CARBONIFEROUS DIAMICTITE DYKES IN THE FALKLAND ISLANDS

Sedimentary dykes hosted in ?Ordovician-Devonian strata on the Falklan d Islands contain diamictite. The dykes, which are discordant to the h ost rocks, are sub-vertical, parallel-sided sheets formed by downward injection of a semi-fluidized sediment. On West Falkland palynomorphs present in 2 of the 11 dykes located demonstrate a Late Visean-Early N amurian age. This is older than the main Lafonian Diamictite Formation (Permian) and indicates that the dykes are a rare preservation of sed iments formed during the main ice coverage of the Gondwana glaciation. Vitrinite reflectance from organic matter in the dykes indicates a sh allow burial history (<2-3 km) for the southwest Falkland Islands impl ying deposition of an incomplete or condensed sequence during Late Pal aeozoic times, although the stratigraphical relationship of the dykes indicates that this may be extended back into the Mid Palaeozoic. The two diamictite dykes located on East Falkland are shown to be younger; probably Permian in age. (C) 1997 Elsevier Science Limited.