A new third-order sequence stratigraphic framework applied to the Triassic of the Parana Basin, Rio Grande do Sul, Brazil, based on structural, stratigraphic and paleontological data

摘要

The Santacruzodon assemblage zone was originally denned as a vertebrate fossil assemblage composed basically of non-mammalian cynodonts found in Santa Cruz do Sul and Venancio Aires municipalities in Southern Brazil. This assemblage zone was positioned at the top of the Sequence Ⅰ, in the Triassic Santa Maria Supersequence, Parana Basin. However, the Santacruzodon assemblage zone does not occur across the entire area of the Santa Maria Supersequence. Based on new paleontological, structural and sedi-mentological data, we propose the existence of a new third-order sequence (Santa Cruz Sequence) between Sequences Ⅰ and Ⅱ in the Santa Maria Supersequence. Satellite image analysis was used to identify regional, NW- and NE-oriented lineaments that limit the occurrence zone. Outcrop data allowed the identification of a regional, angular unconformity that bounds the new sequence. The faunal content allowed the correlation of the new Santa Cruz Sequence with Madagascar's Isalo Ⅱ fauna, corresponding to the Ladinian (Middle Triassic). New names were suggested for the sequences in the Santa Maria Supersequence, since the Santa Cruz Sequence was deposited between the former Sequences I and II. This unit was deposited or preserved exclusively on the hanging wall of normal faults, being absent from the adjacent structural blocks.