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The lack of high-resolution, well-dated records hinders our understanding of the climatic factors driving glacier fluctuations on the Tibetan Plateau. The Hengduan Ranges, on the southeastern Tibetan Plateau, are well suited to determining millennial-scale fluctuations in glacier extent. We investigated glacial landforms in the Mt. Gongga and Mt. Siguniang areas and obtained 46 10Be exposure ages. Age peaks and the maximum age reveal two glacier advances on Mt. Gongga (11.26 ± 0.57 – 11.30 ± 0.92 ka , and 17.34 ± 1.38 – 17.68 ± 1.44 ka); and three glacier advances on Mt. Siguniang (16.44 ± 1.87 – 18.17 ± 1.39 ka , 20.48 ± 1.90 – 22.72 ± 1.74 ka , and 29.98 ± 3.96 – 30.77 ± 2.36 ka). We also analyzed a compilation of 181 recalculated 10Be exposure ages from the Hengduan Ranges. Glacier advances roughly correspond to four millennial-scale cold events (the Younger Dryas, and Heinrich events H1, H2 and H3) and are widely distributed in the Hengduan Ranges, which suggests that cooling, rather than precipitation change, was the main driver of glacier advances on the millennial-scale. Variations in monsoonal precipitation, which regulated the amplitude of glacier advances, were indicated by the depression of the equilibrium-line altitude. • 227 10Be ages indicate widespread glaciations on the millennial-scale on the southeastern Tibetan Plateau during MIS 2. • Glacier advances on the southeastern Tibetan Plateau correlate with drastic cooling events. • Monsoonal precipitation variations dominated the amplitude of glacier advances. [ABSTRACT FROM AUTHOR]

Intense glaciation during the end of Cryogenian time (∼635 million years ago) marks the coldest climate state in Earth history – a time when glacial deposits accumulated at low, tropical paleolatitudes. The leading idea to explain these deposits, the snowball Earth hypothesis, predicts globally frozen surface conditions and subfreezing temperatures, with global climate models placing surface temperatures in the tropics between −20 °C and −60 °C. However, precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined. Here we make new geologic observations of tropical periglacial, aeolian and fluvial sedimentary structures formed during the end-Cryogenian, Marinoan glaciation in South Australia; these observations allow us to constrain ancient surface temperatures. We find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith. The wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2–4 m below the ground surface. These observations, paired with a model of ground temperature forced by solar insolation, constrain the local mean annual surface temperature to within a few degrees of freezing. This temperature constraint matches well with our observations of fluvial deposits, which require temperatures sufficiently warm for surface runoff. Although this estimate coincides with one of the coldest near sea-level tropical temperatures in Earth history, if these structures represent peak Marinaon glacial conditions, they do not support the persistent deep freeze of the snowball Earth hypothesis. Rather, surface temperatures near 0 °C allow for regions of seasonal surface melting, atmosphere–ocean coupling and possible tropical refugia for early metazoans. If instead these structures formed during glacial onset or deglaciation, then they have implications for the timescale and character for the transition into or out of a snowball state. [ABSTRACT FROM AUTHOR]

Mega-streamlined landforms on Earth and Mars have been attributed to aeolian, glaciogenic, fluvial, and tectonic processes. Identifying the forces that shaped these landforms is paramount for understanding landscape evolution and constraining paleo-climate models and ice sheet reconstructions. In Arabia, east-northeast trending, kilometer-scale streamlined landforms were interpreted to have been formed by Quaternary aeolian erosion. We provide field and satellite-based evidence for a Late Ordovician glacial origin for these streamlined landforms, which were exhumed during Red Sea–related uplift. Then we use Late Ordovician paleo-topographic data to reconstruct the Late Ordovician ice sheet using identified and previously reported glacial deposits and landforms. Our reconstruction suggests these glacial features are part of a major, topographically controlled, marine-terminating ice stream, with a minimum length of 1000 km extending from the southeast Egypt to northern and central Arabia and possibly more than twice this length if the glaciomarine and iceberg deposits in the present-day western Iran are part of this system. Our results support models that advocate for a single, major, and highly dynamic ice sheet and provide new morphological-based constraints for Late Ordovician climate models. • Late Ordovician glaciation formed mega-streamlined landforms in Arabia. • Mega-streamlined landforms were exhumed during the Red Sea–related uplift. • The megalineations are part of a major, topographically controlled, ice stream. • The Arabian ice stream (AIS) is one of the largest-known terrestrial ice streams. • Findings support models that advocate a single, major, and highly dynamic ice sheet. [ABSTRACT FROM AUTHOR]

Abstract: The timing of the last Pleistocene glaciation in western North America is becoming increasingly well understood, largely due to improved methods of obtaining numerical ages of glacial deposits and landforms. Among these, cosmogenic radionuclide surface-exposure dating has been widely applied to moraines of mountain glaciers, providing the framework for understanding terrestrial climate change during and since the last glaciation in western North America. During the Late Pleistocene, the Great Basin of the western United States hosted numerous mountain glaciers, the deposits of which can provide valuable records of past climate changes if their ages can be precisely determined. In this study, twenty-nine cosmogenic radionuclide 10Be surface-exposure ages from a suite of moraines in Seitz Canyon, western Ruby Mountains, limit the timing of the last glacial episode in the interior Great Basin, known as the Angel Lake Glaciation. Results indicate that deposition of a terminal moraine and two recessional moraines began just prior to ∼20.5ka and continued until ∼20.0ka. Retreat from the next younger recessional moraine began at ∼17.2ka, and final deglaciation began at ∼14.8ka. These ages are broadly consistent with cosmogenic surface-exposure ages from the eastern Sierra Nevada and the western Wasatch Mountains, in the western and eastern extremes of the Great Basin respectively. Furthermore, these ages suggest that the valley glacier in Seitz Canyon was at or near its maximum extent before and during the hydrologic maxima of Pleistocene lakes in the Great Basin, supporting previous suggestions that a cool and wet climate persisted in this region during the early part of the last glacial–interglacial transition. [Copyright &y& Elsevier]

Abstract: In the Himalayas, the late Pleistocene glacier oscillations have produced spectacular glacial landforms. Detailed reconstructions of the chronology and extent of these oscillations are essential to document the sensitivity of the Himalayan glaciers to past and future climatic changes. In this paper, we present a new cosmogenic helium 3 (3Hec) dating on garnets, that were sampled on moraine blocks and ice-scoured surfaces in a small glaciated valley of the Central Nepal (the Mailun valley), and that provided a detailed chronology of Himalayan glacier fluctuations during the Holocene. Soon after the Younger Dryas, the glacier of the Mailun valley underwent a significant retreat around 10 ka. This retreat was followed by relative stability of the extent of the glacier between ∼8.5 and ∼7.5 ka. A second phase of rapid retreat occurred at ∼7 ka, but rapidly slowed down at ∼5–6 ka. Finally, a last phase of re-advance occurred between 0 and 1 ka. The interpretation of the Equilibrium Line Altitude (ELA) variation, deduced from this chronology (for the Holocene period) and carbon 14 (14C) dating (for the Pleistocene period), shows that the early history of the Mailun valley deglaciation (late Pleistocene) is in good agreement with the global paleoclimatic records. The main extent of the glacier and the major ice volume drop are in phase with the global Last Glacial Maximum (25–17 ka) and with the major worldwide temperature increase following the Younger Dryas, respectively, indicating that the Mailun glacier was primarily driven by temperature oscillations during the late Pleistocene. In contrast, the glacier chronology during the Holocene suggests that the Mailun glacier was modulated by the variation in annual precipitation, and is asynchronous relative to most glaciers of the Northern Hemisphere. The significant sensitivity of the Himalayan glaciers to precipitation might explain the striking lack of synchronism of the Himalayan glaciers both along and across the Himalayan arc. [Copyright &y& Elsevier]

• New cosmogenic nuclide burial-dating model to constrain the age of glacial sediments. • Higher Deckenschotter gravels in the northern Alpine Foreland deposited 1.0-0.9 Ma. • Onset of major glaciations in the Alps occurred during Middle Pleistocene Transition. A set of four outwash terraces in the northern Alpine Foreland motivated Penck and Brückner's classical scheme of four great Alpine ice ages: Günz, Mindel, Riss, and Würm. While it is now established that the Würm corresponds to marine isotope stages (MIS) 5d–2 (∼117–14 ka) and the Riss type locality to MIS 6 (∼191–130 ka), there is no consensus regarding the age of the older glaciations. The two oldest terraces, known as Höhere Deckenschotter (HDS) and Tiefere Deckenschotter (TDS) in Switzerland and neighbouring Germany, contain interbedded tills that directly indicate the first arrival of glaciers into the northern Alpine Foreland. Here, we set out to constrain the timing of the HDS, which signal the first major glaciations in the Alps. To achieve this goal, we devised a new burial-dating model tailored to glaciogenic sediments: P-PINI (Particle Pathway Inversion of Nuclide Inventories). The method applies a source-to-sink framework to a cosmogenic 10Be-26Al inversion model accounting for variable cosmic-ray exposure and non-steady erosion. Taking published 10Be-26Al data from five HDS sites (Feusi, Tromsberg, Siglistorf, Irchel Steig, and Irchel Hütz) and one TDS site (Iberig), we obtain age distributions (±1 σ) that are especially well constrained for Feusi (0.93 ± 0.13 Ma), Iberig (0.93 ± 0.17 Ma), and Tromsberg (0.88 ± 0.14 Ma), less well-constrained for Irchel Steig (0.69 ± 0.25 Ma) and Siglistorf (0.94 ± 0.27 Ma), and very poorly constrained for Irchel Hütz (1.39 ± 0.56 Ma). Consistent with the morphostratigraphy, which dictates that the TDS postdates the HDS, we implemented a Bayesian modelling framework, yielding an age of 0.69 ± 0.12 Ma for Iberig (TDS) and a combined age of 0.95 ± 0.07 Ma for the HDS sites. Based on the P-PINI burial ages as well as the combined, Bayesian burial age, we propose an age around 1.0–0.9 Ma for the onset of the large Alpine glaciations that triggered the accumulation of the HDS outwash sediments. This roughly accords with the first long glaciation of the Pleistocene (MIS 24–22), identified as a step-change to colder climate and larger glaciations towards the end of the Middle Pleistocene Transition. While our results challenge previously reported ages of ∼2 Ma or more for the HDS in Switzerland, they corroborate evidence from the southern Alpine retroforeland and provide quantitative support for the early hypothesis by G.J. Kukla, who ascribed the oldest glacial deposits in the northern Alpine Foreland to around MIS 22. Finally, we suggest that the source-to-sink approach of P-PINI offers a viable alternative to the established isochron burial-dating method in cases involving non-steady exposure and erosion. [ABSTRACT FROM AUTHOR]