The U-Pb dating by LA-ICP-MS of detrital zircons from Canindé Group allowed the
establishment of a direct link between the ages of zircon grains from sandstones of
the eastern edge of the Parnaiba sedimentary basin and the rock units in distal
and/or proximal source areas, and showed that this technique is an indispensable
tool for sedimentary provenance investigation. The studied siliciclastic succession are
composed of diamictic, intraformational breccias, fine to coarse sandstones and, fine
to very fine sandstones which are interdigitated with pelites and mudstones. This
sedimentary sequence is represented by seven facies associations: a) the basal unit
corresponds to lower offshore-shoreface deposits (Af1) of Pimenteiras Formation; b)
gradually westward, crop out rocks of Cabeças Formation represented by subglacial
deposits (Af2) intercalated with, and in erosive character, distal deltaic front deposits
(Af3) - these deposits exhibit more proximal features in the northern, highlighted by
sigmoidal lobes (Af4); c) the Longá Formation exposure is narrower, featuring
deposits of distal deltaic front (Af5); d) the top unit, represented by the Poti
Formation, shows deposits with offshore-shoreface marine features (Af6) in the
northwestern portion, and more continental, with channel bar deposits (Af7), in the
southwestern. The imaging of internal structure of 318 zircon grains of these
sedimentary successions, by Scanning Electron Microscope with Cathode-
Luminescence (SEM-CL), revealed four major populations: a) grains with concentric
zoning (Zr1); b) homogeneous grains (Zr2); c) grains with convoluted zoning or
recrystallized rims (ZR3); d) metamític or fractured grains with exsolved rims (ZR4).
The density distribution diagrams (relative and cumulative probability) of the U-Pb
ages, and the percentages of these ages in pie charts, show clear heterogeneous
distribution of the zircon age spectrum. Paleoproterozoic zircon population (mainly
Orosirian) predominates over Mesoarchean and Mesoproterozoic ones. In addition,
important contribution of Neoproterozoic (largely Tonian) and Cambrian zircon
populations shows up in most of the samples. The K-S test suggests strong similarity
between the sources of Cabeças and Longá formations (p = 0.385) and, a clear
difference of the provenance patterns between the Pimenteiras and Poti formations
(p = 0). Paleocurrent measurements of the fluvial sandstones and of the unimodal
deltaic sigmoids have shown that, during the deposition of Canindé Group, the
source areas were located to the south and southeast of the current border of the Parnaíba basin. These areas include the west sector of the Borborema Province (BP)
and the São Francisco Craton (SFC) with its surrounding Braziliano belts (Brasília
and Rio Preto). Thus, it is suggested that the sediments of the eastern portion of the
Parnaíba Basin, derived from the northern segment of the SFC (Sobradinho block)
and the Central and South subprovinces of the BP. For the latter, the probable
candidates would be the Alto Pajeú tarrain (Cariris Velho – sensu stricto) and the
Riacho do Pontal belt. The sediment supply was fully controlled by marine incursions
(transgressions and regressions) recorded from the Mesodevonian to the
Eocarboniferous.
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