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Borehole core recovered from the Late Carboniferous to early Permian Fitzroy tillite and Port Sussex formations, Falkland Islands : geological background and sample details

By P. Stone


Within the Palaeozoic sedimentary succession of the Falkland Islands the Fitzroy Tillite Formation is the local representative of glacigenic strata deposited widely across Gondwana during Late Carboniferous glaciation. In West Falkland, a terrestrial lithofacies contains a wide range of erratic pebbles, cobbles and boulders; in East Falkland a glaciomarine diamictite contains fewer and generally smaller clasts from a more restricted lithological range. At the top of the East Falkland succession is a transitional zone up to about 10 m thick through which the massive diamictite of the Fitzroy Tilllite Formation passes up into the anoxic black mudstone of the Black Rock Member, Port Sussex Formation. The transitional zone – the Hells Kitchen Member of the Port Sussex Formation – features thinly alternating diamictite, mudstone/siltstone with dropstones and laminated mudstone. It records the fluctuating depositional circumstances during deglaciation. Some of the borehole core recovered during a mineral exploration programme illustrated the complete transitional succession from the massive diamictite, through the thinly interbedded lithologies of the Hells Kitchen Member and into the overlying, post-glacial anoxic mudstone. Various runs of borehole core sampling all or part of this interval have been lodged in the collection of the British Geological Survey (BGS), Keyworth. To supplement the borehole core, erratic clast specimens from the diamictite of both East and West Falklands have also been placed in the BGS collection. Clasts of archaeocyath-bearing limestone (of Early Cambrian age) have been discovered in both areas and had a likely provenance in East Antarctica prior to the break-up of Gondwana. The same region may therefore have been the source for some of the other exotic lithologies found as clasts in the diamictite, particularly in West Falkland

Publisher: British Geological Survey
Year: 2011
OAI identifier: oai:nora.nerc.ac.uk:14415

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