Picture: Seth Shostak
Trendall Locality: The first hint
In an article published in Scientific American, three scientists involved in the original discovery of the Pilbara stromatolites, Roger Buick, John Dunlop and David Groves, describe the possible scene 3.5 billion years ago:
“Let the reader imagine he is standing on the (mud) flats at low tide. The outline of high volcanic cones is visible in the distance through a haze of volcanic ash and of steam from hot lava erupting into the shallow sea; thunderclouds hover near the peaks. Closer at hand the basalt cliffs of the coastline are pounded by waves whipped by high winds.
"Inland the scene is dominated by hummocks of black basalt lava, their surface covered with a rubble of pillow fragments. The observer is surrounded by a flat expanse of grey mud that glistens when intermittent sunlight is reflected from small crystals of gypsum.
"A few tidal streams meander across the flats, draining into the sea through a break in a low bar of black sand. Elsewhere there are scattered pools, shallow and highly saline."
Around the Trendall Locality, in rocks 3.42 billion years old, evidence suggests a lagoon-like environment in a very short period where there was a lull in volcanic activity between the Panorama Formation and the Euro Basalt (see the geological maps). Instead of basalts, a finely grained sediment was laid down – the almost marble-like Strelley Pool Chert of the Pilbara.
As the Geological Survey of Western Australia remarks, the Trendall Locality is "particularly significant because of the exceptional preservation that occurs over just a few square metres of outcrop, and the morphological (shape) development is consistent with biological construction."
Within that small group of stromatolites, one section of ‘egg box carton’ conical stromatolites was taken for care and preservation at the Western Australia Museum in Perth. Remaining is a branching column formed on the side of a stromatolite cone known as ‘Mickey Mouse Ears’ because of the similarity and ornateness.
Since then other areas nearby have revealed well preserved samples as shown in the Virtual Field Trip.
Useful web links:
Geological Survey of Western Australian on the discovery and history of the Trendall Locality: