A sequence stratigraphic model of syn- to post-rifting strata in a transform margin basin is presented. The model uses outcrop, well-log, and seismic data from Neogene strata in the Cuyama Basin of southern California. Modeling results show the timing and extent of eustastic, tectonic, and sediment flux control on facies distribution and sequence development during the transition from syn- to post-rifting conditions.

Two sequences were formed in the Cuyama Basin during the transition from syn- to post-rifting conditions. Deposition of the first sequence followed the end of large-scale normal faulting at 15.5 Ma and was influenced by continuing small-scale normal faulting. Strata at the top of the second transitional sequence is dated at 14 Ma and shows no evidence of fault-related deposition. While preceding sequences were deposited rapidly in thick, highly progradational sequences, the two transitional sequences accumulated slowly in thin, aggradational sequences. Sequences deposited after 13 Ma are similar in thickness, rate of accumulation, and progradational character to those deposited during rifting; however, these younger sequences exhibit strong eustastic control.

During the transition from syn- to post-rifting conditions, the average grain size of nearshore and shelf facies decreases notably. Deep-water facies deposited during the transitional period change from large, rapidly accumulating, coarse grained submarine fans to small, slowly accumulating, very-fined grained submarine fans. Because ample accommodation space existed throughout the transition period, the uniform reduction in grain size, thickness, and rate of accumulation of sediments across the basin likely indicates the end of the syn-rifting period of basin development was accompanied by a large reduction of sediment influx.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah