A distinctive sandstone and breccia lithofacies is channelized and
interfingers with typical deep basin Monterey Formation deposits at Point Fermin,
on the Palos Verdes Peninsula, California. Sea-cliff exposures display a thinning-and
fining-upward sequence of channel-fill deposits consisting of sandstone,
breccia and intraformational breccia, whose base is scoured into thin-bedded
sandstone and shale. Thick-bedded facies A and B sandstone and breccia in the
basal portion of the channel-fill sequence were deposited by high-density sediment
gravity flows whereas facies F intraformational breccia beds in upper portions are
representative of debris flow deposition, transitional to slumping. Thin-bedded
sandstone and shale adjacent to the channel-fill sequence are representative of low-density
turbidity currents separated by intervals of hemipelagic sedimentation.
Sponge spicules and cold-water radiolarians and diatoms within shale beds imply
that the entire sequence was deposited at bathyal depths, probably on the inner
portion of a submarine fan, herein termed the Point Fermin fan.
The glaucophane-rich sandstone and breccia of the fan contrast sharply with
the arkosic composition of most coeval deep-sea fans of the Los Angeles basin,
implying that the Point Fermin fan and its source were isolated from the rest of the basin. Paleocurrent data suggest that the source of the Point Fermin fan detritus
was probably the Palos Verdes uplift to the north. Uplift of the Palos Verdes
anticlinorium during the middle Miocene, and a small concomitant fall in sea level
may have initiated the development of the fan.
Description:
Includes bibliographical references (pages 77-82)
California State University, Northridge. Department of Geological Sciences.