Stratigraphy of the Redding Formation of North-Central California and Its Bearing on Late Cretaceous Paleogeography

Recent studies of the Redding Formation of California provided new information concerning the extent of Cretaceous deposits underlying the southern Modoc Plateau. Understanding the stratigraphy and depositional environments of the Cretaceous rocks in this region is important for both paleogeographic reconstruction and hydrocarbon exploration. The Redding Formation is an approximately 1600-m thick clastic sequence that can be divided into five lithologic members. Biostratigraphic data indicate that the members of the Redding Formation are time-transgressive. The lowest three members were deposited during the middle to late Turonian, whereas the upper two accumulated during the Coniacian to santonian. The disconformity in the section developed during the latest Turonian to early Coniacian. Deposition in the Redding region was restricted to shelf environments and may have been controlled partly by euastatic sea level rise and fall. Initial transgression was directed northward and eastward with turonian strata accumulating across the basin. After the early coniacian hiatus, maximum marine inundation occurred briefly during the Santonian. Then late Santonian conglomerates and sandstones of the highest member prograded rapidly across the basin from the north, and shoaling apparently followed shortly thereafter. The southern limit of these late Santonian conglomerates appears to be the Tuscan Springs region where theymore » interfinger with deep shelf mudstones of the Chico Formation. These mudstones are considered to reflect an eastward swing of the Santonian shoreline around the northern Sierra Nevada. Thus, by the late Santonian, deposition had ceased in the Redding region but continued in a narrow trough to the south and southeast. The observed stratigraphy suggests that a thick sequence of Upper Cretaceous clastics beneath the southern Modoc Plateau is unlikely.« less