oil seep - always anthropogenic?

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oil seep (petroleum seep) classified as anthropogenic. But it seems they can be 
natural?

http://en.wikipedia.org/wiki/Petroleum_seep

Also, what is the relationship between this and tar pit?

Original issue reported on code.google.com by cmung...@gmail.com on 27 Apr 2013 at 10:28

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Quite right, lots of natural petroleum seeps around. A tar pit would be a 
subclass of a petroleum seep. It forms as volatile compounds evaporate away. 
Many tar pits are actually asphalt lakes. See:
http://www.orionmagazine.org/index.php/articles/article/93/ and
http://aem.asm.org/content/73/14/4579.full

Original comment by p.buttig...@gmail.com on 2 May 2013 at 3:25

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It seems (from very cursory reading) that sometimes "seep" is used to refer to 
some kind of opening through which the oil seeps through, and "tar pit" refers 
to the resulting "lake"? If so, is it worth preserving this kind of distinction 
in the ontology?

Original comment by cmung...@gmail.com on 3 May 2013 at 3:10

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I think it's a combination of some opening and the process of seeping that 
makes a "seep" a "seep". Further, some seepage can occur through porous rock 
(or other media) rather than a discontinuity like an opening or fissure. These 
are also referred to as seeps. Thus, in approximately BFO terms, I think "seep" 
is an entity that is coincident with the "site" of some "seeping process". Just 
like a tornado is coincident with some rotating process. When the processes 
stop, the entity is no longer. 

Right now "seep" is a synonym of "spring", which I think is reasonable, but 
"seep" is more like "seep =def. a seep is a spring with a low flow rate" 
(Wikipedia:Spring_(hydrology)). Also, "spring" refers to water springs. Perhaps 
this should be make more general and apply to all fluids while "aquatic spring" 
would refer to the various kinds of water springs?

If the seepant is liquid (rather than gaseous) a "lake" of it can form around 
the seep. Thus, I think we should separate seeps and lakes. We could make 
relations to express that lakes can accumulate around seeps, although this is 
probably more an instance level thing, as it's not necessarily true for the 
whole class.

Right now, our "lake" feature (ENVO:00000020) can take non-water lakes as 
children; however, "lake" is a child of "water body", and this doesn't hold. 
Really, I think the whole "hydrographic feature" class should be revised as 
hydrography may pertain to water bodies and marginal land masses. 

Original comment by p.buttig...@gmail.com on 3 May 2013 at 6:58

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PS: A tar pit would then be a subclass of the "lake" class (or perhaps of a new 
"hydrocarbon lake" class)

Original comment by p.buttig...@gmail.com on 3 May 2013 at 7:00

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Great analysis, I don't have much to add. Sounds like it might be non-trivial 
as it's uncovered some potential logical issues that should be addressed first 
(ie lake/water). It might be an idea to create a separate extension OWL file 
that has additional constraints that can catch these things.

Re: relationship between the seep and tar pit. I imagine we will eventually 
want environmental (really more generally geological) processes, such as the 
actual seepage. This will serve to link the two, much like a biochemical 
pathway diagram connects biochemical entities.

Original comment by cmung...@gmail.com on 3 May 2013 at 7:31

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