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Provenance of upper Paleozoic siliciclastics rocks from two high-latitude glacially influenced intervals in Bolivia

2019; Elsevier BV; Volume: 92; Linguagem: Inglês

10.1016/j.jsames.2019.02.023

1873-0647

Katarzyna Kołtonik, Peter E. Isaacson, Agnieszka Pisarzowska, Mariusz Paszkowski, Carita Augustsson, Marek Szczerba, Jiří Sláma, Bartosz Budzyń, Michał Stachacz, Wojciech Krawczyński,

Paleontology and Stratigraphy of Fossils

The Toregua Formation in northern Bolivia comprises a continuous succession of sedimentary rocks containing two glacial intervals related to the onset of the Late Paleozoic Ice Age (LPIA). The provenance and depositional tectonic setting of the Upper Devonian–Mississippian (lower) and Pennsylvanian (upper) glacial intervals are separated by non-glacial deposits observed in the Manuripi X-1 and Pando X-1 drill cores, from which petrography, geochemistry, detrital zircon UPb and monazite ThU-total Pb dating are described. Zircon age spectra of sandstone clasts and diamictite indicate an upward change in provenance. Zircon age data from the lower glacial interval yielded age groups at 700–500 Ma, 1300–900 Ma and 2200–1820 Ma, while the monazite gave ages in the range of 600-500 Ma. These age populations correspond to the Guaporé Shield and/or the Arequipa Massif. Detrital zircon from the upper glacial interval has a significant age population at 330–300 Ma that reflects prominent input from the Eastern Cordillera. The maximum depositional age of the upper glacial interval was constrained to ca. 308 Ma. Provenance discrimination diagrams, based on major element geochemistry and trace element ratios, suggest that the glacial and non-glacial sediments were mainly sourced from felsic source rocks. The moderate to high chemical index of alteration (CIA <81) and mineralogical index of alteration (MIA = 81–90 values), abundance of siderite clasts and dominance of kaolinite and abraded zircon grains (without correlation between age and zircon roundness) indicate that the lower glacier incorporated material from older sedimentary covers. In the upper glacial interval, the lower CIA (70) and MIA (71) values and the abundance of plagioclase and detrital zircon grains with preserved euhedral shape <400 Ma suggest that local volcanic rocks in addition to sedimentary covers were eroded.