Record details

    Circular, Cryogenic Structures from the Hirnantian Deglaciation Sequence (Anti-Atlas, Morocco)
    Ghienne, J.-F.
    Nutz, A.
    Štorch, Petr
Publication type
    článek v odborném periodiku
Source title - serial
    Journal of Sedimentary Research
    Roč. 83, č. 1
    s. 115-131
    IGCP 591 - International Programme of Geological Correlation
    Rozsah: 17 s. : P
Subject category
    Anti-Atlas (Morocco)
    cryogenic structure
Abstract (in english)
   More than a hundred circular structures are observed at the topmost part of the Late Ordovician glaciogenic record in the central Anti-Atlas, southern Morocco. The structures were formed in the outer glacial platform and characterize the Hirnantian deglaciation sequence. The circular to ovoidal structures, which comprise fluvial sandstone beds and are sealed by shallow-marine strata, occur in closely spaced clusters. The circular structures are interpreted as periglacial in origin, related to cryogenic processes involving the growth and then decay of bodies of segregation ice. The size and diameter are comparable to the latest Pleistocene and current lithalsa-like structures. A conceptual emplacement model is proposed. The Hirnantian lithalsa-like structures constitute firm evidence for a Late Ordovician discontinuous permafrost during the deglaciation stage in the area of present Morroccan Anti-Atlas.
    AV ČR Brno, Geologický ústav
Contributor code
    AV ČR, GLÚ
Source format
Import date
    23. 10. 2014