The late Paleozoic Ice Age along the southwestern margin of Gondwana: Facies models, age constraints, correlation and sequence stratigraphic framework

The Late Paleozoic Ice Age (LPIA) has been well recorded in the uppermost Mississippian–Pennsylvanian of Gondwana. Nevertheless, little is known about the temporal and geographic dynamics, particularly during the early Mississippian. We report on exceptional Tournaisian glaciomarine stratigraphic sections from central Argentina (Río Blanco Basin). Encompassing c. 1400 m, these successions contain conspicuous glacigenic strata with age constraints provided by palaeontological data and U/Pb detrital zircon age spectra. A variety of marine, glaciomarine and fan-deltaic environments indicate relative sea-level variations mainly associated with tectonism and repetitive cycles of glacial activity. Provenance analysis indicates a source from the Sierras Pampeanas basement located to the east. Fifteen sequences were grouped into three depositional models: (1) Transgressive Systems Tracts (TST) to Highstand Systems Tracts (HST) sequences unaffected by glacial ice; (2) Lowstand Systems Tracts (LST) to TST and then to HST with glacial inﬂuence; and (3) non-glacial Falling-Stage Systems Tracts (FSST) to TST and HST. The glacial evidence indicates that the oldest Mississippian glacial stage of the LPIA in southwestern Gondwana is constrained to the middle Tournaisian. In contrast with previous descriptions of Gondwanan coeval glacial records, our sequence analysis confirms complex hierarchical climate variability, rather than a single episode of ice advance and retreat.Supplementary material: Detailed stratigraphic sections, palaeocurrents and compositional analysis and U/Pb detrital Zr methodology and data are available at: https://doi.org/10.6084/m9.figshare.c.5011424

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U-Pb CA-IDTIMS geochronology of the Late Paleozoic glacial and post-glacial deposits in southern Paraná Basin

10.5194/egusphere-egu2020-12101 ◽

2020 ◽

Author(s):

Joice Cagliari ◽

Mark D. Schmitz ◽

Ernesto L. C. Lavina ◽

Renata G. Netto

Keyword(s):

Ice Age ◽

Late Paleozoic ◽

South American ◽

Glacial Deposits ◽

Glacial Sediments ◽

South Central ◽

Late Paleozoic Ice Age ◽

Age Model ◽

Eastern Border ◽

Age Constraints

The Late Paleozoic Ice Age (LPIA), one of the best known and prolonged glaciation events in Earth's history, resulted in the deposition of glacial sediments over Gondwana. The terminal deglaciation, a diachronic event starting earlier at the western and later in the eastern part of the continent, caused sea level rise and the widespread deposition of transgressive sedimentary successions. The Paran&#225; Basin is one of these basins recording both glacial influenced (Itarar&#233; Group) and post-glacial (Guat&#225; Group) deposits. However, the absence of Carboniferous and Permian guide fossils has motivated a chronostratigraphic approach based on plants and palynomorphs, which associated with sparse radioisotopic ages have suggested that transition between the glacial-influenced and the post-glacial succession would have occurred in the Sakmarian, early Permian (Holz et al., 2010). &#160;These results are in conflict with recent studies that indicate LPIA glacial deposits are constrained to the Carboniferous (Cagliari et al., 2016; Griffis et al., 2019). Therefore, in this study we present new high-precision single-crystal CA-ID-TIMS U-Pb radioisotopic ages for the glacial influenced (one samples) and post-glacial (six samples) deposits in the southern Paran&#225; Basin. Along with these new radioisotopic ages, a Bayesian age-depth model was applied to constrain the age of the LPIA demise in the southern Paran&#225; Basin, which also represents the icehouse-greenhouse transition. The resulting age for the Rio do Sul Formation, topmost unit of the Itarar&#233; Group, is Ghzelian (Carboniferous). For the Rio Bonito Formation, basal Guat&#225; Group, all samples are Asselian (Permian). The results reinforce that glacial-influenced deposits in the southern Paran&#225; Basin are constrained to the Carboniferous. Based upon the depth-age model, the icehouse to greenhouse transition likely occurred in the Late Carbon&#237;ferous. The integration between our results and recent published high-resolution U-Pb ages allowed us to detail the Carboniferous-Permian chronostratigraphic framework of the southern Paran&#225; Basin.&#160;References:Holz, M., Fran&#231;a, A.B., Souza, P.A., Iannuzzi, R., Rohn, R. (2010). A stratigraphic chart of the Late Carboniferous/Permian succession of the eastern border of the Paran&#225; Basin, Brazil, South America. Journal of South American Earth Sciences 29, 381&#8211;399.Cagliari, J., Philipp, R.P., Buso, V.V., Netto, R.G., Hillebrand, P.K., Lopes, R.C.L., Basei, M.A.S., Faccini, U.F. (2016). Age constraints of the glaciation in the Paran&#225; basin: Evidence from new U&#8211;Pb dates. Journal of the Geological Society 173, 871&#8211;874.Griffis, N.P., Monta&#241;ez, I.P., Mundil, R., Richey, J., Isbell, J., Fedorchuk, N., Linol, B., Iannuzzi, R., Vesely, F., Mottin, T., Rosa, E., Keller, B., Yin, Q. (2019). Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana. Geology 47, 1146&#8211;1150.

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