Midnight ramblings about a Hell Creek Biostratigraphic geocartoon

[frank bliss <frank@blissnet.com>]

Notes from the Bliss Ranch Hell Creek microsite digs. (Wyoming/Montana 
border north of Gillette Wyoming)   Background: I have been working one 
small Hell Creek Section on my own ranch land for almost one year now. 
The fossils are great (carefully collected) but secondary to my real 
interest, the sedimentary environment.  The fossils are an essential 
means to that end and will eventually end up in a friendly repository 
somewhere.  There may be some biofacies relationships or fossil 
assemblage worthy of note and even a thesis or two.  The discussion 
below is essentially a synopsis of my observations and may possibly be 
entirely geofiction, subject to change at any time.  With that 
disclaimer........

It has been interesting lately down in the gullys.  Almost every week, 
(when the ground was not frozen), for the last year, I have spent 
roughly 12 man hours on site trying to pay my dues.  Recently, I have 
been digging the rocks around laterally and vertically below my initial 
microsite 1 (see my website www.cattleranch.org and hit the dino pages 
for a taste) which has yielded thousands of various Cretaceous fossils 
representing dozens of species) resulting in 5 new serious dig spots so 
far within 300 lateral feet of the initial discovery microsite. Each of 
these have yielded some pretty interesting fauna/faunal assemblage 
relationships.  (Take my word for it at this point as documentation is 
a ways down the road and will necessitate working with a professional 
vertebrate paleontologist as my training is with Invertebrates.)

A few fossil highlights from this week include: one 1.5 inch long by  
5/8 ths inch wide so far unidentified swallowed predator tooth along 
with a few smaller ones, the largest yet Hadrosaur tooth (in my VERY 
limited Hadrosaur tooth collection from these sites of about a dozen 
teeth in a year),  numerous (dozen or so) Leidyosuchus sp. (croc.) 
teeth, 5 or 6 dozen ceratopsian spitters (often size sorted distinctly 
in the different beds), a few small mammal jaws with teeth, (of course 
gar scales, misc small vegetarian teeth, misc. chunky turtle pieces, a 
few ray teeth, and misc. bone pieces). Interestingly today, I sampled 
only one bed (my site 5), about a dozen feet directly below my 
discovery microsite, (site 1) two nicely toothed salamander jaws and 
one 2 tooth lizard jaw fragment along with some albulid fish jaw 
fragments came out along with only very small ceratopsian teeth.  These 
are the first salamander and reptile jaws with teeth that I have found 
in almost a year of sampling the two other main sites. (I may be 
getting better at seeing them though.) As an example of a differing 
assemblage, this particular unit seems very different in it's faunal 
expression from the bed (microsite 1) only a dozen feet above with a 
very small size of fossil detritus present (in contrast to the larger 
fossil material in the site above) but yet shares some of the same 
creatures and a very similar lithological appearance/presentation. Yet 
the clay pebble size present is roughly consistent with the bed above 
so the size difference in the fossil detritus would not seem 
hydraulically imposed.  They are separated only by a 12 ft thick bed of 
clean sand with a few fist sized dino bone fragment/chunks in it. They 
obviously are from different times however as site 1 has superpostion 
over site 5. My original concept of the environmental situation in this 
gullies exposure was way, way too simplistic. Bear in mind that I have 
hand searched at least a cubic meter of each of the 5 seriously sampled 
units and in some cases like site 1 and site 2 (In the next gully over 
and about 200 feet away), much, much more so I have a good feeling for 
the sampling and fauna now.

This may seem rediculously obvious from the discussion above, but more 
that I collect this stuff, the more I realize the different horizons at 
this location either represent very distinct environments faunally (if 
not actually) or perhaps different snapshots of the ecological 
processions of this location and/or a difference of the hydraulic 
sorting capacity of the water all within a very limited vertical 
section of 30 feet. (Streams between the sand dunes and bars in and 
around the streams). It is my goal over the next few years, figure out 
this puzzle.

My initial perception of this somewhat limited section of Hell Creek 
was that of a fairly monotonous and uniform depositional type with 
limited flood deposited layers rich in scoured fossil detritus. This 
thought is obviously wrong based on my own observations.  (I 
preconceived the multiple fossil rich layers but I though they would be 
virtually identical in their composition and presentation.)  I thought 
they would present essentially the same faunal sample over and over 
again.  The differences observed to date seem to be far more than 
random occurrences of a varied fauna or just the effects of hydraulic 
sorting.

Initially most of the exposed section seemed barren but this was only 
as a result of the way that the section weathers and as such, is 
covered by weathered sand from the much more abundant barren sand 
dunes/bars.  It appears that this location has remarkable and 
complicated original facies relationships.  Unfortunately, I also think 
that there has been considerable rearranging spatially of 
sediment/sediment relationships due to soft sediment flow resultant 
from sediment load above.  I consistently fail to trace beds laterally 
over more that a few dozen feet only to find a very abrupt transition 
to a different rock type instantly.  Gravelly sand turns to clay or 
barren sand abruptly and back again with no obvious transition 
laterally as one would expect (I am used to gradual 
environmental/sediment transitions) in a sedimentary environment.  
Therefore, it is my supposition that these sand, sand/gravel and clay 
lenses were probably shaped/reoriented by soft sediment flow sometime 
after deposition and mixing of what originally were superimposed faunal 
sequences occurs as a result.  (Certainly enrichment of the hard fossil 
parts occurred as a result of water scouring/flood concentration.) Any 
interpretation biostratigraphically about succession of faunal 
occurrence would be suspect if this observation holds true.  There are 
numerous other examples of soft sediment deformation on our ranch 
(draped with Hell Creek) with abundant sand tubes (some up to 3 feet 
across and dozens of feet long.  There are also locally disrupted sand 
laminae from dunes which indicate the same phenomena.  It seems to me 
these Hell Creek sediments at this location were squeezed like silly 
putty by the weight of the accumulation above.  The mountains to the 
west must have really been dumping sand to cover this material enough 
to squeeze it big time before it hardened.  An additional obfuscating 
effect of any biofacies relationships would be the obvious cut and fill 
effects of flowing water and wind cutting penecontemporaneously with 
sediment deposition adjacent to the active water course.

You Cretaceous mammal junkies out there will have to wait for the 
sieving to start later this summer before the really rare fossil 
material starts showing up.  I am having too much fun finding new dig 
sites to sieve still moist sand. Mammal stuff rarely comes out of digs. 
More of it comes off the screen.

The main question that arises out of all this is, who else is doing 
biostratigraphic work on Hell Creek?

Frank Bliss
MS Geology/Biostratigraphy
Weston, Wyoming

The joke around the house is that I found some rocks today that do not 
have fossils in them.