Provenance of detrital zircons of the caninde group (Parnaiba basin), northeastern Brazil

摘要

This is the first work focusing on the provenance of Middle Devonian-Early Carboniferous sandstones in the eastern margin of the Parnaiba basin. This sedimentary succession represents the main petroleum system in this basin and is composed, from base to top, of the Itaim, Pimenteiras, Cabecas, Longa and Poti Formations of the Caninde Group. The internal textures and U-Pb analyses of detrital zircons allowed defining potential source areas for the sediments of this group. A global tendency of sea level rise in the Middle Devonian, in the evolutionary context of West Gondwana, resulted in the establishment of epicontinental seas and deposition of transgressive sedimentary sequences. Shales and sandstones of the Pimenteiras Formation represent extensive records of these Devonian seas on this paleocontinent. This succession provides zircon ages from 3443 to 438 Ma. Detrital zircons with ages of 538-486 Ma are the most abundant, suggesting derivation mainly from nearby younger sources in the Southern subprovince of the Borborema or Tocantins provinces. The transition between the Middle Devonian and Mississippian Periods is marked by progressive retreat of epicontinental seas with minor marine incursions (represented by the Longa Formation) and resulted in the continental deposits of the Cabecas and Poti Formations. Paleocurrent patterns in both formations suggest direct derivation from the Borborema province. The Cabecas, Longa and Poti Formations contain numerous zircons with ages ranging from 999 to 722 Ma. This detrital population indicates derivation from rocks formed during the Cariris Velhos event in the central portion of the Borborema province. The Cabecas Formation also provided an extensive number of zircons with ages ranging from 2034 to 1830 Ma. Further, the studied geologic units, except for the Pimenteiras formation, show detrital contingents with ages of 1.0-1.2 Ga, also suggesting provenance from distal areas. However, as the spectrum of zircon ages of the Caninde Group is similar to that of the Brasiliano belts surrounding the Parnaiba basin, these belts may also be considered candidates to provide sediments for the Middle Devonian-Early Carboniferous deposits.