Caiuá group
The Caiuá group is a lithostratigraphic group from the Upper Cretaceous of southern Brazil . It was deposited in the Bauru Basin , a section of the Paraná Basin , over the flood basalts of the Serra Geral Formation .
etymology
The name of the group goes back to the municipality of Caiuá in the west of the Brazilian state of São Paulo .
stratigraphy
The Caiuá Group was deposited in the 370,000 square kilometer Bauru Basin, a sub-basin of the larger Paraná Basin, with an erosive discordance concordantly over the Lower Cretaceous flood basalts of the Serra-Geral Formation from the São Bento Group . In turn, it is overlaid in its hanging wall by the Adamantina formation from the Bauru group or interlocks with it.
The group consists of the following formations (from young to old):
Age
No absolute age information has yet been published for the group, but its maximum age must be less than 132 million years BP (younger than Hauterivium ), the cooling age of the underlying flood basalts.
Distribution area
The rocks of the Caiuá Group are exposed in the Brazilian states of Mato Grosso do Sul , Paraná and São Paulo as well as in northeast Paraguay .
Deposition Conditions and Facies
Lithologically, the rocks of the Caiuá group are red to purple-colored Aeolian sandstones (fine to medium-grain quartz sandstones and subarcoses ), which were deposited in a hot desert climate at the southern end of the Bauru basin. The prevailing wind direction at that time was southwest to south. The sediments formed a 100,000 square kilometer inland sea of sand, the so-called Caiuá desert .
The group usually begins with a massive, 1 meter thick basal breccia with centimeter basalt fragments and concretions made of smectite and carbonate . This is followed by the sediments of large, complex sand dunes with a curved ridge course (interpreted as Draas ), which had formed in the central part of the Caiuá desert (Rio Paraná formation). The dune height subsequently decreased, and interdune sediments were now formed, which correspond more to the edge of the desert and were exposed to fluctuations in the water table (Goio-Erê formation). Finally, dry sand layers of the wide, monotonous desert plains (Santo Anastacio Formation) then sedimented.
Fossil content
Traces of tetrapods were discovered in the Draa sediments of the Caiuá group - proof that life was possible even under extremely arid conditions.
See also
swell
- Fernandes, LA 2006. Caiuá Desert sedimentary environments and facies (Caiuá Group, Late Cretaceous, Brazil). In: Congreso Latinoamericano de Sedimentología, IV y Reunión Argentina de Sedimentología, XI; 2006, San Carlos de Bariloche. Resúmes. Asociación Argentina de Sedimentología / International Association of Sedimentologists. p. 97.
- Fernandes, LA; Costa, R .; Sedor, FA; Silva, LR there; Azevedo, AA; Siqueira, AG 2003. Uma nova icnocenose neocretácea no interior do Deserto Caiuá (Formação Rio Paraná, Bacia Bauru). In: Congresso Brasileiro do Paleontologia, 18th, Brasília. Boletim de Resumos. Brasília DF: Sociedade Brasileira de Paleontologia, 2003. p. 124-125.