Re: "Meteor theory gets rocky ride from dinosaur expert"

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

Here is the Abstract of Keller?s paper:

"In the Chicxulub crater and throughout NE Mexico the impact breccia and 
spherule ejecta layer, respectively, predate the K-T boundary by about 
300,000 years (Keller et al., 2003, 2004). The stratigraphic separation 
between the K-T boundary and the Chicxulub impact ejecta varies from 50 cm 
in the Chicxulub crater, to over 14 m in NE Mexico, with the variation due 
to erosion, non-deposition and paloetopography. New studies from drilling 
and exposures along the Brazos River, Texas, confirm these findings based 
on biostratigraphy, paleomagnetic stratigraphy, geochemistry, stable 
isotopes, and faunal assemblages. In this area, the spherule ejecta
 is reworked near the base of a series of `event beds' representing 
variable storm deposits separated by repeated colonization of the ocean 
floor by invertebrates. The base of these storm beds overlies an undulating 
erosion surface of latest Maastrichtian claystone.
The original spherule ejecta layer appears to be within the underlying 
claystone, in the lower part of chron 29R and near the base of biozone CF1, 
which marks the last 300,000 years of the Cretaceous. Above the `event 
beds' latest Maastrichtian claystone sedimentation continues up to the K-T 
boundary, which is characterized by a sharp (1.4 ng/g) iridium anomaly that 
marks the K-T as a second major impact.
The distance between the top of the `event beds' and the K-T boundary 
varies from 20 cm to 1.6 m depending on local tectonics and erosion. 
Evaluation of the biotic effects of the Chicxulub and K-T impacts upon 
planktic foraminifera, which suffered most severely of all marine 
organisms, reveals no species extinctions associated with the Chicxulub 
impact and no significant species population changes, except for species 
dwarfing as a result of increased biotic stress. These Brazos results 
confirm the 65.3 Ma age for the Chicxulub impact determined from NE Mexico 
and the crater core Yaxcopoil-1. They also show that the Chicxulub impact 
did not cause a mass extinction, but the 65.0 Ma K-T impact did."

I would guess that the spherule layer is coarse material that arrived 
ballistically or as part of a base surge within minutes of the impact (note 
that only relatively low-velocity material can end up close to the crater, 
so it wouldn't ablate in the atmosphere). The "Event bed" is presumably 
tsunami deposits, probably deposited in a few hours rather than 300,000 
(presumably extremely stormy) years. The overlaying claystone is the fine 
stuff churned up by the tsunami settling out over a few days. Of course it 
is latest Maastrichtian. By the way why suddenly no more storms? The 
Ir-rich layer finally is the fine material from the vapour plume that was 
deposited at the top of the atmosphere and settled out globally over 
several months or more
 It is interesting to note that apparently Keller now accepts that there 
was a big impact at the K-Pg boundary and that it was this that caused the 
mass extinctions ? it just didn?t happen at Chicxulub. Also it was 
presumably a great deal larger, since it had much worse biotic effects.
Well it's possible, but it means that the largest and second largest 
impacts of the Phanerozoic occurred within 300,000 years of each other. 
I?ll believe that when someone finds two impact layers somewhere outside 
the Caribbean area where everything hasn?t been churned up by a magnitude 
12 quake, a megatsunami and the subsequent seiches. Also note that this 
second crater must still be around somewhere - it couldn?t have been 
subducted since the composition and age of the minerals in the impact layer 
indicates that it was on continental rock.

Tommy Tyrberg