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Post by Joe Botting on Mar 27, 2014 18:27:21 GMT -5
Hi Ryan - it's great to have another perspective. I agree completely on the use of GPS if it's available (we often use it for insects but haven't yet got into the habit for fossils in Wales, where one can just read the map instead - but not so precisely). To be fair, a lot of fossils are still of enormous value even without an exact locality; if you know something is from a small quarry, or even a large one, that's an awful lot better than nothing. I wouldn't say collections are worthless without the data, but the more data there are, the more useful they get. And for population-scale studies, of course, you should really be collecting your own rather than trusting someone else's locality data. A random, semi-localised collection can be a valuable pointer rather than the dataset itself. Microfossils are a fascinating area, but I've never really gotten very much into them. The exception is sponge spicules, which I have to pay attention to, whether they're articulated or not... You raise a very interesting point about the macro-assemblages being biased. Another question is, though, are the microfossil assemblages biased as well? When the fossils can behave as sedimentary particles, you have all sorts of winnowing and concentration effects, so the biases are acting in different ways. And then there's the issue of species-level distinctiveness... with sponges, for example, the disarticulated spicules might let you distinguish only a couple of species, when there were originally dozens, and similar problems would surely work with most echinoids. I guess the only real answer is to take account of all the available information, macrofossils and micros both. The trick is trying to find a way to do that meaningfully... We spend a lot of our time in Builth trying to reconstruct communities (as far as we can), at least in loose terms. One thing we're looking at right now is depth constraints for as many species as possible to produce a calibrated transect, and for this we need to look at different preservation potential as one of the components. For echinoderms it can be a real problem, but we can normally find isolated ossicles even if there wasn't any exceptional preservation. Of course, sometimes we're looking at transported beds from shallower water, which can really mess up your depth profile if you don't spot it... Have you got a particular goal with the ecology studies, or is it the look-and-see approach (my favourite)? It will be really good to have updates as you go along, so please do raise any specific issues that you come across. What sort of stuff do you get turning up in these samples? All the best, Joe
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ryanc
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Post by ryanc on Mar 28, 2014 4:50:36 GMT -5
You are absolutely right about the micro fossil assemblages having their own biases - they still lack the soft bodied organisms that are generally missing at the macro level and anything like a crinoid that can break up into hundreds of tough calcite plates is likely to be over represented in a sample plus many other biases The micro world just gives another view with slightly different biases to the macro world so by combining the two you can hopefully get a little bit closer to what was really going on in the palaeoenvironment. It's also the only window into layers that are otherwise barren at the macro level (like much of my local chalk ). I have been gradually teaching myself the various techniques for sample processing, sorting and recording of microfossils and acquiring the required gear - I have a full set of certified lab grade sieves and a couple of microscopes. I still need to work on merges of different pictures. At the moment I have been looking at two Albian formations that have very different characteristics - the Red Chalk at Hunstanton (not its official name anymore but people tend to know it as that) and the Gault clay at Folkestone. I was lucky enough to find a bed at Hunstanton where the matrix isn't lithified and can be broken down by simple soaking unlike most of the red chalk which generally has the consistency of brick I have hit a bit of a snag though - it seems to have been a relatively high energy environment so I keep finding damaged or fragmentary forams and ostracod. Additionally there's a high proportion of sand grains in the same size range as the microfossils so it's taking a lot of time to recover specimens. In the gault clay the Forams gradually increase in size from the early gault to the later gault beds so one thing I would like to do would be to try and match up the hunstanton forams to their gault equivalent beds assuming I can find enough matching species. It would also be interesting to see if any species that are not present in the better preserved gault might be present at hunstanton. Regards, Ryan
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ryanc
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Post by ryanc on Mar 28, 2014 7:00:52 GMT -5
And then there's the issue of species-level distinctiveness... with sponges, for example, the disarticulated spicules might let you distinguish only a couple of species, when there were originally dozens, and similar problems would surely work with most echinoids. With echinoids it's not that bad but you need to rely on matching to known macro examples - with that given fragments of primary spines are often quite distinctive and a lot of the little plates often feature the attachment areas for primaries which are also useful for ID's - if you can find enough of the material you could probably make a reasonable stab at the species that were present. The oxford clay is pretty amazing at the micro level - it's incredibly rich in a wide range of organisms - lots of bone fragments (generally unidentifiable but I have found fragments of fish jaws etc.), crustacean fragments, crinoid, echinoid, a variety of teeth and lots of things that are beyond my current ability to identify It's also a good source of early mammal remains but I haven't yet gotten into that... By the way I lost my link to this forum when my last pc's power supply went but now I have re-discovered it you may have to put up with a number of my posts Regards, Ryan
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Post by Joe Botting on Mar 30, 2014 12:24:50 GMT -5
Sounds like an amazing diversity... and a completely different assemblage to what we have in the Ordovician. That's hardly surprising, of course, but it is interesting to see a direct comparison, and of that list for the Oxford Clay, the only ones that would be shared are crinoids. You'd also get conodonts, chitinozoans, ostracodes, trilobites, brachiopods, molluscs (if you're lucky), and so on. The problem is, though, that you just can't process Ordovician mudstones in the same way, so you're relying on dissolution... and will then lose a large chunk of the fauna, depending on preservation. Interesting to hear about the Red Chalk and Gault Clay faunas (I've looked at them both, albeit briefly). The ostracodes could be extremely useful in looking at palaeoenvironmental differences, as they're commonly used for that, and are often diverse - especially in relatively shallow water. It would be very interesting to see if your get similar signals from the comparison of forams, to see which was more sensitive to the differences. Sounds like hard going, sorting out the fossils from the sand grains... good luck with that. Have you got a system for photographing your finds? It would be good to see what you're getting - especially if it involves sponge spicules...
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ryanc
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Post by ryanc on Mar 30, 2014 15:32:56 GMT -5
I have an eye cam that you can slide in to replace an objective lens - it takes reasonable pictures but like my old USB microscope you really need to combine multiple images to get decent images of 3D objects. The ostracod I have found so far in the red chalk are pretty beaten up and only seem to be from one (rather simple) species - this could be the actual situation or quite likely a result of the pounding surrounded by tough quartz grains they seem to have faced - others may have been just too fragile. I shall keep plodding through the rest of the sample to see if more can be found. I have found macro fossils amongst the sample - one large brachiopod, numerous small belemnite guards and some poorly preserved sponges (very similar to the preservation in the grey chalk of the cenomanian). It's been too nice for the microscope this weekend (and Mothers day) but I did wander down to gather a few blocks from my local chalk site - shame it's non-productive for macro fossils but I'm determined to find something decent that will establish the zone. The BGS have it down as undifferentiated chalk with a range of Turonian - Coniacian so not a huge help Did you manage to get out in the good weather?
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Post by Joe Botting on Apr 1, 2014 14:58:30 GMT -5
I have an eye cam that you can slide in to replace an objective lens - it takes reasonable pictures but like my old USB microscope you really need to combine multiple images to get decent images of 3D objects. The ostracod I have found so far in the red chalk are pretty beaten up and only seem to be from one (rather simple) species - this could be the actual situation or quite likely a result of the pounding surrounded by tough quartz grains they seem to have faced - others may have been just too fragile. I shall keep plodding through the rest of the sample to see if more can be found. I have found macro fossils amongst the sample - one large brachiopod, numerous small belemnite guards and some poorly preserved sponges (very similar to the preservation in the grey chalk of the cenomanian). It's been too nice for the microscope this weekend (and Mothers day) but I did wander down to gather a few blocks from my local chalk site - shame it's non-productive for macro fossils but I'm determined to find something decent that will establish the zone. The BGS have it down as undifferentiated chalk with a range of Turonian - Coniacian so not a huge help Did you manage to get out in the good weather? That actually sounds like quite a nice fauna - especially the sponges (yes alright, I'm biased... ). Have you had a go at IDing them? If they're very shallow water species, you might expect them to be different groups to most of the Cenomanian ones. Those ostracodes sound like a bit of pain - those smooth ones we generally call 'baked beans' and leave it at that, even if they're decently preserved. Mashed ones are likely to be beyond anyone. Was off visiting family at the weekend, so no fossils. It won't be long before spring settles in for good, though, so I'm looking forward to that. I did get out briefly last week (back to the new sponge site), and picked up a few more pieces and tiddlers but nothing spectacular - just a couple more new sponges.
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ryanc
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Post by ryanc on Apr 1, 2014 16:02:32 GMT -5
They are simple tubular forms with a suggestion of branching but very fragile amongst the loose sediment - are the spicules useful in determining species? I could dissolve a chunk in acid to harvest some. I have been taking advantage of the warm evenings with good light to practice my fossil devoid chalk method I randomly collect decent sized chunks of chalk from the agricultural quarry a couple of miles from my home whenever I walk the dog out there. Once I get decent weather I then inspect all outer surfaces with magnification to see if I can see any fragments of fossil and barring that I gradually split the chunks down inspecting all exposed surfaces as I go until I'm left with pieces a couple of cm square which then go on the discard pile. It's incredibly soft chalk - the coccoliths are not cemented by anything and its actually quarried for use as a food/pharmaceutical ingredient. It seems quite a deep water environment and clearly far from any land derived sediments thus the purity of the chalk. It has no Milankovitch cycle flint layers and the chalk at the top of the quarry has been discoloured by what I assume is exposure to permafrost during the Anglian glaciation (the only one that got this far south). The chalk has been heavily fractured I wondered if conditions in the benthic zone were anoxic - burrows are quite rare and where present are tiny and filled with iron oxides (which makes them easier to spot) but it could just be that there wasn't much food for benthic life there. I found a tiny partial fish remains yesterday by the splitting method - it doesn't seem to be burrow debris as is usually found so this would again suggest a lack of benthic scavengers. It really is tiny (the whole exposed area is less than a cm and showing dozens of bone fragments) and the preservation is slightly odd - lots of thin crystalline looking near transparent sheets amongst it which I'm puzzling over. I will try and reveal a bit more of it once the pieces have dried out and stabilised a bit but I am encouraged that I may one day find something that will repay my efforts on such an unpromising site Regards, Ryan
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