Origin of
Eocene Depositional Sequences in the Sacramento Basin, California: The Interplay
of Tectonics and Eustasy
Sullivan, Raymond1, Morgan D.
Sullivan2 (1) San Francisco State University, San Francisco, CA (2)
Chevron Energy Technology Company, Houston, TX
The Eocene strata in the Sacramento Basin
can be subdivided into six depositional sequences, and each of these can be
correlated with a third order regressive-transgressive cycle observed on the
global coastal onlap curve. Two types of unconformity bounded sequences are
recognized. The first type is associated with submarine canyon formation. These
canyons were filled with bathyal shales and turbiditic sandstones, and are
represented by the Meganos "C', Capay and Sidney Flat/Kellogg shales. The
second type of sequence is associated with predominantly estuarine/fluvial
sands. Examples include the Hamilton, Domengine and Ione
sands. The close correlation between the chronologic occurrence of these
sequences and the global sea level chart suggests a strong eustatic control on
the timing of the depositional cycles in the basin. Tectonism, however, is
interpreted to have controlled the location of the submarine canyons and the
estuarine/fluvial incisements since they stack vertically and follow the tilt of
the basin toward the depocenter in the southwest margin of the basin. The
interplay of tectonism and relative sea level change also was a determining
factor as to which type of depositional sequence formed in the basin. If
subsidence rates exceeded the rate of relative sea level fall, less of the
shelf was exposed, and submarine canyons were formed. Conversely, when the rate
of relative sea level fall exceeded subsidence rates, then the shelf was
exposed, and widespread fluvial and estuarine systems developed on the basin
margin.