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Chicxulub: Not an Impact structure?

     It seems that in the last decade, scientists have developed a 
fascination with impact structures. This has led to many people looking  
for examples in the rock record, and postulating that a lot of what we 
call volcanic structures, are really impact sites. I have had the 
unfortunate experience of arguing with scientists over this topic, so I 
figured I would voice the unpopular side here, as perhaps an alternative 
view can be put into the spot light.
     Chicxulub is a structure of upper cretaceous age in the Yucatan 
peninsula. It has been known for a while, and much work was done on it 
before the impact hypothesis was put forth. In addition, it had been 
identified as a volcanic sequence, that had at least six major volcanic 
events. 
     As far as an impact crater is concerned, we need to look at the 
evidence. First is the supposed ejecta blanket in Cuba. It has been 
shown that the boulders are in actuality weathering features of the 
surrounding country rock. 
     Second is a the underwater deposits around the Caribbean. These 
were interpreted as being from a single event, a tsunami. However a 
close inspection revealed two separate events, and the material is 
volcanic in composition. 
     Third, the age of the structure is not terminal cretaceous. It 
seems that the supposed breccia sequence, from a single event, has 
interbedded Campanian, and Maastrichtian faunas. This is from a core 
taken in the center of the structure. Bentonite occurs in the sequence, 
and indicates a time of weathering. So it was not a single event, but 
many.
 
     Based on the above, it seems that proximal crater characteristics 
are difficult to define. Based on this alone, one should be cautious in 
making interpretations. It seems better to view this proximal area as a 
volcanic related terrain.
     How does this explain the Ir, and Tektites, and cleavable (shocked) 
quartz? It does'nt. But does that mean an impact occurred by virtue of 
such data? We do not have a look into the past that is clear, rather it 
is muddied by overprinting of various geologic processes, and these can 
obscure the real truth, if there is truth in science. 
     The present is the key to the past is the argument most geologist 
follow, and perhaps this is not always the case. For example, rivers 
leave their beds from time to time, this is known as avulsion. Avulsiion 
has never been witnessed by humans, yet we know that they do( or think 
we do). We do not have a modern analog for this process, so we must 
extrapolate from the rock record. 
     Volcanism today is powerful, but not that overwhelming in 
destruction, geologically speaking. This modern analog is used as a 
comparison for the volcanoes of the past. I would argue that we have not 
seen all this Earth can produce with volcanoes. Meaning that we assume 
various process, and hold them to work for all time. But perhaps, only 
perhaps there are interactions we have not witnessed, and do not have 
record in rock as well.
     The late cretaceous was a time of much volcanic upheaval. The 
Deccan traps,and rapid sea floor spreading, all contributed to the 
moment in time known as the K/T boundary. Perhaps we can relate the Ir, 
tektites, and quartz to volcanic processes. 
     I make no effort to sit here and dissuade the impact argument for 
the terminal cretaceous. I merely would like to suggest that perhaps we 
can find an explanation that encompasses the inconsistencies in the 
crater morphology. The principle of least astonishment could be used 
here in keeping the theories in check. 
     I am for one a skeptic of the impact, but I am not going to force a 
view down someone elses throat. I merely wrote this to show that maybe 
there is another explanation, and one that requires more work to get to, 
but one that better accounts for the data.

Frank Stroik


References: 
Myerhoff, A.A., Lyons, J.B., Officer, C.B., 1994. Chicxulub Structure:           
A volcanic sequence of late cretaceous age. Geology Vol 22,
          NO. 1, P. 3-4

Look at this article, and the references there in for a more indepth 
look at the evidence.

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