Lower Permian aeolian dunes surrounding lakes in Gondwana: Insights on depositional dynamics, cyclicity pattern and climatic control from the Parnaiba basin (Brazil)

The Permian Pedra de Fogo Formation is located in the Parnaíba Basin, northeastern region of Brazil, and high-resolution description of composite sedimentary logs with a total of 66 m led to the recognition of five different facies associations, and exhibits a sediment accumulation of: (1) playa lake; (2) offshore transition; (3) shoreface; (4) aeolian sand sheet; and (5) aeolian dune and interdune. The stratigraphic succession can be separated into three stratigraphic intervals characterized by different facies associations, termed: lower, middle and upper interval. The lower interval is composed by playa lake facies association and lacks aeolian deposits indicating that the water table or its capillary fringe reached the depositional surface, causing a reduction in the availability of dry sand, preventing the development of dunes and aeolian sand sheets. The middle interval consists of offshore transition, shoreface, aeolian sand sheet and aeolian dunes facies associations, indicating wide lake environments with a coastal aeolian system. This interval has a general progradational trend characterized by an increase in the proportion of aeolian deposits to the top. This general progradational stacking pattern is composed of nested shallowing upward high frequency cycles, suggesting that the regressive trend was not linear, being marked by numerous transgressions and regressions of the lacustrine coastline. The upper interval represents the return of the playa lake with tree-ferns stems and leaves at the top, suggesting ephemeral lake system. The depositional context indicates that the mid-palaeolatitudes of Gondwana were not permanently arid or semi-arid during the Cisuralian, since several wetter climate periods also occurred, allowing the development of wide and perennial lake bodies that permitted the maintenance of a rich palaeofauna and palaeoflora. Analysis of aeolian dune foresets dip direction and subsequent correction of the rotation of the South American plate considering the paleogeographic position of the basin during the deposition period, show good compatibility with atmospheric circulation model proposed to Early Permian that indicates winds blowing to N in the Parnaíba Basin.