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