A revised time scale of magnetic reversals for the Early Cretaceous and Late Jurassic

Abstract

A magnetic reversal block model for the Early Cretaceous-Late Jurassic period was developed from four closely spaced profiles across the Hawaiian lineation pattern by Hilde (1973) and Hilde et al. (1974). Larson (1974) independently developed an improved model of this reversal period by reanalyzing the data presented by Larson and Chase (1972) plus a profile collected during Deep Sea Drilling Project (DSDP) leg 32. These two models are similar and contain nearly twice as many reversals as the original late Mesozoic reversal model proposed by Larson and Pitman (1972). These models are combined in this paper and are the basis for a revised magnetic reversal stratigraphy for the Early Cretaceous-Late Jurassic. The model is placed in a framework of geologic time by analyzing magnetic data in the vicinity of DSDP drill holes that reached volcanic basement on various late Mesozoic lineation patterns. The magnetic ages of these sites are plotted as a function of paleontologic ages at the bottom of the holes to determine a revised time scale of magnetic reversals for the Early Cretaceous-Late Jurassic. Fundamental to this analysis are the assumptions that the Hawaiian lineation pattern was generated at a constant spreading rate and that the paleontologic ages in the DSDP holes closely approximate the basement ages. This analysis shows that the M reversal pattern spans the Aptian to Oxfordian stages and ranges in chronologic age from 107 to 153 m.y.