Late Precambrian glaciation of central East Greenland

The Vendian succession of the central East Greenland fjord region is among the best preserved and most extensively exposed in the world and is represented approximately by the Tillite Group, comprising five formations, which from bottom to top are: the Ulvesø Formation (formerly Lower Tillite, dominantly diamictite), the Arena Formation (formerly Inter-Tillite beds, dominantly sandstone and shale), the Storeelv Formation (formerly Upper Tillite, dominantly diamictite, sandstone and conglomerate), the Canyon Formation (dominantly shale and dolostone) and the Spiral Creek Formation (dominantly sandstone, shale and dolostone). The group is underlain by Bed group 20 (limestone) and Bed group 19 (dominantly carbonate, shale and breccia) in different places and in the peripheral areas by older Bed groups of the Eleonore Bay Group. Above, the transgressive Cambrian sandstones of the Kløftelv Formation cap the Vendian sequence, though the exact level of the Precarmbrian-Cambrian boundary may be slightly lower. This paper reviews previous work on the succession and presents numerous new stratigraphic sections and an assessment of the sedimentary structures. The stratigraphic and palaeoenvironmental significance of the succession can therefore be assessed. Both main diamictite horizons contain other facies, which together with sedimentary structural and fabric data indicate that the following sediments have been produced: lodgement tillites, waterlain tillites, proximal and distal glaciomarine sediments (with ice-rafted dropstones), glaciolacustrine sediments, fluvioglacial deposits,  subaqueous and sub-aerial mass-flows and periglacial phenomena. The other sediments of the Tillite Group were deposited in a dominantly shallow marine or lacustrine environment. Deeper water turbidites are recorded in part of the Arena Formation, whilst the upper part of the group indicates periodic emergence. Stromatolites, desiccation cracks and halite pseudomorphs are particularly distinctive in this part of the succession. A hiatus preceded deposition of the Kløftelv Formation, a transgressive unit of tidally-influenced sandstones. Stratigraphic thicknesses vary considerably, and whereas individual formations can be recognised throughout most of the fjord region, intraformational horizons cannot normally be traced for more than several kilometres. The nature of the bottom contact of the Tillite Group remains enigmatic, and transitional sedimentary, unconformable and thrust contacts are all present. It is possible that Bed Group 20 may be the lateral equivalent of the Ulves0 Formation, or of Bed Group 19. Although local palaeogeography was complex during deposition of the diamictites, these rocks indicate that a low-level ice sheet prevailed at the time. Together with Svalbard and western Scotland they represent the periphery of an ice-sheet which stretched across much of northern Europe to the Urals. However, much of Vendian time was not characterised by glacial conditions, and warm climates prevailed when the upper part of the Tillite Group was deposited

'Structure-from-Motion' photogrammetry: A low-cost, effective tool for geoscience applications

High-resolution topographic surveying is traditionally associated with high capital and logistical costs, so that data acquisition is often passed on to specialist third party organisations. The high costs of data collection are, for many applications in the earth sciences, exacerbated by the remoteness and inaccessibility of many field sites, rendering cheaper, more portable surveying platforms (i.e. terrestrial laser scanning or GPS) impractical. This paper outlines a revolutionary, low-cost, user-friendly photogrammetric technique for obtaining high-resolution datasets at a range of scales, termed ‘Structure-from-Motion’ (SfM). Traditional softcopy photogrammetric methods require the 3-D location and pose of the camera(s), or the 3-D location of ground control points to be known to facilitate scene triangulation and reconstruction. In contrast, the SfM method solves the camera pose and scene geometry simultaneously and automatically, using a highly redundant bundle adjustment based on matching features in multiple overlapping, offset images. A comprehensive introduction to the technique is presented, followed by an outline of the methods used to create high-resolution digital elevation models (DEMs) from extensive photosets obtained using a consumer-grade digital camera. As an initial appraisal of the technique, an SfM-derived DEM is compared directly with a similar model obtained using terrestrial laser scanning. This intercomparison reveals that decimetre-scale vertical accuracy can be achieved using SfM even for sites with complex topography and a range of land-covers. Example applications of SfM are presented for three contrasting landforms across a range of scales including; an exposed rocky coastal cliff; a breached moraine-dam complex; and a glacially-sculpted bedrock ridge. The SfM technique represents a major advancement in the field of photogrammetry for geoscience applications. Our results and experiences indicate SfM is an inexpensive, effective, and flexible approach to capturing complex topography

Are longitudinal ice-surface structures on the Antarctic Ice Sheet indicators of long-term ice-flow configuration?

Abstract. Continent-wide mapping of longitudinal ice-surface structures on the Antarctic Ice Sheet reveals that they originate in the interior of the ice sheet and are arranged in arborescent networks fed by multiple tributaries. Longitudinal ice-surface structures can be traced continuously down-ice for distances of up to 1200 km. They are co-located with fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of m yr-1 and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. Associating these structures with the AIS' surface velocity field reveals (i) ice residence times of ~ 2500 to 18 500 years, and (ii) undeformed flow-line sets for all major flow units analysed except the Kamb Ice Stream and the Institute and Möller Ice Stream areas. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow and ice-velocity configuration of the ice sheet may have remained largely unchanged for several thousand years, and possibly even since the end of the last glacial cycle. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition. </jats:p

Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988–2009

The northern Antarctic Peninsula has recently exhibited ice-shelf disintegration, glacier recession and acceleration. However, the dynamic response of land-terminating, ice-shelf tributary and tidewater glaciers has not yet been quantified or assessed for variability, and there are sparse data for glacier classification, morphology, area, length or altitude. This paper firstly classifies the area, length, altitude, slope, aspect, geomorphology, type and hypsometry of 194 glaciers on Trinity Peninsula, Vega Island and James Ross Island in 2009 AD. Secondly, this paper documents glacier change 1988–2009. In 2009, the glacierised area was 8140&amp;plusmn;262 km&lt;sup&gt;2&lt;/sup&gt;. From 1988–2001, 90% of glaciers receded, and from 2001–2009, 79% receded. This equates to an area change of −4.4% for Trinity Peninsula eastern coast glaciers, −0.6% for western coast glaciers, and −35.0% for ice-shelf tributary glaciers from 1988–2001. Tidewater glaciers on the drier, cooler eastern Trinity Peninsula experienced fastest shrinkage from 1988–2001, with limited frontal change after 2001. Glaciers on the western Trinity Peninsula shrank less than those on the east. Land-terminating glaciers on James Ross Island shrank fastest in the period 1988–2001. This east-west difference is largely a result of orographic temperature and precipitation gradients across the Antarctic Peninsula, with warming temperatures affecting the precipitation-starved glaciers on the eastern coast more than on the western coast. Reduced shrinkage on the western Peninsula may be a result of higher snowfall, perhaps in conjunction with the fact that these glaciers are mostly grounded. Rates of area loss on the eastern side of Trinity Peninsula are slowing, which we attribute to the floating ice tongues receding into the fjords and reaching a new dynamic equilibrium. The rapid shrinkage of tidewater glaciers on James Ross Island is likely to continue because of their low elevations and flat profiles. In contrast, the higher and steeper tidewater glaciers on the eastern Antarctic Peninsula will attain more stable frontal positions after low-lying ablation areas are removed, reaching equilibrium more quickly

Indicators of relative completeness of the glacial record of the Port Askaig Formation, Garvellach Islands, Scotland

The Port Askaig Formation (PAF) is a diamictite-bearing succession in the Dalradian Supergroup of Scotland that provides an excellent archive of a Cryogenian glaciation in the Garvellach Islands and Islay, Argyll. The formation is ∼1100 m thick, comprises 5 members and includes 47 diamictite beds, interbedded with siltstones, dolostones and sandstones. Here we document seven features of the PAF that indicate its relative stratigraphic completeness. There are gradual, progressive changes up-section in the lithologies of the diamictites, their interbeds, and clast lithologies. The sharp basal surfaces of the diamictites each show the same, repeated pattern of environmental change, from non-glacial to glacial. Many of the top surfaces of the diamictites show evidence of periglacial conditions. The succession in the PAF records a total of 76 climatically-related stratigraphic episodes: 28 glacial episodes, 25 periglacial episodes and 23 non-glacial episodes. Parts of Member 1 (Diamictites 1–12 and Diamictites 16–18) and Member 2 (Diamictite 31 to the base of Member 3) are most compete on the east coast of Garbh Eileach. The PAF in the Garvellach Islands occurs within a succession that is several kilometres thick, as newly revealed by sea-floor mapping. Compared with other Cryogenian and Phanerozoic glacial successions, the PAF is exceptional in its combination of formation thickness, the number of climatically-related stratigraphic episodes, and the considerable thickness of its host supergroup. Furthermore, these indicators of relative stratigraphic completeness provide evidence that the base of the PAF on the east coast of Garbh Eileach is a succession without a major break in deposition, supporting the account of the strata at and below the base of the PAF in the companion article by Fairchild et al. (2018)

Middle Miocene to Pliocene History of Antarctica and the Southern Ocean

This chapter explores the Middle Miocene to Pliocene terrestrial and marine records of Antarctica and the Southern Ocean. The structure of the chapter makes a clear distinction between terrestrial and marine records as well as proximal (on or around Antarctica) and more distal records (Southern Ocean). Particular geographical regions are identified that reflect the areas for which the majority of palaeoenvironmental and palaeoclimatic information exist. Specifically, the chapter addresses the terrestrial sedimentary and fjordal environments of the Transantarctic Mountains and Lambert Glacier region, the terrestrial fossil record of Antarctic climate, terrestrial environments of West Antarctica, and the marine records of the East Antarctic Ice Sheet (EAIS), the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS), as well as the marine record of the Southern Ocean. Previous and current studies focusing on modelling Middle Miocene to Pliocene climate, environments and ice sheets are discussed.Published401-4631.8. Osservazioni di geofisica ambientale3.8. Geofisica per l'ambientereserve