Transgression and regression in the Sacramento Basin during Late Cretaceous and Paleogene highstands and lowstands with implications for the history of the Sierra Nevada, California: Part 1—Late Cretaceous

An understanding of the distribution, transport direction, geometry, composition, and age of Campanian through lower Oligocene strata in the subsurface of the Sacramento Basin, California, provides an essential framework for interpreting depositional, erosional, and tectonic events in the adjacent Sierra Nevada. These clastic strata were deposited in an alternating series of marine transgressions and regressions in the Great Valley forearc basin, some of which were due to rising and falling sea levels that were global in extent. Fluvial deposits are an important component of 11 different formations, but stream deposits in Cretaceous fluvial-deltaic systems differ in several important aspects from deposits in Paleogene fluvial-deltaic systems. These differences are key to distinguishing sea-level highstands from lowstands, identifying source areas, developing paleogeographic reconstructions, and interpreting the uplift history of the Sierra Nevada. As sea level rose in the late Santonian, the shoreline retreated to the north and east, possibly as far as the Oregon border by ca. 84 Ma. Remnants of this shoreline (Chico Formation) are locally exposed northeast of the city of Chico along Big Chico and Butte Creeks. The abundance of plutonic and metamorphic grains and absence of muscovite in this sandstone indicates that it was derived from the Sierra Nevada. Sediment transport to submarine canyons along the shelf edge was cut off and submarine fans (Guinda Formation) on the floor of the basin were abandoned and blanketed by several hundred feet of hemipelagic mud (Dobbins Shale). When sea-level rise slowed in the early Campanian, transgression ended and regression began. A high-sinuosity river flowing into the basin from Idaho deposited an elongate, fluvial-dominated delta (Kione Formation) north of the city of Sacramento. Over time, the delta prograded south and reached the southeast-trending Willows Fault. This southwest-dipping normal fault had offset the crystalline basement and Dobbins Shale and created the shelf edge. As the river prograded to the fault and migrated to the southeast along it, it fed sediment to the prodelta slope and submarine fans of the Forbes Formation south of the fault. The Kione and Forbes formations are quartzofeldspathic and rich in volcanic grains, plagioclase, and muscovite derived from the Idaho batholith, but metamorphic grains from the Sierra are lacking. Tabular, laterally extensive channel deposits of high-sinuosity trunk streams and linear, narrower, low-sinuosity distributaries are present in the Kione and most of the younger Cretaceous delta systems. As sea-level rise accelerated again in the late Campanian, the shoreline transgressed to the east of the early Campanian shoreline and the Sacramento Shale blanketed the Kione and Forbes formations. That shoreline has been eroded but was at least 10 mi (16 km) east of westernmost exposures of Sierran bedrock. Regression resumed when sea level reached a new highstand and the river began building a new delta in the northeastern San Joaquin Basin, 50 mi (80 km) south of the Kione delta. By this time, the river had apparently migrated farther east into the area of the present Sierran foothills, but its deposits have not been preserved. In the late Campanian and Maastrichtian, the basin continued to subside and tilt to the south and sea level rose in stepwise fashion but was overtaken by sediment input. Regression resumed and the river began migrating back to the west, building cuspate to lobate delta lobes (Starkey and Mokelumne River formations) and submarine fans that migrated westward across the Sacramento Basin and prograded southward into the San Joaquin Basin. The arkosic sand in these deltas and fans is also rich in volcanic grains derived from the magmatic arc northeast of the basin, but metamorphic grains like those in the Chico Formation are absent. The data indicate that the western foothills of the Sierra Nevada were submerged in the late Campanian and the range was a relatively minor sediment source. Southward sediment transport from Idaho continued to be dominant.