Updated glacial chronology of the South Fork Hoh River valley, Olympic Peninsula, Washington through detailed stratigraphy and OSL dating

Four glacial advances are preserved and exposed in the stratigraphy of the South Fork Hoh River valley. The oldest of these advances extended beyond the South Fork valley into the Hoh River valley. The three younger advances are preserved in the stratigraphy cut bank exposures in the valley and geomorphically by moraines and outwash plains. One of these advances represents a re-advance to the same terminal position of the previous advance and has not previously been recognized in this valley or other glaciated valleys in the western Olympic Mountains. This finding advocates for a detailed sedimentologic and stratigraphic approach to glacial deposits and questions whether a similar advance is seen in other glaciated valleys of the region. If so, this may reveal information regarding climate influences on glacial advance not previously considered for this specific time period

Fire and Ice in Central Idaho: Modern and Holocene Fires, Debris Flows, and Climate in the Payette River Basin, and Quaternary and Glacial Geology in the Sawtooth Mountains

This 2-day trip will highlight recent fire and storm-related debris flows in the Payette River region, Holocene records of fires and fire-related sedimentation events preserved in alluvial fan stratigraphic sequences, and geomorphology and geology of alpine glaciations in the spectacular Sawtooth Mountains and Stanley Basin of central Idaho. Storm events and associated scour following recent fires in the South Fork Payette basin have exposed Holocene fire-related debris-flow deposits, flood sediments, and other alluvial fan-building deposits that yield insights into Holocene environmental change. Moraine characteristics and sediment cores from the southeastern Sawtooth Mountains and Stanley Basin provide evidence of late Pleistocene alpine glaciation. A combination of these glacial records with reconstructions of regional equilibrium line elevations produces late-glacial paleoclimatic inferences for the area. Day one of the trip will examine recent and Holocene fire-related deposits along the South Fork Payette River; day two will focus on alpine glaciation in the Sawtooth Mountains (fig. 1). A description of the scope, methods, results and interpretation of the South Fork Payette fire study is given below. Background information on late Pleistocene alpine glaciation in the eastern Sawtooth Mountains is presented with the material for day 2 of the trip. The road log for day 1 of the trip begins at Banks, Idaho, and ends in Stanley, Idaho. Stop locations are shown on figure 2. At Stop 1, we will provide an introduction to interpretation of alluvial fan stratigraphic sections, and discuss the Boise Ridge fault. At Stops 2–4 (Hopkins Creek, Deadwood River, and Jughead creek), we will examine recent debrisflow deposits and Holocene alluvial fan stratigraphic sections. At Stop 5 (Helende Campground), we will look at a series of well-preserved Holocene and Pleistocene terraces and at Stop 6 (Canyon Creek), we will briefly inspect fire-related deposits in higher-elevation alluvial fan stratigraphic sections. The road log for day 2 begins at Stanley, Idaho, and ends in Sun Valley, Idaho. Stop locations are shown on figure 2. Stop 1, at Redfish Lake, will focus on regional equilibrium line altitude reconstructions and on the general pattern of late Pleistocene glaciation on the eastern flank of the Sawtooth Mountains. Stop 2 will be at Pettit Lake, where we will examine the moraine sequence and discuss relative weathering criteria and moraine groupings. At Stop 3, near Alturas Lake, we will discuss lake sediment coring, moraine chronology, and implications for latest Pleistocene paleoclimatic inferences. Stop 4 will be a brief stop at Galena Summit for an overview of the Sawtooth Mountains and a discussion of ice accumulation patterns. The trip will end at a set of moraines in the Trail Creek valley, near Sun Valley, where we will examine moraine morphology and weathering rind data that constrain the moraine ages

Glacial forest refugium in Howard Valley, South Island, New Zealand

Fossils of forest habitat beetles and leaves of Nothofagus menziesii provide evidence of a forest refugium at times between ca. 34 000 and ca. 18 500 cal. a BP at an upland site in Howard Valley, located adjacent to glaciated valleys in South Island, New Zealand. The stratigraphy of the glacial-aged terrace sequence of organic-rich silts and fluvial sand/gravels indicates that soil development occurred episodically for around 15 000 a. Fifty-four beetle taxa represent seven habitat types: forest, forest or scrub, riparian and aquatic, litter, grass/tussock, marshland and moss habitats. Leaf and beetle fossils indicate that forest dominated by N. menziesii persisted at the site for most of the time period represented, and tree line taxa such as Taenarthrus sp. 1 (Carabidae) and Podocarpus sp. (Podocarpaceae) indicate that the site may represent the upper tree limit for full-glacial time. The finding of forest at this elevated site adds to the growing fossil evidence for multiple forest refugia in New Zealand during the last glaciation and is consistent with the pollen records, which have consistently indicated the presence of forest species during the last glaciations

Multiple glacial advances in the Rangitata Valley, South Island, New Zealand, imply roles for Southern Hemisphere westerlies and summer insolation in MIS 3 glacial advances

Stratigraphic evidence and extensive optically stimulated luminescence (OSL) geochronology from an 18-km-long reach of the middle Rangitata Valley, South Island, New Zealand, provide evidence for at least six distinct glacial advances during the last glacial cycle. These include four well-constrained Marine Oxygen Isotope Stage (MIS) 3 and 2 advances at ca. 38 ka, ca. 27 ka, ca. 21 ka and at 18 ka, as well as less well-constrained advances in MIS 4 and/or early MIS 3. Ice occupied a farther downvalley reach of the Rangitata from 38 ka to after 18 ka, indicating that near-full glacial conditions persisted for most of the last 20 ka of the last glaciation, though the glacier still fluctuated significantly, as reflected by the numerous distinguishable advances. Global or regional cooling alone cannot explain the persistence of near-maximum glacial conditions for this extended period, nor can it explain the occurrence of the largest advances ca. 32 ka. Instead, we invoke the northward expansion of the westerlies during MIS 3 as the cause for the early widespread glaciation, wherein enhanced westerly flow under moderate cooling maximised glacial extents. Local insolation favoured extended MIS 3 glaciation until ca. 32 ka. Increasing summer insolation gradually reduced glacial extents after ca. 28 ka

Multiple Glacial Advances in the Rangitata Valley, South Island, New Zealand, Imply Roles for Southern Hemisphere Westerlies and Summer Insolation in MIS 3 Glacial Advances

Stratigraphic evidence and extensive optically stimulated luminescence (OSL) geochronology from an 18-km-long reach of the middle Rangitata Valley, South Island, New Zealand, provide evidence for at least six distinct glacial advances during the last glacial cycle. These include four well-constrained Marine Oxygen Isotope Stage (MIS) 3 and 2 advances at ca. 38 ka, ca. 27 ka, ca. 21 ka and at 18 ka, as well as less well-constrained advances in MIS 4 and/or early MIS 3. Ice occupied a farther downvalley reach of the Rangitata from 38 ka to after 18 ka, indicating that near-full glacial conditions persisted for most of the last 20 ka of the last glaciation, though the glacier still fluctuated significantly, as reflected by the numerous distinguishable advances. Global or regional cooling alone cannot explain the persistence of near-maximum glacial conditions for this extended period, nor can it explain the occurrence of the largest advances ca. 32 ka. Instead, we invoke the northward expansion of the westerlies during MIS 3 as the cause for the early widespread glaciation, wherein enhanced westerly flow under moderate cooling maximised glacial extents. Local insolation favoured extended MIS 3 glaciation until ca. 32 ka. Increasing summer insolation gradually reduced glacial extents after ca. 28 ka

MIS 3 glaciation in the middle Rakaia valley, New Zealand, documented through stratigraphy and luminescence geochronology

Stratigraphy, geomorphology, and luminescence dating of ice-proximal sediments document extensive MIS 3 Rakaia valley glaciation. Basal outwash contains ice-meltout depressions filled with upward-coarsening and progressively deformed outwash, overlain by undeformed ice-proximal diamicton and outwash. The most reliable luminescence date from basal outwash is 35.2 ± 0.7 ka, consistent with site stratigraphic evolution and overlying exposure ages. The site thus indicates MIS 3 ice of similar extent as the main MIS 3/2 advance and demonstrates that ice retreated at least a short distance up-valley between the two advances. The results correlate with similar ages on ice-proximal lake sediments 10 km up-valley, on distal outwash 65 km down-valley, and with cosmogenic radionuclide dates elsewhere in the Southern Alps. This study thus confirms independently that MIS 3 glaciation was nearly as extensive as the main LGM advances in central South Island, New Zealand

Cosmogenic Be-10 and Al-26 exposure ages of moraines in the Rakaia Valley, New Zealand and the nature of the last termination in New Zealand glacial systems

New Zealand glaciers reached their last glacial maximum position at or before ~ 25 ka, and, as early as 23 ka, commenced a slow and continual retreat. New cosmogenic exposure ages and field mapping from the Rakaia Valley in the South Island suggest that extensive ice survived well into the latter half of the Last Glacial–Interglacial Transition (18–11 ka), with the post-15 ka period inferred to have near Holocene climate conditions based on ecological proxy data. By as late as ~ 15.5 ka, glacier termini had retreated as little as 5–10 km from glacial maximum positions. Numerous minor ice still-stand positions and oscillations are recognized, but the record specifically excludes evidence for either a major climatic amelioration at ~ 15–16 ka or a significant glacial re-advance during the Antarctic Cold Reversal (ACR) or the Younger Dryas (YD). We conclude that the currently widespread interpretation of an episodic New Zealand glacial record since the LGM is an artifact of valley-dependent retreat processes. Pro-glacial lake formation and local site conditions combined to give an apparent, but misleading, picture of glacial retreat punctuated by major, climatically driven, re-advances. Copyright © 2010 Elsevier B.V. All rights reserved