Twilight Zone Speleothems

Introduction

Irregular, "lumpy", odd-coloured and strangly-oriented speleothems are typical of the twilight zone where normal speleothem growth is distorted by the growth of algae and other plants and the fact that evaporation tends to be more important than CO₂ out-gassing. Wind effects may also be a factor.

Selected photographs and diagrams

To view full size images, click on the displayed thumbnail image.

"Lumpy" speleothems are common in cave entrances and overhangs:

Carlotta Arch, Jenolan, NSW.
"lumpy" stalactites in overhang.
File: C010113.jpg

Roof of Devils Coachouse, Jenolan, NSW.
"lumpy" stalactites in twilight zone.
File: C010114.jpg

Abercrombie Arch, 2A-1, NSW.
"lumpy" speleothems in twilight zone.
File: C010528.jpg

Abercrombie Arch, 2A-1, NSW.
Closer view of "lumpy" speleothems in twilight zone.
File: C010530.jpg

Abercrombie Arch, 2A-1, NSW.
"lumpy" stalactites in entrance.
File: C010102.jpg

Borenore Arch, 2BN-1, NSW.
Lumpy stalactites in roof of overhang.
File: C000215.jpg

Algal coatings give pastel colours to walls in the twilight zone.

Tinted Cave, 2W-11, Wombeyan, NSW.
Algal-coloured formations in twilight zone.
Many cave entrances in this region have pink-coloured walls and ceilings due to this type of algae.
File: D030205.jpg

Tinted Cave, 2W-11, Wombeyan, NSW.
Algal-coloured formations in twilight zone.
File: D030206.jpg

Phototrophic growth of algae can result in ridges aligned towards or transverse to the light direction.

Wall of Victoria Arch of Fig Tree Cave, 2W-148, Wombeyan, NSW.
Phototrophic speleothems. Main light is from upper-left, with lesser amounts from other entrance to right.
File: D030131t.jpg

Craybacks - a distinctive form on the floors of big cave entrances

See Jill Rawling's web site http://www.speleonics.com.au/jills/byzone/byzoneCray.html for discussion of the genesis of these forms.

Victoria Arch of Fig Tree Cave, 2W-148, Wombeyan, NSW.
"crayback" stromatolitic stalagmite.
The elongated shape may be due to winds blowing the falling water drops. The transverse ribs on its back are thought to be a photo-trophic effect due to algae and other organisms.
File: D030139.jpg

Victoria Arch of Fig Tree Cave, 2W-148, Wombeyan, NSW.
End view of the same "crayback" stromatolitic stalagmite.
File: C011001.jpg

Abercrombie Arch, 2A-1, NSW.
Side of streamway (about 3m high) with current scallops. Above is a side view of a "crayback" stromatolitic stalagmite.

File: C010607.jpg

Abercrombie Arch, 2A-1, NSW.
Group of "craybacks" in twilight zone. Notebook is about 20 cm long.
File: C010110.jpg

Abercrombie Arch, 2A-1, NSW.
Group of craybacks in twilight zone. Light bulb at base suggests scale.

File: C010615a.JPG

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