GEOLOGY AND PALEONTOLOGY OF PALOS - Pubs Warehouse

12
GEOLOGY AND PALEONTOLOGY OF PALOS VERDES HILLS, CALIFORNIA
mudstpne member. The .lower and middle parts of the
Altamira member are assigned to the middle Miocene
and the upper part and the Valmonte and Malaga
members to the upper Miocene. Basalt, generally in
the form of sills, is found in the lower and middle parts
of the Altamira.
The Monterey shale is overlain disconformably by the
Repetto siltstone of lower Pliocene age. The maxi­
mum exposed thickness of the Repetto siltstone is
about 150 feet, the top being marked by an uncom-
formity. It represents a greatly condensed section of
parts of the Repetto formation of the Los Angeles
Basin, which has a thickness of 2,000 to 5,000 feet.
The upper Pliocene, represented in the basin by a
thickness of 2,000 to 3,000 feet of strata assigned to the
Pico formation, is missing.
Uncomformably overlying the Repetto siltstone and
overlapping different parts of the Monterey shale are
350 to 600 feet of deposits assigned to the lower Pleisto­
cene. In most' areas these strata consist chiefly of
sand, designated the San Pedro sand. At places a
calcareous facies, the Lomita marl, is at the base of the
section. A silt facies, either at the base of the lower
Pleistocene strata or between the Lomita and San
Pedro is designated the Timms Point silt. These three
formations are the thin marginal equivalent of an unde­
termined lower part of the Pleistocene of the Los
Angeles Basin, which has a thickness of as much as
2,000. feet.
Marine deposits, generally a few feet thick, have
been found on 9 of the 13 mam marine terraces, all of
which are considered younger than the lower Pleisto­
cene strata and are assigned to the upper Pleistocene.
The most extensive marine terrace deposits are those
on the lowest terrace. They overlie unconformably
the lower Pleistocene or older formations and are desig­
nated the Palos Verdes sand. Nonmarine deposits,
constituting the nonmarine terrace cover, overlie the
marine sediments on the terraces or rest directly on the
terrace platform. They are considerably thicker than
the marine deposits. The marine and nonmarine
terrace deposits are the equivalent of an undeter­
mined upper part of the thick Pleistocene section in the
basin. The nonmarine cover on the lowest terrace
merges into the upper part of the older alluvium of
the basin.
JURASSIC (?) SYSTEM
FRANCISCAN (?) SCHIST
DISTRIBUTION AND IJLTHOLOGY
Schists of doubtful Franciscan age are the oldest
rocks that crop out in the Palos Verdes Hills. These
rocks were noticed by Watts, 20 and some of the litho-
logic types have been described by Woodford. 21 They
were not examined carefully during the present investi­
gation, and their structure was not studied.
The metamorphic rocks are exposed along a wide
anticline modified by minor folds in George F Canyon
and its tributaries and nearby. The upper surface of
the schist, which forms the floor on which the Miocene
strata rest, is evidently irregular, though it conforms
in a general way to the folds in the Miocene rocks.
The schistosity or foliation is generally at fairly low
angles and is roughly parallel to the strike and dip
ao Watts, W. L., Oil and gas yielding formations of California: California Min.
Bur. Bull. 19, p. 54, 1901.
ai Woodford, A. O., The Catalina metamorphic facies of the Franciscan series:
California Univ., Dept. Geol. Sci., Bull., vol. 15, pp. 49-68, pis. 5-7, 2 figs., 1924.
of the overlying Miocene strata, as observed by
Woodford. 22
The metamorphic rocks include a variety of schists.
Green to greenish gray quartz-sericite schist, .red-
weathering to lavender-weathering quartz-talc schist
containing much hematite, and bluish schist consisting
principally of quartz and glaucophane or crossite are
the most common. Woodford 23 described quartz
schist, quartz Talbite schist, and blue schist in which
crossite is more abundant than glaucophane.
A saussuritized basic igneous rock is associated with
the schists. This rock was probably a diabase or
gabbro, but augite is apparently the only unaltered
original constituent. Lawsom'te is common in some
of this altered rock, and much chlorite and glaucophane
are developed along shear planes. iVt places the altered
igneous rock is cut by quartz veins.
A small area of quartz schist, exposed on the crest
of an anticline in a canyon east of Palos Verdes Drive
East, about three-quarters of a mile southeast of
George F Canyon, represents an outcrop of schist or
an exceptionally large boulder in the Miocene strata
close to the schist contact. A little farther down the
canyon, but apparently within the outcrop of Miocene
sandstone, are two smaller poorly exposed masses of
schist, one 5% by 4 feet and the other 4 by 2 feet, that
may represent large boulders or small outcrops of
schist. Such large boulders were not recognized,
however, in the main schist area, where th e relations
between Miocene rocks and schist are clearer, and these
apparent masses may be a further indication of the
irregular schist surface.
Schist was penetrated in the Whites Point tunnel on
the crest of an anticline that appears to be the south­
eastward extension of the anticline just mentioned.
(See section E E', pi. 1.)" On the north limb of the
anticline the schist is decomposed at the contact with
the Miocene strata, forming a layer of green clay about
a foot thick. Most of the schist in the core of the anti­
cline is altered. It contains plates of glaucophane 1 to
2 inches in diameter arid minor amounts of talc and
chloritic minerals. Near the contact with the Miocene
strata on the south limb of the anticline the schistosity
is vertical; 50 feet farther north it is nearly horizontal.
On the crest of the anticline the rock is made up of frag­
ments of micaceous and schistose minerals that form a
matrix in which are embedded angular to slightly
rounded fragments of quartz. Toward the north this
breccia is in contact with a nearly vertical ledge of schist
that strikes at right angles to the tunnel line. The
breccia may represent material that accumulated along
a cliff, but slickensides suggest that the ledge of schist
marks a fault and that the breccia is a fault breccia.
The schist is cut by two systems'of joints. The joints
of one system are virtually vertical and strike almost
at right angles to the tunnel line; those of the other sys­
tem are approximately horizontal. In both systems the
joints are spaced about 8 feet apart.
Six wells drilled in the hills penetrated schist. The
subsurface altitude of the schist in the Palos Verdes
Hills is discussed under the heading "Oil possibilities,"
page 119.
AGE
The age of the schist is unknown other than that it is
obviously pre-Miocene. The occurrence of glauco­
phane schist and altered basic igneous rocks suggests
» Woodford, A. O., op. cit., p. 52.
» Woodford, A. O., op. cit., pp. 54. 57. pi. 7.