The Influence of Depositional Processes on Grain Fabric, Porosity, and Permeability of the Chatsworth Formation

The Cretaceous Chatsworth Formation exposed in the vicinity of Chatsworth, California, is an ancient submarine fan deposited 66 to 83 million years ago. The formation consists of varying proportions of thin-bedded mudstones and thin-bedded to thick-bedded sandstones. Previous research on the Chatsworth Formation has identified some of the sedimentary processes responsible for the deposition of the mudstones and for the sandstones. However, very little detailed work has focused on the origin of the sandstones that are approximately 0.5 or more meters in thickness. Detailed field studies and analysis indicate that the dominant processes responsible for the deposition of the thicker sandstones include turbidity currents and sandy debris flows. Contour currents may have led to the deposition of some sandstone but results are not conclusive. Bioturbation, through randomization of grain fabric and destruction of sedimentary structures, complicates determining the origin of some of the sandstone. A comparison of sandstone fabric related to the different depositional processes shows that the fabric did not significantly vary. Diagenesis has altered much of the initial primary porosity. Lab tested porosity and permeability values, thin section porosity estimates, and porosity values from a previous investigation are found to be in agreement, with average total porosity and average permeability values falling between 15.1-21.6% and 93.6 millidarcies, respectively