Multiple Glaciation of the Upper Franklin Valley, Western Tasmania Wilderness World Heritage Area

Abstract

Part of an extensive ice cap that developed in the Tasmanian Central Highlands during the late Cainozoic discharged southwards into the valley of the Franklin River and its upper tributaries where it merged with smaller glaciers that accumulated behind local snowfences. Glacial landforms and sediments in the now heavily forested valleys indicate that at least three and possibly as many as six glaciations took place. The earliest and most extensive glaciation occurred during the Pliocene or earliest Pleistocene. At this time ice extended at least 27km down the Franklin Valley and covered at least 326km2 of the study area. This ice was confluent with glaciers in the West Coast Range to the west and in the Derwent Valley to the east Such confluence offers the possibility of better correlation of glacial events between western Tasmania and the Central Highlands. The smallest and most recent glaciation occurred during the late Last Glacial Stage when the Franklin Glacier did not exceed 12km in length. The glaciers were characterised by high rates of mass throughput and were of temperate maritime type.

Peat mounds of southwest Tasmania: Possible origins

“…There is evidence for multiple glaciations in the higher mountain ranges of southern and western Tasmania during the Quaternary, with glacial episodes during the Early and Middle Pleistocene being more extensive than those during the Late Pleistocene ( Kiernan 1989; Colhoun et al 1996 ). Hidden Valley at 300–400 m in the Bathurst Range ( Figure 1) has the appearance of an eroded hanging valley, and the nearest positively identified glacial features are cirques in the Ironbound Range ( Figure 1) and at Mt Norold, 15 km northeast of Melaleuca ( Derbyshire et al 1965 ).…”

Glaciation and cave sediment aggradation around the margins of the Mt Field Plateau, Tasmania

“…Weathering rind thickness in the Humboldt Advance tills closely matches that of some tills attributed to Global Isotope Stage 6. Weathering of the Junee and Lawrence tills suggests that they are of at least Middle Pleistocene age, while the deeply weathered Westfield till is probably of Early Pleistocene or Pliocene age (Kiernan 1983b, 1989b).…”

“…Just as the Belton and Humboldt drifts at Mt Field cannot be discriminated statistically, mean rind‐thickness values in tills elsewhere in Tasmania that have been attributed to Global Isotope Stage 2 and Global Isotope Stage 6 also overlap at one standard deviation (Table 3). For example, tills in the Franklin Valley interpreted by Kiernan (1989b) as dating from the Beehive Glaciation (Global Isotope Stage 6) exhibit mean rind‐thickness values of 2.9–6.7 mm (maxima 3.7–9.2 mm) that would allow more than a single glaciation to be involved. Tills deposited during the Dixon Glaciation, which has been assumed to date from Global Isotope Stage 2, exhibit subsurface dolerite weathering rinds that are only slightly thinner (mean 1.5–1.6 mm, maxima 2.3–3.8 mm) than those in the youngest Beehive tills.…”

Late Wisconsin glaciation of Tasmania

“…The description of glacial landforms and ice limits that follows is an updated and integrated version of detailed records for the West Coast Range Bowden (1974), Kiernan ( ), Colhoun (1985, Hammond (1985), Fitzsimons etal. (1992), the northwestern Central Plateau and Mersey Valley (Hannan & Colhoun 1987;, the Forth Valley (Kiernan & Hannan 1991), Cradle Mountain (Colhoun 1980), the Central Highlands and Lake St Clair area (Kiernan 1990a(Kiernan , 1991 and the Franklin Valley (Kiernan 1989). It is not possible to show all names on the small-scale maps (figs 2, 3) of the main areas covered by ice during the Late Wisconsin, and maximum extent of ice in pre Wisconsin time.…”

“…During the late 1970s, 1980s and early 1990s, field mapping and stratigraphic investigations demonstrated that Tasmania had a complex history of multiple glaciation, most of which pre-dated the Late Wisconsin (Kiernan 1982, 1983a, 1989, 1995, Colhoun 1985,Augustinus & Colhoun 1986, Hannan & Colhoun 1987, Barbetti & Calhoun 1988, Kiernan & Hannan 1991, Fitzsimons et al 1992. A number of criteria were used to separate Late Wisconsin from older glacial landforms and deposits.…”