Paleowind Reconstruction in the Midwest Gondwana during the Juro-Cretaceous

The passage of a monsoonal pattern to a zonal atmospheric circulation pattern occurred during the Juro-Cretaceous due to fragmentation of the Gondwana Supercontinent. A predominantly monsoonal pattern is characterized by winds... [ view full abstract ]

The passage of a monsoonal pattern to a zonal atmospheric circulation pattern occurred during the Juro-Cretaceous due to fragmentation of the Gondwana Supercontinent. A predominantly monsoonal pattern is characterized by winds that cross the equator, near the Intertropical Convergence Zone, when there is a very strong barometric contrast between land masses and oceans. This contrast existed in the Juro-Cretaceous among Gondwana and oceans around it. After the fragmentation, as the continental masses were being separated, the barometric contrast was decreasing and the development of the zonal pattern of the present winds took place. This change in the paleowinds direction was recorded in paleocurrents of aeolian sandstones deposited in this interval. There are few studies of the Midwest Gondwana aeolian paleocurrents during the Cretaceous to enable the computational models validation. Such studies indicate monsoonal paleowind system during the early Mesozoic. However, there are doubts about when in the Cretaceous was the breaking of monsoonal pattern and establishment of the zonal pattern of present winds. With a broad integration of acquired and compiled data it was possible to visualize three maps of paleowind reconstruction (Upper Jurassic, base of the Lower Cretaceous and top of the Lower Cretaceous), which pointed to the existence of monsoonal pattern during the Upper Jurassic to the base of the Lower Cretaceous and the entry of zonal pattern in the top of the Lower Cretaceous, proving the hypothesis that the fragmentation of a supercontinent affects the overall atmospheric circulation system with physical data and indicating approximately when occurred the breaking of the paleowind pattern. The targeted basins for this paleocurrent study are the Brazilian Phanerozoic sedimentary basins, as long as they present aeolian sandstones deposits during the Upper Jurassic to Lower Cretaceous interval. Because there were few paleocurrent data of the aeolian sandstones of the Tacuarembó Formation in the Paraná Basin, Uruguay, and São Sebastião Formation in the Jatobá Basin, Pernambuco, these formations have been chosen to complete the project with paleocurrent measures acquisition practices.