CLIMATE by a C Robinson1 the Climate of Kangaroo Island Is Discussed in Detail
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Kangaroo Island Biological Survey CLIMATE by A C Robinson1 The climate of Kangaroo Island is discussed in detail . There have however been periods of drought on the in Burrows (1979) - He noted that: "The moderating island and Burrows (1979) using a system where influence of the surrounding ocean, together with the annual rainfall totals were below the 10 percentile small size and low elevation of the island means that value for the total rainfall record has suffered that Kangaroo Island has a more equable climate than most drought occurred over much of Kangaroo Island in other parts of South Australia". It has a winter rainfall 1869, 1876, 1888, 1891, 1897, 1902, 1914, 1936, maximum and there is a significant east-west rainfall 1959, 1961 and 1967 gradient ranging from 500 to 900 mm (Figs. 20, 21). A rainfall map following Burrows (1979) is shown in Figure 22 shows the rainfall at Kingscote prior to the Fig. 19. Rainfall has been recorded at the lighthouse 1989 vegetation survey and the 1990 vertebrate survey at Cape Borda since 1868 and is shown in Fig. 18. It discussed in this report and it can be seen that in both can be seen at the western end of the island the rainfall 1989 and 1990 winter rainfall preceding the surveys fluctuates comparatively little around the mean of 631 was slightly above average in 1989 and about average mm. in 1990. Maximum and minimum temperatures recorded during the vertebrate survey in 1990 are shown in Appendix II 1000 900 800 700 600 500 400 300 Annual Rainfall (mm) 200 100 0 1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 Year Figure 18. Annual rainfall at Cape Borda 1868 – 1990. 1 A. C. Robinson, SA Department for Environment Heritage and Aboriginal Affairs, PO Box 1047, ADELAIDE, SA 5001 13 Point Marsden Cape Cassini KINGSCOTE Cygnet River Cape Torrens Penneshaw Cape Borda Gosse American River Parndana Cape Willoughby Murray Lagoon Rocky River Tandanya Karatta Vivonne Bay Cape du Couedic Cape Gantheaume Figure 19. Isohyets of mean annual rainfall in mm (after Burrows, 1979) Shading from light to dark indicates rainfall from <<600 to >>900 mm. 14 Kingscote Post Office, 103 Years of Records (1887-1990) 80 16 70 14 60 12 50 10 Rainfall 40 8 Maximum (mm) 30 6 Minimum Mean Daily 20 4 Temperature ( C) Mean Monthly Rainfall 10 2 0 0 J J S N M M Months Penneshaw Post Office 79 Years of Records (1911-1990), Temperature not 90 available 80 70 60 50 (mm) 40 30 20 Mean Monthly Rainfall 10 0 J J S N M M Month Cape Willoughby Lighthouse 109 Years of Records (1881-1990) 90 18 80 16 70 14 60 12 Rainfall 50 10 Maximum 40 8 Minimum 30 6 Mean Daily Rainfall (mm) Mean Monthly 20 4 Temperature ( C) 10 2 0 0 J J S N M M Months Figure 20. Variation in mean rainfall and temperature across the Kangaroo Island study area. 15 Parndana East Research Centre 30 Years of Records (1954-1984) 120 14 100 12 10 80 Rainfall 8 60 Maximum 6 Minimum 40 4 Mean Daily Rainfall (mm) Mean Monthly Temperature ( C) 20 2 0 0 J J S N M M Month Cape Borda Lighthouse 125 Years of Records (1865-1990) 120 16 14 100 12 80 10 Rainfall 60 8 Maximum 6 Minimum 40 Mean Daily Rainfall (mm) Mean Monthly 4 20 Temperature ( C) 2 0 0 J J S N M M Months Cape Du Couedic Lighthouse 73 Years of Records (1907-1990) 120 16 14 100 12 80 10 Rainfall 60 8 Maximum 6 Minimum 40 Mean Daily Rainfall (mm) Mean Monthly 4 20 Temperature ( C) 2 0 0 J J S N M M Months Figure 21. Variation in mean rainfall and temperature across the Kangaroo Island study area. 16 140 120 100 80 Rainfall Maximum 60 Minimum 40 Monthly Rainfall (mm) 20 0 J J J J J J A O A O A O Month Figure 22. Rainfall at Kingscote 1988 – 1990. 17 18 Kangaroo Island Biological Survey GEOMORPHOLOGY AND GEOLOGY by A.P. Belperio2 and R.B. Flint2 INTRODUCTION Only limited resource exploration has been Kangaroo Island comprises a diverse association of undertaken, largely as a result of the Island's isolation, both rocks and landforms that reflect a long and varied and consequently little subsurface data are available. geological history. The geological record on the In addition, much of the outcrop on the island is Island, though fragmented and incomplete, spans the veneered by soils, palaeosols and Quaternary time interval from early Proterozoic to the present. sediments, with useful exposures of older rocks generally restricted to the coastal cliffs. Systematic geological investigations of the Island were undertaken by H.Y.L. Brown in 1898 and R.C. Sprigg The generalised tectonic and geological maps (Figs 23 in 1954, with the present phase of re-mapping and 24) indicate that the framework of the island is currently (1991), being undertaken by the authors. based on Cambrian rocks now deformed into an Daily et al. (1979) compiled the first comprehensive arcuate belt that is a contiguous extension of Fleurieu account of the Island's geology, while numerous other Peninsula. The stratigraphic column (Fig. 25), investigators have concentrated on particular aspects indicates a number of subsequent episodes of of the diverse geology. Some of the more important continental and marine sedimentation separated by contributions have been those of Connard (1967), periods of subaerial exposure and erosion. The Daily and Milnes (1971, 1972), Daily et al. (1980), geological strata, their nature, distribution and Flint (1978), Flint and Grady (1979) and Milnes et al. evolution, are all collectively important in influencing (1982, 1983). the broad geomorphology and landforms of the Island. Figure 23. Tectonic framework of Kangaroo Island. 2 A. P. Belperio and A. B. Flint, Primary Industries and Resources, South Australia. PO Box 151, EASTWOOD, SA 5063 GEOLOGICAL HISTORY Mount McDonnell Formation, Stokes Bay Sandstone, Early Precambrian Smith Bay Shale, White Point Conglomerate, Emu Bay Shale and Boxing Bay Formation. Clastic One of the major Precambrian tectonic provinces in sediments predominate and include feldspathic and South Australia is the Gawler Craton, and exposures micaceous sandstones, poorly sorted conglomerates of crystalline basement include occurrences on and micaceous shale and siltstones, whereas limestone southern Yorke Peninsula and various islands and horizons are thin and rare. Fossils are common, knolls on the sea floor within Investigator Strait. Rock though, including trilobites, worm burrows and types are predominantly orthogneisses, including Archaeocyatha. Bedding structures are well preserved, deformed megacrystic granite, charnockite, with cross bedding, plane bedding and ripple bedding granodiorite, leucogranite and aplite forming part of indicative of major east-west currents during the Donington Granitoid Suite of the Lincoln Complex deposition. (Rankin et al., 1991). The emplacement age for these intrusive granitoid bodies is 1 843+2 Ma (Mortimer et The Kanmantoo Group consists of 8 units - al., 1986). Carrickalinga Head Formation, Talisker Calcsiltstone, Tapanappa Formation, Tunkalilla Formation, No exposures of Lincoln Complex crystalline Balquidder Formation, Petrel Cove Formation and basement occur on Kangaroo Island, though its Middleton Sandstone (in ascending stratigraphic existence at depths of 200 to 2000 m beneath the north sequence). The total thickness is unknown, but is coast has been interpreted from magnetic and gravity considerably more than the 2500m for equivalent units data (Van der Stelt et al., 1992; Belperio and Flint, north of the Cygnet-Snelling fault zone. The sequence 1992). Though concealed now, the Gawler Craton had is characterised by rapidly deposited, poorly sorted a major influence on late Precambrian to Cambrian sandstones, often with interbedded siltstones and sedimentation and orogenesis. mudstones. Pebbly horizons and fossils are rare. The sandstones are massive to well bedded, and along with Late Precambrian channel and fill structures, flame structures, cross bedding and abundant convoluted bedding, indicate The oldest exposed units on Kangaroo Island are late strong palaeocurrents to the east. Precambrian strata of the Adelaide Geosyncline. Exposed only in the core of a regional anticline on Cambrian - Ordovician Dudley Peninsula, their distribution elsewhere on the island is not known due to concealment by younger Sedimentation within the Stansbury Basin and sediments. Kanmantoo Trough ceased in the late Cambrian to early Ordovician with the onset of major deformation Strata include equivalents of the Sturt Tillite, Tapley during the Delamerian Orogeny. Several episodes of Hill Formation, Brighton Limestone and Marino compression and metamorphism (Fig. 27), and Group, but they represent only a thin sequence in intrusion of granite magmas complexly folded and comparison to the thicker and more complete record deformed the sedimentary sequences. The sediments elsewhere in the Adelaide Geosyncline. have been variably deformed with the Cygnet-Snelling fault zone again defining the transitional boundary. Cambrian To the north, orogenesis was relatively weak with broad and open folds, very low greenschist facies During the early Cambrian, marine sediments were metamorphism and good preservation of sedimentary deposited over all of Kangaroo Island (Daily et al., structures and fossils. To the south, deformation was 1979). The Cygnet-Snelling fault zone, which more intense producing complex fold patterns, the delineates the tectonic margin to the Gawler Craton, metamorphic grade was higher reaching mid- was a major influence in controlling sedimentary amphibolite facies, and metamorphism was associated facies (Fig. 25). To the north, basement of the Gawler with development of migmatites and granite Craton was exposed and being eroded. River systems intrusions. The Cygnet-Snelling fault zone displays and deltas fed clastic detritus into a shallow marine evidence of ductile and brittle deformation, containing shelf (Stansbury Basin) resulting in conglomerates, both mylonites and fault breccias.