Year

2011

Degree Name

Doctor of Philosophy

Department

School of Earth & Environmental Sciences

Abstract

Kangaroo Island lies off the South Australian coast, in the Southern Ocean, between 35o 30’ and 36o 30’ south latitude, and 136o 30’ and 138o 30’ east longitude, on a broad expanse of continental shelf that extends southward from the mainland for approximately 100 km. The island itself lies adjacent to three peninsulas and two large gulfs (the Eyre Peninsula, Spencer Gulf, Yorke Peninsula, the Gulf of St. Vincent, and the Fleurieu Peninsula—proceeding in order to the south-east), and forms a boundary between the Lincoln Shelf in the northwest, and the Lacepede Shelf in the southeast.

Kangaroo Island is essentially a south-west extension of the Mount Lofty Ranges. The island is also part of the Adelaide Geosyncline, and forms the southern part of the Fleurieu Arc Segment, encompassing the Kanmantoo Trough. The sub-surface geology is dominated by clastic meta-sediments of Cambrian age. Kangaroo Island incorporates three distinct lithotectonic zones: the Northern Structural Zone comprising relatively unmetamorphosed platformal sediments, the Shear Zone Complex which follows the lines of the Snelling and Signet Faults, and the Southern Basinal Zone encompassing the Kanmantoo Group of metasediments. These rocks are generally poor in outcrop, as they are overlain in most areas by Tertiary laterites or Quaternary calcareous aeolianites. The island is essentially a dissected high lateritic plateau with lowland regions in the north-east and south. Dudley Peninsula is an isolated plateau connected to the island by Quaternary sediments.

This thesis focuses on developing an aminostratigraphical, and chronostratigraphical framework for Bridgewater Formation aeolianite deposition on Kangaroo Island. This required the development of new longer range dating methods, and the use and improvement of existing methods (such as amino acid racemization dating).

Amino acid racemization kinetic experiments were performed on molluscs, foraminifers, and (for the first time) whole-rock carbonate rich sediment, in order to compare the racemization forward rates of various amino acids (GLX in particular) and the changes in the individual amino acid rates across material types, i.e., molluscs, foraminifers, and whole-rock. In the context of the Kangaroo Island samples, and the analysis methods employed, GLX was identified as the amino acid with the most utility (in terms of range, stability, and concentration). It was also revealed that for the Kangaroo Island samples the amino acid GLX was the most compatible (in terms of racemization rate) across many genera of molluscs, and two genera of foraminifers.

This thesis has used luminescence, U-series, 14C, and independently calibrated amino acid racemization dating (for the first time using the amino acid GLX) to establish an aminostratigraphical and chronostratigraphical framework for carbonate deposition on Kangaroo Island. In order to do this a new long-range, single aliquot, luminescence dating method (SARTT-OSL: based upon the multiple-aliquot TTOSL method of Wang et al, 2006a) was developed and more comprehensive preparation treatments for amino acid racemization samples were established. A novel approach for the analysis of single grain AAR results was developed through the use of a statistical method (Ward [1963] hierarchical cluster algorithm). This allowed the identification of the youngest age population in a group of foraminifers (from the same sample) (for aminostratigraphical purposes) and also the identification of clusters of reworked tests within the sample.

The AAR chronology and morphostratigraphical position of raised shelly / cobble/ pebble beach deposits allowed the estimation of a Last Interglacial sealevel for Kangaroo Island, which supports similar sea-level estimates from the mainland (cf. Murray-Wallace and Belperio, 1991; Stirling et al., 1998). The GLX D-L ratios for Last Interglacial marine molluscs, where available, were similar to those found on the South Australia mainland, in Glanville Formation shell-beds (cf. Firman, 1967; Cann, 1978; Belperio et al., 1983, 1984; Hails et al., 1984; Murray-Wallace et al., 1988; Murray-Wallace and Belperio, 1991; Murray- Wallace et al., 2010).

Aeolianite deposition has taken place on Kangaroo Island since at least the latter part of the Early Pleistocene (and in all likelihood some time before this), with the oldest aeolianites recorded (WR AAR age 786+_ 181 ka) being from Stokes Bay on the north coast of the island, and Kelly Hill Caves (WR AAR age 835 +_ 194 ka, and SARTT-OSL age 1.3 +_ 0.1 Ma) on the south coast. The predominant aeolianites were of MIS 7 (Emu Bay, Pennington Bay, Baudin Beach) and MIS 5 (Pennington Bay, Bales Beach, Vivonne Bay, and Baudin Beach) age, with older aeolianites (MIS 11 and 9) being located on the bounding headlands of embayments (particularly on the south coast: Bales Beach and Pennington Bay). The location of the older sediments on headlands is hypothesized to be due to underlying geology acting as keystones or anchors for deposition, allowing the older sediments to build-up to the stage where younger sediments could begin to accrete in the lower topography in the central portions of embayments.

The indirect evidence of Last Interglacial (MIS 5e) raised beach deposits only being located within sediments older than the late Pleistocene points to regressive phase deposition rather than transgressive or highstand deposition of aeolianites (at least for late Pleistocene aeolianites). It is probable in this respect that late Pleistocene aeolianites were being deposited during the regressive phase just after MIS 5e (ca. 116 ka), and the regressive phases after MIS 5c (at Bales Beach ca. 97 ka—OSL age) and 5a.

The stratigraphical and geochronological findings presented in this thesis demonstrate that Kangaroo Island has a long record of the Quaternary coastal environment. This provides an important record that further increases understanding the complexities of carbonate deposition on Kangaroo Island, and its relevance to the broader issues of aeolianite development.

Comments

Thesis contains multiple images from third party source (Google maps); images redacted at request of thesis author.