Figure 14. Temperature history of youngest chert bed vs. age for various sites. The temperature was hindcast by assuming a T1/2 decrease in heat flow with time since crustal formation. Site 1021 does not have cherts even though the deepest sediments recovered contain about 30% opal (Janecek, Chap. 16, this volume). The basal sediments of Site 1010 do have cherts with similar silica contents. The two would suggest that chert conversion increases rapidly at a temperature of about 25°C.

Figure 14. Temperature history of youngest chert bed vs. age for various sites. The temperature was hindcast by assuming a T1/2 decrease in heat flow with time since crustal formation. Site 1021 does not have cherts even though the deepest sediments recovered contain about 30% opal (Janecek, Chap. 16, this volume). The basal sediments of Site 1010 do have cherts with similar silica contents. The two would suggest that chert conversion increases rapidly at a temperature of about 25°C.