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

✍ Scribed by I. Trosdtorf Jr.; A.C. Rocha-Campos; P.R. dos Santos; A. Tomio

• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 535 KB
• Volume: 181
• Category: Article
• ISSN: 0037-0738
• DOI: 10.1016/j.sedgeo.2005.07.006

✦ Synopsis

Four stratigraphically repeated, closely spaced, striated surfaces on Late Paleozoic sandstone at the base of the Itarare Śubgroup, 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.