Lower cretaceous calcareous nannofossil stratigraphy of the Great Valley Sequence, Sacramento Valley, California

Abstract

The calcareous nannofossil stratigraphy of four sections in the Great Valley Sequence of the Sacramento Valley, California, has been investigated in detail. The ages of these sections, which have independently been studied by ammonite, pelecypod and radiolarian biostratigraphers, range from Berriasian to Albian. Nannofossil stratigraphy is more directly comparable to that of stratotype sequences in Europe than are the other fossil groups, but the ages given are generally similar. Two major discrepancies do exist, however. The results of this study indicate that the pelecypod, Buchia aff. B. okensis Zone is Berriasian in age, and not Tithonian as previously believed and that the B. pacifica Zone is partly Berriasian and not entirely Valanginian. Nannofossil data provide useful age calibrations for ammonite stratigraphy. The study illustrates that nannofossil biostratigraphy can be effectively used to date sediments deposited in convergent margin settings. One new species, Nannoconus paskentaensis , is described.