Here’s something a little different this time, as we wanted to give a summary of the recent Perth Basin fieldtrip that Amely helped run, plus discuss our upcoming Perth Basin core workshop. As such, the following is by Chris Watts:

We’ve sadly packed away our hiking boots following a three-day geological fieldtrip through the Northern Perth Basin over the weekend (6-8 Sept), led by Simon Sturrock (Strat Trap), Darren Ferdinando (Murphy Oil), and our very own Amely Allgöwer (MGPalaeo).

The trip focused on the regressive to transgressive, Early Permian sequence exposed along the Irwin River in Coalseam Conservation Park. Between Darren, Simon, and Amely the group integrated sedimentology and ichnofacies with predictive sequence stratigraphic analysis to compare the outcrop to the prospective play in the basin.

On the Friday after AEGC 2019, a group of 27 very punctual geoscientists ranging in age and experience from Cenozoic to Devonian gathered at 8am outside the Crown in Perth and excitedly climbed onto the bus ready for the short drive up to the Mingenew Hotel, which would serve as basecamp for the next few days.

The Pinnacles in Nambung National Park - MGPalaeo Perth Basin fieldtrip 2019
The Pinnacles in Nambung National Park

To break up the drive and show our international visitors some of what Western Australia has to offer, the bus stopped by the Pinnacles in Nambung National Park. The group took some photos of the fascinating landscape before diving into discussion on what exact mechanisms may have formed the Pinnacles. After a lunch stop in Cervantes (which included ice-cream), attendees were treated to a walk out over the stromatolites of Lake Thetis; a small, permanent metahaline lake fed by rain and groundwater. These stromatolites developed during the last 3,000-4,000 years, though the structures they produce have been identified as far back as 3.45 billion years ago in the rock record, making them one of Earth’s ultimate survivors.

Stromatolites at Lake Thetis - MGPalaeo Perth Basin fieldtrip 2019
Stromatolites at Lake Thetis

By the time the group finished admiring the stromatolites, less than 200 km and one more stop stood between the geologists and their evening beers at the Mingenew Hotel. The picturesque view at Dynamite Bay in Green Head, however, was worth the wait. The low-lying cliffs protect the beach from strong winds, making it a perfect place to stop, enjoy a coffee, and soak in the afternoon colours of the bay.

Outcrop of the Holmwood Shale and High Cliff Sandstone along the Irwin River - MGPalaeo Perth Basin fieldtrip 2019
Outcrop of the Holmwood Shale and High Cliff Sandstone along the Irwin River

On Saturday morning, the group boarded the bus with a degree of excitement that only geologists heading to a new outcrop can manage. The outcrops along the Irwin River did not disappoint. The shallowly dipping strata meant participants could walk along the cliff until the Early Permian units of interest were at eye level for easy examination. Discussions at the Irwin River outcrops covered the sedimentary structures, fossils, trace fossils, the environments in which each of the formations were deposited, and their heterogeneity along dip which often leads to confusion when dealing with lithostratigraphic terms. With stunning glacial drop stones, fossil bryozoan, crinoids, corals, and bivalves, plus a large array of inchogenera there was something for everyone.

Rippled and weakly bioturbated sediments in the Irwin River Coal Measures - MGPalaeo Perth Basin fieldtrip 2019
Rippled and weakly bioturbated sediments in the Irwin River Coal Measures

Sunday morning meant it was time to start the drive back to Perth. Along the way we stopped for a quick look at a Pleistocene reef outcrop, formed by a range of branching, palmate, and horizontal coral during the last interglacial period when the sea was 2.5 m above the present level.

Our international visitors were lucky enough to spot wildflowers, kangaroos, and emus on the drive back, before enjoying the sites of wineries in the swan valley. By the time the group returned to the Crown in Burswood, participants were already hard at work planning the next fieldtrip, and discussing the outcrops seen over the past few days.

The fieldtrip group posing around a large dropstone - MGPalaeo Perth Basin fieldtrip 2019
The fieldtrip group posing around a large dropstone

Here at MGPalaeo, we would like to extend a huge thank-you to Deidre Brooks for organising the fieldtrip, Terry from Cross Country Charters for getting us to the outcrops safely, the instructors Simon, Darren, and Amely for an excellent trip, and to all the participants for the wonderful company and animated discussions.

Hopefully the stunning outcrops and in-depth discussions have rekindled everyone’s passion for the Perth Basin. It certainly has ours, and we’ve now started planning a Perth Basin integrated core workshop. If you are interested in attending such a workshop (we haven’t sorted out dates yet), please let us know on [email protected].


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