed in terms of rift and volcanism activity, in interrelations with the former deglaciation. A topographic bulge, presumed of glacio-isostatic origin, limited the downstream drainage of the Jökulsa a Fjolum river enabling the interglacial sedimentation and the excavation of one of the canyons of Dettifoss. Effusive volcanic activity in the rift is important prior to the Sy?ra 4 unit in association with an early abrupt event (SY2: Sy?ra ash), related to a phreato-magmatic eruption at the eastern hyaloclastite ridge or from the Askja volcano and to jökulhlaup events. It corresponds probably to ash Zone B as defined by Sejrup et al., (1989) on the Northern Iceland shelf. The previous activity of hyaloclastite ridge is recorded during the Marine Isotope Stage 6 (MIS 6 = Saalian) and its deglaciation, a younger effusive event is dated at 80 ka. The Interglacial paleo-seismic region is similar to the present one; during deglaciation, the seismic zone is widened, up to 60 km to the East. Continuous micro-seismicity related to dyke intrusion and effusive or phreato-magmatic eruptions develop at the onset of deglaciation. It is discrete during the full interglacials, and most intense during pyroclastic eruptions. A comparison with the Late Glacial/Holocene deglaciation is provided in the same region.     

末次间冰期以来西宁市河谷沉积与环境

在西宁市区开展的钻探工作,获得了河谷平原区第四系的分布及沉积特征。通过对沉积厚度最大部位的2个钻孔岩芯的地层岩性、年代测试、孢粉组合及粒度分析等,探讨了西宁河谷平原区晚第四纪沉积与环境的关系。认为现今西宁市河谷平原内的主体沉积——低阶地沉积及上覆黄土堆积主要是末次间冰期旋回形成,在暖湿气候条件下沉积河流相砂砾石层,在干冷气候期接受风成黄土堆积,推测T3阶地形成于距今7.4万年前后气候由暖湿向干冷的过渡时期。     

贵州铜仁新元古界大塘坡组黄铁矿Re-Os同位素组成及意义

从贵州铜仁西溪堡矿区新元古界大塘坡组第一段“含锰岩系”中选取8件黄铁矿样品,对其进行了Re-Os同位素分析。结果表明其等时限年龄为(459±16)Ma,明显晚于间冰期大塘坡组的沉积时代（670～635 Ma）,表明该地区受加里东晚期的构造热事件影响。此次所分析的所有样品均具有高Re、低Os含量、高Re/Os比值及高187Os/188Os同位素比值,且187Os/188Os初始值为1.02±0.41,明显大于地幔特征值（0.12～0.13）,指示成矿物质来源于壳源。     

Glacial–interglacial changes in Subantarctic sea surface temperature and δO-water using foraminiferal Mg

Laboratory culturing experiments with living Globigerina bulloides indicate that Mg/Ca is primarily a function of seawater temperature and suggest that Mg/Ca of fossil specimens is an effective paleotemperature proxy. Using culturing results and a core-top Neogloboquadrina pachyderma calibration, we have estimated glacial–interglacial changes in sea surface temperature (SST) using planktonic Mg/Ca records from core RC11-120 in the Subantarctic Indian Ocean (43°S, 80°E) and core E11-2 in the Subantarctic Pacific Ocean (56°S, 115°W). Our results suggest that glacial SST was about 4°C cooler in the Subantarctic Indian Ocean and 2.5°C cooler in the Subantarctic Pacific. Comparison of SST and planktonic δ¹⁸O records indicates that changes in SST lead changes in δ¹⁸O by on average 1–3 kyr. The glacial–interglacial temperature change indicated by the Subantarctic Mg/Ca records suggests that temperature accounts for 40–60% of the foraminiferal δ¹⁸O change. We have used the Mg/Ca-based SST estimates and δ¹⁸O determinations to generate site-specific seawater δ¹⁸O records, which suggest that seawater δ¹⁸O was on average 1‰ more positive during glacial episodes compared with interglacial episodes.     

Geology,stratigraphy and palaeoenvironmental evolution of the Stephanorhinus kirchbergensis-bearing Quaternary palaeolake(s) of Gorzów Wielkopolski (NW Poland,Central Europe)

The sedimentary succession exposed in the Gorzów Wielkopolski area includes Eemian Interglacial (MIS 5e) or Early Weichselian (MIS 5d–e) deposits. The sedimentary sequence has been the object of intense interdisciplinary study, which has resulted in the identification of at least two palaeolake horizons. Both yielded fossil remains of large mammals, alongside pollen and plant macrofossils. All these proxies have been used to reconstruct the environmental conditions prevailing at the time of deposition, as well as to define the geological context and the biochronological position of the fauna. Optically stimulated luminescence dating of the glaciofluvial layers of the GS3 succession to 123.6 ± 10.1 (below the lower palaeolake) and 72.0 ± 5.2 ka (above the upper palaeolake) indicate that the site formed during the Middle–Late Pleistocene (MIS 6 – MIS 5). Radiocarbon-dating of the lacustrine organic matter revealed a tight cluster of Middle Pleniglacial Period (MIS 3) ages in the range of ~41–32 ka cal bp (Hengelo – Denekamp Interstadials). Holocene organic layers have also been found, with ¹⁴C ages within a range of 4330–4280 cal bp (Neolithic). Pollen and plant macrofossil records, together with sedimentological and geochemical data, confirm the dating to the Eemian Interglacial.     

Late Pleistocene lithostratigraphy and sequences in the southwestern Mesopotamia (Argentina): Evidences of the last interglacial stage

The aim of this paper is to show the stratigraphic record of the Late Pleistocene corresponding to the distal region of the Paraná River basin. It displays sedimentological, paleontological and geochronological evidences that characterise the last interglacial–glacial cycle. In particular, strong environmental records are shown for the Last Interglacial Stage (LIS). Salto Ander Egg Formation (SAEF) is defined as a new lithostratigraphic unit representative of the Late Pleistocene in southwestern Mesopotamia. This unit is formed of complex fluvial deposits, which contains a heterogeneous collection of sub-environments, of ages ranging from 120 to 60 ky BP. The clast-supported gravel facies containing sparse boulders indicate high flow during a humid climate. The large and middle-scale architectures of fluvial sedimentary bodies evidence the relationship between the sediment accommodation and the sea level oscillations. Three sub-sequences identified in the succession suggest a transgressive trend during the MIS5e, a highstand stage in MIS5c, and a minor transgressive cycle during MIS3. A Brazilian faunal association collected at the bottom of the sequence and sedimentological interpretations display wet and warm climatic conditions, typical of tropical or subtropical environments. Such environmental conditions are characteristic of the maximum of the last interglacial stage (MIS5e) and show a signal stronger than the signal of the current interglacial stage. All these data show a direct correlation between the increases of paleodischarges and the elevation of the sea level. The whole sequence is completed with transitional swampy deposits, accumulated probably during the MIS3/MIS2 transition, and the typical loess of the Tezanos Pinto Formation, mantled during the Last Maximum Glacial.     

A "critical" climatic evaluation of last interglacial (MIS 5e) records from the Norwegian Sea

Sediment cores from the Norwegian Sea were studied to evaluate interglacial climate conditions of the marine isotope stage 5e (MIS 5e). Using planktic forminiferal assemblages as the core method, a detailed picture of the evolution of surface water conditions was derived. According to our age model, a step-like deglaciation of the Saalian ice sheets is noted between ca. 135 and 124.5 Kya, but the deglaciation shows little response with regard to surface ocean warming. From then on, the rapidly increasing abundance of subpolar forminifers, concomitant with decreasing iceberg indicators, provides evidence for the development of interglacial conditions sensu stricto (5e- ss ), a period that lasted for about 9 Ky. As interpreted from the foraminiferal records, and supported by the other proxies, this interval of 5e- ss was in two parts: showing an early warm phase, but with a fresher, i.e., lower salinity, water mass, and a subsequent cooling phase that lasted until ca. 118.5 Kya. After this time, the climatic optimum with the most intense advection of Atlantic surface water masses occurred until ca. 116 Kya. A rapid transition with two notable climatic perturbations is observed subsequently during the glacial inception. Overall, the peak warmth of the last interglacial period occurred relatively late after deglaciation, and at no time did it reach the high warmth level of the early Holocene. This finding must be considered when using the last interglacial situation as an analogue model for enhanced meridional transfer of ocean heat to the Arctic, with the prospect of a future warmer climate.     

Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600 000 years

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by ⁴⁰Ar/³⁹Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations; (ii) varved clayey silts reflecting strong seasonality and an intralake oxic–anoxic boundary, for example, lake‐level highstands during interglacials/interstadials; (iii) CaCO₃‐rich banded sediments which are representative of a lowering of the oxic–anoxic boundary, for example, lake level decreases during glacial inceptions; (iv) CaCO₃‐poor banded and mottled clayey silts reflecting an oxic–anoxic boundary close to the sediment–water interface, for example, lake‐level lowstands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicating the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka bp . Although local environmental processes such as tectonic and volcanic activity influenced sedimentation, the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes, making Lake Van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years.     

A late Pleistocene long pollen record from Lake Urmia, NW Iran

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.