Abstract

Models of late Paleozoic ice-age climate dynamics have remained enigmatic, in part because preservation of mid- to Late Carboniferous, ice-proximal, Gondwanan glacial deposits is limited to very few Gondwanan regions. As such, detailed sedimentologic and stratigraphic analysis of six formations comprising the well-preserved, mid-Carboniferous to Lower Permian (Namurian or Serpukhovian to late Sakmarian), terrestrial, glacially influenced record from the Tamworth Belt, New South Wales, Australia, provides a unique opportunity to test existing models of late Paleozoic climate, characterize regional glaciation, and resolve the internal pacing of climate during the late Paleozoic ice age. Facies analysis based on twelve logged vertical sections and lateral facies relationships suggests that sediment accumulated in an eastward-draining, volcaniclastically influenced alluvial fan (facies association FA1), fluvial (FA2), and lacustrine (FA3) landsystem. 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. The association of these facies, which is termed herein as “distinctly glacial facies” and is taken as direct evidence of glaciation, does not occur through the stratigraphic extent of formations, suggesting that the Tamworth Belt of New South Wales, Australia, was subject to episodic, mountain/valley-type or outlet-type, temperate to subpolar glaciation during the Carboniferous and Early Permian. Climatic shifts and trends occurred on multiple timescales, termed herein “nested cyclicity.” Alternations between distinctly glacial facies and facies that lack evidence of glacial influence, interpreted to record alternating glacial and nonglacial conditions, occurred on timescales on the order of ~ 106 years. The cited age estimates are based on published estimates of glacial interval durations from the region, which in turn reconcile all available radiogenic isotopic data and biostratigraphic zonations. Facies trends within successions recording glacial intervals are interpreted in terms of glacial advance and retreat, which can be estimated to have occurred on timescales shorter than the duration of glacial intervals (shorter-term, sub-106-yr-order timescales) and may include Milankovitch-band cyclicity. These conclusions support the emerging view that the late Paleozoic was characterized by rapid and dynamic climatic shifts on multiple timescales, rather than as one, long protracted event as portrayed by earlier models of Gondwanan glaciation. Furthermore, this study provides an improved understanding of high-latitude climate dynamics and pacing, which may prove useful in constructing improved global models of late Paleozoic climate.

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