46°10'W 46° 45°50' 45°40' 45°30' 45°20' 45°10' 45°W 44°50' 44°40' 44°30' 44°20'W 60°30'S 60°30'S 12 1 Scale: 1:150 000 15 5 21 kilometres 0 2.5 5 7.5 10 10 10 5 0 2.5 5 1 miles 1 1:150 000 Scale 3 10 2 1 5 5 10 2 C O 2 Geological Map of the South Larsen Islands R O 1 60°35' 60°35' N 28 20 A 40 T I O Orkney Islands 2 2 N Saddle Island 3 3 6 I 42 37 A S 20 L 1 40 5 10 A Monroe Island 3 N BAS GEOMAP 2 Series, Sheet 3, Edition 1 2 (3) Triassic 2 30 D 1 1 10 1 43 38 1 40 2 2 55 37 50 5 Weddell Islands Geological interpretation and map compilation by M.J. Flowerdew, T.R. Riley and C.E. Haselwimmer. Geological cross sections compiled by 30 3 80 Rayner Point 63 3 5 5 15 22 30 M.J. Flowerdew and C.E. Haselwimmer. Data preparation, digital cartography, design, and layout by C.E. Haselwimmer. Geological mapping 34 1 10 10 2 and digital map production was undertaken as part of the BAS Environmental Change and Evolution (ECE) programme. 3 10 50 35 5 1 2 Gibbon Bay Base map data for coastlines, rock outcrops, and ice shelves from the Antarctic Digital Database. The Antarctic Digital Database is copyright 10 40 5 15 © 1993-2006 Scientific Committee on Antarctic Research. 89 16 5 1 27 2 70 60°40' 60°40'S 30 Preferred reference for map: 76 3 POWELL 1 296 38 5 22 ISLAND FLOWERDEW, M.J., RILEY, T.R. and HASELWIMMER, C.E. 2011. Geological Map of the South Orkney Islands (1:150 000 scale). BAS 20 60 25 GEOMAP 2 Series, Sheet 3, British Antarctic Survey, Cambridge, UK. 10 7 10 2 4 60 1 25 30 20 10 Johns Peaks5 75 Projection: WGS 1984 Antarctic Polar Stereographic, Central Meridian: 60°W, Spheroid: WGS84. Latitude of true scale: 71°S. 3 3 20 1 45 150 38 30 45 14 SIGNY 20 30 18 85 Published by BRITISH ANTARCTIC SURVEY, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom. This geological map is ISLAND 45 83 83 11 5 8 copyright © British Antarctic Survey, Natural Environment Research Council, 2011. All rights reserved. 5 2 89 RWR 243 D 2 4 1 46°10'W 46° 3 1 22 15 28 12 40 N 255 99 70 24 18 A 46 5 3 75 10 K 239 80 L 27 1 8 1 WR 1 88 70 73 217 12 5 S 46°40'W 20 28 14 I 11 10 45 1 25 3 3 22 Fredricksen Island 68 25 E Moe Island 2 12 176 2 40 L A U R I GEOLOGICAL LEGEND 3 6 5 4 2 17 23 71 10 55 9 KWR 98 91 41 88 56 Geological units are coloured as dark and light tints representing exposed (nunataks) or 22 48 86 88 84 60°45' inferred geology (under ice or snow) 60°45'S 60°45' Matthews Island 5 35 23 A1 80 60 24 2 PERIOD EPOCH/AGE SEDIMENTARY ROCKS PLUTONIC AND METAMORPHIC ROCKS 5 57 41 7 47 60 Spence Harbour Conglomerate 57 CRETACEOUS Early Predominantly conglomerate with thin persistent sandstone interbeds, exposed on eastern Coronation Island and Matthews Island, deposited as debris 3 8 INACCESSIBLE flows and braided stream deposits in alluvial fans within terrestrial to marine fault-bounded basins. Boulders lithologically resembling the Scotia 60°35'S 60°35'S ISLANDS 5 Metamorphic Complex (2) are dominant and suggest a local derivation from the west. Age constraints come from calcareous sandstone boulders at 3 Rayner Point which contain a Late Jurassic - Early Cretaceous fauna and also from a poorly preserved Late Jurassic marine fauna on Matthews Island. Late Basal units in the vicinity of Gibbon Bay, eastern Coronation Island, consist of sparsely fossiliferous (Late Jurassic - Early Cretaceous) dark marine shale, 50 5 the Gibbon Bay Shale. It rests unconformably on the Scotia Metamorphic Complex (1). 60°50'S 60°50'S 60°50'S Powell Island Conglomerate JURASSIC Conglomerate and sandstone exposed on southern Powell Island, deposited as debris flows and braided stream deposits in alluvial fans within terrestrial Middle to marine fault-bounded basins. Boulders resembling Greywacke Shale Formation (1) suggest a local derivation from the north and east. Youngest braided stream deposits at Johns Peaks contain Middle Jurassic flora. 4 Scotia Metamorphic Complex (mixed unit) Early 46°10'W 46°40'W 46°W 45°50'W 45°40' 45°30'W 45°20' 45°10' 45° 44°50' 44°40' 44°30' 44°20'W Scotia Metamorphic Complex (2) with abundant interleaved units of ocean floor derived sequences of uncertain (probable Permian - early Jurassic) age. The oceanic elements include marble, amphibolite and epidote amphibolites, metapelite and metachert which were juxtaposed Greywacke Shale Formation with the Scotia Metamorphic Complex (2) during Late Triassic / early Permian - Triassic sandstone (feldspathic arenite and Jurassic deformation at epidote amphibolite facies metamorphic grade. feldspathic wacke) with minor siltstone, mudstone and The mixed unit is exposed on Signy Island, Coronation Island and the TRIASSIC / diamictite deposited as turbidity currents in submarine Inaccessible Islands. 3 A A1 PERMIAN fans and widely exposed east of Coronation Island. CORONATION ISLAND metres Variably deformed and foliated, metamorphosed to GEOLOGICAL CROSS SECTION FROM CLEFT POINT TO 2000 between anchizone to upper greenschist-facies during the Scotia Metamorphic Complex Roald Glacier POWELL ISLAND LAURIE ISLAND Echo Mountain Beaufoy Ridge Devils Peak Protoliths equivalent to Greywacke Shale Formation (1) but Late Triassic / 1000 3 Spence 4 Late Triassic / early Jurassic. Cleft Point 2 Harbour Cape Robertson early Jurassic metamorphism reached epidote amphibolite-facies grade. CAPE WHITSON 2 Washington Strait Cape Whitson 0 1 2 3 3 2 2 3 2 5 1 -1000 3 (Line A-A1 drawn on the map) 1 1 -2000 2 3 2 3 3 1 3 3 2 2 2 Horizontal scale 1:150 000 Vertical exaggeration x 2 -3000 2 2 2 GEOLOGICAL SYMBOLS 2 -4000 Geological boundary 55 Cleavage or metamorphic foliation Invertebrate fossil Fault 7 Fold hinge line Radiolarian fossil Unconformity Rodding within L-tectonites Fossil leaves REFERENCES 5 46°W 45°40' 45°20' 45° 44°40'W 1. Matthews, D.H. & Malling, D.H. 1967. The Geology of the South Orkney Islands I. Signy Island. Falkland Islands Dependencies 9. Thomson, J.W. 1973. The geology of Powell, Christoffersen and Michelsen islands, South Orkney Islands. British Antarctic Survey Survey scientific reports, 25, 32pp. Bulletin, 33-34, 137-167. 70 Bedding Fault breccia 2. Thomson, J.W. 1968. The Geology of the South Orkney Islands II. The Petrology of Signy Island. Falkland Islands Dependencies 10. Andreis, R.R., Ribeiro, A., Trouw, R.A.J. 1997. Remarks on the petrofacies of Permo-Triassic turbidites from the Antarctic Survey scientific reports, 62, 30pp. Peninsula, South Shetland and South Orkney islands, In: The Antarctic Region: Geological Evolution and Processes, ed. C.A. Ricci, 401-407. 3. Meneilly, A.W. & Storey, B.C. 1986. Ductile thrusting within subduction complex rocks on Signy Island, South Orkney Islands. MAP OF METAMORPHIC FACIES Journal of Structural Geology, 8, 457-472. 11. Dalziel, I.W.D., Elliot, D.H., Jones, D.L., Thonson, J.W., Thomson, M.R.A., Wells, N.A. & Zinsmeister, W.J. 1981. The geological significance of some Triassic microfossils from the South Orkney Islands, Scotia Ridge. Geological Magazine, 118, 15-25. Overturned bedding Ductile shear zone 4. Storey, B.C. & Meneilly, A.W. 1985. Petrogenesis of metamorphic rocks within a subduction-accretion terrane, Signy Island, South 42 AND GEOCHRONOLOGY Orkney Islands. Journal of Metamorphic Geology, 3, 21-42. 12. Thomson, M.R.A. 1981. Late Mesozoic stratigraphy of the South Orkney Islands, British Antarctic Survey Bulletin, 54, 65-83. Extreme 5. Elliot, D.H. & Wells, N.A. 1982. Mesozoic alluvial fans of the South Orkney Islands. In: Antarctic Geoscience, ed. C. Craddock, 13. Thomson, J.W. 1974. The geology of the South Orkney Islands III. Coronation Island. British Antarctic Survey Scientific Reports, Moderate retrogression University of Wisconsin Press, Madison, 235-244. 86, 39pp. retrogression into Scale 1:300 000 6. Cantrill, D.J. 2000. A new macroflora from the South Orkney Islands, Antarctica: evidence of an Early to Middle Jurassic age for the 14. Storey, B.C. & Meneilly, A.W. 1983. Melange within subduction-accretion complex rocks of Fredriksen Island, South Orkney Dolerite Dykes: tholeiitic augite and rarely olivine-bearing dolerite dykes recognised intermittently along the southern Coast of Coronation Island Islands. Geological Magazine, 120, 555-566. into greenschist-facies Powell Island Conglomerate. Antarctic Science, 12, 185-195. and on Matthews Island. K-Ar whole rock geochronology suggests a Late Cretaceous intrusion age for the dolerites. greenschist-facies 7. Trouw, R.A.J., Pankhurst, R.J. & Ribeiro, A. 1997. On the relation between the Scotia Metamorphic Complex and the Trinity 15. Dalziel, I.W.D. 1984. Tectonic evolution of a forearc terrane, southern Scotia ridge, Antarctica. Geological Society of America RMu 187 Peninsula Group, Antarctic Peninsula, In: The Antarctic Region: Geological Evolution and Processes, ed. C.A. Ricci. Terra Special Paper 220, 32pp. Antarctica Publication, Siena, 383-389. A 16. Thomson, J.W. & Harris, J.S. 1984. BAS British Antarctic Territory Geological map 1:500,000, Sheet 1. RMu 188 8. Trouw, R.A.J., Passchier, C.W., Simões, L.S.A., Andreis, R.R.