Why would you find more biogenic sediment on one side of the continent as opposed to the other side?

Biogenic (or biogenous) sediments are ubiquitous in marine environments; the main divisions are readily classified with reference to the amount of carbonate present and the depth of water at which they are found (shallow or deep). The dominant types are (in the order of abundance): deep-sea carbonates (calcareous ooze, foraminifer ooze, nannofossil ooze); deep-sea siliceous deposits (siliceous ooze, diatom ooze, radiolarian ooze); hemipelagic silica-rich deposits (at continental margins below upwelling regions); shelf carbonate deposits (reef and platform carbonates, dominated by coral and algal debris or by foraminifer and mollusk materials, depending on circumstances; reefal debris, lagoonal carbonate muds, etc.); and various types of anaerobic deposits (rich in organic matter and with or without opal or carbonate). Because deep sea covers most of the surface of the planet, the dominant biogenic deposits are deep-sea sediments, and their dominant ingredient is...

Explanation:

81 is a composite number.