Laumontization and Its Relationship to Carbonate Cementation and Dissolution Within Santa Fe Springs Oil Field, Los Angeles Basin, California

Richard L. Coffman

Diagenetic changes (smectite to illite transformations, albitization, carbonate and zeolite cementation and dissolution reactions) have been documented within the Santa Fe Springs oil field and throughout the Los Angeles basin in general. Petrographic examination of well core samples from Santa Fe Springs has resulted in the recognition of a diagenetic "front" at a depth of about 2,580 m. Above this "front" the rocks have extensive laumontization and albitization, whereas below it widespread carbonate cementation is present. Although the laumontite occurs above the carbonate cement, there is no evidence of previous laumontization within or below the carbonate cemented zone. Nearly all plagioclase within the laumontite cemented rocks exhibits extensive albitization, wherea fresh plagioclase grains occur in the carbonate cemented and underlying horizons. This indicates carbonate cementation preceded laumontization and effectively insulated these rocks against further alteration. Secondary porosity is extensive in certain horizons within the carbonate zone, whereas only a small amount of porosity is present in the laumontite zone. This porosity within the laumontite zone appears to be the result of selective dissolution, indicating laumontite is not necessarily a diagenetic basement as has been thought.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.