I spend a lot of time around cypress lagoons, and I often see what looks
like small oily patches on the surface of the water. These look exactly like
droplets of gasoline that have spread out into a fine iridescent layer.
These patches are very different from the brownish organic film that
commonly forms in the lagoons, especially in late summer when temperatures are
hottest and rainfall is rare. The organic film typically covers the entire
surface of a lagoon, and varies with environmental conditions; but these oily
patches are very localized, only hand-sized, and they never thicken or become
suffused with bubbles. The droplets that create them rise up from the
substrate rather than dropping from trees or fauna above the water, and I’m
very interested in understanding what causes this phenomenon.
It’s been suggested to me that since peat accumulates at the bottom of
cypress lagoons, this may be some type of natural petroleum that’s forming in
situ from decomposition. However, these cypress lagoons have developed in an
old dune complex which is only 4-5 kyrs old, and the lagoons where I see the
oily patches most often aren’t likely to be more than 2 kyrs old.
Is that enough time for droplets of natural petroleum to form? I’d be
interested to know whether this is feasible in a geologically young peat
deposit, and whether this could be the cause of the oily patches I’m seeing.
Please contact me off-list with my thanks in advance.
- J. A.
