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