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Chapter 2 A history of Neoproterozoic glacial geology, 1871-1997 - Photograph supplement

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Title: Chapter 2 A history of Neoproterozoic glacial geology, 1871-1997 - Photograph supplement
Author: Hoffman, Paul F.; Schmidt, P. W.; Williams, G. E.; Xiao, Shuhai
Abstract: Companion photographs to the book chapter Hoffman, Paul F. 2011. “A history of Neoproterozoic glacial geology, 1871-1997.” In: Arnaud, E., Halverson, G. P. and Shields-Zhou, G. (eds) The Geological Record of Neoproterozoic Glaciations. Geological Society, London, Memoirs, 36, 17-37.
URI: http://hdl.handle.net/10214/9367
Date: 2011
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada
Rights Holder: The copyright of the photos rests with the author(s) of the chapter or, where stated, the person who took the photo.


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Ch2_Photo_1_Hoffman.jpg 475.0Kb JPEG image Thumbnail Dolostone clast in the Port Askaig Tillite, supported on a pedestal of its own wackestone matrix, on Garbh Eileach, the largest of the Garvellach Islands, south of the Isle of Mull in the west of Scotland. The Port Askaig Tillite was recognized as an ancient glacial deposit by James Thomson (FGS) of Glasgow in 1871 while mapping Islay, 50 km southwest of the Garvellachs. Thomson (1823-1900), best known for his work on Carboniferous corals, recognized the unprecedented antiquity (then ‘Cambrian’) of glaciation he inferred (Photo credit: Paul Hoffman).
Ch2_Photo_2_Hoffman.jpg 645.8Kb JPEG image Thumbnail Extrabasinal granitoid-clast diamictite in the Port Askaig Tillite on Garbh Eileach. Thomson (1871, 1877) contended that sources of particular granitoid clasts did not exist in Scotland, and speculated that they were derived through glaciation from a “Great Northern Continent”. Thomson suggested that the lost continent had eroded away; modern isotopic work shows it was southern Greenland and North America, which were contiguous with Scotland before ~55 Ma. Hammer handle is 33 cm long (Photo credit: Paul Hoffman).
Ch2_Photo_3_Hoffman.jpg 716.4Kb JPEG image Thumbnail Polygonal sandstone wedges decorate the tops of multiple tabular mixtite bodies within the Port Askaig Tillite, here on Eileach an Naoimh, the westernmost of the Garvellach Islands. The wedges indicate subaerial exposure during periods of ice retreat from the continental shelf, which had been populated by stromatolites during deposition of the directly underlying Lossit Limestone. Scale is provided by A. M. (Tony) Spencer, whose exhaustive study (Spencer 1971) amply confirmed the interpretations of Thomson (1877) and those of Kilburn, Pitcher & Shackleton (1965), who argued that the mixtites were deposited by ice-sheets grounded on the surface of the marine sediments (Photo credit: Paul Hoffman).
Ch2_Photo_4_Hoffman.jpg 661.5Kb JPEG image Thumbnail Detail of sandstone wedge intersections on the upper surface of a tabular body of massive mixtite in the Port Askaig Tillite on Eileach an Naoimh, Garvellach Islands, western Scotland. Hammer handle is 33 cm long (Photo credit: Paul Hoffman).
Ch2_Photo_5_Hoffman.jpg 620.0Kb JPEG image Thumbnail Mixtite moraine east of Karlebotn, at the head of Varangerfjord, northeastern Norway, first recognized and described by Hans Reusch (1852-1922), then Director of the Geological Survey of Norway and later Sturgis Hooper Professor of Geology at Harvard University. Reusch (1891) recognized the great antiquity of the glaciation (‘Cambro-Silurian’), whose products he compared with Quaternary glacial deposits with which, as a Norwegian geologist, he was very familiar. The moraine rests on a subglacial pavement atop subhorizontal trough-crossbedded quartzite of preglacial age. The pavement has two directions of glacial striae (NNW and WNW), here viewed looking eastward. The directions are consistent with radial flowage of an ice-sheet centered over Baltica. The moraine belongs to the Smalfjord Formation, the older of two glacial horizons (end-Cryogenian and Ediacaran) in the Vestertana Group (Photo credit: Paul Hoffman).
Ch2_Photo_6_Hoffman.jpg 744.4Kb JPEG image Thumbnail Polished and striated subglacial pavement beneath ‘Reusch’s moraine’ at Bigganjargga, east of Karlebotn, Varangerfjord, Norway, viewed looking in the direction of ice-flowage to the north-northwest, which is nearly normal to the trend of the moraine. The pavement preserves the record of dynamic, presumably thick, wet-base ice. The great Finnish Precambrian geologist J. J. Sederholm (1863-1934) described his visits here as “pilgrimages to a spiritual place” (Photo credit: Paul Hoffman).
Ch2_Photo_7_SchmidtAndWilliams.jpg 528.7Kb JPEG image Thumbnail Highly aggradational ripples, crossed by spaced cuspate anticlines arguably resulting from soft-sediment deformation, in tidal-bundled siltstone of the Elatina Formation (Marinoan) in Warren Gorge, southern Flinders Ranges, South Australia. At Pichi Richi Pass, 25 km to the south, semipositive soft-sediment fold tests in similar lithologies of the Elatina Formation confirmed a near-equatorial palaeolatitude for the Elatina glaciation in a tidewater setting in South Australia (Photo credit: Schmidt & Williams 1995).
Ch2_Photo_8_Xiao.jpg 824.7Kb JPEG image Thumbnail Knife-sharp contact between mixtite of the Tereeken Formation and postglacial peloidal dolostone (Zhamoketi Formation) in Yukken Gol, Quruqtagh (central Tian Shan), northwest China. It was here that Swedish geologist Erik Norin (1937) first attempted to reconcile the paradox of ice-infested waters abruptly followed by clear-water carbonate deposition. As its global nature slowly emerged, the ‘cap’ carbonate problem attracted the attention of influential Finnish geochemical geologist Kalervo Rankama (1973), Canadian carbonate sedimentologist James D. Aitken (1991) and scores of others (Photo credit: Shuhai Xiao).

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