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Revision of Silurian and Devonian Strata of Brazil

Yngve Grahn
Palynology
Vol. 16 (1992), pp. 35-61
Stable URL: http://www.jstor.org/stable/3687652
Page Count: 27
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Revision of Silurian and Devonian Strata of Brazil
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Abstract

The Silurian and Devonian stratigraphy of Brazil has been revised and refined with the help of available data on shelly fossils, spores, graptolites and chitinozoans. The Silurian sedimentation can be divided into four depositional cycles: (1) early-middle Llandovery, (2) late Llandovery-earliest Wenlock, (3) late Wenlock-early Ludlow, and (4) late Ludlow-earliest Pridoli. All four cycles are present in the Amazonas, Parnaíba and probably Jatobá basins, whereas only the two youngest occur in the Solimões Basin. The oldest cycle constitutes the Silurian beds of the Paraná Basin. Glaciations occurred in the Amazonas, Parnaíba and Jatobá basins during middle and late Llandovery. Early Lochkovian beds are widespread in all of these basins, while late Lochkovian-Pragian beds are known only from the Paraná Basin. The chitinozoan faunas in the Silurian-lower Lochkovian show a striking similarity to those from Florida and north Gondwana. Emsian beds are absent in the Solimões and Jatobá basins, but present in the other basins, where the faunas have a pronounced endemism. Eifelian-early Givetian beds are widespread and the faunas show strong influence from eastern North America, although the connection to north Gondwana was still important. Sedimentation was essentially continuous from the Middle Devonian to the latest Frasnian in the Paraná Basin. The Late Devonian in the northern basins can be divided into two depositional cycles, one ranging from late Frasnian to early or possibly late Famennian, and a second of latest Famennian age. The faunas are poor and generally cosmopolitan except for the Parnaíba Basin, where there occurred a rich and diverse endemic shelly and planktonic fauna during the Late Devonian. Continental sedimentation increased during the Famennian, and glaciations occurred near the Devonian-Carboniferous transition.

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