The Great American Carbonate Bank in the Greenland-Scotland Sector — Death, Life and Birth
Smith, Paul; Raine, Robert
The Greenland-Scotland sector is one of the best preserved Cambro-Ordovician margins of Laurentia, with around 2500 km of near continuous exposure, telescoped into major thrust sheets during continental collision with Baltica, but preserved at very low metamorphic grade both on the foreland and in the allochthon. Palinspastic restoration of the margin, factoring in Devonian transpression and Silurian thrusting indicates that Spitsbergen terranes were arrayed to the east of the Greenland Caledonides and that there is up to 400 km of shortening in the orogen. The now dismembered margin is represented by GACB successions in NE Spitsbergen, S Spitsbergen, Bjørnøya, the fjord region of Northeast Greenland and NW Scotland. Quartz arenites of Cambrian Series 2 age are present in these areas and the bases are invariably bounded by a major unconformity, indicating that the locus of initial Iapetus rifting was further outboard than any preserved successions. The minimum distance from shoreface to continental margin is at least 600 km, but the strandline is hidden beneath the Inland Ice and the self-slope break is farther E than NE Spitsbergen, the most outboard terrane. These siliciclastic dominated sequences are readily correlated with the Sauk I megasequence of cratonic North America. The oldest GACB sediments are of late Series 2 age and in most areas a complete succession is present from Sauk I to Tippecanoe II. In the higher thrust sheet of NE Greenland, the GACB deposits are 3.7 km in thickness despite being no younger the Sandbian (early Late Ordovician) in age, reflecting the rapid subsidence of the outer part of the shelf. One exception to this pattern of continuous deposition lies at the NE tip of Greenland, a modern and ancient 90 degree swing in the Laurentian margin, where an enigmatic period of uplift occurred from early in the Cambrian to the Tremadocian, with a maximum uplift of over one kilometre. The crest of the uplift was not inundated until the major flooding event at the base of Sauk IV. In eastern North Greenland, sedimentation continues until the early Wenlock when the shelf foundered in response to Caledonian thrusting associated with the collision of Baltica at 425 Ma. The pattern is different farther to the S in NE Greenland and NW Scotland, where GACB sedimentation terminated at 460 Ma. Although no Taconic deformation is present, this may be a far-field response to Taconic thrusting farther south and west.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013