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Re: Chicxulub's Antipode (Re: cause of death at KT)

Your boundary beds probably contain round microspherules blasted from the
Chicxie crater.  All known boundary sites in the H.C. Formation contain
them.  About 10 years ago while on vacation, I sieved a section of the
boundary clay a couple hundred kilometers north of your ranch and I was
able to find 21 microspherules in about 1.5 cubic meters of sediment  (I
don't remember the sieve size that I used, but if your interested I'll
try to find my notes).  I found that it was best to sieve the *weathered*
portion of the outcrop, because the spherules are already "pre-loosened"
from the matrix.  Fresh rock is a b*tch to sieve because you often have
to pound it into small pieces first, and even then,  the rock often
doesn't completely disaggregate.  I wet-sieved and dry-sieved and had
good luck with both techniques.  The spherules are most often medium sand
size to coarse sand size.  Don't be too rough with the matrix during
sieving.  The microspherules are delicate lil' thangs.

When sectioned and viewed under a petrographic 'scope, the interiors of
these microspherules contain a mixture of unaltered glass (rare),
zeolites, feldspars, and clay.  Under crossed nichols, some
microspherules have a highly diagnostic radial texture.  Some
microspherules have voids near their centers.  Nearly all microspherules
are quite close to perfectly round, but if you're lucky you might find
one with a teardrop shape.

Regarding the larger exotics:
The *easily* identifiable boundary sections of the Hell Creek are always
fine-grained (mudstone and/or claystone), are obviously layered, and
represent primary deposition (in other words, no reworking except for
occasional bioturbation).  So I would assume that ANYTHING that looks
"unusual" or out-of-place in this zone should be sampled.  Large
concretions, pebbles, or other suspected autochthonous material should be
looked at closely.  Weird-colored objects may also be trying to tell you
something (fusion crust tends to weather to a rust color.  There may also
be reaction halos in the sediment around exotic objects).

(Sadly, I traded my vial of Chicxie spherules for a used Brunton a few
years later.  I think the other guy got the better end of the deal.  :-(

Sample on, dude,


On Sun, 03 Sep 2006 11:41:13 -0600 "franklin e. bliss"
<frank@blissnet.com> writes:
> Interesting discussion.  The chances of finding a piece of ejecta   
> that re-entered and survived the atmosphere must be a bit low.  As I 
> walk about the K/T boundary up here, I find lots of misc things but  
> what exactly (besides a blob of glass altered to clay or perhaps a  
> small crater in surrounding lamina) would I be looking for in a 
> piece  
> of re-entered material?
> Frank (Cocky Avian Theropod) Bliss
> MS Biostratigraphy
> Weston, Wyoming
> www.cattleranch.org
> 45.783664% of all statistics are made up at the time
> On Sep 3, 2006, at 9:35 AM, Jeff Hecht wrote:
> > At 2:25 AM +0000 9/3/06, Phillip Bigelow wrote:
> >> On Sat, 02 Sep 2006 22:12:53 -0700 (PDT) don ohmes  
> >> <d_ohmes@yahoo.com>
> >> writes:
> >>> At risk of getting on thin crust--
> >>>
> >>> 1). 65 my is old for deep ocean crust. Might be hard to find 
> some
> >>> that was in the antipodal location at the time. Stuff can move 
> fast,
> >>> like 10cm/a. That is 6500km since KT, IMMC. Might, in fact, be 
> all
> >>> subducted.
> >>
> >>
> >> Regarding the sea floor around India, you might be right.  [I am 
> a
> >> neophyte when it comes to southern Asian tectonics].  But there 
> are
> >> numerous places in today's Pacific Ocean that still contain 65 my 
> old
> >> oceanic crust.
> >
> > According to http://userpage.fu-berlin.de/~data/database/oceanage/ 
> > jgr_paper.html there is some Cretaceous sea-floor crust off the  
> > east coast of India and the west coast of Australia. The actual  
> > antipodes from the KT impact may have been subducted by now, but I 
> > would expect whatever splashed down to have been spread over a  
> > significant area. So there's hope for finding something, but it 
> may  
> > take some work.
> >
> > -- 
> > Jeff Hecht, science & technology writer
> > jeff@jeffhecht.com  http://www.jhecht.net
> > Boston Correspondent: New Scientist magazine
> > 525 Auburn St., Auburndale, MA 02466 USA
> > v. 617-965-3834; fax 617-332-4760

"If you are traveling into the future in a time machine, and you pass a
person from the future who is traveling into the past, it's probably a
good idea to avoid eye contact." - Jack Handey