OR/15/058 Geological reconnaissance: 1871-1939
|Stone, P. 2015. The geological exploration of the sub-Antarctic island of South Georgia: a review and bibliography, 1871–2015. British Geological Survey Internal Report, OR/15/058.|
The first record of geological specimens being collected at South Georgia dates from 1871 when R W Chappell, an American whaling captain, picked up a number of beach pebbles that he later presented to Yale University. These pebbles eventually found their way to Scotland, to Glasgow University, where they were described (as metasedimentary rocks) along with other specimens from the island by Tyrrell (1916). Had Chappell’s specimens been identified earlier, the description of South Georgia’s rocks by Klutschak (1881) might have been rather different. Klutschak, an Austrian adventurer, accompanied a sealing expedition to South Georgia in 1877. He was no geologist, writing (1881: 1967 English translation p.88): “The island’s formation is that of a mountain range some 4 000 to 5 000 ft in height, a range of once mighty but now extinct volcanoes which only reveal their former activity in their sharp, cone-shaped peaks and great beds of lava.” A truer picture emerged as local knowledge of the geology of South Georgia increased substantially at the end of the 19th and beginning of the 20th centuries.
During the German International Polar Year Expedition (1882–1883) rock specimens were collected which were subsequently described by Thürach (1890) as phyllites (some calcareous and some described as ‘phyllitgneiss’), argillaceous slate, tuff and ‘greenstone’. The expedition’s principal purpose was to observe a transit of Venus during the first International Polar Year, for which a base was established in Royal Bay. The phyllite, tuff and slate can all be matched with lithologies exposed in the Royal Bay area and now included within the Sandebugten and Cumberland Bay formations (Stone 1980); the ‘greenstone’ could refer to altered dolerite found in rare intrusive sheets. However, the German expedition’s exploration was limited to the Royal Bay area so the gneiss, reported by Adie (1957a) as “a high-grade paragneiss with sillimanite and andalusite” was most probably a glacial erratic. It may possibly have been derived from the Drygalski Fjord Complex, located in the far south-east of the island, but Gregory (in Ferguson and others 1914) describes the specimen as a ‘shore pebble’ and so an entirely exotic, ice-rafted origin cannot be ruled out.
The German expedition found no fossils so had no evidence for the age of the South Georgia rocks. The first clue to that was obtained twenty years later, when members of the Swedish South Polar Expedition (1901–1903) visited the island during the 1902 austral winter. Andersson discovered in Moraine Fjord (the south-west corner of Cumberland East Bay) a fossil bivalve that was indicative of a late Palaeozoic or early Mesozoic age. He was clearly well-aware of the importance of the discovery, recounting (Nordenskjöld and Andersson 1905, p.362) that recovery of the specimen took four men two days, and involved rock drills and blasting powder. The fossil was found in strata that would now be assigned to the Cumberland Bay Formation. Andersson (1907, 725–726) stressed the importance of the fossil and also commented on the widespread development of spectacular folding: “beautiful folds, which run apparently parallel to the longitudinal axis of the island”.
Back on South Georgia, a considerable advance in geological knowledge was contributed late in 1911 by the German South Polar Expedition (1911–1913). Heim (1912) described the bulk of the island as comprising dark shales and greenish tuffs, with a poorly preserved ammonite found at Prince Olav Harbour seeming to confirm a Mesozoic age for the rocks. As with Andersson’s bivalve, the ammonite was found in strata that would now be assigned to the Cumberland Bay Formation. The other major discovery reported by Heim was the presence of a substantial body of igneous rocks at the south-east end of the island, now divided between the intrusive rocks of the Drygalski Fjord Complex and the volcanogenic Larsen Harbour Complex.
Shortly after the departure of the German expedition, the first attempt at a comprehensive geological assessment of South Georgia began. This was a strictly commercial affair initiated by the Christian Salvesen Whaling Company. When that company established an onshore whaling station in Stromness Bay in 1909, naming it Leith Harbour after the company’s home port in Scotland, the mineral rights to South Georgia were also negotiated with the Government of the Falkland Islands (at the time the island was a Dependency of the Falkland Islands; South Georgia and the South Sandwich Islands now comprise a separate British Overseas Territory). To carry out prospecting work, the Salvesen Company employed David Ferguson, an experienced Scottish geologist and mine surveyor who had close connections with the Geology Department at the University of Glasgow. Ferguson’s work in South Georgia and subsequently in the Falkland Islands and South Shetland Islands has been assessed in some detail by Stone and Faithfull (2013).
Ferguson arrived at Leith Harbour on 7 January 1912, only a month after the departure of the German expedition. Though he would have known nothing of the detail of their work, he gathered some information on their findings from staff at the whaling stations. For example, he was shown a sketch of the poorly preserved ammonite from Prince Olav Harbour that was supportive of the Mesozoic age previously suggested by Andersson’s bivalve. But Ferguson doubted the identification of the fossil and prematurely dismissed the possibility of a Mesozoic age since he had rapidly formed the opinion that the South Georgia rocks were very much older than that. He had misidentified trace fossils found near Leith Harbour as ‘fucoids’ (a common misconception at that time) and, subsequently supported by Gregory (1915), thought that these supposed marine plant fossils had an Early Palaeozoic aspect. He also knew of Pirie’s putative graptolite from the South Orkney Islands, the geology of which he had discussed with William Speirs Bruce (leader of the Scotia expedition) before departing for South Georgia (Stone and Faithfull 2013). Ferguson favoured a correlation between the superficially similar rocks from the two Scotia Arc components, so saw Pirie’s fossil as confirmation of an Early Palaeozoic age for at least part of the South Georgia succession.
Pirie concurred. Back in Glasgow he had seen Ferguson’s specimen collection whilst preparing a contribution to the planned eighth volume in the series of Scotia scientific reports. This volume was never published but a galley proof of Pirie’s description of the geology of the South Orkney Islands (Pirie 1913) is held by the British Antarctic Survey. In it, Pirie wrote that Ferguson’s South Georgia specimens “present remarkable similarity to the greywackes of the South Orkneys, and I think it extremely probable that they will prove to be, if not of identical age, at least older than Upper Palaeozoic.”
Overall, the South Georgia sedimentary succession was interpreted by Ferguson as a conformable series of three divisions, which he differentiated largely on the basis of colour. In two relatively small areas of the island, in Cumberland East Bay and at Godthul (Figure 2), he thought that the middle division lay unconformably on much older sedimentary strata with a more complex structural history. He was partially correct in that the intensely folded and cleaved succession now assigned to the Sandebugten Formation has been overthrust by the less pervasively deformed Cumberland Bay Formation in Cumberland East Bay (Dalziel and others 1975) and at Godthul and around Royal Bay (Stone 1980), but there is no unconformity. Although Ferguson noted and photographed folding at numerous localities and mentions thrusting several times in his field notes (held by the University of Glasgow Archive Services) and in a single sentence in his published account (Ferguson 1915, p.812), the implications of such deformation were largely ignored in the geological map and cross-section that he constructed (Ferguson 1915, plates 81 and 82). Further, his reliance on colour for correlation led to unlikely outcrop patterns, in places requiring horizontal beds over considerable areas. This structural arrangement was demonstrably absent and it is odd that Ferguson’s experienced mentors at Glasgow University, Professor J W Gregory and Dr G W Tyrrell, did not identify this fundamental problem prior to the publication of their joint summary in the Geological Magazine (Ferguson and others 1914) and three individual, complementary papers in the Transactions of the Royal Society of Edinburgh (Ferguson 1915; Gregory 1915 ; Tyrrell 1915). Perhaps Tyrrell’s focus was entirely on petrography, whilst in his comprehensive biography of Gregory, Leake (2011, p.146) notes that the interpretations of South Georgia “reveal Gregory’s poor knowledge of structural geology.” However, Gregory did accept the evidence of the ammonite fossils as establishing a Mesozoic age for at least part of the South Georgia succession. Correspondence held by the Hunterian Museum, University of Glasgow, shows that he had arranged to borrow the specimen collected by the German Expedition (Heim 1912).
A second, although very minor contribution to the geology of South Georgia was facilitated by the Salvesen whaling company during the 1913–14 austral summer. Two zoologists from what was then the British Museum (Natural History), G E Barrett-Hamilton and P Stammwitz, collected data and biological samples from whales at the Leith Harbour factory, but also gathered a small selection of rock specimens. These were never described but are still held in London at The Natural History Museum. There are ten specimens and although they are poorly located, their character is compatible with a provenance in the Leith Harbour area. The scientific investigations came to an unfortunately premature end when Barrett-Hamilton died at Leith Harbour after a heart attack.
After publication of Ferguson’s (1915) account of South Georgia’s geology, and despite the support provided by Gregory and Tyrell, it was not long before his interpretation was challenged. Shackleton’s ill-fated Endurance expedition had called at South Georgia on its voyage south in November 1914, and the expedition’s geologist, J M Wordie (another of Gregory’s protégés), had done much geological work during a stay of about four weeks. Despite the subsequent vicissitudes of the Endurance expedition and being badly injured during service with the Royal Field Artillery towards the end of the Great War, Wordie eventually published a summary of his geological observations. Therein (Wordie 1921, p.19), he dismissed Ferguson’s “unfortunate attempt at subdividing the sedimentary series” of South Georgia, supported its likely Mesozoic age, and stressed the importance of folding. By the time Wordie published, Shackleton had embarked on his final expedition (during which he died, at South Georgia, on 5 January 1921) aboard the Quest, with G V Douglas as geologist. In that expedition’s report, Douglas (1930, p.9) noted with respect to the geology of South Georgia: “J M Wordie’s paper … appeared after the Quest had sailed, and the present writer arrived independently at the conclusions to which Wordie had also come.” The rock specimens collected during the Quest expedition were described by Tyrrell (1930), in the last of his series of papers concerned solely with South Georgia petrography. Macdonald and others (1987) note that this experience enabled Tyrrell, in his 1930 paper, to produce one of the best of the early stratigraphical schemes for South Georgia even though he never visited the island.
The conclusions of Wordie were also supported by Holtedahl (1929) who had studied the geology of South Georgia during the Norwegian Antarctic Expedition, 1927–1928. Holtedahl was able to examine much of the island and concluded that there was a single sedimentary succession of Mesozoic age. Expedition members found more fossils to support that age, notably a collection from Annenkov Island that included an ammonite and several types of bivalve. The other important aspect of Holtedahl’s work was his assessment of the igneous rocks in the SE of the island. He suggested an interbedded relationship between basalt lavas and the youngest part of the sedimentary succession, with still younger intrusive granite and gabbro. During a brief visit to Cooper Bay (CB on Figure 2) he noted the highly sheared contact between igneous and sedimentary rocks that is now known as the Cooper Bay Shear Zone.
Soon after Holtedahl’s study, South Georgia was revisited during the 1928–1929 austral summer by L Kohl-Larsen, who had first arrived in 1911 as a member of the German South Polar Expedition; on that occasion, appendicitis had forced him to leave the expedition and recuperate at the Grytviken whaling station. On his second visit, which was not primarily concerned with geology, Kohl-Larsen recovered more fossils (bivalves and ammonites) from Annenkov Island. These, together with Holtedahl’s collection, were formally described by Wilckens (1932, 1937, 1947) as being undoubtedly Early Cretaceous in age. Wilckens (1933) also attempted to integrate the geology of South Georgia into the broader pattern of the Scotia Arc, stressing that correlation with Tierra del Fuego was more likely than the links with the South Orkney Islands favoured by Pirie (1913) and Tyrrell (1915). Writing of his experiences in South Georgia, Kohl-Larsen (1930) demonstrated that David Ferguson was well-remembered by the whaling community. A location near Leith Harbour was pointed out to him where “an English (sic) geologist had found plant fossils”. Kohl-Larsen acquired explosives from the whaling station and blasted out a collection of specimens that he sent back to the Senckenberg Museum in Frankfurt, Germany. The ‘plants’ — the fucoids of Gregory (1915) — were correctly identified and described as marine trace fossils by Wilckens (1947). In a previous publication Wilckens (1932) had similarly challenged most of the interpretations made by Gregory (1915) of Ferguson’s ‘fossil’ specimens.
Holtedahl’s rock specimens were described by Barth and Holmsen (1939). In his 1929 account Holtedahl had been deeply suspicious of Wegener’s ‘displacement’ hypothesis, but Barth and Holmsen (1939) had enjoyed a decade more to consider the matter and were less dismissive of continental drift. Although their contribution was primarily an account of petrology and geochemistry, Barth and Holmsen concluded with a short section on the “Origin of the South Antillean Arc”. Whilst admitting that the nature of the tectonic forces involved remained a puzzle, they envisaged an origin by continental drift (Barth and Holmsen 1939, p.62) — “if we believe, with Wegener, in a single huge continent that split into fragments which drifted apart.” Visualising two of those fragments as South America and the Antarctic Peninsula, linked by a narrow isthmus, Barth and Holmsen continued:
South Georgia would be one of those pieces.
The Second World War (1939–1945) imposed a starkly different set of priorities and effectively curtailed geological exploration in South Georgia and the wider South Atlantic region. However, one outcome of wartime activity that was to have important scientific consequences in the longer term went by the code name Operation Tabarin. As described by Dudeney and Walton (2012) and Luxton (2014), this saw the covert establishment of British naval outposts in the South Shetland Islands and northern Graham Land in response to the perceived threats from German commerce-raiding warships and possible interventions from Argentina. At war’s end, the naval operation was transformed into a civilian organisation and renamed, now overtly, the Falkland Islands Dependencies Survey (FIDS). This organisation was to play a major role in South Georgia’s post-war geological renaissance.
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