Geochronology of the southern Baltic Sea sediments derived from 210Pb dating Publication date: March 2020 Source: Quaternary Geochronology, Volume 56 Author(s): Tamara Zalewska, Paweł Przygrodzki, Maria Suplińska, Michał Saniewski Abstract Based on the vertical distribution of 210Pb activity concentrations in bottom sediment, linear accumulation rates (LAR) and mass accumulation rates (MAR) were determined for 31 locations in the southern Baltic Sea region by applying models: Constant Flux Constant Sedimentation Rate (CF:CS) and Constant Rate of Supply (CRS). The dating of sediment layers in selected locations was also carried out. The reliability of the results was verified using radiotracers: 137Cs and, for the first time, 90Sr. The results obtained were the basis for the development of maps of continuous distributions of LAR and MAR values in the areas where a particular type of bottom sediments were found: silt-clay, sandy silt, silty sand and mixtites covering the region of the southern Baltic. The maps constitute a tool supporting basic and applied research. Data for marine open areas were supplemented with sediment accumulation rate data for the areas of the Szczecin Lagoon and the Vistula Lagoon. The linear accumulation rates of bottom sediments of the southern Baltic varied from 0.61 to 3.54 mm y−1 while mass accumulation rates ranged from 390 g m−2 y−1 to 910 g m−2 y−1, largely reflecting the LAR values.

Chronostratigraphy, depositional patterns and climatic imprints in Lake Acigöl (SW Anatolia) during the Quaternary Publication date: March 2020 Source: Quaternary Geochronology, Volume 56 Author(s): François Demory, Claire Rambeau, Anne-Elisabeth Lebatard, Mireille Perrin, Syed Blawal, Valérie Andrieu-Ponel, Pierre Rochette, Hülya Alçiçek, Nicolas Boulbes, Didier Bourlès, Cahit Helvaci, Rainer Petschick, Serdar Mayda, Anne-Marie Moigne, Sébastien Nomade, Philippe Ponel, Amélie Vialet, Mehmet Cihat Alçiçek, Georges Aumaître, Karim Keddadouche Abstract A 601 m long sedimentary sequence was drilled in Lake Acigöl, located in the lakes region of SW Anatolia, near the Denizli travertine from which the oldest hominin of Turkey was unearthed. Among all dating methods applied to the sedimentary sequence, paleomagnetism, through the recognition of geomagnetic chrons, was the most successful and led to a quasi linear age model, with the 601 m long sedimentary record covering the last 2.3 Ma. An attempt to use the atmospherically deposited 10Be as a dating method was not very successful but provides interesting clues on this new method. Long-term lake level changes are depicted through lithological variations, in particular the carbonates and evaporites abundance. This change could be influenced by both long term cooling during the last 2 Ma and tectonic activity, which may in particular be responsible for a maximum water depth at around 1.8 Ma. Despite active tectonic influence, the sedimentary facies description and the magnetic susceptibility record (cleaned from tephra intervals) show that climate fluctuations (i.e., glacial-interglacial alternations) are likely recorded in the sedimentary succession, with warm periods marked by enhanced carbonate precipitation and cold and dry periods characterized by more detrital input linked to reduced vegetation cover and consequently more erosion in the catchment area. Preliminary pollen data, used to interpret magnetic susceptibility fluctuations, show that an average dry and open landscape prevailed around Acigöl lake during the whole record.

Using in situ-produced 10Be to constrain the age of the latest surface-rupturing earthquake along the Middle Kedrovaya fault (Baikal rift) Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): Oksana Lunina, Dewen Li, Yanwu Lyu, Youpeng Wang, Ming Li, Yu Gao, Andrei Gladkov, Ivan Denisenko, Anton Gladkov, Keqiang Wang, Shimin Zhang, Dmitrii Perevoznikov Abstract The 30-km-long Middle Kedrovaya (MK) fault, on the northwestern flank of Lake Baikal, is one of the most impressive late Quaternary seismogenic structures in the Baikal rift. In places, surface fault scarps expose striated bedrock fault planes and offer some opportunities to examine the faulting history. Using cosmogenic 10Be exposure dating, we measured the exposure ages of one of the MK scarps (54.44630°N, 108.51524°E, elevation 985 m). This ~12-m-high normal fault scarp is composed of cataclasites in early Proterozoic granitoids of the Irel complex. We analyzed 12 of 18 samples, collected every 0.5 m, from 0.45 m above the toe of the exposed fault plane, which dips 55° in its lower half (samples 1–6) and 45° in upper half (samples 7–12). Exposure ages are the following from the toe upward: sample 1, 2.26 ± 0.53 ka; 2, 1.54 ± 0.55 ka; 3, 0.80 ± 0.55 ka; 5, 1.44 ± 0.55 ka; 6, 2.13 ± 0.62 ka; 8, 1.45 ± 0.48 ka; and 9, 1.40 ± 0.52 ka. The relationship between the oldest calculated ages (samples 1 and 6) and the relative sampling height along the scarp suggests that a recent surface-rupture event with a vertical component of 2.05 m (i.e. net slip of 2.5 m) occurred on the cliff ~2.2 ± 0.6 ka. Striations on the fault plane in the sampling points 1 and 6, as well a close date of 2145–2463 cal years BP calculated from radiocarbon age of a paleoseismic rupture within the Cape Shartly, ~62 km further southwestward, support this interpretation. The close ages assume that the dated deformations were related to a single Mw = 7.4 earthquake, the coseismic effects of which extended at least 82 km (the rupture length between the Cape Shartly and the NNE termination of the MK paleoseismic rupture zone). A more concentrated age mode of about 1.46 ± 0.53 ka (samples 2, 5, 8 and 9), which is in an incorrect stratigraphic order in reference to the older ages, is assumed to result from local erosion or partial shielding. Cosmogenic dating of fault scarps and seismogenic landslide scarps in bedrock potentially offers an independent method of reconstructing the late Quaternary paleoseismology of the northwestern flank of Lake Baikal. Graphical abstract

Cosmogenic 3He exposure ages of basaltic flows from Miller Knoll, Panguitch Lake, Utah: Using the alternative isochron approach to overcome low-gas crushes Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): David W. Marchetti, Allen L. Stork, D. Kip Solomon, Thure E. Cerling, Wil Mace Abstract Determining the ages of young volcanic rocks is important for understanding the tectono-magmatic development of geologic terranes. Usually, if rocks are old enough the 40Ar/39Ar or K–Ar techniques can provide reliable ages. However, when rocks are younger, they often lack enough daughter product to resolve an age. Cosmogenic 3He methods provide an alternative for determining the eruption age of relatively recent mafic/intermediate lava flows. We sampled morphologically young basaltic andesite flows south of Miller Knoll, near Panguitch Lake on the Markagunt Plateau in southern Utah. We took two samples in close proximity from two different areas on the flows and separated both olivine and pyroxene. The typical protocol is to crush mineral separates on-line to determine an inclusion-hosted magmatic 3He/4He component. Then the powders are heated in a furnace to release the total 3He and 4He component and the crushed component is subtracted to determine the cosmogenic 3He component. Unfortunately, in the case of the Miller Lake flows, 3He yield from on-line crushes was below detection. An alternative isochron approach, which obviates the need for crush data, was first described by Cerling and Craig (1994) and more fully by Blard and Pik (2008). In this approach the 3He/4He of the total gas released from furnace heating is plotted vs. 1/4He. If the samples plot on a line, then the resulting y-intercept is the magmatic 3He/4He and the slope of the line is the cosmogenic 3He component, which determines the exposure age. Our data create good isochrons (MSWD = 0.76 and 0.14) with magmatic 3He/4He of 4.7–4.9 Ra. Concentrations of cosmogenic 3He are 2.13 and 2.61 × 107 atoms g−1after correction for radiometric 4He using the R correction factor and measured and estimated U and Th concentrations in whole rock and minerals, respectively. Using the LSDn scaling routine and an online exposure age calculator, we determine zero erosion exposure ages of 32 ± 3 ka for the upper part of the flow and 34 ± 4 ka for the lower part of the flow.

Characteristics of a relative paleointensity record from loess deposits in arid central Asia and chronological implications Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): Guanhua Li, Dunsheng Xia, Erwin Appel, Hao Lu, Youjun Wang, Jia Jia, Xiaoqiang Yang Abstract Loess-paleosol sequences in the arid central Asia (ACA) provide valuable material for evaluating the evolution of paleoclimate and dust circulation in the Northern Hemisphere. However, determination of loess chronology has yet remained a main obstacle for paleoclimate interpretation. In this study, analyses of relative paleomagnetic intensity (RPI) were conducted in a loess section on the northern piedmont of the Tianshan Mountains covering the period since the last interglacial. The RPI record was found to be generally comparable with other recognized RPI stacks, confirming a globally consistent variation of the geomagnetic dipole field. Based on the RPI age model, the attempt to achieve paleoclimate assessment gives rise to largely similar variations to the North Atlantic records. Consequently, these results suggest that the RPI correlation could serve as a promising way to evaluate the age control of loess in the ACA. Nevertheless, in consideration of the complicated topography and loess deposition very close to the dust source, four main factors including carbon contamination, the reliability of luminescence signals, in situ depositional processes and complexity of remanence acquisition, may possibly contort the chronological determination in the ACA loess. Thus, cautions are still indispensable for paleoclimate interpretation with any solely chronological model and more work is therefore required to achieve a comprehensive understanding of loess chronological setting in this area.

U–Th disequilibrium, (U–Th)/He and 40Ar/39Ar geochronology of distal Nisyros Kyra tephra deposits on Datça peninsula (SW Anatolia) Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): Gonca Gençalioğlu-Kuşcu, Göksu Uslular, Martin Danišík, Anthony Koppers, Daniel P. Miggins, Bjarne Friedrichs, Axel K. Schmitt Abstract Kyra is an important tephra unit for Nisyros pre-caldera stage due to a number of subunits with various compositions (basaltic andesite to dacite) and distal dispersion on surrounding Greek islands (Tilos and Chalki) and Datça peninsula (Turkey). As for the most Nisyros tephra units, the available radiometric ages of Kyra tephra are not compatible with the relatively well-established Nisyros tephrostratigraphy. This beclouds the characterization of both proximal and distal Kyra tephra and also the understanding of Nisyros pre-caldera volcanism. In order to provide new insight into Nisyros tephrochronology, we here present the first (U–Th)/He and 40Ar/39Ar ages of Kyra distal andesitic pumice previously reported on Datça peninsula. (U–Th)/He dating of apatite (DZS pumice, Sındıköy) yielded weighted mean ages of 134.8 ± 19.8 ka (2σ, single-crystal aliquots, n = 12, MSWD = 0.21) and 139.6 ± 15.0 ka (2σ, multi-crystal aliquots, n = 5, MSWD = 0.78). Combined U–Th disequilibrium and (U–Th)/He dating of zircon (DZS pumice) yielded an age of 131.1 ± 8.6 ka (2σ, single-crystal aliquots, n = 8, MSWD = 0.58). The inverse isochron 40Ar/39Ar age of DAH (Hızırşah) pumice (plagioclase, 135.7 ± 28.2 ka, 2σ, MSWD = 1.70) is almost comparable with the (U–Th)/He ages, while the plateau ages of DAB (Belen) pumice are relatively older (plagioclase, 144.8 ± 26.6 ka, 2σ, n = 17, MSWD = 0.61; hornblende, 151.5 ± 19.5 ka, 2σ, n = 27, MSWD = 1.41). DAB pumice has also more evolved glass composition (mainly dacitic) compared to andesitic DAH and DZS pumice. Therefore, DAB tephra is considered as a different Kyra subunit. All new ages on distal Kyra tephra are in accordance with the Nisyros tephrostratigraphy and indicate a long-lasting eruptive history (~20 ka) of the tuff cone that formed Kyra sequence. Considering the available ages for the Kos Plateau Tuff (KPT) eruption (161 or 165 ka) and the presence of stratigraphically older Nisyros tephra units than Kyra, there should be no significant time gap between the KPT eruption and the onset of Nisyros subaerial volcanism. In addition, the recent findings on distal Kyra tephra will probably provide new opportunities for correlating the undefined tephra units that have comparable composition and age reported in both marine and terrestrial settings. Thus, our study will indirectly contribute to paleoenvironmental/climatological and tephrochronology studies around the Mediterranean region.

Multimodal-TERESA, a 210Pb-based radiometric dating model for recent sediments under largely varying rates of supply Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): J.M. Abril Abstract Lead-210 from natural atmospheric fallout is widely used in multidisciplinary studies for dating recent sediments. In anthropogenically-impacted and/or high energy systems the 210Pb flux onto the sediments may show non-random temporal variability, leading to the failure of classical dating models. The problem of how identifying and dating such cases remained unsolved, and it is the goal of the present work. Empirical evidences from varved sediments prove that initial activity concentrations of excess 210Pb (210Pbexc) and sediment accumulation rates (SARs) show large and independent temporal variability. M-TERESA model describes such variability by using multimodal frequency distributions and decodes the chronology from the 210Pbexc versus mass depth profile. The new model can solve scenarios with largely varying rates of supply, which fall beyond the limits of the piecewise versions of the classical models. Its use is demonstrated with some complex 210Pbexc profiles from varved sediments and synthetic cores for which an alternative and complete reconstruction of palaeofluxes and SARs is possible. The paper is supported by a wide set of supplementary material, including numerical codes for applying TERESA. The proposed methods are also useful for improving the reliability of routinely applications of the 210Pb-based radiometric dating of recent sediments.

Reassessment of the eruptive chronology of El Metate shield volcano (central-western Mexico) based on a comprehensive rock-magnetic, paleomagnetic and multi-approach paleointensity survey Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): Nayeli Pérez-Rodríguez, Juan Morales, Marie-Noëlle Guilbaud, Avto Goguitchaichvili, Rubén Cejudo-Ruiz, María del Sol Hernández-Bernal Abstract We study seven out of the thirteen lava flows associated to El Metate shield volcano using paleomagnetic, absolute intensity and rock-magnetic experiments. Characteristic paleomagnetic directions were successfully determined from most of the flows. A combined mean direction of D = 346.4° and I = 32.1° (N = 34, R = 33.73, k = 121.74, α95 = 2.2) was obtained for the early flows (Flow 1 − Flow 3). Flow 6a (a flow from the late emplacement stage) yielded a statistically distinguishable mean paleomagnetic direction of D = 359.2° and I = 29.6° (N = 9, R = 8.97, k = 294.6, α95 = 3.0). Furthermore, the significant between-flow variation of absolute paleointensity values obtained using two different methodologies, which resembles the trend followed by that of the global model SHA. DIF 14k intensity curve for the period 1000 AD 1600 AD, disagrees with previous hypothesis supporting a short emplacement period between 50 and 100 years for the whole sequence. Additionally, paleodirectional and paleointensity dating of the studied flows allowed to refine the eruptive chronology indicating that early flows were produced over a short time period, whereas at least two of the later flows were erupted 200 years later; the activity ending just prior to the arrival of the Spaniards in ∼1520. Under these circumstances, and in light of the presented high quality paleomagnetic and paleointensity data, the assumed monogenetic nature of El Metate volcano seems to be questionable.

The first radiometric age by isochron 26Al/10Be burial dating for the Early Pleistocene Yuanmou hominin site, southern China Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): Lan Luo, Darryl E. Granger, Hua Tu, Zhongping Lai, Guanjun Shen, Christopher J. Bae, Xueping Ji, Jianhui Liu Abstract The Yuanmou H. erectus site is generally considered to be one of the oldest hominin sites in southern China. The chronology of this site has been repeatedly investigated using magnetostratigraphy since its first discovery in the 1960s. However, there are multiple interpretations of the magnetostratigraphy due to the complexity of the sedimentary environment, resulting in a one million year age discrepancy by different studies. Because Yuanmou's age has yet to be verified radio-isotopically, we apply isochron 26Al/10Be burial dating to constrain the existing magnetostratigraphy. Six samples from a gravel bed 38 m above the fossil layer were collected, yielding an age of 1.54 ± 0.06 (0.11) My. Based on the estimated sedimentation rate, we interpolate an age of 1.72 ± 0.03 My for the fossil layer. This result is consistent with the most recent paleomagnetic stratigraphy of 1.7 My for the Yuanmou H. erectus fossils. Combined with other recent chronological studies of paleoanthropological sites across Asia, this study supports a model for earlier hominin dispersals out of Africa.

Cyclostratigraphic age constraining for Quaternary sediments in the Makarov Basin of the western Arctic Ocean using manganese variability Publication date: February 2020 Source: Quaternary Geochronology, Volume 55 Author(s): Kwangkyu Park, Jung-Hyun Kim, Hirofumi Asahi, Leonid Polyak, Boo-Keun Khim, Michael Schreck, Frank Niessen, Gee Soo Kong, Seung-Il Nam Abstract The Quaternary paleoenvironmental history of the Arctic Ocean remains uncertain, mainly due to the limited chronological constraints, especially beyond the 14C dating limits of accelerator mass spectrometry (AMS). The difficulty in establishing reliable chronostratigraphies is mainly attributed to low sedimentation rates and diagenetic sediment changes, resulting in very poor preservation of microfossils and altered paleomagnetic records. In the absence of independent chronostratigraphic data, the age model of Pleistocene sediments from the Arctic Ocean is mainly based on cyclostratigraphy, which relates lithologic changes to climatic variability on orbital time scales. In this study, we used the Mn/Al record measured from the sediment core ARA03B-41GC retrieved from the Makarov Basin in the western Arctic Ocean. The Mn/Al variation was tuned to the global benthic oxygen isotope stack (LR04) curve under different assumptions for computational correlation. Regardless of assumptions, our computational approach led to similar ages of about 600–1,000 ka for the bottom part of the core. These age models were up to about 200 ka older than those derived from lithostratigraphic approaches. Interestingly, our new age models show that the Ca/Al peak, a proxy for a detrital input from the Laurentide Ice Sheet, first occurred about 150 ka earlier than those previously proposed. Therefore, our results suggest that the glaciers in northern North America developed more extensively at about 810 ka than in earlier glacial periods, and influenced the sedimentary and paleoceanographic environments of the Arctic Ocean much earlier than previously thought. In order to establish a more comprehensive age model, more work is needed to validate our findings with different sediment cores recovered from the western Arctic Ocean.