Tuesday, 21 April 2015

21 April 2015: Stromatolites and Cockle Shells

21 April 2015: Stromatolites and Cockle Shells
On the road again next morning, we made a stop not found on any tourist brochure – at the now abandoned lead mine at Mary Springs, where BoyRob worked as a surveyor as a young lad. He shared many hard / funny stories of real life in remote places.

Acorn Banksia

Finding garnets at Mary Springs mine

We followed the 160km Top Trail Drive, commencing at Billabong Roadhouse/ Overlander. There were so many places to stop and explore along the Shark Bay World Heritage Drive that we were glad we had allocated more than a pit-stop to view the Hamelin Pool boardwalk, stromatolites and old Telegraph Station; Eagle Bluff; walks and viewpoints overlooking Shark Bay Marine Park; and Shell Beach and the cockleshell quarry.

Stromatolites: 20 April
Stromatolites are layered bio-chemical accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by microbial mats of microorganisms, especially cyanobacteria. Fossilized stromatolites provide ancient records of life on Earth, some dating from more than 3.5 billion years ago.  They peaked about 1.25 billion years ago and subsequently declined in abundance and diversity, so that by the start of the Cambrian Period they had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victim to grazing creatures. A variety of stromatolite morphologies exists, including conical, stratiform, branching, domal, and columnar types. We stopped at Lake Thetis, outside Cervantes to view the magnificent domal specimens in the shallow waters. Aboriginal legend here says they are the eggs of the Rainbow Serpent.

Stromatolites at Lake Thetis


Stromatolitic bacteria restrict their vigorous activity to night time. Fine grain sediments are bound together by excretions, adhered atop one another by the bacteria's flagella, forming layers that correspond to periods of high activity. Thus these sometimes elaborate structures, constructed by microscopic organisms working somewhat in unison, are a means of providing shelter and protection from a harsh environment. Scientists have argued for origin of stromatolites due to the presence of organic globule clusters within the thin layers of the stromatolites, of aragonite nanocrystals (both features of current stromatolites), and because of the persistence of an inferred biological signal through changing environmental circumstances.

Cyanobacteria are thought to be largely responsible for increasing the amount of oxygen in the primeval earth's atmosphere through their continuing photosynthesis. Cyanobacteria use water, carbon dioxide, and sunlight to create their food. A layer of mucus often forms over mats of cyanobacterial cells. In modern microbial mats, debris from the surrounding habitat can become trapped within the mucus, which can be cemented together by the calcium carbonate to grow thin laminations of limestone. These laminations can accrete over time, resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight to the organisms for photosynthesis.

Stromatolites: 21 April
Modern stromatolites are mostly found in hypersaline lakes and marine lagoons where extreme conditions due to high saline levels exclude animal grazing. We stopped at one such location - Hamelin Pool Marine Nature Reserve, Shark Bay WA and went out on the boardwalk to view its excellent specimens. Apparently in 2010, a fifth type of Chlorophyll was discovered by Dr Min Chen from stromatolites in Shark Bay.(info Courtesy Wikipedia)

Stromatolites at Hamelin Pool

Hamelin Pool Telegraph Station

The coastal region hosting these rare stromatolites is stunning with its red cliffs, azure waters, different marine environments, abundant birds and wildlife.

Crayfish boats
Pied Oystercatcher

Cormorant rookery

Pied Cormorant

It was amazing to find whole beaches of hard packed cockle shells which were quarried 
for building blocks and monuments.

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