I thought that they find gold, diamonds, and other valuable things underground in the southern hemiphere.  They also found trillions of barrels of "unfinished oil" here in the US.  Brazil has alot of thier own "in house" oil production to help with thier energy independance.

There are probably many people trying to keep the dollar in one piece.  
Does history have examples of "huge treasures" be it nat rescources, gold, silver, or oil with it never being leaked?  
I'll bet on greed here twice.  
Would Oil co's be exploring, finding and developing oil in warm countries that have a weak military vrs the artic cold?  ROI?  Seems too obvious...IMO, These poor southern countries wouldn't like some cash?  I think it is unlikely that there are huge reserves of oil waiting to be found
Who said "Look at what oil companies do not what they say" wasn't it Deffes?  
Pumping up gold - Just what do these guys own or have $ invested in?
On the otherhand I have some pre WWll German marks (paper)
from my wifes grandmother.  They changed in value so quickly that they didn't bother to reprint.  They would just use a rubber stamp of all things to "double" the value(seriously).  Looks absurd with a "rubber stamp" on it.

There's just much less land, and also fewer large rivers, low-lying plains etc. south of the equator, which would seem to explain it.

There are many explanations for this, mostly down to location and population. For instance it is no accident that the US, Russia and Europe have developed oilfields in close proximity- that is where the major demand is. Plus the presence of stable government is a clearly a critical factor for development of any kind.  

Although there are rumours there is a North Sea size field in the Great South Basin (google for it) to the southeast of New Zealand, which has never been developed due to lack of capital and distance to markets.