The loess that accumulated in and around Bluefish Caves was carrying organic material along with the mineral sediment — bone fragments, plant remains, and other biological materials that became entrained in the loess during transport and were deposited alongside the purely mineral component.

The result was a sediment sequence that preserved not just the material washed or blown directly into the caves but also a broader sample of the organic material from the surrounding landscape.

Loess is not a perfect preservation medium — it is porous and not waterproof, and organic material in loess can be subject to chemical weathering over time.

But in the cold conditions of the northern Yukon, where the sediment has been partially or fully frozen for much of the past 24,000 years, the preservation conditions have been good enough to maintain the organic material — including the collagen in bone that is the source of the carbon used for AMS dating — in a condition suitable for scientific analysis.

The stratigraphic sequence of the loess deposits at Bluefish Caves is one of the aspects of the site that has generated the most discussion.