Magnetostratigraphic Tests of Sequence Stratigraphic Correlations from the Southern California Paleogene

Abstract

ABSTRACT Several sequence stratigraphic analyses have been conducted on the Eocene-Oligocene rocks of the San Diego region and of the western Transverse Ranges in southern California. Recently developed magnetic stratigraphy and 40Ar/39Ar dates, as well as previously neglected biostratigraphic data, provide a high-resolution chronostratigraphic framework to test correlation of these sequence stratigraphic interpretations to the global onlap-offlap chart (Haq et al. 1987, 1988; Hardenbol et al. 1998). In the San Diego area, previous stratigraphic analyses miscorrelated nearly all sequences and sequence boundaries to the global time scale; some correlations are off by as much as ten million years. In the western Transverse Ranges, three contradictory sequence stratigraphic analyses are evaluated. The revised dates of the sequence boundaries show poor correlation with the onlap-offlap chart of Haq et al. (1987, 1988) or Hardenbol et al. (1998), and some units are misdated by as much as six million years. In both regions, few sequences were correctly predicted by the onlap-offlap chart, suggesting that tectonic controls were more important than eustatic controls in this tectonically active region. The errors in so many sequence stratigraphic correlations when tested by high-resolution chronostratigraphic data should caution geologists about using sequence stratigraphic age assignments uncritically. Sequence stratigraphic correlations are only as good as the chronostratigraphy on which they are based.