Hitta hit:
T-bana: Universitetet
Frescativägen 40

Ordinarie öppettider:
Tisdag-söndag 10-18


  • Huvudmeny

Cretaceous plants of Australia

The Cretaceous is the longest period of the Phanerozoic Eon and saw dramatic environmental and biotic changes that set the scene for the development of our modern world. Australia has extensive sedimentary deposits of this age, and these host rich but geographically scattered assemblages of both terrestrial and marine fossils. The southern supercontinent, Gondwana, continued its fragmentation during the Cretaceous (Veevers 2000). Australia´s isolation initiated in the Middle Jurassic with rifting along the northern margin of the continent (Keep & Haig 2010). This rifting progressed in an anticlockwise fashion around the continent through the Cretaceous (Veevers et al. 1991), generating a series of rift and passive-margin sedimentary basins that today preserve an impressive record of Mesozoic animal and plant remains (together with significant resources of coal, oil and gas). The preserved fossils suggest that the fragmentation of eastern Gondwana had profound effects on biotic provincialism and subsequent development of insular floras and faunas in Australasia during the succeeding Cenozoic Era (Archer et al. 1994, McLoughlin 2001).

The Australian continent underwent rotation in the Cretaceous but remained at middle to high latitudes (Veevers et al. 1991), encompassing an area roughly equivalent to Europe. Extensive basins of fluvial sediments that had accumulated in Australia´s interior during the Jurassic, were flooded by vast shallow seaways during the Early Cretaceous (Valanginian—Albian: 140—100 million years ago). At their transgressive maxima, these marine incursions subdivided the continent into several discrete landmasses, and may have promoted allopatric speciation in the continental biota. The thick sheets of predominantly fine siliciclastic sediments deposited in these palaeoenvironments now form the seals for extensive aquifers (Dettmann et al. 1992), and preserve rich assemblages of coccoliths, radiolarians, foraminifera and palynomorphs that allow precise dating of the rock successions (Apthorpe 1979, Haig 1979, Morgan 1980, Helby et al. 1987, Shafik 1990, Howe et al. 2000). Such biostratigraphical studies have been particularly important for correlating strata within and beyond the Australasian region (Hollis 1997, Raine 2008) because volcanic materials suitable for radiometric dating are scarce and the long normal polarity signature (the Cretaceous Magnetic ‘Quiet Zone´) that characterizes the middle part of the period (McElhinny & Burek 1971) inhibits fine magnetostratigraphic resolution.
 
Many studies over the past four decades have undertaken the description of the Australian Cretaceous floras, although a large number of assemblages remain undescribed or inadequately documented. There are extensive collections of Australian Cretaceous plant fossils in various Australian state museums but, beyond Australia, the Swedish Museum of Natural History probably holds the largest single collection of Australian Cretaceous plants in the form of a large assemblage from Boola Boola (in Victoria), and smaller collections from various sites around the continent.

Summarized from McLoughlin & Kear 2010

Cretaceous sedimentary basins of Australia with major plant macrofossil localities marked by red dots

References

Apthorpe, M. C., 1979. Depositional history of the Upper Cretaceous of the Northwest Shelf, based upon foraminifera. Australian Petroleum Exploration Association Journal 19(1), 74-89.

Archer, M., Hand, S. J. and Godthelp, H., 1994. Patterns in the history of Australia´s mammals and inferences about palaeohabitats. In History of the Australian vegetation: Cretaceous to Recent, R.S. Hill, ed., Cambridge University Press, Cambridge, 80-103.

Dettmann, M. E., Molnar, R. E., Douglas, J. G., Burger, D., Fielding, C., Clifford, H. T., Francis, J., Jell, P., Rich, T., Wade, M., Rich, P. V., Pledge, N., Kemp, A. and Rozefelds, A., 1992. Australian Cretaceous terrestrial faunas and floras: biostratigraphic and biogeographic implications. Cretaceous Research 13, 207-262.

Haig, D. W., 1979. Cretaceous foraminiferal biostratigraphy of Queensland. Alcheringa 3, 171-187.

Helby, R., Morgan, R. and Partridge, A. D., 1987. A palynological zonation of the Australian Mesozoic. Association of Australasian Palaeontologists Memoir 4, 1-94.

Hollis, C. J., 1997. Cretaceous-Paleocene Radiolaria from eastern Marlborough, New Zealand. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences Monograph 17; New Zealand Geological Survey Paleontological Bulletin 73, 1-152.

Howe, R. W., Haig, D. W. and Apthorpe, M. C., 2000. Cenomanian-Coniacian transition from siliciclastic to carbonate marine deposition, Giralia Anticline, Southern Carnarvon Platform, Western Australia. Cretaceous Research 21, 517-551.

Keep, M. & Haig, D.W., 2010. Deformation and exhumation in Timor: Distinct stages of a young orogeny. Tectonophysics 483, 93-111.

McElhinny, M. W. and Burek, P. J., 1971. Mesozoic palaeomagnetic stratigraphy. Nature 232, 98-102.

McLoughlin, S., 2001. The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism. Australian Journal of Botany 49, 271-300.

McLoughlin, S. and Kear, B.P. 2010. The Australasian Cretaceous scene. Alcheringa 34, 197-203.

Morgan, R., 1980. Palynostratigraphy of the Australian Early and middle Cretaceous. Geological Survey of New South Wales, Palaeontology Memoir 18, 1-153.

Raine, J. I., 2008. Zonate lycophyte spores from New Zealand Cretaceous to Paleogene strata. Alcheringa 32, 99-127.

Shafik, S., 1990. Late Cretaceous nannofossil biostratigraphy and biogeography of the Australian western margin. Bureau of Mineral Resources, Geology and Geophysics, Australia, Report 295, 1-164.

Veevers, J. J. (ed.), 2000. Billion-year Earth History of Australia and Neighbours in Gondwanaland. GEMOC Press, Sydney. 400 pp.

Veevers, J. J., Powell, C. McA. and Roots, S. R., 1991. Review of seafloor spreading around Australia. I. Synthesis of the patterns of spreading. Australian Journal of Earth Sciences 38, 373-389.

Global palaeogeographic reconstruction for the Early Cretaceous showing the high southern latitude position of the Boola Boola flora. Click for larger image.