The Jurassic-Cretaceous transition was marked by the fragmentation of the West Gondwana supercontinent and consequent opening of the Atlantic Ocean. The pre-rupture stages were characterized by epeirogenic uplifts associated with voluminous magmatic accumulation in the infracrust. Additionally, expressive volcanic flows occurred in the central portion of the West Gondwana, composing the Central Atlantic Magmatic Province (CAMP). A post-CAMP thermal subsidence stage allowed the installation of massive lakes coincidently with the depocenters of the Parnaíba Basin, which is recorded in the Jurassic-Cretaceous Pastos Bons Formation (PBF). The PBF is a predominantly constituted of thick reddish mudstones interbedded to tabular sandstones. The basal portion is composed of fossiliferous black shales, the Muzinho Shale. Due to discontinuous exposures and fault displacements, the stratigraphy of the Mesozoic of the Parnaíba Basin keeps poorly understood and the is a necessity for more detailed faciological and sedimentological studies. In this sense, this research performed a sedimentological lecture of these deposits in order to elucidate the paleoenvitonment and Paleogeography of the PBF in the context of the West Gondwana, through outcrop-based facies analysis and cyclostratigraphy. The provenance of this succession was investigated through compositional sandstones diagram, quartz hot cathodoluminescence and heavy minerals analyses. The Muzinho Shale beds were evaluated through petrography, XRD and SEM/EDS. The PBF is composed of four facies associations, interpreted as central lake (FA1), sheet-like delta front (FA2), lakeshore (AF3) and ephemeral fluvial channels (FA4). FA1 is composed of drying/shallowing upward cycles, defined by millimeter-scale black shales interlayered with limestones, that grade to reddish shales and laminated/stratified sandstones. Shales are composed by quartz, illite, smectite and calcite. The fossiliferous levels include young and adult macroforms in the same horizon, sandwiched by crinkly laminations with organic rich Fe-smectites. FA1 indicate sedimentation in the center of the lakes, in eutrophic and anoxic conditions. Mass mortality events were probably induced by contamination of the ater column due to H2S release by cyanobacteria. The transition to mudstones and sandstones reflects the evolution of underfilled to overfilled lakes, as the sediment and water supply were increased. FA2 is composed of tabular sandstones in thickening upward cycles, which record unconfined flows and progressive lake filling, with consequent reworking of the top of the beds by wave action. FA3 is constituted of shallowing upward cycles, marked by wave marks, adhesion structures or mud cracks. FA4 is defined by fining upward cycles developed by ephemeral fluvial channels, with conglomerates and sandstones grading to mudstones. This succession defines open and stratified lakes, dominated by settling and unconfined flows, in hyperpycnal regime. The stratigraphic framework of the PBF is composed of four depositional cycles, constituted of centimeter to millimeter-scale cycles, bounded by flooding surfaces and unconformities. These cycles define a retrogradational-progradational-retrogradational stacking pattern, with increasing accommodation space upward conditioned by post-CAMP thermal subsidence pulses and variations in sediment supply. The Mesozoic succession suggests migration of the West Gondwana toward Equatorial regions during Jurassic-Cretaceous, with aridity attenuation relatively to the Permian-Triassic. The sandstones of the PBF indicate provenance from recycled orogens and craton interior, whereas cathodoluminescence data indicate predominantly volcanic sources. In order to test possible correlations with adjacent units, we verified the heavy minerals assemblage of the PBF is very similar to the Corda Formation, and both differ from the fluvial deposits of the Grajaú Formation. The ZTR, GZi and RZi indexes are higher for sandstones of the PBF and Corda Formation, and lower for the Grajaú Formation. The fluvial deposits distinguish mainly by sillimanite and high hornblende content (>50%). These data indicate polycyclic minerals and mixed sources for sandstones of the Parnaíba Basin. The Mearim Group exhibits volcanic contribution supplied by CAMP basalts and low to medium grade metapelitic sources. This last was possibly supplied by Neoproterozoic rocks of the Médio Coreaú Domain, Borborema Province. Differently, the Grajaú Formation was supplied by type-I Brazilian granites. This geological evolution indicates change in provenance areas or exhumation of common source areas during the Mesozoic of the Parnaíba Basin.
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