Fleurieu Peninsula Research Articles

Observations on the tectonic evolution of the southern Adelaide Fold Belt

The Mount Lofty Ranges, Fleurieu Peninsula and Kangaroo Island regions of South Australia expose a section across the west and northwestern margin of the southern Adelaide Fold Belt that was deformed and metamorphosed during the Cambro-Ordovician Delamerian Orogeny. In the external parts of the belt, thrust complexes involving basement and a late Proterozoic platformal succession show a characteristic asymmetry reflecting west to northwest vergence towards the Australian craton. In the more internal zones, convergent deformation involving large-scale upright folding and high- T, low- P metamorphism of mainly Cambrian sediments, which were in part turbiditic, occurred between c. 516 and c. 490 Ma. In this part of the belt the distribution of heat and, possibly, strain reflects intimately the advective movement of magmas within the orogenic belt. Convergent deformation in the southern Adelaide Fold Belt was immediately preceded by rapid subsidence initiated during the deposition of the upper parts of the Normanville Group and which continued during deposition of the Kanmantoo Group. Mafic alkaline volcanism attendant with Normanville Group deposition is indicative of lithospheric thinning at c. 526 Ma.

The microstructural anatomy of a major thrust zone on Fleurieu Peninsula, South Australia

Microstructures from a traverse through Early Proterozoic gneiss and Adelaidean and Cambrian metasediments on southern Fleurieu Peninsula, South Australia, show strong mylonitic textures in their common shallowly east‐dipping foliation. The intensity and style of mylonite development is strongly linked to rock type: quartz‐biotite schist has undergone crystal plastic deformation including twinning, deformation banding, intragranular creep, subgrain formation and dynamic recrystallization. Grain boundary sliding and slip on basal planes of cleavage forming micas are dominant in metapelite. Gneiss in the Early Proterozoic inlier shows plastic deformation of quartz augen, brittle deformation of feldspar porphyroclasts and basal slip on phyllosilicates. The Adelaidean calc‐silicate rocks structurally beneath the Early Proterozoic inlier are the weakest unit on the traverse and accommodate the biggest displacement. The sense of shear has been derived statistically from porphyroclast asymmetries, S‐C planes and...

The last interglacial shoreline in Australia — A review

Marginal marine strata of last interglacial age occur in a range of morphostratigraphic settings around the Australian coastline. The lithofacies are similar to their Holocene equivalents but are partly lithified, elevated and laterally displaced inland. Uranium-series ages for corals and molluscs from widely separated localities around the Australian coastline are generally in accord with the accepted age for Oxygen Isotope Substage 5e (125,000 ± 10,000 BP), the value generally accepted for the last interglacial maximum. Amino acid racemisation has principally been applied to correlation of sequences with benchmark sites dated by the uranium-series method. Elevations of preserved last interglacial shorelines do not support the notion that Australia is a stable continent. Significant neotectonic anomalies include Cape Cuvier (+10.5 m), Fleurieu Peninsula (+6 m), the Coorong Coastal Plain (+10 m) and Tasmania (+32 m), each indicating contrasting degrees of local uplift. The Tasmanian sequences are the highest occurrence on the Australian continent and have been attributed to uplift as a result of mantle hotspot processes. With the exception of these tectonically uplifted sites, the height of the last interglacial sea surface around the Australian coastline is consistently below the 6 m level globally attributed to this high sea level stand. In Australia, the most consistent datum is from western Eyre Peninsula where a level 2 m above present mean sea level is ubiquitous. The more southerly limit of coral growth and wider distribution of subtropical molluscan fauna are in accordance with warmer ocean waters during Substage 5e (approximately 2°C). The extent of racemisation in molluscan fossils from southern Australia also excludes the possibility of a more equable latitudinal distribution of MAT during Substage 5e.

Geographical variation in Eucalyptus baxteri s.l. and the recognition of a new species, E. arenacea

Morphological variation in Eucalyptus baxteri (Benth.) Maiden & Blakely ex Black is described throughout its range. There are two geographical forms, the principal differences between which are seedling morphology and the time of transition from juvenile to intermediate growth phase. The forms are hereby recognised as two species. E. baxteri s.str. has adult leaves broad near the apex, warty flower buds, often large fruits, and an early transition to intermediate foliage. It occurs in South Australia on Kangaroo Island, Fleurieu Peninsula, Barossa Range and near Wandilo, and in Victoria on the Grampian Ranges, Great Dividing Range and coastal areas, E. arenacea sp. nov. has tapering adult leaves, generally more slender, non-warty flower buds with longer, narrower pedicels and peduncles. Fruits are generally smaller with the disc less raised. Seedlings typically show a later transition to the intermediate foliage. It occurs on Mt Stapylton in the Grampian Ranges and the desert sand country of north-western Victoria and south-eastern South Australia. It is parapatric with E. baxteri on Kangaroo Island and Fleurieu Peninsula, and is restricted to sand deposits. A previous cladistic analysis suggested that E. baxteri s.l. is paraphyletic, E. arenacea sp. nov. being the sister taxon to E. baxteri s.str. and E. akina (an endemic of the Grampian Ranges). A sequence of evolutionary events is hypothesised by using the cladogram, the distribution of the taxa on different soils, and the geological history of the region.

Context for the Kartan: a preliminary report on excavations at Cape du Couedic rockshelter, Kangaroo Island

Lying within sight of the South Australian mainland, the 4000km2 land mass of Kangaroo Island presents a continuing archaeological mystery. In the mythology of southern coastal Aborigines, it was Karta island of the dead (Tindale and Maegraith 1931; Berndt 1940) a spirit place beyond the reach of living people. However, reports of the discovery of stone artefacts on the island by Howchin in 1903 and Tindale and Maegraith in 1931 demonstrated that Aboriginal people once had occupied the island, beyond the recollection of oral history. The suite of stone implements recorded by Tindale was distinctive. It consisted primarily of large, unifaciallyflaked cobble choppers, unidirectional block cores ('horsehoofs' and 'karta'), steep-edged, thick flake tools, pitted hammerstones, occasional massive 'waisted axes' and very few flakes. Most artefacts were made from the island's abundant quartzites and metasandstones, with occasional use of quartz. This assemblage was unlike any stage of the industrial sequence identified at Devon Downs rocksheiter (Hale and Tindale 1930). Tindale named the Kangaroo Island industry the 'Kartan culture'. Scattered finds of similar implements had been made in the Flinders Ranges north of Adelaide, and along the Fleurieu Peninsula to the south. This suggested to Tindale that the Kartan might date to the last ice age, when Kangaroo Island was connected to the mainland through lowered sea levels. Tindale also recognised similar implements in collections of artefacts from Tasmania. The location of Kartan artefacts on relict, stranded shorelines around Murray Lagoon reinforced the idea of Pleistocene antiquity, as did the similarity of the cobble artefacts to examples from Sumatra and Malaya, which were thought to date to the Upper Pleistocene. Putting all of these clues together, Tindale (1937:59) suggested that the Kartan artefacts represented the toolkit of the earliest immigrants to Australia from southeast Asia _ the people who had reached Tasmania and Kangaroo Island while these places were accessible by glacial land bridge. Consequently, Tindale placed the Kartan as the earliest phase of the industrial succession which he described for Australian prehistory (Tindale 1957, 1968, 1981). Fieldwork to locate Kartan sites continued from the 1940's through to the 1960's by Cooper (1943, 1960, 1966, 1968a, 1968b), Bauer (1959, 1970) and others. More than 100 sites were recorded on the island and adjacent mainland peninsulas. However,

Organic-walled microfossils from the Early Cambrian of South Australia

Microfossils which are hollow, possess a two-layered vesicle wall, and occur as single elements or, more rarely, as compound forms, have been recovered from the Early Cambrian Heatherdale Shale, on the Fleurieu Peninsula, South Australia. The microfossils, which range in size from 4 to 14.5 μm, are informally and tentatively assigned to the genus Sphaerocongregus Moorman 1974. Superficially they resemble forms assigned to Pyritosphaera Love 1958 and its probable junior synonym, Bavlinella Shepeleva 1962. Topotypes of these genera, however, have yet to be studied using SEM techniques, and their morphologic details remain uncertain. The organic composition of the present microfossils is supported by energy-dispersive X-ray analyses. Samples of the Heatherdale Shale were also analysed using pyrolysis techniques; the organic matter is, however, over-mature with respect to petroleum generation, and no geochemical assessment of original kerogen type is possible.

Descriptions ofPharyngodon asterostoma n.sp. andP. tiliquae Baylis, 1930 (Nematoda: Oxyuroidea) fromEgernia cunninghami (Scincidae) in Australia

Two species ofPharyngodon (Oxyuroidea; Pharyngodonidae),P. asterostoma n.sp. andP. tiliquae Baylis, 1930 are described from a specimen ofEgernia cunninghami (Family Scincidae) from Fleurieu Peninsula, Blowhole Creek, New South Wales, Australia.P. asterostoma is easily distinguished from all other members of the genus by the form of the caudal bursa of the male and the oral opening of the male which is in the form of a six-pointed star.P. tiliquae is most similar toP. hindlei Thapar, 1925 fromTiliqua scincoides in Australia but is distinguished by the length of the tail in the male. Comparison of the structure of the caudal bursa in species from different regions of the world suggests that the most primitive species occur in Australia and the most evolved in the New World. ac]19821005

Landslides in South Australia : Selby, J Proc 3rd Australia-New Zealand conference on geomechanics, Wellington, 12–16 May 1980, V2, P69–72. Publ Wellington: New Zealand institution of Engineers, 1980

Many South Australian landslides are due to mass movement of hillslope debris and have occurred during periods of intense rainfall. Earth flows, incorporating rotational movement, occur in Permian Sediments on the Fleurieu Peninsula and are due to the effects of land clearing. Massive rotational slumping, occurring in bedded rocks, has been recorded at several localities as have numerous rockslides in quarries, open cut mines, and road cuts.

Strain variation between quartz grains of different crystallographic orientation in a naturally deformed metasiltstone

Abstract The shapes of isolated quartz grains in a metasiltstone from the Fleurieu Peninsula, South Australia, vary markedly, the amount of strain undergone by individual grains being strongly influenced by crystallographic orientation relative to the finite strain axes. The least-deformed grains have c-axis orientations clustered about the principal strain directions; that is, they have orientations for which the resolved shear stress on the (0001) 〈a〉 and {1010} 〈c〉 slip systems would have been close to zero during coaxial deformation. A simple theoretical approach suggests that the geometry of the bulk strain should influence the observed c-axis fabric of these least-deformed grains. The fabrics should vary from (a) a pronounced maximum parallel to Z with a subsiduary distribution in the XY-plane for pure flattening strain, through (b) fabrics with maxima parallel to X and Z and a weak maximum parallel to Y, to (c) fabrics with a pronounced maximum parallel to X and a subsiduary distribution within the YZ-plane for pure constriction. The most elongate quartz grains in the metasiltstone show a strong maximum of c-axes parallel to the intermediate strain axis, Y. This suggests predominant prismatic slip in a direction at a large angle to the c-axis, probably on {1010} 〈a〉. The bulk strain undergone by the specimen is an integral of the variable strains in the component minerals, and the extremes (the least deformed or the most elongate grains) cannot be regarded as anomalous if a realistic strain estimate is to be obtained.

Variation in fold axis geometry and slaty cleavage microfabric associated with a major fold arc, Fleurieu Peninsula, South Australia

Abstract The slaty cleavage in the sigmoidal Adelaide Fold Belt of South Australia is a predominantly planar fabric with only a weak down‐dip lineation. However, in a gradation towards the Rapid Bay area of south‐west Fleurieu Peninsula, the linear element of the slaty cleavage becomes more pronounced. This increase in fabric linearity is accompanied by a progressive change in fold axis orientation, from approximately horizontal fold axes pitching at a high angle to the mineral lineation (which is typical for the fold belt) to reclined folds with axes at a low angle to the lineation. The variation in fold axis orientation is similar to that calculated by Sanderson (1973) for increasing X:Y strain. The region of more linear fabrics and reclined folds is on the inner arc of a major change in‐ the fold‐belt orientation. The inner segment of this fold arc has undergone a more constrictional strain history than the outer segment, thereby producing both the rotation of the fold axes and the more linear slaty cl...

The development of slaty cleavage, fleurieu peninsula, south australia

In low grade, biotite-rich metasiltstones and slates from the western side of Fleurieu Peninsula, the slaty cleavage is defined by elongate deformed old biotites and by the coincident elongate dimensions and (001) planes of thin, well aligned new biotites. Histograms of frequency versus (001)- S 1 angle ( S 1 defined by aligned thin muscovite used as the reference plane) were determined in thin section for both populations. The old biotites show a symmetrical bimodal distribution of (001) about S 1, with maxima at around 20° either side of S 1. This distribution, together with the preserved intracrystalline strain, indicates that these old grains deformed largely by slip on (001) with some modification of grain boundaries by diffusive transfer. The new biotite grains are very well aligned (standard deviation 3.8°) and show no sign of mechanical deformation. They have not been mechanically rotated into alignment but must have nucleated and grown in a specific orientation. The proportion of new to old grains increases with metamorphic grade, causing a rapid strengthening of the crystallographic alignment. In slates and phyllites with similar microstructure, the mica fabric determined by X-ray texture goniometry cannot be used as a quantitative measure of the geometry and magnitude of the bulk strain, as the intensity of the crystallographic fabric will be strongly influenced by the proportion of new mica, which is itself greatly affected by the metamorphic grade during slaty cleavage formation.

Large‐scale horizontal displacements in Southern Australia — Contrary evidence from Palaeomagnetism

Abstract Palaeomagnetic results from 40 dykes sampled on Eyre Peninsula and Yorke Peninsula, South Australia, are inconsistent with the clockwise rotation of the ‘foot’ of Yorke Peninsula by fault‐drag during the Early Ordovician. A reinterpretation of earlier data from Tasmania also indicates that the east‐west structural trends in the Mount Reed volcanic arc and Dundas Trough are primary. The effects of shearing were probably restricted to linear displacements without causing rotation of adjacent structural elements. Late Precambrian and Cambrian palaeomagnetic data from Fleurieu Peninsula and Kangaroo Island have also been analysed. They do not clarify the pattern of structural evolution in the southern part of the Adelaide Orogen because the magnetic remanence was probably acquired syntectonically.

The Avifauna of Kangaroo Island and Causes of Its Impoverishment

Kangaroo Island has 54 per cent of the species of landbirds that breed on Fleurieu Peninsula, 14 km distant, and about 80 per cent of the species on Yorke or Eyre Peninsulas. Though often visited by ornithologists during the last 67 years, 55 species of landbirds known on the mainland hare never been recorded, 33 others have been recorded less than five times. The marked avifaunal impoverishment of the island is probably not because of differences in habitat or vegetation, but because these 88 species have immigrated very seldom to the island. The pattern of distribution of 226 species of landbirds over southern Australia, including Tasmania and the islands in Bass Strait, suggests that nearly 25 per cent of these arrived postglacially in coastal South Australia. Probably only 25 of the 90 species absent from Kangaroo bland were there in the past but have became extinct. Sixteen of these occur in Tasmania but not on any Bass Strait island and are presumably extinct there also. One native species has established itself on Kangaroo Island in the last 67 years. The theoretical expectation that island populations should have more variable bills or tarsi than mainland populations was confirmed respectively for male Acanthiza pusilla and female Phylidonyris pyrrhoptera.