Abstract

In the Santa Barbara coastal area, the distinctive sequence of siliceous rocks in the Miocene Monterey Formation is divided into five informal members. The uppermost member is free of carbonate except in dolomite nodules. In the lower four members all rocks contain carbonate, and in the middle of this carbonate-bearing sequence is a thick unit of organic-rich phosphatic calcareous shale. The lithostrati-graphic sequence, which persists along the entire coast, will be viewed completely at Naples Beach, Gaviota Beach, and Damsite Canyon.

Due to westward increase in postdepositional temperatures and burial depths, rocks underwent increasing diagenesis westward. The upper two members of the Monterey (a carbonate-free member and a carbonate-bearing member) will be examined in progressive stages of diagenesis in which: (1) all rocks are diatomaceous (at Elwood Beach); (2) some rocks are diatomaceous, and some rocks bear diagenetic opal-CT (at Naples Beach); (3) all rocks bear diagenetic opal-CT (at Gaviota Beach); (4) some rocks bear diagenetic opal-CT and some bear diagenetic quartz (at Damsite Canyon); and (5) nearly all rocks bear diagenetic quartz (at Black Canyon). A locality (Jalama Canyon) will also be examined where the presence of diagenetic quartz, which formed in rare carbonate-bearing beds, does not indicate the diagenetic “grade” of surrounding strata.