Diagenetic evolution of clastic sediments in the Los Angeles Basin: Time and temperature effects

The relationship between thermal history and clastic diagenesis in the Los Angeles basin of southern California is analyzed in this dissertation. Syndepositional tectonism there has yielded a thick package of Miocene to Pliocene-aged sediment which was sourced from a geologically varied yet locally restricted source terrane. Different parts of the basin have had different tectonic and thermal histories which have yielded a unique opportunity to isolate the effects of thermal history against factors such as sediment age and source terrane that could make a comparative analysis impossible.; Vitrinite reflectance, a standard measure of thermal maturity, proved unsuccessful in the analysis of sediments from the Los Angeles basin. Therefore, apatite fission track (FT) analysis was used as a tool to determine thermal history. FT analysis reveals that early heat escape from the basin was along active fault zones. Sediment deposited along the flanks of the basin near zones of major faulting were heated quickly after deposition as compared to sediments deposited in the deeper central part of the basin or farther from major fault zones.; Integrated thermal history provides a better indication of plagioclase dissolution than do maximum temperature or vitrinite reflectance, which have been used in other areas. This study also shows that thermal history also plays an important role in the diagenetic transformation of smectite to illite. Samples from the Los Angeles basin having similar present-day temperatures but different thermal histories show different degrees of illitization. Therefore, smectite illitization cannot be used as a simple geothermometer.; The results of this dissertation show that thermal history analysis of a young, active basin can be made using apatite fission track analysis. It also shows that such care in determining thermal history is worthwhile in diagenetic studies. Rather than relying on more qualitative methods such as vitrinite reflectance, quantitative measurement of thermal history can be used to measure diagenetic maturity, which can aid in the understanding of diagenetic processes.