Geologic Column

[Guest Lunkhead]

Ignorant question from an "armchair archaeologist":

Are there any single rock outcrops or locations where animals of more than one era are found in succession? In other words, is there any one place where you find Mesozoic animals, then higher up in the same outcrop you find Cenozoic animals?

 

Just wondering.

 

Thanks

Chris

[Pseudopalatus]

You're referring to natural, ideal geological columns? Usually, there are only pieces of the column (meaning, you probably will not find an uninterrupted geological sequence from the Earth's Archean Eon all the way to the present in usual circumstances). Erosional periods happen throughout history, and almost everywhere... So you're bound to find that there are gaps (we call them "unconformities") in any rock sequence representing millions of years. For example, here in eastern New Mexico, we have mesas demonstrating rock strata from Triassic Period, overlain by layers from the late Jurassic, which in turn are overlain by middle Cretaceous rocks at the top... and gaps of forty to sixty million years between each representing time periods of erosion rather than deposition. These missing layers are usually found elsewhere where deposition did occur, allowing us to fill in the gaps with data from other regions. As a result of global observations of this type compiled together, we have a complete, 'idealized' geological column.

 

Of course, there are places where you can find fossils of one geological era above fossils of another... one notable locale is here in eastern New Mexico, where one can find mammoth fossils from less than 1,000,000 years ago in the same ten square kilometers and same rock sequence as 100 million year-old Cretaceous shells and 220 million year-old reptile fossils. It's only that there are gaps between these layers.

 

An example of a truly 'complete' geological column may be found in North Dakota... uninterrupted rock layers from the Cambrian to the Recent. These are listed in detail, along with other locations where such columns are found, on this page:

http://www.talkorigins.org/faqs/geocolumn/

 

I hope this helped!

 

-Donny

[Mythranil]

I was in a field camp in central Montana where there were three separate geological columns within 20 square miles that represented the entire geological history of that area (although this included gaps from erosional periods, too). The blocks were Precambrian, Cambrian through Triassic, and Jurassic through Quaternary.