Sapropel
“Black ooze from oxygen-starved seas”
Sapropel is a dark, organic-rich sedimentary deposit that forms on the floors of stagnant, oxygen-depleted water bodies. These carbon-rich layers are important in understanding past ocean circulation and climate, and they serve as potential source rocks for petroleum generation.
organic matter (algae, bacteria), clay minerals, pyrite, calcite, diatom remains
Mediterranean Sea floor, Black Sea, Baltic Sea, ancient deposits in North Africa, Cretaceous ocean basins worldwide
1-2 (soft, organic-rich)
Mediterranean sapropels form in cycles tied to Earth's orbital wobble — every 21,000 years, increased African monsoon rainfall floods the sea with fresh water, cutting off oxygen to the deep and creating a new dark layer.
Test Your Knowledge
What astronomical cycle controls the formation of sapropel layers in the Mediterranean Sea?
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