8/14/2019 Rottnest Island - Ogling some stromatolites at Serpentine Lake

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8/05/09 6:47 AMFremantlebiz - Paul's Letter from Australia

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Fremantlebiz - Paul's Letter from Australia

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Friday, May 8th, 2009

Time Event4:49a Rottnest Island - Ogling some stromatolites at Serpentine Lake

Stromatolite |strmatlt| - noun - a calcareous mound built up of layers of lime- secreting cyanobacteria and trapped sediment, found inPrecambrian rocks as the earliest known fossils, and still being formed in lagoons in Australasia. Origin 1930s: from modern Latin

stroma, stromat- layer, covering + - lite. So sayeth the Oxford dictionary about the meaning of the word.

Theres stromatolites at Rottnest. During our visit last October they were covered by water. However, a couple of weeksago in late April we managed to have an excellent viewing of the ones ringing the western end of Serpentine Lake:

Stromatolites at the western end of Serpentine Lake

These domal stromatolites are no longer active. Its possible the cyanobacterial slime which formed them possiblysuccumbed to a too prolonged lowering of water levels in the past, or maybe when levels were generally higher than now?According to Western Australian geologist Phillip Playford in his Guidebook to the Geology of Rottnest Island(1988) thereare still living stromatolites beneath the water further east in Government House Lake. Three meters deep is the maximum.They are being formed beneath benthic mats of microbial organisms up to 10 cm thick. Furthermore, the cyanobacteria inthat lake had established sufficient stromatolite material on bottles discarded by tourists in the early twentieth century todeduce that limestone layering was taking place at the rate of about 1.5 mm a year.

Last October we saw some of this slimy, oxygen generating, benthic material adrift in shallow water on the northern edgeof Lake Herschell. The colours displayed in the image below are reasonably true. The bright green stuff underneath the

slime is unassociated seasonal shallow-water algae.

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8/14/2019 Rottnest Island - Ogling some stromatolites at Serpentine Lake

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8/05/09 6:47 AMFremantlebiz - Paul's Letter from Australia

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A piece of cyanobacterial mat adrift in shallow water - October 2008

To most people stromatolites are just rocks, but my wife and I have been intrigued by them since 30 years ago when wevisited an amazing live deposition in the Indian ocean connected hypersaline Hamelin Pool near Shark Bay. We viewedthem as distant 'cousins.' Their dependence was on a much more discrete, less obvious layering of cyanobacteria.

Weve also collected some fossil specimens from further north at an inland Devonian desert deposit which were about 400

million years old. The Devonian period is known for the significant evolutionary expansion of amphibians and seed bearingplants, as well as other pre-dinosaur and pre-mammalian life forms. However, stromatolite building (and radicalenvironmental change) has been going on much longer, since at least 3.5 billion years ago.

Theres also a significant living colony of stromatolites at the salty Lake Clifton, which is a little over an hour and halfsdrive south of Fremantle. Weve yet to visit those cousins.

MMIX Paul R. Weaver.

Click the Sribdlogo for downloadable PDF versions of my Rottnest essays:

Click here to visit 'dogandcatwatcher', my YouTube website.

Original still photographs are stored online in a cache at my Panoramio website or my Picasa site. Most of themhave a brief description and a link back to a relevant essay. Images on Panoramio can usually be enlarged several timesby clicking them.

About the writer

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Check out each month's subject index on the Calendar Page for my "common-man" monologues about survival in 21stcentury Australia plus a little history occasionally. An original essay is added most days as part of an undertaking towrite at least couple of million words. Zzzzzzzz!

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