Magnetostratigraphy and Environmental Magnetism of the Aptian--Albian Boundary of a Sedimentary Core from the Sergipe-Alagoas Basin

The Early Cretaceous was dominated by greenhouse conditions coupled with increased ocean crust production rate, which led to critical climate, geographic and oceanographic changes and abrupt shifts in redox conditions in the oceans. Regarding Earth’s magnetic field, the Aptian time interval recorded a high rate of polarity reversals. However, after 121.4 Ma, a long period of polarity stability, known as the Cretaceous Normal Polarity Superchron (CNPS), was established for ~38 Myr. Although, there is debate on the causes and consequences of this extreme event, the exact behavior of the geomagnetic field during the Aptian–Albian is still poorly understood, and data from volcanic and sedimentary rocks are usually conflicting. Here we integrate paleomagnetic and biostratigraphic data across the Aptian–Albian transition in the Sergipe-Alagoas Basin (Brazil). Studies suggesting the correlation between magnetostratigraphic and biostratigraphic data for this interval in the Brazilian sedimentary basins are rare, as well as for the South Atlantic marginal basins. Additionally correlations with the Tethyan realm are still unclear. Magnetic parameters, such as magnetic susceptibility, with a resolution of 25 cm, and anhysteretic remanent magnetization (ARM), with a resolution of 2.1 m, were collected over the ~200 m-long succession of Core SER-03 in the Sergipe-Alagoas Basin. ARM acquisition curves were separated into discrete coercivity components and they were interpreted as related to detrital magnetite and/or eolian dust inputs. The entire section spans 6 Myr, including the Aptian–Albian boundary. Our interpretation of environmental magnetism parameter, therefore, allow us to trace shifts between wet and dry climate conditions. Therefore, these data will aid to develop an age model framework in order to assist this uncovered region and future comparisons with Tethyan sections (e.g., Vocontian Basin - France and Poggio Le Guaine - Italy).