Stratigraphic modeling of the Cenomanian-Turonian level, Açu and Jandaíra formations at the southwest edge of the Potiguar Basin
Keywords:
Stratigraphic Modeling, Açu Formation, Jandaíra Formation, carbonates, siliciclastics, depositional sequence, Potiguar BasinAbstract
Stratigraphic modeling was applied in this research to characterize the transition from the siliciclastic succession of the Açu Formation to the carbonate system of the Jandaíra Formation at the southwestern edge of the onshore Potiguar Basin in northeastern Brazil. To achieve the proposed objectives, five key stratigraphic surfaces were identified, three of which were sequence boundaries (LS1, LS2 and LS3) and two were maximum flooding surfaces (SIM1 and SIM2), constituting two third-order depositional sequences. Sequence 1 (lower) and sequence 2 (upper). The simulations, using the Dionisos® software, were calibrated with the lithological and Gamma-Ray profiles from 9 wells. The transgressive systems tract of sequence 1 was deposited between 95 Ma (LS1) and 93,6 Ma (SIM1) and consists of siliciclastics. The highstand systems tract of the same sequence, deposited between 93,6 Ma (SIM1) and 92,8 Ma (LS2), is characterized by siliciclastic sedimenta-tion up to 93 Ma. From this age, the carbonate sedimentation started, favored by a conspicuous reduction in siliciclastic input, due to a climatic change or supposedly an interaction between tectonics and climate. The transgressive systems tract of sequence 2, deposited between 92,8 Ma (LS2) and 92 Ma (SIM2), is made up of a mixed sedimentation with a predominance of carbonates. The highstand systems tract, deposited between 92 Ma (SIM2) and 91 Ma (LS3), is made up of carbonates with an intermittent supply of siliciclastic sediments. The terrigenous input was deposited at a low sedimentation rate (around 40 m/Ma) up to 93 Ma. After this period, the siliciclastic depositional rate ranged between 0 m/Ma and 10 m/Ma, while the carbonate sedimentation deposit started in 93 Ma at an average rate of 38 m/Ma. The modeled fluvial discharges of sequence 1 correspond to a constant flow of around 520m3/s, while those in sequence 2 ranged between 150m³/s and 1.100m3/s. The high discharges would be the result of sporadic storms which normally occur in arid climates, the weather condition interpreted to prevail during the deposition of this sequence. These results corroborate the interpretations of the depositional model for this period in the Potiguar Basin, demonstrating that this methodology has become an important tool to build a dynamic facies model in frontier exploration areas.
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