A magnetic polarity time scale for the Early Cretaceous and Late Jurassic

Abstract

The ages of polarity chrons in previous M-sequence magnetic polarity time scales were interpolated using basal sediment ages in suitably drilled DSDP holes. This method is subject to several sources of error, including often large paleontological age ranges. Magnetostratigraphic results have now tied the Early Cretaceous and Late Jurassic paleontological stage boundaries to the M-sequence of magnetic polarity. The numeric ages of most of these boundaries are inadequately known and some have been determined largely by intuition. An examination of relevant data suggests that 114 Ma, 136 Ma and 146 Ma are optimum estimates for the ages of the Aptian/Barremian, Cretaceous/Jurassic and Kimmeridgian/Oxfordian stage boundaries, respectively. Each of these boundaries has a good correlation to the M-sequence of magnetic reversals. The magnetostratigraphic tie-level ages are linearly related to the spreading distance and have been used to calculate a new magnetic polarity time scale for the Early Cretaceous and Late Jurassic. All stage boundaries in this time interval were correlated by magnetic stratigraphy to the proposed new time scale which was then used to estimate their numeric ages. These are, with the approximate relative errors of placement within the M-sequence: Aptian/Barremian 114 Ma (+0 .5Ma) Barremian/Hauterivian 121 Ma (-2 .0,+1 .5Ma) Hauterivian/Valanginian 126 Ma (-0 .5,+3 .0Ma) Valanginian/Berriasian 131 Ma (-0 .5,+2 .5Ma) Berriasian/Tithonian 136 Ma (+1 .0Ma) Tithonian/Kimmeridgian 143 Ma (+0 .5Ma) Kimmeridgian/Oxfordian 146 Ma (+0 .2Ma) The absolute errors of these interpolated stage boundary ages depend on the accuracy of the tie-level ages.