The
reason for the enormous variability in continuity of the Repetto
top seal is that the overlying Pico Formation is in unconformable
contact with the Repetto Formation, exhibiting hundreds of feet
of erosional relief (Henry, 1987, his plate 3). For example, in
the northwest part of the basin in the Torrance and Wilmington Onshore
areas, basal sandstones of the Pico Formation are in direct contact
with upper Repetto sandstones, with consequently little potential
for vertical seal. However, in the Wilmington Offshore area, there
is approximately 100 ft (30.5 m) of continuous shale above the Repetto
Formation. Farther to the southeast in the Belmont Offshore area,
the basal Pico unconformity rises with respect to the Repetto Formation,
resulting in preservation of additional upper Repetto strata and
introduction of extreme variability in the lithologic nature of
the Pico-Repetto contact. In the West Newport fault block, there
is continuous shale top seal above the Repetto Formation, 100 to
200 ft thick (30.5 to 61.0 m). Toward the northeast (Sunset Beach
area), the basal section of the Pico Formation commonly consists
of a 100- to 200-ft (30.5- to 61.0-m) sandstone above a sandy section
of the upper Repetto (Henry, 1987, his plate 2). Farther northward
in the West Coyote, Leffingwell, Santa Fe Springs, and Montebello
areas, the upper Repetto Formation is shalier, consisting of multiple
upward-coarsening parasequences separated by hundreds of feet of
shale. Consequently this part of the basin is inferred to contain
a higher potential for top seal of injected gases.
8 Map:
8
Reference:
Henry,
M. J., 1987, Los Angeles Basin—an overview, in Clarke, D., and Henderson,
C., eds., Oil-producing areas in Long Beach: American Association
of Petroleum Geologists Field Trip Guidebook, Pacific Section, p.
1–29.
