[Rockhounds] Re: Pennsylvania fern fossils --Llewellyn Fmn

Wed Nov 5 11:20:36 PST 2008

Hi i live near Hazelton Pa.can you send me photo of the sponges fossils?

Thanks Steve
--- On Mon, 11/3/08, Mr EMan <mstreman53 at yahoo.com> wrote:

> From: Mr EMan <mstreman53 at yahoo.com>
> Subject: [Rockhounds] Re: Pennsylvania fern fossils --Llewellyn Fmn
> To: "Rockhounds at drizzle.com: A mailing list for rock and gem collectors" <rockhounds at lists.drizzle.com>
> Date: Monday, November 3, 2008, 9:47 PM
> You asked how you get "shale-like" fossils next to
> a coal seam and that is fairly much how the are always
> found.  If you meant "slate-like" fossils that too
> is consistent with the Llewellyn but challenges a common
> belief about anthracite deposits. 
> 
> The St Clair fern deposits are within the Llewellyn
> Formation which also contains a full range of sedimentary
> rock types. Shale is the appropriate term for the fern
> bearing matrix and is wholly consistent with coal sequences:
> delta deposited highly graded milky quartz pebbles which
> become conglomerates, peat bogs which are coal-forming
> layers, sandy beaches becoming sandstones, mud-bottomed
> offshore ledges yielding fossil laden slates and deep water
> siltgoing to siltstones. Fossils are found in all the above
> but preservation is best in the very fine-grained slates.  
> 
> The fact that mica grains are rarely found with macro
> fossils suggests that the slilt particle sizes the ferns
> formed in were carried even farther out off shore by
> remaining in suspension longer.  Ergo the ferns must also
> have sloshed around and floated for sometime before sinking.
>  yet I've never found a bent stem and they should be
> common if it was violent storms which ripped them from the
> bogs and carried them out to sea. There are many small
> plants, seed pods, and even insect wings in the St Clair
> location.  Larger limbs and broad long leaves are also
> sorted but are rare in the St Clair shale deposit being more
> common closer to shore. Whilst ferns are more rare in
> courser, near-shore deposits.  This suggests the fern stems
> either float better, else are more easily destroyed by
> larger grain sizes and either way is fodder for a PHd
> thesis.
> 
> So in answer again; shale is very common in coal measures.
> I've never seen any coal without some associated shale. 
> There has long been a belief that anthracite formation
> conditions will destroy all textures along with any fossil
> traces but St Clair is clear proof that this isn't
> always true with regard to adjacent deposits of non-coal
> rocks. I've some amazing corporlites from the Llewellyn
> which could have been dropped there last week from their
> appearance.
> 
> In anthracite regions, slate seems to consistently harder
> and may be a combination of burial depth, reduced
> weathering, more recent exposure from strip mining and/or
> organic cementing. Many exposures have a hacky fracture--
> across bedding planes and could be legitimately called
> near-slates. BTW, other local shales include the
> Martinsberg(sp) and Chattanooga.   The use of the term
> "slate" is used by locals and possibly stems from
> the deceiving similar appearance to the adjacent "Slate
> Belt" workings and workers migrating between the two
> industries 
> 
> Be it remembered that coal producing bogs were at the
> margins twixt un-vegetated inland highlands and coastal
> lagoons. In a time of no soil nor plant-supporting
> Eco-systems on the highlands, even routine rainstorms
> created very violent frequent flooding which ripped through
> the bogs and washed vegetation out to sea regularly. Stream
> beds of quartz pebbles are very common in coal seams. This
> cycle provided a constant load of silt off shore.
> 
> The fern bearing shales of the St Clair represent
> vegetation that was washed out into the relatively quiet
> muddy bottoms where silt accumulated in what was oxygen
> starved conditions(aka reducing)that retarded decay. The
> constant supply of silt provided for rapid burial and the
> finely detailed fossils we know today.
> 
>  The white mineral coating St Clair ferns(pyrophyllite) is
> believed to be a weathering replacement of the pyrite that
> formed in the plant tissue cavities during the fossilization
> sequence. The pyrite was derived from sulphur rich organic
> matter in a reducing environment.  In fact the pyriteoids I
> find there almost always contain a white dust I assume is
> pyrophillite.
> 
>  There might be some slate-like affinities within the
> Llewellyn but by far it is a classic high organic shale.  I
> don't have the graphs at hand but there are temperature
> and depth plots that confirms that for anthracite to form,
> it had to have a very deep burial (5-8 miles?)  This is
> sufficient to produce slate but the whole conditions
> weren't met for  slate to form, near the coal seams
> anyway. Theoretically, heat and depth conditions should have
> destroyed all traces of fossils in forming slate but, 300
> million years later we have the beautiful white fern fossils
> of St Clair. I surmise that something in the coalification
> process prevents the conversion of shale to slate. Just
> 10-20 miles from St Clair are true slate beds which
> produced, what anyone over 40, probably remembers as the
> "chalk-board" they used in grade school.
> 
> Speaking of the Llewellyn formation, are there any coal
> experts watching?  I've found balls of sandy
> oolitic-looking objects within shales near Hazelton/Latimer
> which resemble sponges. I would like someone that might have
> a potential identification on what these are.
> 
> Elton
> 
> --- On Mon, 11/3/08, smkell45 at aol.com
> <smkell45 at aol.com> wrote:
> 
> > I've been reading about St. Clair material. People
> keep
> > calling the matrix "slate". My specimens
> from
> > there frequently are very detailed and not at all
> distorted
> > as they might be if there was? more than a little?
> slate
> > producing metamorphism. Also a thought that slate
> splits
> > along planes perpendicular to the pressure, not along
> > sedimentary layers containing the fern fossils. I also
> was
> > told that this was a worked out anthracite location.
> How do
> > you get shale type fossils and matrix next to an
> anthracite
> > location.? Somebody set me straight. smkell
> > 
> 
> -- 
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