Facies Composition and Stratigraphic Position of the Quaternary Upper Yenisei Sequence in the Tuva and Minusa Depressions

—The paper concerns the sediment sequence, which is widespread in the Yenisei valley and in the Tuva and Minusa depressions and also present in the valleys of the southern Chulym plain. The sediments of this sequence were previously described as “Neogene mud-shedding”, as well as moraines, alluvial fan deposits, alluvium of Middle Pleistocene high terraces, and lacustrine sediments. The giant ripple marks on the Upper Yenisei terraces was commonly interpreted as ribbed moraines; however, in recent studies, these ridges have been repeatedly referred to as marks of giant current ripples. Besides, some recently published papers provide description of geology of this sequence fragments suggesting its deposition by cataclysmic floods. Geomorphological analysis of the area shows Pleistocene glaciers to have been localized within the medium–high mountainous areas. The glaciers did not reach the Tuva and Minusa depressions and occupied large areas only in the Todzha basin and on the periphery of the Darkhat basin, forming a glacial dam at its outlet, which resulted in glacial-dammed lakes filling the basin completely. These lakes outburst, and the resultant flooding led to the deposition of megaflood sediments, which we refer to here as the Upper Yenisei sediment sequence. A detailed analysis of its facies architecture revealed similarity of these sediments to those of the Sal’dzhar and Inya sequences in Gorny Altai. Most of the Upper Yenisei megaflood sediments are localized in topographic lows of the Tuva and Minusa depressions. Beyond the Altai–Sayan mountainous area, the megaflood sediments of the Upper Yenisei sequence compose high terraces of the Yenisei, Chulym, Chet’, and Kiya rivers in the southern Chulym plain. The formation of Upper Yenisei sequence dates to the first half of the Late Pleistocene, inasmuch as it contains inset alluvial sediments of the second terrace of the Yenisei River. The available data allow suggesting that the Upper Yenisei sequence formed in the first Late Pleistocene regional glaciation. The Sal’dzhar sequence in Gorny Altai and the fourth terrace of the Ob’ River on the Fore-Altai plain are stratigraphic analogs of the Upper Yenisei sequence. The Upper Yenisei and Sal’dzhar sequences can thus be considered future regional markers serving as a link for the local stratigraphic schemes of the Altai–Sayan mountainous area and adjacent West Siberian plains. The results obtained call for verification by geochronological dating, first of all, by modern luminescence dating methods covering a wider chronological interval than radiocarbon dating.

Supplemental Material: From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China

<div>Zircon SIMS, LA-ICP-MS, and SHRIMP U-Pb geochronological dating, major, and trace element data (listed in Supplemental Tables S1 to S5, respectively).<br></div>

Supplemental Material: From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China

<div>Zircon SIMS, LA-ICP-MS, and SHRIMP U-Pb geochronological dating, major, and trace element data (listed in Supplemental Tables S1 to S5, respectively).<br></div>

New radiometric data from the South Maradi Pan-African formations, southern Niger

The Pan-African Province (PAP) of South Maradi (Niger) corresponds to the northeastern part of the Benin–Nigerian Shield. In this framework, schist belts outcrop in NE–SW bands of mylonitic gneiss, associated with granitoid intrusions. This study focuses on geochronological dating of the South Maradi PAP formations. Four samples were dated by K–Ar on a MI-1201 IG mass spectrometer and two of them were re-dated by U–Pb on a inductively coupled plasma mass spectrometer. The Dan Issa porphyritic gneiss indicated two weighted average U–Pb zircon ages: 638.3 ± 3.0 Ma (MSWD = 5.4) and 589.6 ± 1.9 Ma (MSWD = 0.39). Dating of the Maraka schist using the U–Pb on zircon method gave a weighted average age of 617.9 ± 2.8 Ma (MSWD = 2.3), while the same sample recorded a K–Ar age (whole rock) of 505 ± 15 Ma. The Rourouka porphyroid granite gave a K–Ar (whole-rock) age of 508 ± 10 Ma. The Fiawa-Garin Wali mylonitic gneiss indicated ages of 491 ± 10 Ma (K–Ar on feldspar) and 475 ± 10 Ma (K–Ar on whole rock). These preliminary radiometric data reveal the polycyclic character of the Pan-African remobilization which ranges from the Neoproterozoic to the early Paleozoic.

Illuminating Intcal During the Younger Dryas

ABSTRACTAs the worldwide standard for radiocarbon (14C) dating over the past ca. 50,000 years, the International Calibration Curve (IntCal) is continuously improving towards higher resolution and replication. Tree-ring-based 14C measurements provide absolute dating throughout most of the Holocene, although high-precision data are limited for the Younger Dryas interval and farther back in time. Here, we describe the dendrochronological characteristics of 1448 new 14C dates, between ~11,950 and 13,160 cal BP, from 13 pines that were growing in Switzerland. Significantly enhancing the ongoing IntCal update (IntCal20), this Late Glacial (LG) compilation contains more annually precise 14C dates than any other contribution during any other period of time. Thus, our results now provide unique geochronological dating into the Younger Dryas, a pivotal period of climate and environmental change at the transition from LG into Early Holocene conditions.

Land plants and terrestrial environmental changes during the onset of the end-Triassic event

&lt;p&gt;The end-Triassic mass extinction is considered to have been caused by voluminous and repeated emissions of CO&lt;sub&gt;2&lt;/sub&gt; and/or methane and other gases from magmatic activity in the Central Atlantic Magmatic Province. Despite improved geochronological dating and correlation between the magmatic activity and the extinctions, exactly how the biotic crisis commenced remains poorly understood. Here, we compile palynological and palaeobotanical data, bulk organic &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C, biomarkers, mercury and other geochemical proxies, charcoal, and sedimentology, from a Rhaetian terrestrial succession in southern Sweden. Our results provide an insight into the climatic, environmental and ecosystem changes that took place at the onset of the mass extinction event.&lt;/p&gt;

Geochronology and sedimentary environment at the Udu-dong archeological site, Chuncheon, South Korea

The Udu-dong archeological site in Chuncheon, South Korea, dates back to the Proto–Three Kingdoms Period (approximately 100 BC to AD 350). Many artifacts, including some earthenware, have been excavated in these ancient dwelling sites. We applied three geochronological dating methods (radiocarbon, optically stimulated luminescence (OSL), and archeomagnetic dating) to the archeological remains of this large-scale human settlement and reconstructed the history of depositional processes prior to human settlement. The timing of the ancient community’s settlement was investigated by radiocarbon dating of the charcoal fragments collected from old furnaces. Archeomagnetic dating allowed us to constrain the time period of the settlement’s abandonment by dating the last use of fire. The timing and development of fluvial deposits underlying the settlement site were reconstructed by OSL dating combined with sedimentary facies analysis. Our results show that, following the deposition of coarse sediments starting 10,000 years ago, the region formed a stable floodplain environment starting around 3000 years ago; people began to form clustered settlements approximately 50 years later. For the subsequent 150 years or so, the area was heavily used as a settlement site, with people evenly distributed across it, before eventual abandonment of the site around AD 200–250. Because the sedimentary deposits do not show any significant facies change during this period, we conclude that any catastrophic events were not the main reason for settlement abandonment. This study suggests that combining scientific and archeological analyses have significant benefits for studies of such archeological sites. Therefore, continuous collection of such data can provide important information for the excavation and protection of prehistoric or historic sites.

Palaeoclimate characteristics in interior Siberia of MIS 6–2: first insights from the Batagay permafrost mega-thaw slump in the Yana Highlands

Syngenetic permafrost deposits formed extensively on and around the arising Beringian subcontinent during the Late Pleistocene sea level lowstands. Syngenetic deposition implies that all material, both mineral and organic, freezes parallel to sedimentation and remains frozen until degradation of the permafrost. Permafrost is therefore a unique archive of Late Pleistocene palaeoclimate. Most studied permafrost outcrops are situated in the coastal lowlands of northeastern Siberia; inland sections are, however, scarcely available. Here, we describe the stratigraphical, cryolithological, and geochronological characteristics of a permafrost sequence near Batagay in the Siberian Yana Highlands, the interior of the Sakha Republic (Yakutia), Russia, with focus on the Late Pleistocene Yedoma ice complex (YIC). The recently formed Batagay mega-thaw slump exposes permafrost deposits to a depth of up to 80 m and gives insight into a climate record close to Verkhoyansk, which has the most severe continental climate in the Northern Hemisphere. Geochronological dating (optically stimulated luminescence, OSL, and 14C ages) and stratigraphic implications delivered a temporal frame from the Middle Pleistocene to the Holocene for our sedimentological interpretations and also revealed interruptions in the deposition. The sequence of lithological units indicates a succession of several distinct climate phases: a Middle Pleistocene ice complex indicates cold stage climate. Then, ice wedge growth stopped due to highly increased sedimentation rates and eventually a rise in temperature. Full interglacial climate conditions existed during accumulation of an organic-rich layer – plant macrofossils reflected open forest vegetation existing under dry conditions during Marine Isotope Stage (MIS) 5e. The Late Pleistocene YIC (MIS 4–MIS 2) suggests severe cold-stage climate conditions. No alas deposits, potentially indicating thermokarst processes, were detected at the site. A detailed comparison of the permafrost deposits exposed in the Batagay thaw slump with well-studied permafrost sequences, both coastal and inland, is made to highlight common features and differences in their formation processes and palaeoclimatic histories. Fluvial and lacustrine influence is temporarily common in the majority of permafrost exposures, but has to be excluded for the Batagay sequence. We interpret the characteristics of permafrost deposits at this location as a result of various climatically induced processes that are partly seasonally controlled. Nival deposition might have been dominant during winter time, whereas proluvial and aeolian deposition could have prevailed during the snowmelt period and the dry summer season.