Print this pageQuartz Cement Volume Constraints on Burial History Analysis: An Example from the Eocene of Western Venezuela
AWWILLER, DAVID N., and LORI L. SUMMA
We have used recently published quartz cement precipitation kinetics to help constrain the complex burial history of Eocene sandstones from the foothills of the Venezuelan Andes. These sandstones underwent a significant burial and uplift cycle in the Eocene-Oligocene, but conventional burial history indicators do not unambiguously constrain the event. Vitrinite and fluid inclusion data indicate that maximum burial temperatures were 130-150 degrees C. Cooling below the annealing temperature of apatite occurred 36-32 Ma. However, the time spent near maximum temperature prior to uplift was unknown.
We analyzed quartz cement volumes at several outcrops of known stratigraphic age to address this problem. At one site, quartz cement varied from <5% in coarse-grained sands to 18% in fine-grained sands. The broad range in cement volume is ideal for assessing temperature history using quartz precipitation kinetics. Two possible scenarios were tested: (1) uplift immediately following burial, and (2) uplift postdating burial by several million years. Quartz cement volumes suggest that scenario (2) is correct, with 6 million years at maximum burial most likely.
In general, the quartz cement paleothermometer is most effective for quartzose sandstones which encompass a broad range of grain size and contain little detrital clay matrix. The optimum time-temperature window is approximately 10-100 million years at maximum temperatures of 80-140 degrees C. Outside these bounds, quartz precipitation kinetics are such that the rocks tend to be either completely cemented, or not cemented at all.