How important can fossils be? Options

[ustrax]

Here at home, I usually take a walk with my dog to a nearby field.
In this particular site, some kms far from the sea, the ground is littered with fossils of small shelled creatures.
They are scattered all over at the surface, let's say that if you pick ten rocks, one of them has something.
There are also fragments embeded in larger basaltic blocks.
We are in the Sintra Hills (they are the green area here and here, the green arrow marks the field I am talking about) region which were formed in a process that spawned from 80my to 30my due to magmatic intrusion, it is known that this lifted what was once the ground forming cliff where we can now see dinosaur footprints.
The question is, that piece of ground will soon be predated by house building.
What I would like to know is:
#01 - What might have happened there in the past?
Did that area was part of the ocean that retreated when hills raised?
Did it suffered some king of tsunami event that brought all the creatures to dry land?

#03 – Can someone tell me, from the images (they're not good I know, I'll try to take some more) what kind of creatures are we looking at? There is one species appearing more often, some kind of creature with spiral mother-of-pearl shell...

#02 - What could we expect to find digging under the surface?

#03 – Is it worthy to take measures to delay the beggining of constructions or is this just an ordinary situation?

Thanks!

[djellison]

I used to live in the Cotswolds, quite a long way from the Sea
http://maps.google.com/maps?f=q&hl=en&...&iwloc=addr

We were a few hundred metres above sea level - and when you dug in the garden you would find massive limestone rocks full of fossil shells. A symptom of the fact that the whole area used to be underwater when sealevels were much much higher. I found hundreds and hundreds of things like this - http://www.mii.org/Minerals/Minpics1/FossilLimestone.jpg

I don't imagine there would be any danger in some science being lost by a housing development - but there would be no harm in colllecting a few, noting where they came from and visiting a local museum or university to ask them about it.

Doug

[ustrax]

I don't imagine there would be any danger in some science being lost by a housing development - but there would be no harm in colllecting a few, noting where they came from and visiting a local museum or university to ask them about it.

Thanks for answering Doug...That's the kind of stuff you can find there...
I'm not saying that this is a major finding, but I really enjoy that piece of ground and if there was the possibility of turning that place into a open air museum (if more than this shells could be found by digging...) instead of houses, I would be in the front line for it...

[helvick]

Ustrax,

I can't see the object clearly enough to tell at all but if it's a fossilized spiral shell then there's a pretty good chance that it's an ammonite. I've found a handful over the years - all on beaches in and around limestone\shale cliffs.

[ustrax]

Thanks helvick, one of those would be great but when I used the world spiral I was referring to the union of the shells...I'll try to get some more images and fossiles today, I believe I discovered what they are...
If so, they are from the Jurassic, the period when the hills were formed

[Juramike]

Yup. Looks like you nailed it!

Gryphae are very very common in some periods of the lower Jurassic. In the area around Lyon, France, there was an environment in time where they were EXTREMELY common. (I think it was the Sinemurian era of the lower Jurassic [In France, the lower Jurassic period is split into it's own period, the Liassic]. Many of the local walls and sidewalks in Lyon are chock full of Gryphae shells.

If you can, poke around a bit to see if you can find other fossils other Gryphae (they might be smaller). From my own experience, Gryphae pretty much dominated the local environment, but you might be able to find small brachs (brachiopods) and maybe a few ammonites, belemnites, or even snail shells.

Once construction begins, see if digging goes down to a layer below the gryphae bed. You might find really cool, and different types of fossils there. And if there are hills with exposed cliff faces, check out the layers above the gryphae zone.

During much of the Jurassic, Europe had a shallow tropical sea (I think it was the Tethy's ocean) and lotsa little critters roamed in near warm shallow waters. Over the next several million years the waters retreated and reinundated the area giving neat layers of fossils and building up impressive limestone beds. Most likely during one of those times a shallow muddy layer of living gryphae (similar environment to today's oyster beds) lived, died, and eventually got buried and fossilized in place.

Check out: http://www.scotese.com/earth.htm [Uber-cool animations]

Happy hunting!

-Mike

[ustrax]

If you can, poke around a bit to see if you can find other fossils other Gryphae (they might be smaller). From my own experience, Gryphae pretty much dominated the local environment, but you might be able to find small brachs (brachiopods) and maybe a few ammonites, belemnites, or even snail shells.

Thanks Juramike!
There are others, for example, the one in the middle of the image I present is some kind of cockle and there are also some vestiges of what it seems like vegetation...
What I would like to know is if they are there because of the lifting of the terrain or they were already there, in a shallow sea that retreated...Is there a way of knowing so?

[ElkGroveDan]

As others have noted Ustrax, marine fossils are pretty typical -- the world over for that matter. There's probably no need for protection or intervention unless a unique discovery is made. In some parts of the world local governments mandate archaeological or paleontological studies before construction begins for this very purpose.

As for fossils at elevation, the limestone that comprises Mt. Everest even holds fossils - I believe ammonites like those Helvick described have been collected at the highest elevations. It's all about subduction and uplift which more or less never ceases on geologic time scales.

On a personal not one of my favorite "fossils above sea level" locations is Guadalupe Mountain, the highest point in Texas - 8700 feet. The entire range is an ancient fossilized and uplifted reef (Permian). Seabed fossils are everywhere. There in fact is so much ancient shell material that the calcium carbonate has dissolved and recrystallized over the eons leaving the most amazing clear crystals sticking out of rocks between crinoid fossils.

I highly recommend this as a tourist site for physically fit, scientifically inquisitive types. It's also right on top of the famous Carlsbad Caverns, tucked in the corner where Texas and New Mexico meet (near El Paso and Las Cruces.) Don't go in the summer it's extremely hot and arid in that region.

[elakdawalla]

Marine fossils can be quite common, depending on where you live. In north Texas, where I grew up, everything was underlain by Cretaceous limestone containing all kinds of wonderful fossils. In fact, in the eighth grade (when I was 13), for biology class we were assigned a project to go out around the city and collect 20 different fossils. That was fun. My Dad and I drove all over the place with rock hammers and found ammonites, various kinds of bivalves, turitella shells, sea urchins, worm tunnels, crinoid stems, all sorts of things. I must have found half a dozen different kinds of fossils just in my own back yard, from the rocks that had been dug out of the ground when they leveled the lot to put in our house.

--Emily

[ustrax]

Thanks ElkGroveDan and Emily for the comments...
I know where I'll be on Saturday morning...
Any advice on how to extract fossiles that are not loose on the ground like the ones I've picked?

[lyford]

I don't imagine there would be any danger in some science being lost by a housing development - but there would be no harm in colllecting a few, noting where they came from and visiting a local museum or university to ask them about it.

Here in Sunny California, if you build it, you must make sure you aren't destroying any significant archeological or paleontological finds....
Plus all those freeway road cuts make for easy geology trips - it even makes our state homepage!

Happy Hunting, Ustrax!

[Juramike]

Any advice on how to extract fossiles that are not loose on the ground like the ones I've picked?

My favorite tool is a small chisel (no hammer). If you can gently poke or gently pry a fossil loose from friable matrix, you are a winner.

In general, if you have to pound a fossil out of limestone, the chances are pretty good that the fossil is weaker than the limestone. "It is usually the last hit that cuts through the fossil".


A really cool geotourist location is Col de Rousette in the Vercours of France. It is the limit of the Versours massif. Behind you is the massive limestone (Cretaceous) that was an ancient coral reef that built up to several thousands of feet in shallow tropical waters. In front of you are the darker lower hills of the Drome region of France. They are of the same age, but the waters were just a little too deep for the corals to grow (coral needs sunlight), so it never built up the massive coral reef complex. Eventually the whole area was uplifted by the collision with the African plate with Europe (forming the Alps).

The current southern edge of the Vercours massif was determined over 100 MYA by the limit of sunlight in an ancient tropical sea....

-Mike

[elakdawalla]

My favorite tool is a small chisel (no hammer). If you can gently poke or gently pry a fossil loose from friable matrix, you are a winner.

Just make sure it's a chisel that's meant for rock. While enthusiastically working on that class project I grabbed a chisel at random from my Dad's toolbox and worked happily away at several fossils, never noticing what destruction I was wreaking on my Dad's nice woodcarving chisel Poor Dad!

--Emily

[tty]

As for fossils at elevation, the limestone that comprises Mt. Everest even holds fossils - I believe ammonites like those Helvick described have been collected at the highest elevations. It's all about subduction and uplift which more or less never ceases on geologic time scales.

Not only is Mount Everest marine sedimentary rock, but it is a general rule that high mountains, volcanos excepted, are sedimentary and usually marine. This is a natural consequence of plate tectonics. Mountain chains form in collisions zones between plates and so it is the marine rocks at the edges of continents that get squashed up into mountains. As a matter of fact mountains of any appreciable height consisting of old precambrian rocks are rare enough to be geological curiosities. Parts of the Uintas in northeastern Utah is an example.

I certanly second ElkGroveDan's recommendation to visit the Guadalupe mountains (and Carlsbad Caverns). However here are a few other reef complexes worth seeing:

Florida Keys, which are a fringing reef complex from the last (Sangamonian) interglacial, The sea level is a few meters lower this interglacial, so they just stick up over the surface.

For the Aussies I recommend a visit to Kimberley. There is an odd limestone range going practically all around Kimberley that is actually a well-preserved Devonian reef complex. If You take the Gibb River road you get an opportunity to actually see a cross section through a large fringing reef in the Windjana gorge. You can also walk *under* the reef in Tunnel Creek (at least in the dry). In its way it is just as remarkable as the Great Barrier Reef.

[Gray]

Your second image looks like the internal mold of a bivalve (cockle) shell. Sometimes the original shell is preserved, as in your first image. In other cases the shell is dissolved and what remains is the solidified mud that filled in the shell after the animal died. Both are interesting as fossils. but the original shell make a much better display.
As Juaramike suggested a small chisel, old screw driver or a dulled icepick might help to pry the fossils from the rocks. You might need to excavate some of the rock around the fossil before you pry it out.

Good luck. I'd like to see some of the "treasures" that you recover.