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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.

Tommy Tyrberg