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Bluff Downs fossil site

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Coordinates: 19°41′S 145°33′E / 19.683°S 145.550°E / -19.683; 145.550
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This is an old revision of this page, as edited by EddaBeck (talk | contribs) at 05:52, 25 May 2021 (Moved "dating" to its own section (vs. as sub-section under "fossils") and added a little more info). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

The Bluff Downs fossil site is a paleontological site of Pliocene age in northern Queensland, Australia, and is one of the most significant fossil sites of Pliocene age in Australia due to its unique fauna and specific dating[1][2]. The fossil site lies on the banks of Allingham Creek on the pastoral property of Bluff Downs Station, northwest of Charters Towers on the Cape York Peninsula[3]

Dating

Precise dating of vertebrate fossil sites in Australia is rare, and many Cenozoic-age sediments remain undated.[2] As of 2000, only two Pliocene vertebrate-bearing fossil faunas were specifically dated, Bluff Downs Local Fauna and the Hamilton Local Fauna in Victoria[4]. Unusually, the Bluff Downs Local Fauna have been specifically dated. This is because there is a minimum age control in the form of a basalt layer (the Bluff Downs Flow) directly overlies the fossiliferous deposit. According to stratigraphy, the fossils must have been deposited before the basalt and thus, since the Bluff Downs Flow has been dated to 3.62 ±0.5 million years old[2]; the fossils were deposited prior to this. The fossils were also deposited directly above another basalt flow, the Allensleigh Flow, allowing a maximum age control. The fossils were likely deposited between 5.2 and 3.6 million years ago during the late Pliocene period[2], which matches dates estimated through biocorrelation. The Allingham Formation has been radiometrically dated to no less than 4 ±0.12 million years old, placing it in the early Pliocene[5]

Geology

Volcanic Activity and Nulla Basalt Province

Bluff Downs fossil site is located within the Nulla Basalt Province, one of four late Cenozoic basalt provinces identified in 1956.[6] The Nulla Basalt Province is dated to the late Pliocene (3.6 to 2.58 million years ago) or early Pleistocene (2.58 – 0.8 million years ago).[6] and consists of multiple olivine basalt flows from lava flows associated with four periods of volcanic activity which occurred 4.5-4.0, 2.3, 1.3 and 1.1 million years ago (according to radiogenic argon determination methods of dating).[2] The dating of the flows matches the ordering suggested by analysis of aerial photographs.[7] These flows of olivine basalt lavas are located on the eastern flank of the Great Dividing Range, and overlie Palaeozoic rock formations as well as sediments from the early Cenozoic, all of which have been partially weathered due to a humid and tropical palaeoenvironment.[7] The most recent volcanic activity in the region occurred 13, 000 years ago, according to sediments underlying the youngest of flow, the Toomba Flow.[2] These flows are relatively thin[7] and were similar to flows which can be observed in present-day Hawai’i. The Bluff Downs Flow directly overlies the fossiliferous sediment (known as the Allingham Formation) in which the Bluff Downs Local Fauna are found, and helped to protect the fossils from erosion[2]

The Allingham Formation

The Allingham Formation, named by Archer and Wade in 1976, is the section of the Nulla Basalt Province which contains the fossils which the Bluff Downs Local Fauna are attributed to.[2] It consists of a mixture of sediment that originated on land and was washed away after eroding into nearby waterbodies (terrigenous sediment), clays, silts, sands (including calcareous sands), and Chara limestones (calcareous nodules that were deposited directly over the fossiliferous sediment and consequently overlain by basalt).[8][2] These sediments were formed in lakes and rivers (i.e. are lacustrine and fluviatile), indicating the presence of various water bodies such as lakes, rivers and streams in the palaeoenvironment at the time of deposition. There were several different depositional events[8] and analysis of the sediments suggests that during the early Pliocene, a stream widened to form a shallow lake.[9]

Fossils

Many vertebrate fossils have been found in the terrigenous sediments of Bluff Downs fossil site, including both broken and complete bones and skulls, though articulated skeletons (that is, with the bones in the same position as upon the organism’s death) are rare.[9] The Bluff Downs Local Fauna is derived from the vertebrate species found in these fossils.

Bluff Downs Local Fauna

The Bluff Downs Local Fauna, named and described by Archer in 1976, includes numerous vertebrate species found at the Bluff Downs Fossil Site,[2] many of which are similar to but slightly older than the Chinchilla fauna (associated with Chinchilla Fossil Site, also in Queensland), according to more ancestral physical features.[9] This collection of vertebrate species was noted to be considerably biodiverse by Archer,[9] and features many ancestors of the species we now recognise as uniquely Australian, as well as unusual extinct species of megafauna, such as Diprotodonts and Thylacoleonids.

The Bluff Downs Local Fauna includes several large reptilian predators, such as crocodiles and a giant varanid (monitor lizard), which has long puzzled palaeontologists as no large predatory terrestrial mammals have been found at the site.

The fauna include species such as the:

Palaeoenvironment

The palaeoenvironment of Bluff Downs during the Pliocene featured large bodies of water. This is inferred from the presence of fluviatile and lacustrine sedimentary deposits, as well as the presence of certain species from the site including pygmy geese and darters, short-necked turtles and long-necked tortoises, which suggest shallow, turbid lagoons were a feature of the prehistoric landscape.[8] The presence of crocodiles and tortoises indicates that these water bodies were at the very least seasonal, as these animals migrate for water.[9] The current understanding is that many of these water bodies were permanent features.[8]

There may have also been a river-based, or riparian, rainforest[8] as species including a land snail and ringtail possum suggest that there were at least patches of closed forests present.[10]

The palaeoenvironment as a whole has been compared to present-day Kakadu,[10] with permanent water bodies, patches of forest and an overall high level of precipitation and humidity, features central to Kakadu’s geography, and the species found at the site mirror this.

References

Notes

  1. ^ "Fossils in Bluff Downs, QLD". The Australian Museum. 10 November 2018. Retrieved 25 May 2021.{{cite web}}: CS1 maint: url-status (link)
  2. ^ a b c d e f g h i j Mackness, B. S.; Whitehead, P. W.; McNamara, G. C. (August 2000). "New potassium‐argon basalt date in relation to the Pliocene Bluff Downs Local Fauna, northern Australia". Australian Journal of Earth Sciences. 47 (4): 807–811. doi:10.1046/j.1440-0952.2000.00812.x. ISSN 0812-0099.
  3. ^ Australian Museum
  4. ^ Mackness, BS; Wroe, S; Muirhead, J; Wilkinson, C; Wilkinson, D (2000). "First Fossil Bandicoots from the Pliocene". Australian Mammalogy. 22 (2): 133. doi:10.1071/am00133. ISSN 0310-0049.
  5. ^ Beck, R.M., Archer, M., Godthelp, H., Mackness, B.S., Hand, S.J. and Muirhead, J., 2008. A bizarre new family of Marsupialia (incertae sedis) from the early Pliocene of northeastern Australia: implications for the phylogeny of bunodont marsupials. Journal of Paleontology, 82(4), pp.749-762.
  6. ^ a b Twidale, C. R. (December 1956). "A physiographic reconnaissance of some Volcanic Provinces in North Queensland, Australia". Bulletin Volcanologique. 18 (1): 3–23. doi:10.1007/BF02596610. ISSN 0258-8900.
  7. ^ a b c Wyatt, D. H.; Webb, A. W. (November 1970). "Potassium‐argon ages of some northern Queensland basalts and an interpretation of late Cainozoic history". Journal of the Geological Society of Australia. 17 (1): 39–51. doi:10.1080/00167617008728722. ISSN 0016-7614.
  8. ^ a b c d e Mackness, Brian (December 1995). "Anhinga malagurala, a New Pygmy Darter from the Early Pliocene Bluff Downs Local Fauna, North-eastern Queensland". Emu - Austral Ornithology. 95 (4): 265–271. doi:10.1071/mu9950265. ISSN 0158-4197.
  9. ^ a b c d e Archer, M, & Wade, M, 1976. ‘Results of the Ray E. Lemley Expeditions. I. The Allingham Formation and a New Pliocene Vertebrate Fauna from Northern Queensland’. Memoirs of the Queensland Museum, vol.17, no. 3, pp. 379-97.
  10. ^ a b Boles, WE and Mackness B, 1994. ‘Birds from the bluff downs local fauna, Allingham formation, Queensland’. Records of the South Australian Museum, 27, pp.139-149.

Sources

  • Rich, T.H.; Archer, M.; Plane, M.; Flannery, T.F.; Pledge, N.S.; Hand, S. & Rich, P.V. (1982). Australian Tertiary mammal localities. In: "The Fossil Vertebrate Record of Australasia", (ed P.V. Rich & E.M. Thompson). Melbourne: Monash University. pp. 525–572. ISBN 0-86746-153-5.
  • "Bluff Downs". Fossil sites of Australia. Australian Museum. 11 August 2009. Retrieved 6 March 2011.
  • Archer, M, & Wade, M, 1976. ‘Results of the Ray E. Lemley Expeditions. I. The Allingham Formation and a New Pliocene Vertebrate Fauna from Northern Queensland’. Memoirs of the Queensland Museum, vol.17, no. 3, pp. 379–97.
  • Beck, R, Archer, M, Godthelp, H, Mackness, BS, Hand, SJ, & Muirhead, J, 2008, ‘A Bizarre New Family of Marsupialia (Incertae sedis) from the Early Pliocene of Northeastern Australia: Implications for the Phylogeny of Bunodont Marsupials’ Journal of Paleontology, vol. 82, no. 4, pp. 749–762, doi: 10.1666/06-124.1.
  • Boles, WE and Mackness B, 1994. ‘Birds from the bluff downs local fauna, Allingham formation, Queensland’. Records of the South Australian Museum, 27, pp. 139–149.
  • Hand, SJ, Archer, M, Gilkeson, CF, Godthelp, H, & Cifelli, R, 1992, ‘Earliest known Australian Tertiary mammal fauna’, Nature (London), vol. 356, no. 6369, pp. 514–516, doi: 10.1038/356514a0.
  • Mackness, BS, Whitehead, PW, & McNamara, GC, 2000, ‘New potassium-argon basalt date in relation to the Pliocene Bluff Downs Local Fauna, northern Australia’, Australian Journal of Earth Sciences, vol. 47, no. 4, pp. 807–811, doi: 10.1046/j.1440-0952.2000.00812.x.
  • Mackness, BS, Wroe, S, Muirhead, J, Wilkinson, C & Wilkinson, D, 2000. ‘First Fossil Bandicoots from the Pliocene’, Australian Mammalogy, vol. 22, no.2, pp. 133–136.
  • Scanlon, JD & Mackness, BS 2001, ‘A new giant python from the Pliocene Bluff Downs Local Fauna of northeastern Queensland’, Alcheringa (Sydney), vol. 25, no. 4, pp. 425–437, doi: 10.1080/03115510108619232.
  • Thomson, S and Mackness, B, 1999. ‘Fossil turtles from the early Pliocene Bluff Downs Local Fauna, with a description of a new species of Elseya’, Transactions of the Royal Society of South Australia, vol. 123, no. 3, pp. 101–105.
  • Twidale, CR, 1956, ‘A physiographic reconnaissance of some Volcanic Provinces in North Queensland, Australia’, Bulletin of Volcanology, vol. 18, no. 1, pp. 3–23, doi: 10.1007/BF02596610.
  • Wyatt, DH & Webb, AW, 1970. ‘Potassium‐argon ages of some northern Queensland basalts and an interpretation of late Cainozoic history’, Journal of the Geological Society of Australia, 17(1), pp. 39–51.

19°41′S 145°33′E / 19.683°S 145.550°E / -19.683; 145.550

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