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Hi, we visited Port Mulgrave last weekend as I did about 10 years ago and was wondering if the protrusions in the bed rock were bones and if anyone can recognise what they are. I got a glimpse of what the inside looked like could it be fossilised marrowbone?

IMG_2708.JPG

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Tidgy's Dad

It seems to be a concretion like structure forming around the u-shaped burrow Rhizocorallium which i recall is found fairly often at Port Mulgrave. 

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Agree with concretion.

Not sure if fossil inside - closer look would be necessary...how big is it ?

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Hi they are about 10cm wide and I think the burrows you suggest go only up to 2 cm wide. Some were different shapes too, one of the protrusions did resemble a hip bone 

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Tidgy's Dad

Up to 2 cm fits in with the scale for Rhizocorallium. 

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The borings inside the nodule are from a modern U-shaped rock boring worm, something like Polydora. You can often find them still with the live worms in place in the intertidal zone - they're particularly fond of boring into pre-existing fine cracks and discontinuities such as the interface with a fossil.

Here's a belemnite (Megateuthis) that's been affected on one side: 

 

 

 

 

IMG_2792.jpg

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WhodamanHD

Does look a lot like burrows.

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10 minutes ago, TqB said:

The borings inside the nodule are from a modern U-shaped rock boring worm, something like Polydora. You can often find them still with the live worms in place in the intertidal zone - they're particularly fond of boring into pre-existing fine cracks and discontinuities such as the interface with a fossil.

Here's a belemnite (Megateuthis) that's been affected on one side: 

 

 

 

 

IMG_2792.jpg

Yep, than i am with conretion without fossil. Nevertheless informative piece !

 

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2 hours ago, TqB said:

The borings inside the nodule are from a modern U-shaped rock boring worm...

How is it that the borings in question terminate at a lithified cap? Would that not mean that they were made before the capping sediment was fully deposited?

~~.jpg

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17 minutes ago, Auspex said:

How is it that the borings in question terminate at a lithified cap? Would that not mean that they were made before the capping sediment was fully deposited?

~~.jpg

The cap surface is a recent concave fracture (probably caused by hammer blows from the top, judging from the photo) so any borings in it have simply been lost in the missing piece. These burrows are very, very common around there. :) 

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2 minutes ago, TqB said:

The cap surface is a recent concave fracture (probably caused by hammer blows from the top, judging from the photo)

I'm afraid I don't follow you. The feature I am talking about appears to be a lithified layer of sediment, into which the tubes barely penetrate.

How would the borers have entered the rock, if not through this capping material? :headscratch:

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doushantuo

Maybe the upper surface is an omission surface?:headscratch:

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1 hour ago, Auspex said:

I'm afraid I don't follow you. The feature I am talking about appears to be a lithified layer of sediment, into which the tubes barely penetrate.

How would the borers have entered the rock, if not through this capping material? :headscratch:

 

It isn't a cap but a hollow, weathered, elongated fracture surface. The worms would have bored along a hairline crack starting at the top of the nodule (there are other vertical cracks visible at the back of the nodule which very likely have more inside).

 

This is how I see it:

5af5a402b4acd_ScreenShot2018-05-11at14_51_27.png.7727af693d988f355ceb0d581ee43553.png

 

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