ADAM'S SILURIAN

[Wrangellian]

Nice job on the prep - With that method I don't know how you avoid punching thru the matrix suddenly and putting a ding in the fossil each time, but I guess it's doable if the matrix is soft and thin enough?

[Tidgy's Dad]

5 minutes ago, Wrangellian said:

Nice job on the prep - With that method I don't know how you avoid punching thru the matrix suddenly and putting a ding in the fossil each time, but I guess it's doable if the matrix is soft and thin enough?

Thank you for the compliment. 

For years I've used pins and needles and a steady hand, plus a jeweller's loupe. 

Now I have a lovely pin-vice and though the eyesight's a bit more wonky, the hand's still steady.

This one and the Elrathia and agnostids I did recently are fine as much harder than the soft matrix around them, as you suggest, but with harder sandstones and limestones it's a tiny bit at a time at the right angle to avoid dinking! 

Hopefully, I'll get a chance to do some harder work on the Middle Silurian Wenlock limestone coming up soon. 

[Bobby Rico]

6 hours ago, Tidgy's Dad said:

But wait a minute, thunk I, when I was gazing lovingly at this specimen yesterday. I've never tried to prep this little fellow. 

So out with the new pin-vice spiky thing  kindly sent to me by the wonderful @JohnBrewer

Here are the results :

Lovely! 

@Peat Burns you may be interested in this and the previous few posts. 

 

Nice work Adam I think I need to get a pin vice too. How long did you work on it?

 

Cheers Bobby 

[Tidgy's Dad]

6 hours ago, Bobby Rico said:

Nice work Adam I think I need to get a pin vice too. How long did you work on it?

 

Cheers Bobby 

Not sure. 

It is pretty small and the matrix very soft.

An hour? Two?

Not long. 

[ynot]

[Wrangellian]

9 hours ago, Tidgy's Dad said:

Not sure. 

It is pretty small and the matrix very soft.

An hour? Two?

Not long. 

That sounds about how long it would take me! (maybe more) 

With the nearsightedness, I've got magnifying-glass eyes, but my hands aren't that steady.

[Tidgy's Dad]

So, a detour northwards even beyond the Lake District now as we visit Newlands, Girvan, Ayrshire, Scotland to look at a piece I've just had the id for thanks to  @TqB and @piranha

Thanks guys! 

It's from the 'Pentamerus Grits,' now known as the Newlands Farm Formation, Lower Llnadovery, a 1.7 cm piece of the calcareous green algae Cyclocrinites favus, part of which seems to be growing over the shell of a Pentamerus oblongus brachiopod. 

Here you can see more clearly how it seems to be growing on the shell fragment.

 

[Tidgy's Dad]

In the same rock is this tiny thing. 

It's only 2 mm or so across and is definitely a coral or a bryozoan or something else entirely. 

 

[ynot]

22 hours ago, Tidgy's Dad said:

d is definitely a coral or a bryozoan or something else entirely.

Yep, it has to be one of those three.

[Tidgy's Dad]

Just now, ynot said:

Yep, it has to be one of those three.

I'm still testing out my new sense of humour. 

Bought it at a garage sale. 

Yup, I'm certain it's one of those three. 

[-Andy-]

The green algae almost looks like hadrosaur skin!

[Tidgy's Dad]

Just now, -Andy- said:

The green algae almost looks like hadrosaur skin!

It does,you're right! 

Which would be quite something in the Silurian!

[Spongy Joe]

10 hours ago, Tidgy's Dad said:

I'm still testing out my new sense of humour. 

Bought it at a garage sale. 

Yup, I'm certain it's one of those three. 

Can't compete with that humour, I'm afraid... but I am sure that it's a very young colony of a bryozoan. Or something else entirely.

[Tidgy's Dad]

I've been busy back with the Cumbria Llandovery stuff. 

The next batch were all found in Skelghyll (Skelgill), Nr. Ambleside, Cumbria about thirty years ago. 

Graptolite classification has changed somewhat since then, and many of the names of genera and species have too. 

I am very uncertain of some of these ids, so don't be afraid to shout out. 

First up, from the Lower Skelgill Formation of the Stockdale Group, so Lower Rhuddanian in age and pretty close to the base of the Silurian, is Normalograptus normalis. 

The Great Ordovician Extinction event nearly did for the graptolites, as with so many other groups, but some Diplograptids survived ( not including dendroids in this) and it is thought that from the family Climacograptidae emerged the Normalograptidae from which all the other Silurian graptolites, the Neograptinids including the Monograptids and Retiolitids evolved. 

The specimen is 8 mm long.

Hmmm. Terrible photo, here's a better one. 

And another close up : 

 

[Spongy Joe]

Nice to see some of these survivors!

 

Since Mrs. Spongy is working on latest Hirnantian graptolites on the other side of the desk from my sponges, I've been trying to pick up the odd bit of knowledge on these, so as not to embarrass myself too much. Basically, it's a bit more complicated, but that's basically right. 

 

It turns out that there are many more species in South China than there were in the UK Hirnantian, and a few different lineages also made it into the Silurian (e.g. neodiplograptids). However, as you say, probably all of these ultimately originated from normalograptids, and represent a first phase of diversification in the plankton, following the mass extinction - and before the benthic animals recovered at all.

 

Identifying normalograptids is apparently an absolute nightmare, though: it all depends on the exact thecal shape, and measurements. Of course, a lot of the Silurian in the UK is slightly deformed, which interferes with... oh, measurements. A perfect proximal end helps a lot, too - many are not identifiable from fragments. At least, she keeps complaining when the ones I pass her aren't perfect!

    The sort answer: I'd put a question mark on the 'normalis' part!

 

Mrs. Spongy says, "How wide is it? Exactly? The thecal shape looks wrong for normalis, anyhow... it should be really sharply geniculate, and these are a bit more rounded."

[doushantuo]

NICE!!!

N. arvulus?

below: a 3d example of N.scalaris.

[TqB]

Neat specimen and informative! Keep the graptolites coming, Adam.  

[Tidgy's Dad]

19 hours ago, Spongy Joe said:

Nice to see some of these survivors!

 

Since Mrs. Spongy is working on latest Hirnantian graptolites on the other side of the desk from my sponges, I've been trying to pick up the odd bit of knowledge on these, so as not to embarrass myself too much. Basically, it's a bit more complicated, but that's basically right. 

 

It turns out that there are many more species in South China than there were in the UK Hirnantian, and a few different lineages also made it into the Silurian (e.g. neodiplograptids). However, as you say, probably all of these ultimately originated from normalograptids, and represent a first phase of diversification in the plankton, following the mass extinction - and before the benthic animals recovered at all.

 

Identifying normalograptids is apparently an absolute nightmare, though: it all depends on the exact thecal shape, and measurements. Of course, a lot of the Silurian in the UK is slightly deformed, which interferes with... oh, measurements. A perfect proximal end helps a lot, too - many are not identifiable from fragments. At least, she keeps complaining when the ones I pass her aren't perfect!

    The sort answer: I'd put a question mark on the 'normalis' part!

 

Mrs. Spongy says, "How wide is it? Exactly? The thecal shape looks wrong for normalis, anyhow... it should be really sharply geniculate, and these are a bit more rounded."

Thanks, Joe, I was going to shout out to you after i'd posted a couple more as i recalled your saying  Mrs Spongy was something of a graptolite expert. 

But I thought the thecae on N. normalis were flatter or more sharply rounded to be honest. N. parvulus is more pointy. 

The specimen is pretty much exactly 1 mm in width. 

[Bobby Rico]

I second that we don’t see enough graptolites. 

[Tidgy's Dad]

19 hours ago, doushantuo said:

NICE!!!

N. arvulus?

below: a 3d example of N.scalaris.

Thanks. I love these three dimensional graptolites, you can even buy them on line, i might do so someday. 

If you mean N. parvulus , it did just sneak over from the topmost Ordovician to the very lowest biozone of the Silurian, but it seems too comb like and has more erect thecae, in my opinion. 

[Tidgy's Dad]

On 5/27/2018 at 9:28 PM, TqB said:

Neat specimen and informative! Keep the graptolites coming, Adam.  

Thank you, I will. 

23 hours ago, Bobby Rico said:

I second that we don’t see enough graptolites. 

Okay so here's a shed load more.

A graptolite block from higher in the Skellgill Formation, so near the top of the Rhuddanian (Lower Llandovery), part of the Middle Skelgill beds. I found so many graptolites at this level. 

The block is only 5 cm by 3.5 cm on it's surface but is packed with several different species of graptolite and bits. This shows nicely that the graptolites had diversified nicely after the setback at the end of the Ordovician.  Many of these graptolites are preserved in 3D in pyrite, and though some are beginning to oxidise a little, it's no problem and they still look beautiful, if a little tarnished.

Now, I hope I'm correct in saying that the one shown in more detail below, the curved one with the sharp hooked thecae, is Monograptus trianagulatus fimbriatus. This used to be M. fimbriatus and was the zone marker for this level, but it is now the M. triangulatus biozone, though I think these come from the new magnus zone immediately above (if I have the right level). The graptolite in question is 9 mm long and a little less than 1 mm wide. 

Hope I'm right with this id, because the rest of the ids to come are based in part on the assumption that this is the magnus zone as only here is M. trinagulatus found with Neodiplograptus magnus which is the next specimen shown from the same block. 

These were probably the most common graptolites in the pieces I took home from this level. 

 

[Tidgy's Dad]

Oh, well, I thought it was a beautiful graptolitic rock, and a wonderfully interesting graptolite. 

Never, mind, I shall continue......

In the same block are some of this species which I am saying could be Neodiplogratus magnus, a) because it looks like it; b ) because it is listed as an abundant species in the magnus zone with the abundant M. triangulatus just above the triangulatus zone  and I found a lot of them; c) because it's suitably large and ; d) because i'm not sure what else it could be.    

It's 7 mm long (there are longer ones but the preservation of some of this is excellent) and just over a mm wide. 

 

[Spongy Joe]

Just catching up... Yep, that looks like Monograptus triangulatus (sic), and indeed it does look like it could be N. magnus... but that's a bit harder to be sure of.

 

For the N. normalis, though, we're actually thinking it could be a Glyptograptus sp. instead - not only is the bit narrow, but those lower angles on the thecae are definitely rather rounded... it's one of those situations where having multiple specimens helps, partly because a slight difference in the angle these are flattened at can significantly change the appearance.

 

Lovely things, though, as ever! We collected graptolites from this interval during an undergraduate training trip to the Howgills... a little whole ago!

[Tidgy's Dad]

Yes, triangulatus. I need a decent night's sleep i think. I have altered a couple of other errors too. 

I did have few others, but they've all gone over the years, so, if Glyptograptus, at that lowest level, there are a few, but  G. tenuis is a tenuous possibility? (sorry, I couldn't resist). 

So, if M. triangulatus and Neodiplograptus magnus are correct, then this would be the magnus zone, one above the triangulatus zone as the two are only found together there. 

So in this photo we can see another M triangulatus near centre and just above and to the right of it, dead centre of photo, a similar graptolite but a little smaller, not hooked so much and more steeply curved. Could this be M. pseudoplanus, which is found at the same level? There is another specimen of the possible Neodiplograptus magnus above these and another species trailing away to the right of them off the edge of the photo which i'll post a better picture of in a minute. 

Or two.

Thank you, Joe, and please thank Mrs Spongy for her assistance on my behalf. 

This curled one i'm talking about, right in the middle, that i think is M. pseudoplanus is 4.2 mm across (straight line measure) and about .75 mm wide. 

 

 

 

[Tidgy's Dad]

The one trailing away to the right is pictured again here. 

It runs from and under the curled and hooked M. triangulatus fimbriatus, under the curved but not so hooked  M. pseodoplanus and upwards to the right of the picture. I think this is the monograptid Atavograptus atavus which is found at this level with the other graptolites I've already mentioned. It is 12 mm long but only a little more than half a mm wide.