Quaternary mammal faunas and their stratigraphy in the northern Monaro region, southeastern Australia

Abstract

This thesis documents the history of Quaternary mammalian faunas from the northern Monaro region of the southern highlands of Eastern Australia. The area currently has a cold semi-arid climate and, together with a series of fossil localities of different ages, provides an opportunity to examine the relationships between faunal changes and palaeoenvironments in this part of Australia during the Quaternary. Fossil material from seven localities within the northern Monaro region is described together with the geology of the sites in which they occur. The localities are Pilot Creek, Bunyan Siding, South Bunyan, Bulong, Tannery Creek, Ryries Creek and Rock Flat Creek, all on tributaries of the Murrumbidgee River near Cooma. Detailed stratigraphic studies, incorporating several dating techniques have been employed at the two major fossiliferous deposits, Pilot Creek and Bunyan Siding. A stratigraphic sequence 1s proposed in which the contained faunas are ordered chronologically. The oldest dated mammal fossil-bearing deposit in the region is at Bunyan Siding. It is an alluvial deposit and comprises two fossiliferous Quaternary units, which disconformably overlie Miocene palaeolake sediments of the Bunyan Formation. The Quaternary units are described as two new formations, the Jilliby Folmation and Nestle Brae Formation. They are interpreted as having been formed in a fluvial environment consisting of large and small meandering channels and adjacent floodplains. Dating of the site using palaeomagnetism and optically stimulated luminescence establishes a Middle Pleistocene age (120- 780 ka) for both units. Two local faunas are recognised at Bunyan Siding, the Jilliby Local Fauna and Nestle Brae Local Fauna, each defined and named after the stratigraphic units that contain them. The other major locality, Pilot Creek, is a valley-fill sequence comprising a series of channel cut-and:-fill units and marginal alluvial fans of Late Pleistocene and Holocene ages. Five stratigraphic units are recognised and described in detail including the description of two formations, Pilot Creek and Willow Bank. Each unit contains a local fauna. Fourteen radiocarbon dates enable absolute ages to be placed on some of the units. The oldest fossiliferous unit in the Pilot Creek sequence is the Pilot Creek Formation which has been radiometrically dated at circa 25 ka years BP. The next youngest unit in the sequence is an alluvial fan deposits, QF1 which has been dated at 11 ka. A third unit, the Willow Bank Formation, is a channel-fill unit which truncates both the Pilot Creek Formation and the QF1 unit. Dates from the Willow Bank Formation range from 6 ka to 2 ka. A second alluvial fan unit, QF2 inset into the Pilot Creek Formation, is dated at 4.5 ka. A recent alluvial unit, PESA, is at the top of the sequence. From the stratigraphy of th~ valley units five local faunas have been defined, providing a faunal record in the valley spanning the last 25 ka.