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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Lower Sespe arkosic sandstones and petromictic conglomerates of late Eocene and Oligocene age rim the Ventura basin in California and are interpreted as high-gradient, braided river deposits. Lower Sespe deposits contain a high ratio (over 20/1) of bedload/suspended load. Lenticular, poorly sorted, imbricated, bar-shaped conglomerate units interbedded with graded to parallel-laminated sandstone beds are typical of lower Sespe deposits. Graded and reverse graded conglomerate units, graded
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sets of avalanche cross-stratification, cuspate cut-and-fill structures, and antidune cross-stratification also characterize the lower Sespe conglomerate facies. These features all indicate a braided stream model for lower Sespe deposits.
Steep gradients during lower Sespe deposition are suggested by: (1) clast size data (average maximum clast size = 41 cm), (2) a predominance of upper flow regime structures (85% of all structures measured), and (3) high consistency ratios (mean consistency ratio = 0.78) of paleocurrent data.
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