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ABSTRACT: Sedimentation and Paleogeography of the Chico Formation, Sacramento Valley, CA

John S. Russell

The Chico Formation is a sandstone-dominated sequence that records relatively shallow-water, marine, transgressive sedimentation across the shelf on the northeastern margin of the tectonically active Great Valley fore-arc basin in California during the Late Cretaceous (Coniacian-late Campanian). A transgression-formed continuum of fluvial and shallow marine foreshore and shoreface environments to deeper water inner and outer shelf environments is recorded within the overall, vertical succession of facies within the Chico Formation. Within this continuum, shallower water facies are characterized by sedimentary structures and textures indicative of high-energy, storm-dominated processes, such as hummocky and swaley cross-stratified sandstones. Deeper water facies are domina ed by lower energy, fairweather-formed sedimentary structures and textures, such as parallel laminated mudstones. Using the spatial and temporal distributions of lithofacies on a regional scale, the paleogeography of the study area may be reconstructed for successive stages of the Late Cretaceous. These reconstructions document a northwestern-southeastern-directed transgression. At the peak of this transgression, in the late Santonian to early Campanian, outer shelf environments were well developed in the northern portions of the outcrop belt, and shallower water shoreface environments were present in southern localities of the outcrop belt.

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