Queensland Cretaceous trip

[izak_]

A couple of weeks ago we returned from a two week trip to Queensland. I have thousands of photos to go through so will just be sharing snippets of the trip here for now, but will have lots more photos to post once I start preparing things. The majority of our trip was spent in the Eromanga Basin, a very extensive Mesozoic basin covering much of Queensland and some parts of other states. After this, we spent a couple of days at a Cambrian site for trilobites.

 

After two days of driving we reached our first destination in central QLD. This area is well known for early Cretaceous crabs and ammonites, particularly on one property near the town we stayed in. Friends who have visited this site seemed to hold it in high regard, they said they walked through the fields picking up nodules which were full of crabs. We didn't get our hopes up out of fear of disappointment, but it turned out our friends weren't exaggerating! 

 

 

We spent our first couple of hours following a dry creek bed which had occasional nodules containing crabs and shells. A few crabs and ammonites were found between us, and we were extremely happy! But then, I went for a walk up a hill to see if there was anything else of interest. Slightly up the hill from where we were was a horizon which was clearly the source of the nodules, the ground was littered with them! This horizon could be traced for kilometres and proved to be extremely productive. Overall, we found dozens of crabs, ammonites and even a couple of lobsters. I wish I took more photos as usual

 

A typical nodule as found.

 

Ammonites in situ.

 

A couple of other finds including crabs and ammonites.

 

Between here and our next destination we noticed some nice ripple marks in an outcrop of Winton Formation. 

 

 

More to come...

 

[Kohler Palaeontology]

Very Nice! Can't wait to see what else you find!

 

Kind Regards,

Kohler Palaeontology

[izak_]

Most of the rest of the trip took place on various properties near Richmond, a 5 hour drive from the crab site. This post will focus on one property which we spent a few days on thanks to a friend who got us access. 

 

The geology on this property was tremendous! The Rolling Downs Group is best known from drill cores since it tends to outcrop very poorly. It is mostly comprised of soft shales, siltstones and limestones which only outcrop in deep gullies or channels. This results in the standard Rolling Downs Group topography - hundreds of kilometres of undulating hills and a generally flat overall landscape. Occasionally rocks do outcrop here, but they are generally brief horizons of more resistant rocks like limestone concretions. This property was different though, it had a huge escarpment of Cainozoic basalt which offered a unique opportunity to study the underlying geology. The basalt layer is relatively thin, but still far more resistant than any of the underlying Cretaceous sediment. This resistant layer of basalt has stayed in place for many millions of years while the surrounding Cretaceous rocks have weathered away, leaving a beautiful plateau which sticks out like a sore thumb from the rest of the landscape. 

 

Much of the edge of the escarpment is covered in basalt boulders and scree, but there are occasional bluffs of Cretaceous sediment. This is one of the best examples I've seen. It shows the boundary between the Wallumbilla Formation (Ranmoor Member) and the Toolebuc Formation. Above the lowest part of the Toolebuc Formation is some sub-basaltic sediment, and then the contact between this and the Sturgeon Basalt. 

 

 

A closeup of the basalt contact from a nearby cutting.

 

 

Ranmoor Member

 

 

I assume there is a fault further south from here since the stratigraphy is much higher. There are no complete sections visible like in the first photo, but it is possible to follow the base of the Toolebuc formation (the top of the last section) up to the base of the overlying Allaru Mudstone. It is quite amazing to be able to view the section from between the Wallumbilla Formation all the way up to the Allaru Mudstone within the same valley! 

 

The base of the Toolebuc Formation as viewed in the southern part of the valley. This is the same level as can be seen in the public quarries near Richmond and is also full of inoceramus shells, but also has some sections of more siliciclastic mudstone.

 

 

Further above this is the concretionary horizon that can be seen NW of Richmond. These concretions contain vertebrate material, bivalves, ammonites, etc.

 

 

This horizon was very productive for ichthyosaur material. The material is typically very weathered, especially when the concretion hasn't entirely encased the specimen. 

 

Some post cranial material including phalanges from a dry creek bed.

 

 

A very weathered specimen comprising of jaw fragments and some larger blocks (not pictured) containing more of the skull and vertebrae. 

 

 

A nice skull section. Here it is possible to see the extent of the concretion around the skull, with everything not covered in the harder limestone being weathered or gone. The teeth underneath the matrix will hopefully etch out well in acid. 

 

 

A very weathered skull with some vertebrae. It is a shame it's so weathered (much of the bone is gone) but both scleral rings are still visible, plus cross sections of teeth on both sides. Will post photos of it cleaned up at some point. 

 

Some more photos of concretions.

 

Further above the concretionary horizon of the Toolebuc Formation is the base of the Allaru Mudstone. This formation generally outcrops poorly, but horizons of limestone containing inoceramus shells are sometimes common. This material is strikingly similar to other Allaru Mudstone sites we visit, so it was great to see it in relation to the Toolebuc.

 

 

The top of the Sturgeon Basalt covered in Pimelea decora.

 

 

To be continued when I sort through more photos...

[Ludwigia]

Great stuff! Keep 'em coming!

[JohnJ]

Outstanding finds, Izak!  Your trip looks like it was fascinating!

[KCMOfossil]

Thanks for sharing such great finds in this fascinating biome.

[Jared C]

Your trip reports are among my favorite to read. Keep it up!

[SPrice]

It's like being at a "Fossils - R- Us" store...you're gonna need a bigger shopping cart, for sure and for certain!

 

I would be like filling the buckets, the front and back seats and have my mates ride on the roof.

 

Thanks for sharing and the pics are super deluxe! more, more, more...please and thank you.

[Mikrogeophagus]

Very enjoyable read! Thank you

[val horn]

wow

[Kohler Palaeontology]

Love that Ichthyosaur material!

 

Would there be fossils in the outcrop of the Winton Formation, like footprint fossils maybe? I know most of the bones from the Winton Formation are preserved in black soil.

 

Kind Regards,

Kohler Paleontology  

Edited August 30 by Kohler Palaeontology
wanted to ask a question.

[Jeffrey P]

Thanks for sharing your wonderful finds, photos, and report. Your contributions have certainly expanded my appreciation of Australia's geology and paleontology wonders. Spectacular material. Believe it or not, it is the lobster claw that really stands out for me. Congratulations. 

[Girlandherwhitewolf]

Amazing fossils and photos!  Bet it was super peaceful in the outback too 🏜️

[izak_]

Thank you all, I'm glad you're enjoying it so far!

 

8 hours ago, Kohler Palaeontology said:

Would there be fossils in the outcrop of the Winton Formation, like footprint fossils maybe? I know most of the bones from the Winton Formation are preserved in black soil.

I didn't see any here unfortunately. The lowest part of the Winton Formation still has some marine influence and is a few hundred metres lower than most of the main dinosaur bearing horizons from my understanding. There are volcaniclastic concretions around Isisford which contain crocodilians, fish and dinosaurs which are interpreted as being in the lowest part of the Winton formation, so they can occur lower down too. 

 

[Kohler Palaeontology]

Very interesting!  I saw a documentary with Steve Irwin once where he found dinosaur tracks out west. But where you are seems to be more marine.

 

Kind Regards,

Kohler Palaeontology

[izak_]

This next lot of photos is from a different property a half hour drive from the last. The formation present here is the Allaru Mudstone, and most of these finds are from a thin shelly horizon which outcrops in a few places on the property. 

 

Some typical examples of the shelly horizon containing Inoceramus. It seems to be a thin band of limestone concretions within a soft blue shale, but it can be difficult to tell due to poor outcropping. 

 

 

A good chunk of Richmondichthys which was in three seperate blocks. The first chunk shows some weathered scales, and the other two have weathered scales and part of the skull. This one is currently in acid and is looking promising so far! 

 

 

 

A lump of limestone (see similarity to the Allaru Mudstone photos from the last post)

 

 

Along the edges of some of the channels were interesting reworked deposits of the shelly limestone. The deposits were fairly thick and iron stained, I assume they're fairly old. Above these deposits were layers of reworked Inoceramus shell fragments cemented together by calcium carbonate. 

 

 

The reworked Inoceramus layer

 

 

The reworked stuff was a gold mine for fish material!

 

Fish skulls

 

 

Fish tail

 

 

Squid material was very common

 

 

Worm tubes

 

 

Spot the ichthyosaur vertebrae!

 

 

Some lumps of fish containing a partial skull, ribs and vertebrae (the operculum can be seen above the letter 'A' but is difficult to make out here). This was in many pieces over several metres so there is a lot missing...

 

 

 

Edited August 31 by izak_

[mighty micraster]

Those places look very productive.

Great stuff.

[Jaybot]

Dream trip, dream finds, thank you for sharing!  The icthyosaur rostrum is definitely my favorite.