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Re: Triceratops survived till very end of Cretaceous
Doubly delurking....and to clarify.
Cut and fill sedimentary structures are pervasive in most of the Hell
Creek/Lance in my locality. All the seriously fossiliferous microsites that I
have followed (as in completely excavated) are (mud pebble/fossil detritus with
a coarse sand matrix) channel deposits in a lens shape that are usually
truncated on one or more sides by an erosional break that I attribute to
removal by current and filling by sorted finer, non-fossiliferous shifting
sands and channels moving about. Fluvial sediments are extensive here and with
any sediment choked system, meandering is common. 20 foot high sand bars are
common in cross section on the outcrop. Deposition and redeposition is
repetitive in occurrence. Cutting into older sediments happened continuously
as part of the sediment transport system from source to sink. Reworking of
sediments and fossil detritus was certainly extensive. I have numerous obvious
examples easily seen in the outcrop. The river system here was HUGE leaving
700 feet of sands/muds behind for my enjoyment over a 14 mile wide exposure. I
have free access to and have examined with some detail outcroppings over 45,000
acres of Wyoming/Montana.
I would argue that it isn't easy (but not surprising) to find a large dinosaur
fragment within a foot of the contact though. I've never seen such a thing
over a decade of living year round on the upper Hell Creek and working same.
In my experience, it isn't common to find anything fossiliferous on a
macroscopic scale that high in the section. I speak only from my work area
though (as in you could look for hours and find nothing). The K/T boundary
here is well exposed over about 10 continuous miles (that I've looked at by
walking the entire length) and that is of course a proportionally small
exposure. Other sites I've never seen certainly may differ.
Presence of a bone at a particularly higher stratigraphic level than is common
for that species to occur, does not prove the existence of that living organism
let alone that it was thriving in the ecosystem at that time. It only proves
that the bones were still intact and being moved around and deposited at that
location and time. Otherwise, one may argue that dinosaurs were present in
Pleistocene here at my ranch.
This particular section of Hell Creek/Lance argues loudly for a gradualistic
decline in diversity and density either by actual occurrence or by some bias in
the preservational record. I have been somewhat systematic in my searches for
microsite occurrence and specific absence/presence by location over the course
of my observations here. The fact is at this location, the higher you go in the
Hell Creek, the lower diversity I observe. You would be hard pressed to find a
even crocodile tooth in the upper 100 feet of Hell Creek here on the
Montana/Wyoming Border and even the ubiquitous Gar Scales are scarce in the
upper 50 feet and essentially absent in the top 25 feet below the first Black
Shale of the K/T. Even the harvester ant's have trouble finding them that high
in the section. Lots of Selenite and human tool making artifacts though.
On Jul 12, 2011, at 10:02 PM, Lee Hall wrote:
> It's not surprising to find a dinosaur bone close to the top of the
> Hell Creek. It just provides evidence that they were still around. As
> far as reworking things higher in the stratigraphic section- that
> won't happen unless a channel incises into the older rocks. I've
> found petrified wood 'round the Hell Creek/Fort Union contact lots of
> times, too, along with turtle and croc bones. A paper about them would
> be just as informative, honestly.
> Lee Hall
> Museum of the Rockies-Montana State University
> On Tue, Jul 12, 2011 at 9:32 PM, frank bliss <email@example.com> wrote:
>>> One more time.
>>> I would give a good chance that the horn fossil was reworked by the
>>> sedimentary regime. ie, deposited, reworked by stream/river meander and
>>> redeposited again dozens of times in it's trip "down stream". Triceratops
>>> horns can be quite tough. I find Hell Creek fossils in more recent
>>> sediments all the time. Particularly, Pleistocene loess blown in below a
>>> microsite. The 65 million year old fossils easily contaminate the newer
>>> material surviving yet another re-transport/re-deposition yet again. Late
>>> Cretaceous Hell Creek Rivers redepositing older fossils multiple times was
>>> the rule, not the exception IMHO.
>>> As I drive up section toward the K/T boundary (two miles west of my house),
>>> the Hell Creek becomes much harder to find microsites and fossiliferous
>>> outcroppings in. I know where there is a partial Triceratops outcropping
>>> within 50 stratigraphic feet of the boundary however. The boundary "zone"
>>> itself is essentially barren of fossils. I've only found ravaged petrified
>>> wood there without going micro and I've spent some time looking at it.
>>> My point is, things can be reworked to above the boundary easily. It
>>> appears to me from my isolated viewpoint that faunal diversity and
>>> abundance declines up section considerably here on the Montana/Wyoming
>>> border as you approach the K/T. They won't find many fossils up that high
>>> in the section.
>>> Frank Bliss
>>> MS Biostratigraphy
>>> Weston, Wyoming
>>> On Jul 12, 2011, at 8:08 PM, firstname.lastname@example.org wrote:
>>>> From: Ben Creisler
>>>> I don't have the official article citation--it's not been posted on the
>>>> Biology Letters website yet. However, there are many news stories out about
>>>> the discovery of a Triceratops horn only 5 inches from the K/Pg boundary in
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