The Upper Cretaceous Paleontology and Stratigraphy of the Simi Hills, Los Angeles and Ventura Counties, California

• Main Author: Zebal, George Patterson
• Format: Others
• Published: 1943
• Online Access: https://thesis.library.caltech.edu/5662/1/Zebal_gp_1943.pdf; Zebal, George Patterson (1943) The Upper Cretaceous Paleontology and Stratigraphy of the Simi Hills, Los Angeles and Ventura Counties, California. Master's thesis, California Institute of Technology. doi:10.7907/C81A-AS44. https://resolver.caltech.edu/CaltechTHESIS:03312010-113315988 <https://resolver.caltech.edu/CaltechTHESIS:03312010-113315988>

<p>The Upper Cretaceous strata of the Simi Hills in the region of Dayton and Bell Canyons are divided into two series of lithologically dissimilar beds. The lower shale series is further divisible into three members. The basal member of the lower series is a fossiliferous shale, probably 200 feet thick, which is overlain by an alternating series of fossiliferous, calcareous sandstones and sandy shales, attaining a thickness of approximately 1,000 feet. The upper member of this group is an unfossiliferous gray shale with an estimated average thickness of 200 feet. The beds of the lower shale series are unconformably overlain by the Topanga formation and faulted against the massive sandstones. The upper massive sandstone series is remarkable for its lithologic homogeneity and uniform development throughout the area of its exposure. Broken in only two places by relatively thin shale beds, the monotonous layers of arkose total 5,500 feet in thickness. Due to faulting and differential overlap by other formations, the total thickness of the Upper Cretaceous deposits cannot be measured. The structure, though locally complex, is in the main rather simple. The Simi Hills form the southeastern flank of the Simi syncline. An accessory syncline is developed in the northern stretches of the Upper Cretaceous exposure. Three moderately large faults are present in the area of the report.</p> <p>The species assemblage is similar to that of the Glycymeris veatchii fauna of the Santa Ana Mountains. It can be divided into two subdivisions which are referred to the Turritella chicoensis perrini division and the Meta- placenticeras pacificum division of the upper part of the Glycymeris veatchii fauna.</p> <p>The incomplete basal shale member in the Simi Hills is correlated with the upper portion of the Holz shale member of the Williams formation in the Santa Ana Mountains. The middle and upper members of the lower shale series, and at least the lower 1,500 feet of the massive sandstone series are termed equivalents of the Pleasants sandstone of the Williams formation which forms the uppermost member of the Cretaceous deposits of the Santa Ana Mountains.</p>