Karen Casciotti continues MIT's Marine Chemistry course (12.742, Fall 2006) with a session on how the two dominant biogenic components of marine sediments, biogenic opal and calcium carbonate, behave after burial. The lecture works through dissolution and preservation processes for silica and CaCO3 as they settle through the water column and accumulate on the seafloor, and how competing rates of production, dissolution, and burial produce the patchy global distribution of these sediment types. Casciotti connects the chemistry back to paleoceanography, showing how sediment records of opal and carbonate are used to reconstruct past ocean conditions, and to broader biogeochemical cycling of silicon and carbon in the ocean. Running eighty-one minutes, the session assumes familiarity with earlier lectures on diagenesis and builds directly on that foundation with more quantitative treatment of dissolution kinetics and sediment preservation patterns.