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Lithostratigraphy of the Macharetí and Mandiyutí Groups of Southern Bolivia: Evidence of the Late Paleozoic Glaciation

Heidi Anderson
University of Idaho, Department of Geosciences Moscow, Idaho; [email protected]

During Carboniferous time Bolivia experienced a sharp climatic gradient with warm water carbonate deposition (Copacabana Fm.) in northern Bolivia and glacially-influenced siliciclastic deposition (Macharetí and Mandiyutí groups) in southern Bolivia. The Macharetí and Mandiyutí groups, consisting mainly of sandstones, shales, and diamicts, contain abundant evidence of glacially influenced deposition (faceted and striated clasts). While evidence of direct ice contact (glacial pavement) is absent in southern Bolivia, northern Argentina preserves a glacial pavement within the Macharetí group. Deposition of the Macharetí group was primarily in paleotopographical lows in channels, while thinner sections were deposited on paleohighs. Sandstones and diamicts in the Macharetí and Manditutí groups have abundant slumping and soft sediment deformation features, documenting earlier suggestions of syndepositional tectonism. Overall depositional systems appear to shallow from dominantly marine to continentally influenced. Petrographic studies are beginning to differentiate sands within the Macharetí and Mandiyutí groups which initially appeared compositionally and texturally similar. Petrographic work is identifying provenance terranes. At present, studies of clasts within the two groups suggest the introduction of volcanoes within the source area. This new source area may also be used to differentiate sands within the Macharetí and Mandiyuti groups.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid