Stone runs in the Falkland Islands: Periglacial or tropical? Marie-Françoise André a, ⁎ , Kevin Hall b , Pascal Bertran c , Joselito Arocena d a Laboratory of Physical Geography, GEOLAB-UMR 6042-CNRS, Blaise Pascal University, 4 rue Ledru 63057 Clermont-Ferrand Cedex 1, France b Geography Program, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N 4Z9 c INRAP / Institut de Préhistoire et de Géologie du Quaternaire, Bâtiment de Géologie, Avenue des Facultés 33405 Talence, France d Environmental Science and Engineering, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada V2N 4Z9 Received 16 February 2007; received in revised form 28 June 2007; accepted 4 July 2007 Available online 6 August 2007 Abstract “Stone runs” is the Falklands vernacular term for openwork boulder accumulations, which include extensive blockstreams like the famous Darwin “stone-river” and associated features such as stone stripes. Since the early 20th century, they have been interpreted as the product of a suite of periglacial processes, including frost-wedging, gelifluction, frost heave, frost-sorting and snowmelt runoff. Following a literature review, the results of recent field investigations of the valley-floor blockstreams of East Falkland are presented. Access to the internal structure of these forms provides evidence for the existence of a three-fold profile, with clear vertical size gradation presenting striking similarities with an inverted weathering profile. Micromorphological analyses, SEM, XRD, thin sections and grain-size analyses lead to the hypothesis of an alternative model of stone run formation. It is suggested that the material forming the stone run profile lato sensu (including the superficial pavement) is not of periglacial origin, but derives directly from the stripping and accumulation downslope of a regolith, possibly Tertiary in age and formed under subtropical or temperate conditions. The valley-floor stone runs should, therefore, be considered as complex polygenetic landforms that may have formed according to a six-stage scenario, including in situ chemical weathering, regolith stripping by mass movements, soil formation, further regolith stripping, downslope accumulation and matrix washing-out (all phases possibly achieved by the Early Quaternary). Periglacial reworking of the stone run material would have operated at a “final” stage, i.e. during Quaternary cold stages, with boulder bioweathering and limonite-staining operating during the temperate intervals including the present one. The suggested antiquity of the Falklands blockstreams is in accordance with Caine's pioneer interpretation of Tasmania blockfields and with recent analyses and cosmogenic datings of blockfields from Scandinavia and North America. © 2007 Elsevier B.V. All rights reserved. Keywords: Falkland Islands; Stone runs; Blockstreams; Blockfields; Quaternary periglacial conditions; Tertiary regolith 1. Introduction “Stone runs” is the Falklands vernacular term generally used in scientific literature to describe “accumulations of boulders with no fine material and virtually no vegetation which occur on slopes or valley bottoms at all levels” (Aldiss and Edwards, 1999); they include extensive blockstreams and associated conspic- uous stone stripes (Figs. 1 and 2). Stone runs, whose extent in the Falkland Islands is unrivaled elsewhere, are a distinctive member of the blockfield family, but they differ from the typical blockfields in so far as they Available online at www.sciencedirect.com Geomorphology 95 (2008) 524 – 543 www.elsevier.com/locate/geomorph ⁎ Corresponding author. Tel.: +33 4 73 34 68 22; fax: +33 4 73 34 68 24. E-mail address: m-francoise.andre@univ-bpclermont.fr (M.-F. André). 0169-555X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2007.07.006