Oasis Spring

Oasis Spring

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Oasis Spring, Cape York

Oasis Spring is a permanent bauxite spring in Weipa Plateau supported by an aquifer overlying, but separate to, the Great Artesian Basin. Weipa Plateau is a remnant of the extensive, deeply weathered western coastal plains of Cape York Peninsula[8]. This plateau is an estimated 50 km wide with slight elevation of up to 15 m near the coast, rising to 70 m in the east[8]. The gently rolling hills of the plateau are dissected by discontinuous drainage and deep incisions that have been carved out by major rivers such as the Archer and Wenlock Rivers[6][2][8].

Based on information collected during a drilling program conducted by[9], the following sequence of geological layers near Oasis Spring is consistent with the broader geological profile of the Weipa Plateau[1][3][7].

1. Soil—red and yellow kandosols[1] mixed with bauxite pisoliths (i.e. small round bauxite pebbles).
2. Bauxite—a bauxite layer occurs directly below the soil layer and is characterised by pisoliths.
3. Ferricrete—a ferricrete layer, containing cemented iron-oxide and some pisoliths, occurs immediately below the bauxite.
4. Mottled Zone—a mottled zone consisting of iron-oxide and kaolinite occurs directly below the ferricrete layer.
5. Plasmic Zone (a)—a pallid or bleached zone of sandy clay consisting of an upper clay (kaolinite) and fine quartz sand unit underlain by a quartz, coarse sand to pebbly conglomerate with varying amounts of kaolinite.
6. Plasmic Zone (b)—a pallid or bleached zone of well-compacted clay (kaolinite).

Groundwater discharge can occur where a permeable geological layer (e.g. Bulimba Formation) overlies a less permeable layer (e.g. Rolling Downs Group). At this site plasmic zone (b) is composed of well-compacted clay that acts to slow or prevent vertical groundwater flow. Given sufficient rainfall and recharge, this can result in groundwater accumulating above the clay and flowing laterally until it is discharged to the surface (e.g. Oasis Spring). In addition, groundwater may accumulate on less permeable kaolinite in other geological layers (e.g. mottled zone) and flow laterally until it is discharged to the surface or able to continue vertical movement.

Oasis Spring occurs in a 240-metre arc at approximately 40 metre elevation near the contact between the Bulimba Formation and underlying the less permeable plasmic zone of the Rolling Downs Group. A relatively deep perennial gully incises the spring head at approximately its centre point and this becomes the main spring watercourse (Oasis Creek). Oasis Spring coalesces into a main stream approximately 100 metres downstream of the spring head. Oasis Creek flows into Nimrod Creek which then joins the Wenlock River in its freshwater, non-tidal reaches. In addition to the clear running streams, permanently saturated ground exists in parts of the springs eastern flank. Oasis Spring features strong perennial flow at the spring head and downstream for 800 metres even during the peak of the dry season. In 2008 permanent flow into Nimrod Creek was observed until August, although this flow slowly declined as the dry season progressed.

Lyon and Franklin (2009)[5] have indicated that the water draining from the springs is acidic with an observed pH of 3.8 at the point of discharge and noted that the pH of the groundwater decreases with increasing distance from the spring. A number of factors have been identified that may contribute to spring acidity including rainfall acidity, chemical weathering, plant activity, decay of vegetation, termite activity, bacteria activity and fungi activity. Recent research supports the contribution of anerobic microbial degradation to groundwater chemistry[4]. In addition, isotopic values at the spring suggest groundwater has meteoric origins, representing a mix of rainfall events[4].

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References

1. ^ a b Eggleton, RA, Taylor, G, Le Gleuher, M, Foster, LD, Tiley, DB & Morgan, CM (2008), 'Regolith profile, mineralogy and geochemistry of the Weipa bauxite, Northern Australia.  55(S1):17-43.', Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia., vol. 55, no. S1, pp. 17-17-43..
2. ^ Fell, DG (2009), Flora survey of freshwater spring forests, Steve Irwin Wildlife Reserve, Cape York Peninsula, Australia., Australia Zoo, Australia.
3. ^ Jell, JS (2009), Review of the geology of the Wenlock River Basin with particular emphases on the XX Springs Complex, Cape York, Queensland, Australia.
4. ^ a b Leblanc, M, Tweed, S, Lyon, BJ, Bailey, J, Franklin, CE, Harrington, G & Suckow, A (2015), 'On the hydrology of the bauxite oases, Cape York Peninsula, Australia.  528: 668-682.', Journal of Hydrology., vol. 528, pp. 668-668-682.
5. ^ Lyon, B & Franklin, CE (2009), Natural Values of Perched Bauxite Springs, Australia Zoo, Australia.
6. ^ Taylor, G, Eggleton, RA, Foster, LD & Morgan, CM (2008), 'Landscapes and regolith of Weipa, northern Australia', Australian Journal of Earth Sciences. [online], vol. 55, no. SUPPL. 1, pp. S3-S16. Available at: Scopus.
7. ^ Willmott, W (2009), 'Cape York Peninsula: Areas of International Conservation Significance. The Geological Story of Cape York Peninsula.', 2009, Report for the Department of Environment and Resource Management, Queensland Government, Queensland, Australia.
8. ^ a b c Winders, MF (2009), The Wenlock River. A submission supporting its Proposed Declaration as a Wild River., Department of Environment and Resource Management, Queensland Government., Queensland, Australia.
9. ^ Winders, MF (2010), Further Submissions Concerning the Boundaries to the Coolibah Springs Complex, Wenlock Wild Rivers Declaration., Department of Environment and Resource Management, Queensland Government., Queensland, Australia.

Last updated: 10 April 2017