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The AAPG/Datapages Combined Publications Database
CSPG Special Publications
Abstract
Sedimentation
Late Devonian Glacially-Influenced Marine Sedimentation in Western Gondwana: The Cumana Formation, Altiplano, Bolivia
Abstract
Located above Famennian shallow marine shales (Colpacucho Formation) and at the base of the latest Devonian and Early Carboniferous Ambo Group of the Bolivian Altiplano a diamictite unit and associated lithofacies (Cumana Formation) can be traced for more than 80 km along strike from Isla del Sol to the Copacabana and Cumana peninsula (Lake Titicaca, La Paz Department). The unit has a variable thickness, reaching up to 130 m. Clasts within the diamictite are subangular to well rounded and range from coarse sand to boulder size. Their variable composition, together with the presence of striated and faceted clasts, suggest a glaciated heterogeneous source area. Two major lithofacies associations (LA) have been identified. LA1 is dominated by laminated mudstone with dropstones and is interpreted as ice-rafted and suspended sediment deposits. Above LA1 and with a locally erosional base is LA2, consisting of massive matrix-supported diamictite with deformed sandstone lenses and boulders. LA2 is interpreted as being the result of proglacial deposition at the margin of tidewater glaciers, with resedimentation by postdepositional mass-movement processes, along with partial reworking by underflow currents. Paleogeographic reconstruction of the region suggests that the “eohercynian belt” to the east, the Arequipa massif to the west, or the Puna arc to the south are possible local sources. The overlying Early Carboniferous clastic Kasa Formation shows probable continued glaciation of the source area.
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