Siliceous Ooze And Siliceous Rocks

Of all the subjects in sedimentology, this is the one where I've found it hardest to get any solid information, especially such as might be suited for beginners.I hope that you don't think that I'm just asking you to do my homework for me, I've been googling around this subject literally for weeks. And yet some things are still slightly beyond my grasp.Let's start with a (hopefully) easy question (I shall number them for your convenience, this is number 1).(1) When I first came across the term "radiolarian chert" I supposed that it was a term analogous to "oolitic limestone": i.e. the word radiolarian meant that in thin section one could see that it was composed of radiolarians. But I haven't found anyone saying so directly.Gradually, by observing usage, I came to suspect that I was putting the emphasis in the wrong place and that the word chert implied that sufficient recrystalization had taken place that no radiolarian structures were to be seen any more; and that the radiolarian origin was a matter of inference rather than observation. But I can't find anyone directly stating that either.All anyone tells me is that it's chert of radiolarian origins, but not how it is so identified.I could make similar remarks about diatomaceous chert (mutatis mutandis).Can anyone help me with this? Thank you.

Hi,It would be great that if this has any link to the Creo/Evo debate (particularly the flood) that you could mention how exactly during the course of discussion.If it does not well, I hope you get the answers you are looking for.

Thread copied here from the Siliceous Ooze And Siliceous Rocks thread in the Proposed New Topics forum.

I'm no geologist but I will express my layman's understanding.Chert is a flint-like (in fact, flint is a variety of chert) rock that has a structure that is ideal for preserving fossils.
Radiolarian chert is a type of chert that contains microfossils.
Oolitic limestone is a type of sedimentary rock that is sometimes composed of chert, but is often composed of one of several other minerals, and most commonly calcium carbonate. I don't see any reason to presume that they all contain radiolarians.As for relevance, radiolarian chert is notable for preserving protozoa since the beginning of the Cambrian, the period where life rapidly diversified. Charles Darwin saw this period as one of the main objections against his theory.

Well, I have found this creationist stuff about chert, here. The problem is that it's complete nonsense.The reason I wanted to bring the subject up on this forum is that when I search the internet for geology forums most of 'em are dead, and failed, and no-one is posting there, whereas this forum is alive, and geologists actually contribute to it.But I'm not really looking for a "Creo/Evo debate". As you can see from my OP, I'm just looking for the facts.

You haven't really tried to learn about what you're talking about. Let alone what I'm asking about. I set it out in the OP. I don't want to be told what is true. I want to know what evidence substantiates the truth.I do not see why I need to spend even five seconds of my time on someone who writes "Oolitic limestone is a type of sedimentary rock that is sometimes composed of chert". But perhaps you can explain.Your statements about Charles Darwin are meaningless and irrelevant until you can explain their relevance and their meaning.Edited by Dr Adequate, : No reason given.

Hi Dr.A,I'm no geologist but looking at the US national parks website on Chert it looks like your first interpretation was closer to the truth, but rather than their structure being visible in thin sections the radiolarans are apparent as small spherical inclusions, when the chert is crushed and treated with hydrofluoric acid it will leave the radiolarans' silica shells intact.TTFN,WKEdited by Wounded King, : No reason given.

Thanks.I'd heard about hydrofluoric acid, but again, no-one quite answers my question, Does the hydrofluoric acid just reveal that radiolarian tests exist in the chert, or does it actually reveal that the chert is made of radiolarian tests?

I think that you are right that the radiolarians as a source of the silica in the matrix of the chert is simply an inference based on their abundant presence in more complete form in the same sediments. The hydrofluoric acid extraction certainly doesn't demonstrate that the origin of the silica is from the radiolarians.I think it is called Radiolarian chert simply because of the inclusion of many radiolarian microfossils, I suspect that in their absence there wouldn't really be any way to know the origin of the silica in the matrix, and you might argue there isn't even with their presence but it seems a reasonable inference.TTFN,WK

Since chert can form in a number of ways and is often diagenetic, I wouldn't call something a radiolarian chert unless I saw radiolarians in it.Now if I infered it to be the result of a radiolarian ooze where all the tests become desolved, due to the nature of the rocks above and below it, I would say that rather than calling it a radiolarian chert. A chert of probable radiolarian origin.BTW hydrofluoric acid is used to desolve silica, and since most radiolarian tests are made of silica I wouldn't use it to remove radiolarians from a rock (they would all be gone). You and WK are probably thinking of using hydrofluoric acid to remove various palynomorphs including pollen from rocks.Hope that helps.Edited by petrophysics1, : No reason given.

Naw, it is used to extract Radiolarian tests, the process is described here in a paper from the 70s. The structure of the tests is apparently different enough that they dissolve more slowly than the matrix they are embedded in, but obviously you can't leave them in the acid too long or as you say they will also dissolve.TTFN,WK

Thanks for the info. Not being a micropaleontogist (or paleontologist for that matter) when doing biostratigraphy I just send my samples to one.You have to know how to delegate jobs as you can't be an expert in everything.P.S. No wonder I didn't know about that the paper was written in 1972, 2 years after I took paleontology.Edited by petrophysics1, : add P.S.

Similar, if I'm not mistaken, to using acetic acid (AKA strong vinegar) to eat the matrix of limestone first.