Print this pagePaleomagnetic Studies on Neogene Rocks from Southern California
Bruce P. Luyendyk
For the past 13 years, the paleomagnetism of Neogene age volcanic and
sedimentary rocks in southern California has been studied. Volcanic rocks
studied are mostly early and middle Miocene. Sedimentary rocks studied are
mostly middle and late Miocene dolostones from the Monterey Formation. Clockwise
declination anomalies are prominent and are interpreted as indicators of
clockwise tectonic rotation. West of the San Andreas fault in the western
Transverse Ranges and Channel Islands, clockwise rotation began during the
middle Miocene, paused in late Miocene, and resumed in the Pliocene. An
exception is the San Gabriel Mountain region, which possibly has rotated
counterclockwise since late Miocene. East of the San Andreas fault, clockwise
rotations took place in the central M jave Desert during the early Miocene. The
Orocopia Mountains region may have rotated clockwise during the middle Miocene.
The Eastern Transverse Ranges rotated clockwise mostly during post-Miocene time
and some parts of the Mojave Desert rotated counterclockwise. 
Magnetic
reversal
stratigraphy has been studied for a few sections in the Monterey Formation.
Control is dictated by the abundance of dolostone beds, as other lithologies do
not possess a primary remanence. Five sections along the north coast of the
Santa Barbara Channel have been correlated to the magnetic polarity time scale
by J. S. Hornafius. Study of two thick sections of early Miocene flows from the
Soledad basin by R. R. Terres yielded a detailed scheme of secular variation.
Elsewhere, flow sequences are too short and dis ontinuous in time to yield a
magnetic
reversal stratigraphy.
AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.