Deglaciation and neotectonics in South East Raasay, Scottish Inner Hebrides

2021 ◽  
pp. sjg2021-006
Author(s):  
David E. Smith ◽  
Callum R. Firth ◽  
Tim M. Mighall ◽  
Phill A. Teasdale
Keyword(s):  
Younger Dryas ◽  
Vertical Displacement ◽  
Laminated Sediments ◽  
Fault System ◽  
Fault Movement ◽  
Quaternary Glaciation ◽  
Major Fault ◽  
The Last Glacial Maximum ◽  
Lacustrine Deposit ◽  
The Last Glacial

Changes in the physical landscape of SE Raasay at the end of the last Quaternary glaciation are examined. The area is marked by a major fault system defining the Beinn na Leac Fault Block, and field survey shows this to comprise a rollover anticline in the SW, with extensional movement towards the NE along an oblique transfer fault, the Main Beinn na Leac Fault. The fault system was reactivated after the Last Glacial Maximum (the LGM). Survey of a distinctive ridge of detached scree along the Main Beinn na Leac fault shows it to have involved a single movement of at least 7.12m vertical displacement, arguably the greatest fault movement since before the Younger Dryas in Scotland. The present work confirms that the scree became detached during the Younger Dryas, but finds that it overlies a lacustrine deposit of at least 5.6m of laminated sediments from a lake which had begun to accumulate earlier. Radiocarbon dating of peat overlying the lake sediments gave 10,176 – 10,315 cal. BP, but morphological and stratigraphical evidence indicates that drainage of the lake occurred earlier and only shortly before movement of the scree. Possible causes of displacement at the fault system are briefly discussed.

Late Pleistocene environments of the Bighorn Basin, Wyoming-Montana, USA

2020 ◽  
pp. 1-14
Author(s):  
Thomas A. Minckley ◽  
Mark Clementz ◽  
Marcel Kornfeld ◽  
Mary Lou Larson ◽  
Judson B. Finley
Keyword(s):  
Late Pleistocene ◽  
Environmental Changes ◽  
Isotope Analysis ◽  
Younger Dryas ◽  
Ecological Change ◽  
Bighorn Basin ◽  
Bulk Organic Matter ◽  
Intermontane Basins ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract Limited numbers of high-resolution records predate the Last Glacial Maximum (LGM) making it difficult to quantify the impacts of environmental changes prior to peak glaciation. We examined sediments from Last Canyon Cave in the Pryor Mountains of Montana and Wyoming to construct a >45 ka environmental record from pollen and stable isotope analysis. Artemisia pollen was hyper-abundant at the beginning of the record. Carbon isotope values of bulk organic matter (>40 ka) showed little variation (-25.3 ± 0.4‰) and were consistent with a arid C3 environment, similar to today. After 40 cal ka BP, Artemisia pollen decreased as herbaceous taxa increased toward the LGM. A significant decrease in δ13C values from 40–30 cal ka BP (~1.0‰) established a new baseline (-26.6 ± 0.2‰), suggesting cooler, seasonally wetter conditions prior to the LGM. These conditions persisted until variation in δ13C values increased significantly with post-glacial warming, marked by two spikes in values at 14.4 (-25.2‰) and 13.5 cal ka BP (-25.4‰) before δ13C values dropped to their lowest values (-26.9 ± 0.2‰) at the onset of the Younger Dryas (12.8 ka). These results provide insights into late Pleistocene conditions and ecological change in arid intermontane basins of the Rocky Mountains.

scholarly journals The deglaciation of coastal areas of southeast Greenland

The Holocene ◽  
2018 ◽  
Vol 28 (9) ◽  
pp. 1535-1544 ◽  
Author(s):  
Laurence M Dyke ◽  
Anna LC Hughes ◽  
Camilla S Andresen ◽  
Tavi Murray ◽  
John F Hiemstra ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Younger Dryas ◽  
Greenland Ice Sheet ◽  
Coastal Areas ◽  
Glacial Cycle ◽  
Last Glacial ◽  
The North ◽  
Exposure Ages ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Large marine-terminating glaciers around the margins of the Greenland Ice Sheet have retreated, accelerated and thinned over the last two decades. Relatively little is known about the longer term behaviour of the Greenland Ice Sheet, yet this information is valuable for assessing the significance of modern changes. We address this by reporting 11 new beryllium-10 (10Be) exposure ages from previously uninvestigated coastal areas across southeast Greenland. The new ages are combined with existing data from the region to assess the timing of glacier retreat after the Last Glacial Maximum. The results show that deglaciation occurred first in the north of the region (~68°N) and progressed southwards. This north–south progression is attributed to the influence of the warm Irminger Current on the ice margin. Areas in the south of the region were isolated from the warm waters by the shallow bathymetry of the continental shelf. This demonstrates that oceanographic forcing paced the deglaciation of southeast Greenland through the Younger Dryas and early Holocene. In most areas of southeast Greenland bedrock ages are systematically older than their counterpart boulder samples; this offset is likely the result of inherited 10Be content in bedrock surfaces. This suggests that subglacial erosion during the last glacial cycle was insufficient to completely remove pre-existing 10Be content. Alternatively, this pattern may be the signature of a substantial retreat and advance cycle prior to final Holocene deglaciation.

scholarly journals Estimation of phylogenetic divergence times in Panagrolaimidae and other nematodes using relaxed molecular clocks calibrated with insect and crustacean fossils

Nematology ◽  
2017 ◽  
Vol 19 (8) ◽  
pp. 899-913 ◽  
Author(s):  
Lorraine M. McGill ◽  
David A. Fitzpatrick ◽  
Davide Pisani ◽  
Ann M. Burnell
Keyword(s):  
Molecular Clocks ◽  
Fossil Calibration ◽  
Quaternary Glaciation ◽  
Tree Methods ◽  
Divergence Dates ◽  
Phylogenetic Divergence ◽  
The Last Glacial Maximum ◽  
Relaxed Molecular Clock ◽  
Insight Into ◽  
The Last Glacial

This study presents the use of relaxed molecular clock methods to infer the dates of divergence between Panagrolaimus species. Autocorrelated relaxed tree methods, combined with well characterised fossil calibration dates, yield estimates of nematode divergence dates in accordance with the palaeontological age of fossil ascarid eggs and with the previously estimated date of 18 Ma (range 11.6 to 29.9 Ma) for the divergence of the Caenorhabditis lineage. Our data indicate that Panagrolaimus davidi from Antarctica separated ca 21.98 Ma from its currently known, most closely related strain. Thus, P. davidi may have existed in Antarctica prior to the Last Glacial Maximum, although this seems unlikely as it shares physiological and life history traits with closely related nematodes from temperate climates. These traits may have facilitated colonisation of Antarctica by P. davidi after the quaternary glaciation, analogous to the colonisation of Surtsey Island, Iceland, by P. superbus after its volcanic formation. This study demonstrates that autocorrelated relaxed tree methods combined with well characterised fossil calibration dates may be used as a method to estimate the divergence dates within nematodes in order to gain insight into their evolutionary history.

scholarly journals Piecing together the Lateglacial advance phases of the Reussgletscher (central Swiss Alps)

2018 ◽  
Vol 73 (3) ◽  
pp. 241-252 ◽  
Author(s):  
Max Boxleitner ◽  
Susan Ivy-Ochs ◽  
Dagmar Brandova ◽  
Marcus Christl ◽  
Markus Egli ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Radiocarbon Dating ◽  
Younger Dryas ◽  
Swiss Alps ◽  
Clear Indication ◽  
Lake Lucerne ◽  
Last Glacial ◽  
Exposure Dating ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Exposure dating has substantially improved our knowledge about glacier advances during the Younger Dryas (YD) and the early Holocene. The glacier development after the Last Glacial Maximum (LGM) and the timing of morphologically evidenced, earlier Lateglacial re-advances is, however, still widely unknown. In this study we used 10Be surface exposure and radiocarbon dating to address these phases and corresponding landforms in the catchment of the former Reussgletscher (central Swiss Alps). We obtained clear indication for moraine deposition prior to the YD. The oldest samples predate the Bølling–Allerød interstadial (>14.6 ka). Morphostratigraphically even older lateral moraines, probably corresponding to terminal positions in the Lake Lucerne, could not be dated conclusively. Due to the geomorphological constraints of the sampling environment, the establishment of a local pre-YD chronology remains a challenge: moraines with adequate numbers of datable boulders were rarely preserved, and age attributions based on few samples are complicated by outliers.

scholarly journals Glacial landform-sediment assemblages in the Canadian High Arctic and their implications for late Quaternary glaciations

1999 ◽  
Vol 28 ◽  
pp. 195-201 ◽  
Author(s):  
C. Ó Cofaigh ◽  
D.S. Lemman ◽  
D.J.A. Evans ◽  
J. Bednarski
Keyword(s):  
Thermal Regime ◽  
Late Quaternary ◽  
Thermal Conditions ◽  
High Arctic ◽  
Early Holocene ◽  
Canadian High Arctic ◽  
Fine Grained ◽  
Quaternary Glaciation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractModern terrestrial glaciers in the Canadian High Arctic range from polythermal to cold-based. Where polythermal glaciers override thick unconsolidated sediment, longitudinal compression and glaciotectonic thrusting produce thrust-block moraines. In contrast, the dominant geomorphic record of cold-based glaciers consists of lateral and proglacial meltwater channels. Geomorphic and sedimentary evidence indicates that late Quaternary fiord glaciers were also characterized by variations in basal thermal regime. Erratic dispersal trains and striated bedrock record the flow of warm- based ice during the Last Glacial Maximum. Emergent grounding-line fans and morainal banks, deposited during deglaciation, consist of heterogeneous glaciomarine deposits that record well-developed subglacial drainage and high sedimentation rates. However, in other fiords, subaqueous outwash and fine-grained glaciomarine deposits are absent and deglaciation is recorded by lateral meltwater channels graded to raised glaciomarine deltas, suggesting these glaciers were predominantly cold-based during retreat. Regionally, deglacial depocentres are located at pinning points within fiords and a prominent belt of glaciogenic landforms at fiord heads records stabilization of ice margins during early Holocene retreat, rather than the limit of late Quaternary glaciation. Collectively, these observations refute previous reconstructions which inferred a climatically controlled switch from cold- to warm-based thermal conditions in fiord glaciers during early Holocene deglaciation, and indicate that the dominant controls on thermal regime were glaciological.

Temperature and precipitation in the southern Central Andes during the last glacial maximum, Heinrich Stadial 1, and the Younger Dryas

2020 ◽  
Vol 248 ◽  
pp. 106592
Author(s):  
Jürgen Mey ◽  
Mitch K. D’Arcy ◽  
Taylor F. Schildgen ◽  
David L. Egholm ◽  
Hella Wittmann ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Younger Dryas ◽  
Central Andes ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Temperature And Precipitation ◽  
Southern Central ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals Climate-induced speleothem radiocarbon variability on Socotra Island from the Last Glacial Maximum to the Younger Dryas

2020 ◽  
Vol 16 (1) ◽  
pp. 409-421
Author(s):  
Steffen Therre ◽  
Jens Fohlmeister ◽  
Dominik Fleitmann ◽  
Albert Matter ◽  
Stephen J. Burns ◽  
...  
Keyword(s):  
Soil Carbon ◽  
Carbon Cycling ◽  
Last Glacial Maximum ◽  
Younger Dryas ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Soil Carbon Cycling ◽  
Socotra Island ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. In this study, the dead carbon fraction (DCF) variations in stalagmite M1-5 from Socotra Island in the western Arabian Sea were investigated through a new set of high-precision U-series and radiocarbon (14C) dates. The data reveal an extreme case of very high and also climate-dependent DCF. For M1-5, an average DCF of 56.2±3.4 % is observed between 27 and 18 kyr BP. Such high DCF values indicate a high influence of aged soil organic matter (SOM) and nearly completely closed-system carbonate dissolution conditions. Towards the end of the last glacial period, decreasing Mg∕Ca ratios suggest an increase in precipitation which caused a marked change in the soil carbon cycling as indicated by sharply decreasing DCF. This is in contrast to the relation of soil infiltration and DCF as seen in stalagmites from temperate zones. For Socotra Island, which is influenced by the East African–Indian monsoon, we propose that more humid conditions and enhanced net infiltration after the Last Glacial Maximum (LGM) led to dense vegetation and thus lowered the DCF by increasing 14CO2 input into the soil zone. At the onset of the Younger Dryas (YD) a sudden change in DCF towards much higher, and extremely variable, values is observed. Our study highlights the dramatic variability of soil carbon cycling processes and vegetation feedback on Socotra Island manifested in stalagmite DCF on both long-term trends and sub-centennial timescales, thus providing evidence for climate influence on stalagmite radiocarbon. This is of particular relevance for speleothem studies that aim to reconstruct past atmospheric 14C (e.g., for the purposes of 14C calibration), as these would rely on largely climate-independent soil carbon cycling above the cave.

Stratigraphic constraints on late Pleistocene glacial erosion and deglaciation of the Chukchi margin, Arctic Ocean

2007 ◽  
Vol 67 (2) ◽  
pp. 234-245 ◽  
Author(s):  
Leonid Polyak ◽  
Dennis A. Darby ◽  
Jens F. Bischof ◽  
Martin Jakobsson
Keyword(s):  
Arctic Ocean ◽  
Younger Dryas ◽  
Laurentide Ice Sheet ◽  
Bering Strait ◽  
Glacial Erosion ◽  
Ice Shelves ◽  
Sediment Stratigraphy ◽  
The Last Glacial Maximum ◽  
Water Depths ◽  
The Last Glacial

AbstractAt least two episodes of glacial erosion of the Chukchi margin at water depths to ∼ 450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ18O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ18O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide meltwater pulse at the Younger Dryas onset. The Bering Strait opening is also marked in the composition of late deglacial Chukchi sediments.

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