ABSTRACT: Kinetic Control on Clastic Diagenesis in the Los Angeles Basin as Determined by Apatite Fission Track Analysis

Ronda L. Geving, Robert K. Suchecki, Shari E. Kelley

The relationship between diagenesis and thermal history in Miocene-Pliocene sediments of the Los Angeles basin were determined from analysis of illite/smectite ratios, apatite fission tracks, extent of feldspar dissolution, and carbonate cementation in argillaceous sediments and sandstones from subsurface and outcrop samples. The extent of the smectite-to-illite tranformation and feldspar dissolution as a function of depth can be spatially related to principal faults and fault-bounded structural elements of the basin. The rate of smectite illitization and of feldspar dissolution increases near principal fault zones. Major cementation of sandstones by calcite and baroque dolomite cements is largely restricted to areas located along major fault zones; however, less extensiv calcite cementation is found in the deeper parts of the basin central syncline.

Time-temperature histories based upon track length histograms of fission tracks in apartite grains indicate that the more tectonically active flanks of the basin had higher thermal gradients during the latest Miocene to latest Pliocene compared to the central-basin structural block. For example, in the Brea Olinda field located along the Whittier fault zone, thermal gradients of 35°C/km are interpreted since deposition of latest Miocene sediments whereas thermal gradients affecting a well 9 mi from the Whittier fault zone were much lower until 1-2 Ma, when the gradient increased to 35°C/km. Taken together, these data indicate that the diagenesis of clastic sediments in the Los Angeles basin is strongly controlled by reaction kinetics and that the temperatures associated with structural domains in the basin have exerted the dominant control on reaction extent.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990