Paul E. Olsen, Dennis V. Kent, Mohammed Et. Touhami, and John Puffer

ABSTRACT

       Early Mesozoic tholeiitic flood basalts of the Central Atlantic Magmatic Province (CAMP) are interbedded throughout much of their extent with cyclical lacustrine strata allowing Milankovitch calibration of the duration of the extrusive episode.  This cyclostratigraphy extends from the Newark basin of the northeastern US, where it was first worked out, to Nova Scotia and Morocco and constrains the outcropping extrusive event to less than 600 ky in duration, roughly 20 ky after the Triassic-Jurassic boundary, and to within one pollen and spore zone and one vertebrate biochron.  Based principally on the well-known Newark astronomically calibrated magnetic polarity time scale with new additions from the Hartford basin, the rather large scatter in recent radiometric dates from across CAMP (>10 my ), centering on about ~200 my, is not likely to be real.  Rather, the existing paleomagnetic data from both intrusive and extrusive rocks suggest emplacement of nearly all the CAMP within less than 3 my of nearly entirely normal polarity.  The very few examples of reversed magnetizations suggest that some CAMP activity probably occurred just prior to the Triassic-Jurassic boundary.  The volumetrically massive volcanic wedge of seaward dipping reflectors present in the subsurface off the southeastern US, may be part of the same igneous event, suggesting that the CAMP marks the formation of the oldest Atlantic oceanic crust.