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Sikacalling

Hi there,

 

I collected this from core we were drilling during coal exploration near Blackwater.

Queensland museums so called specialists have tried to tell me its an artifact of the drilling from photos, but i can tell you its most definitely not drilling related, mind you i didnt tell them im a geologist and i was the one that logged the core as it came out. I've had it now for three years.

 

it comes from the Rangal coal measures, within two meters of a coal seam. the structures (what ever they are) intersect the darker bands (which knowing the deposit will contain fossilized plant fragments) which bend upward at the point of intersection.

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Sikacalling

another image

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Sikacalling

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Tidgy's Dad

Hello, and a very warm welcome to TFF from Morocco! :)

I'm rather afraid to say that I agree with the museum people. 

It seems to me that the marks are on the outer surface of the core sample and cross over several bedding planes.They are pretty evenly spaced around the circumference of the sample, not facing in one plane which you'd expect from fossils. 

These are drill marks, in my opinion. 

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DPS Ammonite

What can you tell us about the properties of the light and dark rocks. What are they?  Can you show us a view of the core looking parallel to the length. Is the core round everwhere or are their distortions that coincide with the dark and light layers bend? 

 

Have you tried to cut a piece of the core lengthwise to see if the structures are similiar in the center?

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Sikacalling

i can definitely definitely say these are NOT drill marks (I've been coring in this area for 8 years), conventional core drill bits can often leave stretches on a core where the rock is reasonably soft, but this will be a single indentation down the length on the core due to the "catcher" unless the catcher has been modified to assist in catching highly faulted ground in which case a second scratch will be found on the opposite side of the core. but this was not the case in this core which shows no scratching what so ever. the Core indents slightly on the side of the core where the structures are most visible and bulges slightly on the opposite side. the same sort of structures are visible on the bulging side of the core but are not as clearly defined.

 

As i say this is Shallow freshwater semi swamp from the Late Permian. the Darker bands are mudstone and like i say will probably contain some plant fragments, these will be from periods where there was little input into the system allowing the water to stagnate. the lighter bands are fine sandstone, so will have been deposited in higher input events. these are possibly seasonal or inter-event bands (such as flood events with high input followed by stable periods). 

 

 


 

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Edited by Sikacalling

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Sikacalling

bottom

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Sikacalling

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DPS Ammonite

Could the banded areas have been water saturated and experienced soft sediment deformation (escape structures?) either a long time ago or when it was drilled?

 

Which way is up on the core?

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Sikacalling

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Sikacalling

the area is highly faulted (although not so much in this section as the bedding is flat in this case) and has been buried quite deep. the coal is premium PCI anthracite coal which tells us it was under high temperatures and pressure before being faulted to the surface. the rock its self is quite competent and is quite hard. the sequence is correct with the bottom being the oldest and the top being the youngest.

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DPS Ammonite

My educated guess is soft sediment deformation caused by migration of fluids and gasses. The geometry is rather weird. Maybe a sedimentologist or oil and gas geologist can figure out how they were formed and which way the fluids and gasses were traveling.

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Sikacalling

i cant really get a good picture with my phone so i cant show it properly but the fan structures at the bottom and the dark band intersects have a central strcuture which you can follow from the bottem up. the little "fan" bits off it have pulled the darker sediments up between the fans.

 

my first thought is that it reminded me of root systems when seen in cross section

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Sikacalling

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DPS Ammonite

It almost looks like there was compression to the right and left of the core that caused the fan structures to form and the dark and light layers to bend. Maybe a structural geologist could also help.

 

You might consider posting this on Mindat. Even though it is not a mineral, many geologists use the site and may be able to tell you what is going on. 

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TqB

I agree it looks as if you have cone in cone structures.

@mikemH - that's a great example!

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Fossildude19

 

Welcome to the Forum. :)

 

+1 for Cone in Cone structures

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DPS Ammonite

Cone in cone structures form from minerals such as gypsum and calcite that grow from a point source into a cone and displace that surrounding sediments. The cones can grow in several directions. Usually these are seen as 3 D structures on the exterior of rocks. I have never seen these in a cross section: very interesting. See this paper: https://www.sciencedirect.com/science/article/pii/S2095383615300523

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Oxytropidoceras
On 8/21/2018 at 3:16 AM, Sikacalling said:

the Darker bands are mudstone and like i say will probably contain some plant fragments, these will be from periods where there was little input into the system allowing the water to stagnate. the lighter bands are fine sandstone, so will have been deposited in higher input events. these are possibly seasonal or inter-event bands (such as flood events with high input followed by stable periods). 

 

The lack of bioturbation of the layers indicates that alteration layers of sand and mud accumulated quite rapidly. They are likely tidalites with the sand representing flood tide deposition and mudstone representing ebb tide (clay drape) deposition in the tidal cycle.

 

Longhitano, S.G., Mellere, D., Steel, R.J. and Ainsworth, R.B., 2012. Tidal depositional systems in

the rock record: a review and new insights. Sedimentary Geology, 279, pp.2-22.

https://www.researchgate.net/publication/236979795_Tidal_depositional_systems_in_the_rock_record_A_review_and_new_insights

https://www.researchgate.net/profile/Sergio_Longhitano

 

Archer, A.W., Elrick, S., Nelson, W.J. and Dimichele, W.A., 2016,  Cataclysmic burial of

Pennsylvanian Period coal swamps in the Illinois Basin: Hypertidal sedimentation during

Gondwanan glacial melt-water pulses. In Contributions to Modern and Ancient Tidal

Sedimentology: Proceedings of the Tidalites 2012 Conference: International Association of

Sedimentologists Special Publication (Vol. 47, pp. 217-231).

https://repository.si.edu/handle/10088/30890

 

DiMichele, W.A. and Falcon-Lang, H.J., 2011. Pennsylvanian ‘fossil forests' in growth position

(T0 assemblages): origin, taphonomic bias and palaeoecological insights. Journal of the

Geological Society, 168(2), pp.585-605.

https://repository.si.edu/handle/10088/15971

 

Yours,

 

Paul H.

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