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Título

U-PB ZIRCON PROVENANCE DATA OF THE JURASSIC-CRETACEOUS SUCCESSION OF CENTRAL PARNAÍBA BASIN - STRATIGRAPHY, PALEOGEOGRAPHY AND MAJOR SEDIMENT SHIFTS RELATED TO THE GONDWANA BREAK-UP.

Texto do resumo

The Parnaíba Basin, northeast Brazil. preserves the history of Gondwana until its breakup. The Jurassic-Cretaceous succession comprises the Corda Formation (Jurassic) composed by aeolian dunes, sand sheets and wadis; the Grajaú Formation (Aptian) composed by thick coarse braided river facies unconformably covering the older, and transition to a hypersaline lake system of the Codó Formation (Aptian); and deltaic facies successions that unconformably covers the lake sediments, the Itapecuru Formation (Albian). This succession register a complete transgressive-regressive cycle related to the break-up of West Gondwana in which Codó Formation represents the maximum flooding. This work discusses the Jurassic-Cretaceous tectonic-stratigraphic evolution based on sedimentary provenance using LA-ICP-MS U-Pb and Lu-Hf data on detrital zircons. Samples were collected along the margins of the Tocantins River, close to Imperatriz and Açaílândia cities, and partially recovered from the Coroatá borehole (2-1-CO-MA), in Maranhão state, NE Brazil. U-Pb zircon results reveals that the Corda and Grajau formations present mainly Neoproterozoic (53-73%). Subordinated Mesoproterozoic (6-17%), Paleoproterozoic sources (14% to 20%) and minor Archean (1% to 3%) and Paleozoic (1 to 2%) populations were analyzed. In the Codó and Itapecuru formations, we have noticed an increase on the Archean (Codó: 2 to 9%; Itapecuru: 5 to 18%), Paleoproterozoic (Codó: 24 to 27%; Itapecuru: 31 to 53%) and Paleozoic (Codo: 6 to 10%; Itapecuru: 2 to 5%) zircon populations coupled with a remarkable decrease on the proportion of Neoproterozoic (Codó: 43-50%; Itapecuru: 28 to 46%) and Mesoproterozoic (Codó: 5 to 10%; Itapecuru: 2 – 11%) sources. From these two latter formations, we have dated detrital zircon from outcrops and borehole located respectively in the western and Central portions of the Parnaíba Basin. In the Codó Formation, we have noticed that the Archean population from the central borehole samples is slightly more prominent (7-9%) than those from the western outcrop sample (2%), whereas in the Itapecuru Fm. is the opposite, with the western outcrop sample reaching 18% in the Archean population. For the borehole data of the Itapecuru Formation, we also observed the tendency of increase of Archean population and decrease of Neoproterozoic sources from its lower to the upper samples. All samples show a predominant Neoproterozoic population, probably due to the reworking and cannibalization of the older Paleozoic sediments of the Parnaíba Basin, in which also present a pronounced Neoproterozoic signature, equivalent to ages found in the Borborema Province. We interpreted that the Archean sources that increases to the top of the Mesozoic succession is equivalent in age to the Archean terranes of the Amazon Craton, west of the basin. Paleocurrents to NE in the Codó and Itapecuru Formations corroborates to this hypothesis. The most evident source shift occurs between the Aptian and Albian, and it is equivalent to the maximum flooding in the end of the Aptian, probably caused by basement structures reactivation, coeval to the Gondwana breakup, and uplift of Archean terranes close to the western basin border. The authors gratefully acknowledge support from Shell Brasil Petróleo Ltda. and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation (Technical Cooperation #20.219-2).

Palavras Chave

BACIA DO PARNAÍBA; Proveniência Sedimentar; Zircões detríticos