ABSTRACT: Late Cretaceous and Early Tertiary Depositional Environments of the Northern Sacramento Basin Revealed by Seismic-Stratigraphic Analysis

John E. Damuth, Martin H. Link, Steven H. Gabay

Seismic-stratigraphic analysis of regional seismic data across the Willows-Beehive Bend gas field reveals a prograding shelf-slope depositional sequence, including basin, submarine-fan, slope, and shelf deltaic deposits, that progressively infilled the northern Sacramento fore-arc basin during the Campanian. The base of the Forbes Formation and the base of the Princeton Gorge fill form the lower and upper boundaries, respectively, of this sequence. Upper Cretaceous submarine-fan and basin-plain deposits from the strata between the Sierran basement and the base of the Forbes and progressively onlap the basement from west to east. The lower to middle Forbes Formation is characterized by high-amplitude discontinuous reflections and consists of mud-rich submarine-fan deposits with laterally restricted, sand-prone channel/levee complexes and broader depositional lobes. In contrast, the upper Forbes consists of mud-rich slope deposits characterized by broad, southward-dipping clinoforms. Submarine-canyon/gully fills are common and return discordant hummocky to chaotic reflections. The overlying Kione Formation consists of sand-rich, delta-front deposits that return high-amplitude, gently dipping subparallel reflections and are transitional into the slope deposits of the uppermost Forbes. The Kione was partially eroded during cutting of the Princeton Gorge submarine canyon in the early Tertiary. The lower (Eocene) Princeton Gorge fill shows highly variable reflection character and seismic facies that suggest multiple episodes of submarine erosion and deposition. At least three northwest-southeast-striking fault zones, including the Willows fault, disrupt these formations and appear to have strike-slip components.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990