Eocene marine to nonmarine (deltaic) deposits, Lower Piru Creek, Los Angeles and Ventura Counties, California
A 790-m thick vertical section of lower middle Eocene sandstone represents a regressive deltaic sequence that grades upward from delta front through lower delta plain into upper delta plain. The sandstone crops out as a narrow strip of overturned east-west strata and south-plunging open folds within the Topatopa Mountains, 16 km north of the town of Piru, California. The sandstone gradationally overlies prodelta/transition-zone siltstone of uppermost Capay stage (early Eocene) and underlies, with a 15/sup 0/ angular unconformity, Eocene to Oligocene nonmarine boulder conglomerate of the Sespe Formation. The lower 95 m of the sandstone is characterized by an upward-coarsening sequence, fine at the base to medium at the top, laminated to bioturbated sandstone. Bioturbation is as high as 75% with Ophiomorpha burrows common. Shallow marine mollusks diagnostic of the Domengine stage (late early through early middle Eocene) occur within lenses of medium sandstone. These rocks were deposited in a shoreface environment on a delta front. Above the delta-front deposits are about 100 m of coarse sandstone. Structureless and bioturbated sandstone is dominant, but herringbone cross-bedding, planar cross-bedding 10-150 cm high, planar lamination, and scour-and-fill structures are common. Structures are interpreted as megaripples, sand waves, and channels in a tidal sand-flat environment. Coal lenses higher in the section are interpreted to be marsh deposits. Bioturbation can be up to 80% and Ostrea occurs locally. This tidal flat differs from most cited modern examples because it lacks a mud component or associated mud-flat deposits. The tidal sand-flat and marsh deposits were formed within a lower delta plain. Overlying these rocks is a 205-m interval of interfingering tidal-flat and braided-river deposits.
- Research Organization:
- California State Univ., Northridge
- OSTI ID:
- 6931072
- Report Number(s):
- CONF-8604187-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:4; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Depositional environments of Domengine Formation, near Coalinga, Fresno County, California
Early Eocene Molluscan biostratigraphy, Mount Pinos-Lockwood Valley area, northern Ventura County, southern California
Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
CALIFORNIA
CENOZOIC ERA
COAL DEPOSITS
COAL SEAMS
CONGLOMERATES
DEPOSITION
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
MINERAL RESOURCES
NORTH AMERICA
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
TERTIARY PERIOD
USA