Distinguishing different classes of mass-transport deposits in LPIA strata exposed in eastern Paraná Basin, Brazil

• Published in: Journal of South American earth sciences 2023-08, Vol.128, p.104434, Article 104434
• Main Authors: Kraft, Ronaldo Paulo, Vesely, Fernando Farias
• Format: Article
• Language: English
• Subjects: Deglaciation; Diamictites; Paraná Basin; Permocarboniferous
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2023.104434

Ice age mass-transport deposits (MTD) occur in multiple stratigraphic intervals within the Permocarboniferous Itararé Group, in the Paraná Basin, and are exposed in several disconnected quarries and road cuts around the region of Mafra, southern Brazil. The most typical deposits are diamictites with muddy matrix, but silty-sandy diamictites and metric intercalations of deformed layers of sandstones and siltstones occur subordinately. Similar MTD facies have been described from better exposed and time equivalent successions in western Argentina. There, because of the km-scale exposures, MTDs can be mapped in their plenitude, giving better insights about their emplacement. In this paper, we describe the Brazilian MTDs and infer their modes of transport and deposition supported by comparisons with published Argentinean examples. Based on matrix constitution, presence of coherent blocks and rafts, and sedimentation phases, at least four types of MTDs can be identified: 1) Mud-rich MTD and isolated sandstone blocks; 2) Resedimented MTD represented by diamictites with folded blocks of diamictite, possibly corresponding to two phases of remobilization; 3) Sand/silt-rich MTD (evolved stage), and formed by deformed bands of sandstones and siltstones (mature stage); and 4) MTD with rafts of heteroliths and sandstone blocks. Usually MTDs rest on and scour into a fine-grained substrate such as thin-bedded turbidites and shale. The regional geological setting at Mafra points to an open embayment. The collapse of inclined depositional slopes related to high sediment supply associated with deglaciation was the major control on MTD development. However, the inferred proximity of the ice margin during slope failure was variable, suggesting MTD formation during different stages of a glacial cycle. •MTDs occur in different stratigraphic positions in Itararé Group during the LPIA.•The constitution of the MTD depends on the protolith and stage of evolution.•Comparing Paganzo with Mafra added knowledge about LPIA Mass Transport Deposits.