GRADSTElN, F. M., and Z. HUANG, Atlantic Geoscience Centre, Dartmouth, Nova Scotia, F. P. AGTERBERG, Geological Survey of Canada, Ottawa, Ontario, Canada, J. G. OGG,* Purdue University, West Lafayette, IN, and J. HARDENBOL, Exxon Production Research Co., Houston, TX

ABSTRACT: A Mesozoic Time Scale

A geologic time scale for the Triassic, Jurassic and Cretaceous was constructed by integrating radiometric ages, biostratigraphic subdivisions, and marine magnetic anomalies. First, maximum likelihood estimates and direct estimates of stage boundaries were derived from a database of 340 stratigraphically meaningful radiometric dates and interpolation of the M-sequence magnetic polarity time scale. Low-temperature radiometric age estimates are statistically deviant from high-temperature age estimates for eight of the Cretaceous stage boundaries, and were omitted from further consideration. These unequally spaced ages of the 30 Mesozoic stages comprise the dependent variable for a smoothing cubic spline-fit interpolation. The independent variables for the cubic spline-fit, which govern he relative duration of stages when radiometric age control is of low precision, are 219 equal-spaced ammoniate sub-zones for the Triassic-Jurassic, and equal-stages for the Cretaceous. Uncertainties are computed for each stage boundary age, and the 2-sigma values are given in parentheses. The resulting period boundaries are Cretaceous/Tertiary at 66.0 Ma+0.2(2s), Jurassic/Cretaceous at 141.2 Ma+1.9, Triassic/Jurassic at 210.0 Ma+4.2, and Permian/Triassic at 248.0 Ma+3.7. The stage boundaries have 2-sigma uncertainties less than 2 m.y. within the Cretaceous period, and generally less than 4 m.y. within the Jurassic and Triassic.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.