Using the illite/smectite paleo-thermo-chronometer

TL;DRAbstract

In the last decade extent of smectite-to-illite reaction in shales, % illite (%I) in mixed-layer illite/smectite (I/S), has achieved status as a paleothermometer approaching vitrinite reflectance (%Ro). Scores of examples show downhole increase in %I that parallels %Ro. As with %Ro, published kinetic models predict %I as a function of time (t) and temperature (T). Comparison of predicted and measured %Ro and %I is used to calibrate burial/thermal history. Unfortunately, there is no chronology in %l or %Ro that is independent of an assumed burial/thermal history. Long I at low T can give the same values as short t at higher T. Obtaining K-Ar dates on newly formed illite, with the ability to model the date and %I using burial history and kinetics, provides a true paleothermochronometer for constraining thermal history. Even if illite formed over a time interval, giving a mean age, the model can also calculate a mean age. The difficulty with shale illite K-Ar ages is that the diagenetic c

Chat with Paper

AI Agents for this Paper