The distribution and paleoclimate implications of periglacial landforms in eastern Australia

Abstract

It is widely recognised that during the Late Quaternary, glaciation was limited in Australia, especially away from Tasmania. This contrasts with the widely recognised occurrence of periglacial landforms in SE Australia, particularly in Australian Alps and Tasmania.However, very little research has been undertaken into these landforms. The aim of this thesis is to investigate the extent and timing of Late Quaternary periglacial conditions in south-eastern Australia and to understand the geomorphic processes and environments associated with these landforms. This thesis presents an updated understanding of the distribution, morphology and climatic significance of periglacial landforms in eastern Australia. The thesis is divided into two sections. The first section is focused on modern 'active' periglacial landforms found primarily in the mountainous areas of Tasmania and focuses on two studies of modern freeze-thaw processes in western Tasmania. At higher elevations (1000 m) notable freeze-thaw features are active at the present time including stone banked lobes on Mt Rufus. Freeze-thaw features were identified to only 150 m above sea-level near Queenstown. However, these low elevation freeze-thaw landforms are small scale features associated with short periods where shallow ground ice forms.The second section of the thesis focuses on relict periglacial landforms that display no evidence of modern activity and most likely relate to late Quaternary cold climate conditions. It primarily focuses on the block deposits of eastern Australia, their morphology, distribution and climatic significance. Block deposits and associated landslide deposits from northern New South Wales to Tasmania were mapped. Four sites were studied in more detail and dated using surface exposure dating (SED). They yielded ages ranging from early Holocene to OIS 5 which are internally consistent within sites but vary widely between sites. These data provide evidence for repeated phases of periglacial activity during the last glacial cycle. At Guyra, several phases of mass movement were recognised with large scale landslides associated with a much earlier warm and humid climate dominating the landscape. Freeze-thaw landforms of the late Quaternary are superimposed on these older forms. The scale of last glaciation cooling is indicated by evidence for a possible nivation hollow bounded by a pronival rampart located near the town of Guyra (29°30'S). From this site a cooling range of 8-11°C is inferred, but additionally, relatively moist conditions are required for the nivation feature to form.The concept of a relatively humid glaciation also emerges from the mapping of the freezethaw landforms on a regional basis. In particular the occurrence of block deposits and screes in northern New England in patterns matching the modern precipitation gradient indicates that freeze-thaw was preferentially concentrated in a zone parallel to the coast. It is inferred that this zone represented an area of intermediate moisture landward of the divide separa...

Pronival ramparts

“…Shakesby et al, 1987), Africa (e.g. Lewis and Illgner, 2001) and Australia (Slee, 2015) (Table 1). The putative relict pronival rampart at Guyra in mainland Australia identified by Slee (2015) is particularly interesting in terms of the uniqueness of the site.…”

“…Grab, 1996) with little morphological detail provided. Active ramparts are more widespread (Table 2), but none have been documented in Africa (Hedding, 2014), Australia (Slee, 2015) or New Zealand (Brook and Williams, 2013). Given the current and former global distribution of cold climates, pronival ramparts are probably underrepresented in the literature.…”

“…Use of a combination of techniques such as ground radar, climate modelling and sedimentology (see Slee, 2015) coupled with relativeage dating or calibrated-age dating could be particularly useful when analysing the probable mode of origin for pronival ramparts. Several other techniques adapted from engineering geology could also be particularly useful when assessing the genesis of actively-accumulating ramparts.…”