The Influence of Relative Sea Level on Nearshore Sedimentary Processes in a Transform Margin Basin: The Miocene Cuyama Basin, California

Bryce W. Hoppie

Sedimentary facies of Miocene clastic shallow marine systems in the Cuyama Basin, California, are used to characterize the complete evolution of nearshore and shelf systems in a marginal marine transform basin. Characterizing the Miocene shallow marine facies of the Cuyama Basin is useful for predicting reservoir distribution in other transform basins of the Pacific Rim where facies preservation is incomplete.

Nearshore sedimentary processes in the Cuyama Basin repeatedly shift from tide to wave-dominated during periods of low and high relative sea levels, respectively. Early-Miocene nearshore facies of the Vaqueros Formation were deposited during low relative sea levels and are locally tide-dominated. During generally high relative sea levels of the middle-Miocene and deposition of the Branch Canyon Formation, nearshore processes changed to wave-dominated. This change is repeated in the late-Miocene Santa Margarita Formation where both tide and wave-dominated facies exist, but correlate to times of low and high relative sea levels, respectively.

The correlation of tidally-dominated deposition to lowstands and wave-dominated deposition to highstands in the Cuyama Basin may reflect an intrinsic property of marginal marine transform basins. Because transform margin basins are generally small and enclosed, relative sea level lowstands could expose peripheral landmasses that subject the basin to partial embayment and enhanced tidal forces. During highstands, however, ocean circulation is less restricted, and the basin is exposed to large swells associated with storms; both factors lessen the influence of tidal forces and cause wave-dominated deposition to prevail.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California