David Coppedge at Creation-Evolution Headlines reports on the latest iteration of the Chicxulub impact theory and the K-T boundary.
This has bothered me for some time, because the whole discussion illustrates what I have come to see as a major logical failing in modern stratigraphic interpretation, especially in regard to the interpretative principle that the present is the key to the past.
In a nutshell, the idea that flat, horizontal contacts between thick, areally-widespread formations can be analogized to the present time, is unrealistic because of the ubiquity of erosion.
The above image illustrates the point quite nicely. Much work has been done to support the theory that the iridium layer above the Hell Creek formation (essentially at the position of the red line above) marks the K-T boundary. Thus, fossils buried below the boundary are Cretaceous, and those above are Tertiary.
But now look at the contrast between the current topography and the geometry of the outcrop--could it be more stark?
The main point is that EROSION is the dominant process of the present. Nowhere in historical time do we find thick subaerial layers being deposited and left undisturbed long enough to accumulate the thickness and areal extent of the Hell Creek and its other equivalents, such as the Lance Formation (see here for an map: www.und.nodak.edu/instruct/jhartman/Research/PDFs/2002-117-Johnson%20et%20al%20sp361.pdf)
The connection with the K-T border is that conditions must have been extremely unique for the ash that marks the border to fall on horizontal, uniform rock layers and then remain undisturbed by erosion for the amount of time required by current interpretations for the accumulation of both the overlying and underlying horizontal layers.
Think about it: where are the widespread, thin horizontal ash layers from Mt. St. Helens?
Coppedge reports on the slap in the face that the cometary extinction theory had for uniformitarianism:
"'It flew in the face of the position that geologists and paleontologists at the time had for gradual explanations for everything that happened in the Earth’s past, a position that went by the name of uniformitarianism,' said Walter Alvarez. 'The notion that this mass extinction was caused by an impact, or even the notion that there was a sudden mass extinction, raised a lot of dispute at the time, and people strongly challenged the idea.'"
However, you can't have it both ways. If the Fort Union and Hell Creek formations were laid down slowly, uniformitarianism predicts that they should have been heavily eroded. If they were laid down quickly, then the fossils they contain can't be representative of different geologic time periods.
Draping actualism over uniformitarianism results in a useless predictive paradigm, because anything is possible, and nothing is improbable.
Unless it allows people to entertain the hypothesis of a catastrophic global marine transgression. I'm not holding my breath.