Lateral differences in Monterey rocks along the Santa Barbara coast indicate that diagenesis is more advanced toward the west, as noted by Bramlette (1946). Silica changes toward the west from biogenic opal-A (in diatom frustules) to diagenetic opal-CT and then to diagenetic quartz. This study describes the original equivalence and the cause of lateral diagenetic differences and then examines lithologic changes and diagenetic processes in laterally equivalent strata.Continuous exposure for 55 km, simple homoclinal structure, paleogeography, and detailed analysis of 14 stratigraphic sections together show that sediments were laterally equivalent, as originally deposited. Rocks principally contain: biogenic or diagenetic silica (5 to 90 percent), detrital minerals (5 to 70 percent), carbonates (0 to 80 percent), and organic matter (1 to 25 percent). Distinctive stratigraphic differences in rock composition are used to define five informal members, including an uppermost member nearly free of carbonate and four lower carbonate-bearing members. Each member is laterally continuous and shows consistent sedimentary features and compositions.Boundaries between members are also laterally age-constant.Original equivalence indicates that lateral diagenetic differences were caused by postdepositional conditions. Overburden thicknesses (post-Luisian strata thicken, east to west, from 300 to 1850 m) and temperature-sensitive characteristics of kerogen (0/C atomic ratios decrease, east to west, from >0.2 to <0.1) show that increased temperature and burial caused the westward increase in diagenesis. Robert R. Compton's and James C. Ingle's knowledge and enthusiasm for the Monterey Formation fostered my interest, and Larry A. Beyer and Robert E. Garrison encouraged and supported the research from the beginning. Assistance in research was provided by many persons. I particularly thank my mother, Mary Carol Isaacs, for her companionship and support during a number of field trips exploring diatomaceous deposits in Oregon, California, and Nevada and for her encouragement and assistance in field work along the Santa Barbara coast. Great thanks are given to Larry A. Beyer of the U.S. Geological Survey, Menlo Park, through whose interest and substantial support many instruments (including pycnometers and X-ray diffraction apparatus) and services (including chemical analyses) were made available to me. Special thanks are also given to Robert R. Compton of Stanford University for field assistance, section measurement, and collection of many extremely fresh rocks from the field area. B. E. Felber of Mobil Research and Development Corporation's Field Research Laboratory in Dallas, Texas, generously arranged for an supervised X-ray diffraction analyses of clay minerals. In addition, Wilson L.
