Stratigraphic and Sedimentologic Evaluation of the Carboniferous Ice-Proximal Record from Eastern Australia Reveals Climatic Variation from Multiple Timescales

Lauren Birgenheier¹, Christopher R. Fielding¹, Michael C. Rygel², and Tracy D. Frank^1
1Geosciences, University of Nebraska-Lincoln, Lincoln, NE
²Geology, State University of New York-Potsdam, Potsdam, NY

A regional scale stratigraphic and sedimentologic investigation of the Carboniferous ice-proximal record from eastern Australia has revealed dynamic climatic variability on multiple timescales. Strata record alternating glacial and non-glacial intervals of deposition on 1-5.5 m.y. timescales. From the Namurian through late Westphalian (Serpukhovian through mid-Moscovian), Carboniferous glacial intervals (C1-C4) become increasingly longer in duration, and evidence for glacial conditions becomes more widespread with increasingly ice-proximal facies, illustrating a longer term pattern of increasing climatic austerity. Detailed sedimentologic examination of five Carboniferous glacially-influenced formations from New South Wales, Australia shows direct evidence of glaciation is not present throughout the stratigraphic extent of formations and facies trends are, thus, interpreted in terms of temporal patterns of glacial advance and retreat. The timescale of glacial advance and retreat can be constrained to <1-5.5 m.y. timescales (less than the duration of Carboniferous glacial intervals C1-C4) and may record Milankovitch band cyclicity. Facies analysis based on logged vertical sections and lateral facies relationships suggest sediment accumulated in a volcaniclastically influenced alluvial fan (facies association-FA1), fluvial (FA2), and lacustrine (FA3) landsystem with an eastward regional sediment dispersal pattern. Evidence for proglacial outwash fan (sandar), glaciofluvial, and glaciolacustrine deposition is preserved in the form of texturally diverse diamictite, outsized clasts in fine-grained facies, and rhythmically laminated sandstone and siltstone. Stacking patterns are interpreted to record glacial advance and retreat in a region subject to episodic, mountain/valley-type or outlet-type, temperate to subpolar glaciation.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas