Re: Interior Seaway

[Crpntr@ix.netcom.com (Kenneth Carpenter)]

Skip Dahlgren asked:

>Would it be accurate to say that the present Gulf of Mexico is 
>equivalent to, although smaller than, the "shallow inland sea" that 
>ran north to south across this continent during much of the Mesozoic, 
>separating the young Rockies from the eastern half of the continent?  
>Am I safe to assume that it could be considered as the last remnant of 
>that sea?  Are there any estimates as to the depth range of that 
>ancient inland sea?  

No, because the Gulf of Mexico reaches abyssal depths of over 4 km, 
whereas the Interior Seaway only reached depths of a few thousand m.  
Water depth estimates vary considerably.  Benthic forams suggest depths 
of 1000+ m, however, benthic macro-invertebrates (non-platyceramids) 
indicate water depths did not exceed light penetration depths.  This 
latter depends on how much suspended material there was.  Such depths 
could range between 200-600 m.  Platyceramids and other large flat 
inoceramids may have had a symbiotic relationship with sulfur 
metabolising bateria living within their mantles, so may not have been 
as depth dependent.

As for the Gulf of Mexico being the remnant of the seaway, it is 
probably not correct to view it as such because the Gulf of Mexico began 
forming in the Jurassic with the breakup of Pangea.  The Interior seaway 
persisted into the Paleocene as evidenced by the marine facies of the 
Canonball Formation in North Dakota.  At one time, it was thought that 
this represented a southern arm of the seaway, but the invertebrates 
have a boreal appearence, so may have been a post-Cretaceous 
transgression of a northern arm.