PESA WA 2nd annual weekend field trip – Perth Basin

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On Friday, 12 October, 27 PESA members made their way to the Priory Hotel, Dongara to network, enjoy dinner and drinks and kick start the field trip headed by Darren Ferdinando, our trip leader.

First stop on the Saturday was to survey magnificent spectacle of the cliffs at Coalseam Park. Along the banks of the Irwin River are some magnificent outcrops, with strata gently dipping, such that a hike up the river brings you to successively younger beds. The first rocks we looked at in the high cliff near the car park were, the imaginatively titled High Cliff Sandstone. This magnificent sandstone with good reservoir characteristics, was only the start of the expedition, and shales and siltstones appeared as we walked up river. We were tremendously grateful to Amely Allgoewer, without whose presence on the trip, our description and facies identification using trace fossils would have been distinctly more vague.

There were some lovely fossil examples throughout the section, but especially in the aptly named Fossil Cliff Member.

Moving up through the section we came into the Irwin River Coal Measures. These comprise of thin and pretty ordinary coaly beds, and also sandstones that many have speculated could make reservoirs. However looking at these sandstones at this locations did not fill us with hope, based on the highly cemented nature of the rocks. That said, our reservoir modeller on the trip, Ishtar, declared that it would be fine as a large gas reservoir.

Even further up the section, we came to some sediments from a glacial environment, with huge dropstones.

On Sunday,  we visited a hill on a farm to search for an unconformable contact between granitic basement and Kockatea Shale. We split into groups and investigating, then reconvening on the highest hill to discuss what we had learned. This was then followed by the descent down past an outcrop of Kockatea with Early Permian stromatolites preserved.

Special thanks to Darren Ferdinando and Robin Hill, for leading this trip with knowledge and personality, and also to Rob Ross, who made all of the arrangements behind the scenes, but was unable to attend the trip.

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