13  - Manganese layer within chert
On the bottom right below the loose covering of 
of chert fragments is a thick layer of manganese oxide.  Note that the layers of the chert are significantly thinner above the manganese layer than those below the layer and shown in slide #12.  This manganese layer may well have been produced by deep sea hot springs that were belching out a black, metallic smoke  which settled onto the surrounding deep sea floor. The hot water supplying these hot springs may be the reason for the alteration of the chert to jasper that occurs beneath the layer.  Note that the dark black stains decrease as you to to the upper left of the photo.

Additional information on the origins of the manganese

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