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Coal, geologically mostly all about the same age

Cantclimbtom

Active member
Hi all,
In my ignorance I hadn't realised that in terms of geological periods... coal is the same age. I found the explanation interesting. Many of you here are knowledgeable about geology and probably heard this years ago, but for the others...

https://youtu.be/b34al8YmQSA
 

Andy Farrant

Active member
That's not strictly true, as there are plenty of other coal deposits of different ages elsewhere in the world. For example, there are Cretaceous coals in North Africa, whilst many of the coal deposits in South Africa are of Permian age (Karoo). Similalry Australia's mineable black coals range from Permian to Jurassic in age (mostly Permian). the lignites in Germany and Poland are of Miocene age. However, the Carboniferous Period was notable for the abundance of coal forming forests. Palaeogeography, climate and the type of faunas was a big factor in this. Rocks of this age are common in NW Europe and the USA, so Carboniferous coals are the most abundant in the UK. There was a coal (lignite) mine in Palaeogene strata near Gravesend in Kent which was briefly worked during WWII.
 

LJR

Member
A nice theory. It's a pity the piece of "coal" that he shows at the start is actually a press formed briquette!
 

RobinGriffiths

Well-known member
The other significant thing about the Carboniferous was the cyclical nature of marine trangression and regression giving rise to the well known cyclothems (repeated sequences grading from marine to delta to terrestial deposits). It's quite likely that this depositional regime was also significant in preserving organic material.
 

Cantclimbtom

Active member
LJR said:
A nice theory. It's a pity the piece of "coal" that he shows at the start is actually a press formed briquette!
I wasn't sure what to make of that choice. Could it be it is compressed coal and therefore a clever example of coal in various consumed forms, or could it be he couldn't be ar5ed and just grabbed a lump of something from a bag of cheapo fuel from his mum's coalshed (Coal'ole) thinking nobody would notice. We'll probably never know

RobinGriffiths said:
The other significant thing about the Carboniferous was the cyclical nature of marine trangression and regression giving rise to the well known cyclothems (repeated sequences grading from marine to delta to terrestial deposits). It's quite likely that this depositional regime was also significant in preserving organic material.
If you could dumb it down at all please, I know I for one would benefit. marine transgressions - is that a wicked and sinful dolphin?
 
Pah! to all this geology stuff.

The lump in question is a good facsimile for a Durham Ovoid ( a crushed and formed, smokeless (nearly) fuel) available from my local merchant (and other places), good price, burns well and not much clinker, I'm even polluting the atmosphere as I type 'cos it's a bit chilly.  He's based at Morrison Busty which was the site of a coal mine which also worked witherite, a hydrothermally deposited substance, I think LJR may even have mentioned in his AditNow persona some time ago.

Jim
 

Fjell

Active member
Ice ages, lots of them if I recall. Also means there are carbonate platforms with a dozen karst erosion horizons within them. A thousand vertical metres of limestone pavements on top of each other.

And there were so many trees O2 got up to 35%. You wouldn?t have paid extra for Nitrox, which would have been a real bonus I?m sure you would agree.
 

RobinGriffiths

Well-known member
ChrisJC said:
Or the land falling & rising.

Indeed. I'm no expert, but quite a few articles seem to point towards the advancement and subsidence of deltas as being a mechanism for the cycles. I'm sure a proper geologist can put us right.
 

mrodoc

Well-known member
On this topic, sort of, I am wondering what the equivalent in hectares of forest the amount of coal we have taken out of the ground in a few centuries adds up to. Might make climate change deniers look up and take notice considering how many millions of  years it took to lay down originally.
 

pwhole

Well-known member
mikem said:
RobinGriffiths said:
marine trangression and regression
Seas rising (inundating) & falling

A possible marine transgression in the middle of Sheffield - and then a session in freshwater at the end. Actually, just checking my notes (frantically searching!), those are freshwater mussels :)
 

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wellyjen

Active member
mrodoc said:
On this topic, sort of, I am wondering what the equivalent in hectares of forest the amount of coal we have taken out of the ground in a few centuries adds up to. Might make climate change deniers look up and take notice considering how many millions of  years it took to lay down originally.

http://www.calu.bangor.ac.uk/Technical%20leaflets/050404%20CALU%20calculating%20woodland%20energy.pdf estimates 1.278GJ from 50 years of growth from a hectare. Wikipedia reckons 25GJ per ton from coal, so roughly 20 hectares of woodland burnt entirely for the same energy as a ton of coal. You then have to wait 50 years for that woodland to grow back.
 

wellyjen

Active member
wellyjen said:
mrodoc said:
On this topic, sort of, I am wondering what the equivalent in hectares of forest the amount of coal we have taken out of the ground in a few centuries adds up to. Might make climate change deniers look up and take notice considering how many millions of  years it took to lay down originally.

http://www.calu.bangor.ac.uk/Technical%20leaflets/050404%20CALU%20calculating%20woodland%20energy.pdf estimates 1.278GJ from 50 years of growth from a hectare. Wikipedia reckons 25GJ per ton from coal, so roughly 20 hectares of woodland burnt entirely for the same energy as a ton of coal. You then have to wait 50 years for that woodland to grow back.

Government figures on UK coal production from 1853 to 2000. Total dug out the ground 18,431x10^6 tons. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1005760/Coal_since_1853.xls
So that is equivalent to burning 368 x 10^9 hectares of forest.
The surface area of the UK is around 25 x 10^6 hectares, so over around 147 years we burnt the coal equivalent of 14,720UK sized forest, or an average of 100 a year. Can someone check my figures and sums, 'cause that is a gargantuan amount of carbon.
 

Brains

Well-known member
Compared to wood, peat or lignite coal is very high in carbon, especially the steam coals...
The marine cycles were driven by changes in sea level and land level due to many factors, such as glaciation compaction and tectonic uplift and downthrow.
Typically a sequence would run from deepwater fine muds, through fine silts and sands to coarse deltaic sands and even gravels, to a soil or seat earth followed by a coal. For whatever reason the sea would return and a marine band with seashells be formed and a repeat of the sequence. The sediment indicates a deep water basin into which a delta progresses, breaks surface and is colonised with vegetation, followed by immersion and repeat. The marine bands contain both long lived species typical of the environment and short lived species that date each incursion. Examination of the coal reveals a fine detail of plant debris containing leaves, twigs, seeds and pollen in various states of thermal alteration from low grade metamorphism. Gas, rather than oil may be produced and migrate to hydrocarbon traps, leaving the dense high carbon coals.
Some theories state that the coal swamps were subject to extreme seasonal variation, so that summer abundance turned into deciduous drifts of leaves etc that couldnt be decomposed by detritivore organisms in a cold "arctic" winter. Repeat over countless years to produce deep organic deposits that become coalified.
In modern forests the fall of debris is usually consumed and recycled seasonally without a build up, but the coal beds represent years of accumulation. Often quoted is the deltaic swamp of Okefenokee Swamp as a "coal measure type" feature, but it seems that not enough organic detritus is being built up?
 

wellyjen

Active member
Speleotron said:
How do we have hecters of coal? Shouldn't it be a unit of volume not area?
You don't. Tons of coal and their equivalent calorific value on hectares of forest. How much area of forest you'd need to burn to get the same energy as burning a ton of coal.
 

mikem

Well-known member
But the "English" countryside during the interglacials is now thought to have been more like parkland, than dense forest (so mostly open grassland full of grazing animals, with occasional trees / scrub), which would mean a much greater hectarage / time period required.
 

wellyjen

Active member
mikem said:
But the "English" countryside during the interglacials is now thought to have been more like parkland, than dense forest (so mostly open grassland full of grazing animals, with occasional trees / scrub), which would mean a much greater hectarage / time period required.
We could burn the grass and animals too! The tops of some of the mountains were always probably clear of trees too. I was using it as an example of an area people had a feel for, not how it ever actually was.
 
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