What is NOT a biogenic source of marine sediment?

Marine sediments can be categorized into biogenic, lithogenic, and authigenic sources. Biogenic sediments are derived from the remains of living organisms, while lithogenic sediments are formed from the erosion of rocks and minerals.

Silt from river runoff, which is primarily composed of tiny particles that come from the erosion of land or rocks, represents lithogenic sediment rather than biogenic sediment. This makes it distinctly different from the other options, which originate from once-living marine organisms.

Shell fragments are remnants of marine organisms like mollusks, while calcium carbonate is a key component made by calcifying organisms, such as corals and certain plankton. Fish remains also fall into the category of biogenic sources as they are the biological remnants of marine life. Thus, the sediment formed from silt resulting from river runoff does not originate from biological processes, making it the correct choice as the option that is not a biogenic source of marine sediment.