Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation

Lily S. Pfeifer, Gerilyn S. Soreghan, Stéphane Pochat, Jean Van Den Driessche

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (μ 1.5 km) succession of exclusively fne-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fuvial deposition, primarily based on a local emphasis of subaqueous features in the upper μ 25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratifcation, and mudcracks record the intermittent in-fuence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of μ 4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and defated deposits of other types (e.g., fuvial outwash) where fne-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted signifcant ice at moderate elevation.

Original languageEnglish (US)
Pages (from-to)379-392
Number of pages14
JournalBulletin of the Geological Society of America
Volume133
Issue number1-2
DOIs
StatePublished - 2020
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geology

Fingerprint

Dive into the research topics of 'Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation'. Together they form a unique fingerprint.

Cite this