Origin of Late Paleozoic, multiple, glacially striated surfaces in northern Paraná Basin (Brazil): Some implications for the dynamics of the Paraná glacial lobe

Autor: I. Trosdtorf, Antonio C. Rocha-Campos, Alexandre Tomio, P. R. dos Santos
Rok vydání: 2005
Předmět:
Zdroj: Repositório Institucional da USP (Biblioteca Digital da Produção Intelectual)
Universidade de São Paulo (USP)
instacron:USP
ISSN: 0037-0738
DOI: 10.1016/j.sedgeo.2005.07.006
Popis: Four stratigraphically repeated, closely spaced, striated surfaces on Late Paleozoic sandstone at the base of the Itarare Subgroup, in northern Parana Basin, were generated by subglacial erosion during advances of the grounding zone of the tidewater terminus of the Parana glacial lobe on unconsolidated sand. The sandstone corresponds to a channelized, sheet-like, proglacial outwash fan accumulated sub-aquatically in front of the tidewater terminus of a temperate, warm-based glacier, at the margin of the marine flooded Parana Basin. Sandy-siltstone beds intercalated with the sandstone and resting on top of the striated surfaces represent aggradational mud deposited from settling of fine debris plumes (overflows). Erosion was mostly by abrasion (wear) of the sand bed under a glacier sliding over an unfrozen substratum. Evidence of ploughing is minimal. The glacier bed is thought to have behaved rheologically as a rigid, essentially undeformable substratum. Discontinuities in the distribution of striations on the surfaces indicate that ice may have at places decoupled from its bed. The section studied documents an upward fining and deepening deglacial sequence, comprising four stratigraphic cycles of accumulation of sand, formation of a striated surface followed by deposition of mud. Cycles are correlated with short-lived, probably fast, seasonal advances of the tidewater terminus during general retreat of the Parana lobe. Ice advances were not associated with deposition of subglacial diamicton or lodgement of clasts but to erosion of sand probably by ice protuberances under the sliding glacier.
Databáze: OpenAIRE
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